Central Nervous System

Front 1

Cerebrum

Back 1

The two cerebral hemispheres which form the bulk of the brain have a surface consisting of folds = gyri and grooves = sulci and fissures; its tissues consist of surface gray matter and some embedded nuclei of gray matter and various expanses of white matter; each hemisphere is divided into five lobes, the frontal lobe, the temporal lobe, the parietal lobe, the occipital lobe and the insula; the cerebrum is the seat of consciousness where all forms of sensory information are received and interpreted and where voluntary commands are issued to skeletal muscles; it is also the location for emotional processing and higher thought processes including learning, problem solving, memory, etc.

Front 2

Cerebral cortex

Back 2

The gray matter on the surface of the cerbrum which is from 2 - 4 mm thick and is subdivided into six cellular layers; the cerebral cortex is the seat of consciousness where all forms of sensory information are received and interpreted and where voluntary commands are issued to skeletal muscles; it is also a location for emotional processing and higher thought processes including learning, problem solving, memory, etc.

Front 3

Gyrus/gyri

Back 3

The folds of gray matter which form the cerebral cortex; having the gray matter distributed in folds and grooves increases the surface area of the cortex to facilitate diffusion of nutrients, respiratory gases, and wastes between the nervous tissue and the adjacent cerebrospinal fluid and the blood stream.

Front 4

Fissure

Back 4

The larger deeper grooves on the surface of the cerebral hemispheres which tend to be partial dividers of the hemisphere into its specific lobes; these grooves also increase the surface area of the brain surface which makes room for more gray matter and also provides access to the blood supply in the nearby pia mater and subarachnoid space.

Front 5

Sulcus/sulci

Back 5

The smaller shallower grooves on the surface of the cerebral hemispheres which divide the surface of each hemisphere into its specific convolutions = gyri; having the gray matter distributed in folds and grooves increases the surface area of the cortex to facilitate diffusion of nutrients, respiratory gases, and wastes between the nervous tissue and the adjacent cerebrospinal fluid and the blood stream.

Front 6

Longitudinal fissure

Back 6

The deep groove which separates the left and right hemispheres of the cerebral cortex and it is occupied by the superior and inferior venous sagittal sinuses which are housed within an extension of the dura mater.

Front 7

Cerebral hemispheres

Back 7

The right and left halves of the cerebrum which are subdivided into 5 lobes: frontal, parietal, temporal, occipital, and insula; the two hemispheres are anatomically and functionally asymmetrical with the contralateral hemisphere having slightly enlarged parietal and occipital lobes, the differences is related largely to which hand is dominant (handedness); their tissues consist of surface gray matter and some embedded nuclei of gray matter and various expanses of white matter.

Front 8

Lobe

Back 8

The anatomic subdivision of a cerebral hemisphere, with the boundary usually marked by a slightly deeper sulcus or an even deeper fissure; its tissues consist of surface gray matter and some embedded nuclei of gray matter and various expanses of white matter.

Front 9

Frontal lobe

Back 9

The anterior lobe of the cerebral hemisphere named for the overlying frontal bone, this lobe receives and interprets olfactory sensation, initiates voluntary commands to skeletal muscles; it is also a main location for personality traits and higher thought processes including learning, problem solving, memory, etc.; its tissues consist of surface gray matter and some embedded nuclei of gray matter and various expanses of white matter.

Front 10

Temporal lobe

Back 10

The inferior lateral lobe of the cerebral hemisphere named for the overlying temporal bone, this lobe receives and interprets auditory sensation and equilibrium sensation; it is also a main location for coordination of auditory and visual aspects of language; its tissues consist of surface gray matter and some embedded nuclei of gray matter and various expanses of white matter.

Front 11

Parietal lobe

Back 11

The superior lateral lobe of the cerebral hemisphere named for the overlying parietal bone, this lobe receives and interprets cutaneous and somatic sensations and taste; it is also a main location for general association areas; its tissues consist of surface gray matter and some embedded nuclei of gray matter and various expanses of white matter.

Front 12

Occipital lobe

Back 12

The posterior lobe of the cerebral hemisphere named for the overlying occipital bone, this lobe receives and interprets visual sensation; its tissues consist of surface gray matter and some embedded nuclei of gray matter and various expanses of white matter.

Front 13

Insula

Back 13

The lobe of the cerebral hemisphere which is located deep within the lateral cerebral fissure under the parietal, frontal, and temporal lobes; it is a location for visceral and autonomic function, including taste; its tissues consist of surface gray matter and some embedded nuclei of gray matter and various expanses of white matter.

Front 14

Olfactory bulbs

Back 14

The enlarged ventral projections of the frontal lobes, adjacent to the cribiform plate of the ethmoid bone, where the olfactory nerves begin.

Front 15

Diencephalon

Back 15

The connection between the cortex and the brain stem which consists of the thalamus, hypothalamus, epithalamus and pineal gland, and third ventricle; it contains a variety of ascending and descending white fiber tracts as well as gray matter organized into nuclei which function in regulating internal homeostasis, in memory processing and in emotional response.

Front 16

Brain stem

Back 16

The distal portion of the the brain, extending from the diencephalon to the spinal cord, and connecting to the cerebellum by several pairs of cerebellar peduncles, the brain stem consists of the reticular formation, midbrain, pons, and medulla oblongata; it contains major ascending and descending white fiber tracts, is the origin for several pairs of cranial nerves, and contains gray matter nuclei involved in regulating internal homeostasis, e.g., state of arousal (asleep versus awake), respiratory rate, heart rate, vasomotor tone, and coordination of swallowing, vomiting, coughing, sneezing, and hiccupping.

Front 17

Midbrain

Back 17

The upper portion of the brain stem, connecting the diencephalon to the pons, which contains the cerebral aquaduct which connects the 3rd and 4th ventricles; it contains major ascending and descending white fiber tracts, and contains gray matter nuclei involved in the reflex movements of the head and trunk in response to visual, auditory and other stimuli.

Front 18

Pons

Back 18

The bridge between the midbrain and the medulla oblongata consists of gray matter nuclei, including the pneumotaxic area and apneustic area which help control breathing rate, and white fiber tracts.

Front 19

Medulla oblongata

Back 19

The lower portion of the brain stem, connecting the pons to the spinal cord and the location of the pyramids; it contains major ascending and descending white fiber tracts and the location where most such tracts, sensory and motor, cross from right to left within the CNS; and it contains gray matter nuclei involved in the regulation of heart rate, vasomotor tone, respiratory rate, and coordination of swallowing, vomiting, coughing, sneezing, and hiccupping.

Front 20

Pyramids

Back 20

The visible features of the ventral surface of the medulla oblongata which contain the largest descending white fiber motor tracts to skeletal muscles and the site where these fibers cross over from right to left or vice versa (crossing to the contralateral side is called called decussation in the brain stem).

Front 21

Decussation of the pyramids

Back 21

The routing pathway within medulla oblongata where the largest descending white fiber motor tracts to skeletal muscles cross over from right to left sides of the body and vice versa.

Front 22

Cerebrum

Back 22

The mass of nervous tissue inferior to the occipital lobes (separated from them by the transverse fissure) and posterior to the medulla and pons which consists of two hemispheres connected by a central vermis; cerebellar gray matter is found on the surface and within the white matter (arbor vitae) and this gray matter is involved in (1) the subconscious movement and coordination of skeletal muscles for skilled movements, for posture and balance, (2) the sense of equilibrium, and (3) contributes to emotional states.

Front 23

Cranial nerves

Back 23

The series of twelve pairs of nerves which originate in various portions of the brain and exit the skull through specific foramina to serve the tissues and structures of the head and neck and certain thoracic and abdominal viscera.

Front 24

Meninx/meninges

Back 24

The first layers of protection over the brain, spinal cord, and cranial and spinal nerves are three layers of fibrous connective tissue; the dura mater (tough and thick), arachnoid membrane (delicate), and pia mater (tough and thin).

Front 25

Cranial meninges

Back 25

The portion of the three meninges protecting the CNS in the dorsal body cavity; these layers cover the brain within the brain case of the skull; the first layers of protection over the brain and cranial nerves are these three layers of fibrous connective tissue; the dura mater (tough and thick), arachnoid membrane (delicate), and pia mater (tough and thin).

Front 26

Spinal meninges

Back 26

The portion of the three meninges which cover the spinal cord and spinal nerves within the spinal canal of the vertebral column in the dorsal body cavity; the first layers of protection over the spinal cord and spinal nerves are these three layers of fibrous connective tissue; the dura mater (tough and thick), arachnoid membrane (delicate), and pia mater (tough and thin).

Front 27

Dura mater

Back 27

The outermost and thickest, most fibrous, layer of the meninges covering the brain and spinal cord, composed of dense irregular fibrous connective tissue, a structure which contain some of the larger blood vessels, particularly the venous sinuses; it forms a protective physical barrier for the CNS.

Front 28

Epidural space

Back 28

The anatomical location external to the dura is merely a potential space in the cranium, since the dura is fused to the cranial periosteum, while, in contrast, in the vertebral canal, it generally contains adipose tissue.

Front 29

Subdural space

Back 29

The anatomical location between the dura and the arachnoid is merely a potential space because under normal circumstances, the arachnoid is directly attached to the dura mater.

Front 30

Arachnoid

Back 30

The middle layer of the meninges, a thin, spongy membraneous covering of the brain and spinal cord with a spider-web-like appearance which does not conform to the irregularities of the surfaces of the brain and spinal cord; it is composed of a delicate loose fibrous connective tissue; the space under the arachnoid and above the pia mater, the subarachnoid space, contains cerebrospinal fluid.

Front 31

Pia mater

Back 31

The inner layer of the meninges, a thin but tough membraneous covering which adheres smoothly to the surface of the brain and spinal cord and conforms to all the irregularities of their surfaces; it is composed of a very thin layer of dense irregular fibrous connective tissue; the smaller surface blood vessels of the brain and spinal cord are contained within this layer; at spinal levels, the pia mater gathers laterally, pierces the arachnoid and attaches to the dura, forming the denticulate ligament -- this* stabilizes the spinal cord within the vertebral canal and decreases the likelihood of cord damage when physical trauma occurs. (*The filum terminale has a similar function.)

Front 32

Subarachnoid space

Back 32

The space under the arachnoid and above the pia mater which contains cerebrospinal fluid.

Front 33

Meningitis

Back 33

Inflammation of the meninges of the brain and the spinal cord, most often caused by a bacterial or viral infection and characterized by fever, nausea and vomiting, intense headache, and stiff neck; bacterial forms tend to have more severe prognosis.

Front 34

Falx cerebri

Back 34

The scythe-shaped mid-saggital fold of the dura mater occupying the longitudinal fissure between the two cerebral hemispheres and which contains the sagittal venous sinuses.

Front 35

CSF= Cerebrospinal fluid

Back 35

The protein-poor serous plasma filtrate which is secreted by choroid plexus cells in each of the four ventricles of the brain and which circulates through the ventricles of the brain, the central canal of the spinal cord, and the subarachnoid space, and returns to the blood stream at the arachnoid villi; it functions as a shock absorption fluid cushion for the brain and spinal cord and as a second circulatory fluid delivering oxygen and nutrients to the nervous tissue.

Front 36

Brain ventricles

Back 36

The series of four interconnecting cavities of the brain, lined by ependymal cells and with a specialized choroid plexus which produce the cerebrospinal fluid that fills these chambers.

Front 37

Lateral ventricles

Back 37

The largest pair (right and left) of the ventricles of the brain which are irregular with projecting horns which are located in the interior of the cerebral hemispheres; contain a choroid plexus which secretes CSF which circulates through them and passes to the third ventricle.

Front 38

Third ventricle

Back 38

The third of the ventricles of the brain, a narrow vertical space within the thalamus of the diencephalon which receives CSF from the lateral ventricles and passes CSF on via the cerebral aquaduct to the fourth ventricle; contain a choroid plexus which secretes CSF.

Front 39

Fourth ventricle

Back 39

The fourth of the ventricles of the brain, a narrow space between the pons and upper medulla oblongata anteriorly and the cerebellum posteriorly which receives CSF from the cerebral aquaduct and passes CSF on to the central canal of the spinal cord and outward into the subarachnoid space; contain a choroid plexus which secretes CSF.

Front 40

Choroid plexus

Back 40

One of the delicate fringelike processes, consisting almost entirely of blood vessels, which project into each of the four ventricles of the brain which are lined by specialized ependymal cells which secrete cerebrospinal fluid.

Front 41

Blood-CSF Barrier

Back 41

A physiological mechanism that alters the permeability of brain capillaries, so that some substances, such as certain toxins and drugs, are prevented from entering brain tissue, while other substances are allowed to enter freely; physically it consists of the capillary endothelial cells and their basement membranes and the processes of astrocytes associated with the capillary beds that serve the brain and spinal cord tissue.

Front 42

Interventricular foramina

Back 42

The two openings or short tubes which drain the CSF from the lateral ventricles into the third ventricle.

Front 43

Cerebral aqueduct

Back 43

The canal connecting and transporting CFS from the third to the fourth ventricle which is located in the midbrain.

Front 44

Median aperture

Back 44

A median opening permitting CSF to move from the fourth ventricle to the subarachnoid space.

Front 45

Lateral apertures

Back 45

A pair of lateral openings permitting CSF to move from the fourth ventricle to the subarachnoid space.

Front 46

Arachnoid villi

Back 46

The finger-like projections of the arachnoid membrane which project into the cranial venous sinuses within the dura mater along the major fissures of the brain where they are in close proximity to the venous blood and where cerebrospinal fluid can be transferred from the subarachnoid space back into the bloodstream.

Front 47

Dural sinuses

Back 47

The series of large, somewhat irregular, blood-filled venous spaces with roughly triangular cross-sections which are located within the dura mater where the dura follows the contours of the major fissures of the brain; typically there are four major dural sinuses, the superior sagittal, straight, and two transverse sinuses; these venous spaces are the locations for the arachnoid villi through which cerebrospinal fluid = CSF is reabsorbed to be returned to the venous blood supply of the brain.

Front 48

Subarachnoid space

Back 48

The series of large, somewhat irregular, blood-filled venous spaces with roughly triangular cross-sections which are located within the dura mater where the dura follows the contours of the major fissures of the brain; typically there are four major dural sinuses, the superior sagittal, straight, and two transverse sinuses; these venous spaces are the locations for the arachnoid villi through which cerebrospinal fluid = CSF is reabsorbed to be returned to the venous blood supply of the brain.

Front 49

Circumventricular organs

Back 49

Several small structures located around the edges of the third and fourth ventricles, lacking the regular blood-brain barrier and thus serving as significant sites for neural-endocrine interaction. [They include the area postrema, the median eminence, the subcommissural organ, the subfornical organ, and the organum vasculosum of the lamina terminalis. Sometimes also included are the funiculus separans, the neurohypophysis, and the pineal body.]

Front 50

Hydrocephalus

Back 50

A usually congenital (less often acquired, e.g., from tubercular meningitis) progressive condition in which an abnormal accumulation of cerebrospinal fluid in the cerebral ventricles causes enlargement of the skull and compression of the brain, destroying much of the neural tissue, and possibly increasing the size of the fontanelles and even the top of the head in newborns where skull bones have not united. aka water on the brain.

Front 51

Nucleus

Back 51

A group of specialized nerve cells, or a localized mass of gray matter, carrying out specific functions in the brain; a term less often applied to gray matter in the spinal cord.

Front 52

Basal nuclei

Back 52

A series of four to six paired (right and left) subcortical nuclei occupying space within the interior of the boundary area between frontal and temporal lobes of the cerebral hemispheres which receive input from cortical motor and somatosensory areas and provide output to the thalamus and midbrain; these connections (along with output from the cerebellum) are essential for execution of normal smooth coordinated voluntary movements.

Front 53

Epithalamus

Back 53

A thin mass of nervous tissue (gray and white matter) located in the dorsal posterior subdivision of the diencephalon, and forming the roof of the third ventricle, and including the pineal gland; its gray matter is involved in emotional and visceral responses to odors and its white fibers form a link between the limbic system and other parts of the brain.

Front 54

Thalamus

Back 54

A pair of large ovoid masses of gray matter situated in the posterior part of the diencephalon on either side of the third ventricle which process sensory impulses (except olfaction) by gating out irrelevant sensory information while directing relevant information to the cerebral cortex and it is also important in motor control; it is divided into two major part: dorsal and ventral, each of which contains many nuclei.

Front 55

Hypothalamus

Back 55

The part of the brain which lies below the thalamus, forming the major portion of the ventral region of the diencephalon and which functions to regulate bodily temperature, water balance, carbohydrate and fat metabolism among other metabolic processes, and autonomic activities and also contributes to the regulation of internal homeostasis by neurosecretory functions which control the activity of the pituitary gland.

Front 56

Intermediate mass

Back 56

An apparently functionless mass of gray matter in the midline of the third ventricle that is found in many but not all human brains and is formed when the surfaces of the thalami protruding inward from opposite sides of the third ventricle make contact and fuse.

Front 57

Mammillary region

Back 57

A small portion of the inferior surface of the hypothalamus containing nuclei associated with memory.

Front 58

Feeding center

Back 58

Collections of neurons in the hypothalamus which evaluate and respond to changes in the blood levels of various nutritional metabolites, e.g., blood glucose, by issuing commands to brain stem centers that initiate behaviors leading to ingestion of foods; aka hunger center.

Front 59

Satiety center

Back 59

The ventromedial region of the hypothalamus which is activated by hyperglycemia and by stretching sensations from the stomach to act to inhibit the feeding center of the hypothalamus, thus inhibiting food intake.

Front 60

Thirst center

Back 60

The region of the hypothalamus which is close to the site of production of ADH; this center receives input from osmoreceptors, possibly the same ones responsible for control of ADH release; the threshold for thirst is a plasma osmolarity of about 295 mOsm/L and is rapid in onset; this center also receives input from baroreceptors when blood volume decreases and this center is responsive to angiotensin II.

Front 61

Pineal gland

Back 61

A small endocrine organ situated in the diencephalon beneath the back part of the corpus callosum in the roof of the third ventricle of the brain which secretes the hormone melatonin; in the human it appears to play a role in sleep-wake cycles and may contribute to the regulation of the onset of puberty.

Front 62

Melatonin

Back 62

The hormone, a derivative of the amino acid tryptophan, produced by the pineal gland; in humans rising levels induce sleep; it also inhibits the stimulation of gonadotropin (LH) activity before puberty.

Front 63

Infundinulum

Back 63

The stalk connecting the hypothalamus to the pituitary gland and the route for the vessels of the hypothalamic-hypophysial portal system.

Front 64

Pituitary gland

Back 64

A small oval endocrine gland attached to the base of the brain by the infundibulum and housed in the sella tursica fossa of the sphenoid bone; it is regulated by the hypothalamus; it consists of an anterior and a posterior lobe, the secretions of which control many of the other endocrine glands and influence growth, metabolism, and maturation; anterior lobe hormones include growth hormone, thyroid-stimulating hormone, adrenocorticotropic hormone, prolactin, luteinizing hormone, follicle-stimulating hormone and melanocyte-stimulating hormone and posterior lobe hormones include antidiuretic hormone = vasopressin and oxytocin. nickname - the master gland.

Front 65

Tentorium cerebilli

Back 65

A fold of the dura mater forming a roof over the cerebellum within the posterior cranial fossa, except for an anterior median opening through which the mesencephalon passes, and separating the cerebellum from the basal surface of the occipital and temporal lobes of the cerebral cortex; it supports the occipital lobes of the cerebrum, and has its posterior and lateral border attached to the skull and its anterior border free.

Front 66

Folia

Back 66

The folds of gray matter which form the cerebellar hemispheres; having the gray matter distributed in folds and grooves increases the surface area of the cortex to make room for additional neurons, and to facilitate diffusion of nutrients, respiratory gases, and wastes between the nervous tissue and the adjacent cerebrospinal fluid and the blood stream.

Front 67

Arbor vitae

Back 67

The white matter or myelinated nerve tissue of the cerebellum, which has a treelike outline in a median section.

Front 68

Falx cerebelli

Back 68

The smaller of the two folds of dura mater separating the hemispheres of the brain that lies between the lateral lobes of the cerebellum; a short process of dura mater projecting from the internal occipital crest below the tentorium, and bifurcating into two diverging limbs passing to either side of the foramen magnum.

Front 69

Reticular formation

Back 69

A diffuse network of nerve fibers and neurons collected in various nuclei in parts of the brainstem, which receives afferent axons from a variety of sources, especially from the face; this system is important in arousal, maintaining consciousness, wakefulness and muscle tone and contributes to sensory adaptation by filtering out repetitive stimuli.

Front 70

Reticular activating system

Back 70

The combination of the reticular formation in the brain stem and its connections which functions to produce arousal by responding to sensory stimuli (visual, auditory, cutaneous, olfactory, etc.) with impulses sent to higher centers; this system

Front 71

Cardiovascular center

Back 71

A major autonomic nucleus located deep inside the medulla which received visceral sensory information about blood pressure, blood oxygen levels, blood pH, etc., and integrates this information to regulate the rate of the heartbeat and the level of muscular tension in the blood vessels primarily via autonomic sympathetic visceral motor impulses. is suppressed by general anesthetic gases; efferent impulses are also transferred in descending pathways to control respiratory and cardiac rhythms.

Front 72

Medullary rhythmicity area

Back 72

A collection of neurons in the reticular formation within the medulla oblongata involved in establishing or modifying the pattern for breathing; within this area are two key components: (1) the ventral respiratory group (VRG) (formerly the inspiratory area) which autorhythmically stimulates spontaneous ventilation, resting or tidal breathing (eupnea), and (2) the dorsal respiratory group (DRG) (formerly the expiratory area) which responds to situations beyond those of the resting or tidal breathing (eupnea) to alter the pattern for ventilation in response to the physiological needs of the body for O2 and CO2 exchange and for blood acid-base balance.

Front 73

Pontine respiratory center

Back 73

A collection of neurons in the reticular formation within the medulla oblongata involved in establishing or modifying the pattern for breathing; within this area are two key components: (1) the ventral respiratory group (VRG) (formerly the inspiratory area) which autorhythmically stimulates spontaneous ventilation, resting or tidal breathing (eupnea), and (2) the dorsal respiratory group (DRG) (formerly the expiratory area) which responds to situations beyond those of the resting or tidal breathing (eupnea) to alter the pattern for ventilation in response to the physiological needs of the body for O2 and CO2 exchange and for blood acid-base balance.

Front 74

Substantia nigra

Back 74

A layer of large pigmented nerve cells in the midbrain (mesencephalon) which produce dopamine and whose destruction is associated with Parkinson's disease; it is involved in metabolic disturbances associated with Parkinson's disease and with Huntington's disease.

Front 75

Associatio fibers

Back 75

The various interneuron processes (axons and dendrites) which transmit nerve impulses between the various gyri and nuclei within a single cerebral hemisphere.

Front 76

Commissural fibers

Back 76

The various interneuron processes (axons and dendrites) which transmit nerve impulses from the various gyri and nuclei within a single cerebral hemisphere to corresponding locations in the opposite hemisphere; e.g., many of the fibers in the corpus callosum and anterior and posterior commissures.

Front 77

Projection fibers

Back 77

The various interneuron processes (axons and dendrites) which transmit nerve impulses from the various gyri and nuclei within the cerebral hemispheres to various locations in other parts of the brain and spinal cord; e.g., the various ascending and descending tracts of white matter connecting the cerebrum to the rest of the CNS.

Front 78

Corpus callosum

Back 78

The arched bridge of commissural white fibers, situated above the thalamus, which forms the roof of the lateral and third ventricles and which connects the two cerebral hemispheres, allowing communication between the right and left sides of the brain.

Front 79

Functional areas

Back 79

The general classification of regions of the cerebral cortex by main function; there are three types of functional areas: (1) sensory areas which receive and interpret somatic sensory impulses including cutaneous sensations, the five special senses, and some aspects of proprioception (however, little visceral sensory information is routed to the cortex), (2) association areas which integrate sensory information with emotional states, memories, learning and rational thought processes, and, (3) motor areas which generate impulses which innervate voluntary skeletal muscles.

Front 80

Sensory areas

Back 80

Specific areas of the cerebral cortex which receive and interpret somatic sensory impulses, e.g., olfaction in the frontal lobe, cutaneous sensations in the parietal lobe, visual sensations in the occipital lobe, taste, hearing, and equilibrium in the temporal lobe; visceral sensory impulses are received and interpreted in the diencephalon, cerebellum, and brain stem.

Front 81

Motor areas

Back 81

Specific areas of the cerebral cortex, diencephalon, cerebellum, brain stem and spinal cord which generate impulses which innervate all effectors in the body, e.g., voluntary skeletal muscles, involuntary muscles, and glands, both endocrine and exocrine.

Front 82

Association areas

Back 82

Specific areas of the cerebral cortex which integrate sensory information with emotional states, memories, learning and rational thought processes.

Front 83

Primary motor cortex

Back 83

The location, just anterior to the central sulcus in the frontal lobe of the cerebral cortex, of the gray matter motor neurons which initiate impulses routed through the medulla and spinal cord which represent the conscious voluntary commands to the prime movers of skeletal muscle groups for specific actions; it is highly organized with specific regions representing each part of the body.

Front 84

Primary sensory cortex

Back 84

The location, just posterior to the central sulcus in the parietal lobe of the cerebral cortex, of the somatic sensory neurons which receive impulses routed through the thalamus, medulla and spinal cord which respond with the first conscious perceptions/awareness of cutaneous sensations arriving from stimulated receptors in the skin and subcutaneous tissues; it is highly organized with specific regions representing each part of the body.

Front 85

Frontal eye field

Back 85

A specific motor area within the frontal cortex which controls the voluntary scanning movements of the eyes, such as tracking a bird in flight, by sending impulses to the extrinsic muscles of the eyes.

Front 86

Limbic system

Back 86

A group of interconnected subcortical structures, (e.g., the hypothalamus, the hippocampus, and the amygdala) involved in olfaction, emotion, motivation, behavior, and various autonomic functions.

Front 87

Electroencephalogram (EEG)

Back 87

A diagnostic test which records a graphic record of the electrical activity of the brain (brain waves) using highly sensitive electrodes attached to the scalp and connected to an electroencephalograph; commonly used in the evaluation of neurological diseases, e.g., seizures, epilepsy, etc.; aka encephalogram.

Front 88

Brain waves

Back 88

Brain waves, or the EEG, are electrical signals that can be recorded from the brain, either directly or through the scalp; the kind of brain wave recorded depends on the behavior of the subject, and is the visible evidence of the kind of neuronal (brain cell) processing necessary for that behavior; the most common coherent patterns are classified as alpha (subject relaxed), beta (subject concentrating, alert, anxious, panicky), delta (sleep or disconnection from body), and theta (creative, pleasurable or confused states).

Front 89

Brain lateralization

Back 89

A significant division of labor recognized in the cerebrum in which (1) somatic sensory information from and somatic motor commands to the left side of the body are routed from/to the right cerebral hemisphere and vice versa; (2) the left side of the brain is dominant for language skills in 95% of right-handed individuals and in 60-70% of left-handed individuals; (3) for a majority of individuals the left cerebral hemisphere is also dominant for math skills and logic; (4) for a majority of individuals the right cerebral hemisphere is dominant for spatial abilities, face recognition, visual imagery, and musical skills.

Front 90

Neurosecretory cells

Back 90

A diverse group of specialized cells derived from nervous tissue which produce regulatory hormones which are secreted into the blood stream to circulate and reach their target organs to trigger a response; within the central nervous system, neurosecretory cells are found primarily in the hypothalamus where the secretions are transferred to the pituitary gland and in the pineal body; within the peripheral nervous system, neurosecretory cells are found in the adrenal medulla and within the walls of the gastrointestinal tract.

Front 91

Neuromodulators

Back 91

Molecules which potentiate or inhibit the transmission of a nerve impulse but are not the actual means of transmission itself; while they are similar to neurotransmitters, they do not directly trigger impulse transmission, but facilitate or suppress the initiation of impulse transmission; another difference is that neuromodulators may simultaneously affect larger regions within the CNS than simply an individual synapse.

Front 92

Acetylcholine (ACh)

Back 92

A CNS & PNS neurotransmitter which is a derivative of choline; it is synthesized, stored and released at the ends of nerve fibers at the neuromuscular junction. in the somatic and parasympathetic nervous systems, and in the brain where it may also act as a neuromodulator.

Front 93

Biogenic amines

Back 93

a wide variety of small compounds derived by simple enzymatic modification of various individual amino acids which have active physiological properties such as serving as hormones, local hormones, neurotransmitters, neuromodulators, etc.

Front 94

Neuropeptides

Back 94

Any of various short-chain peptides (oligopeptides) found in brain tissue, such as endorphins; many neuropeptides are also synthesized and released as hormones by non-neuronal cells; these neuroactive molecules coordinate, integrate, and regulate physiological processes in all organisms, throughout all phases of development; acting as neurohormones, neurotransmitters, and/or neuromodulators, they maintain physiological homeostasis and influence important behavioral patterns.

Front 95

Enkephalins

Back 95

Either of two closely related CNS neuropeptides (pentapeptides) having opiate qualities (producing pain relief by central inhibition of incoming pain impulses) and occurring in the brain, spinal cord, and other parts of the body.

Front 96

Endorphins

Back 96

Any of a group of large peptide neurohormones that bind to opiate receptors and are found mainly in the brain; they reduce the sensation of pain and affect emotions.

Front 97

Dynorphins

Back 97

A class of opioid peptides which have modulatory effects on several CNS functions, including memory acquisition, stress and movement.

Front 98

Gas neurotransmitter

Back 98

A recently discovered group of novel neurotransmitters which are small soluble molecules synthesized on demand (when the action potential arrives) by certain neurons; these compounds then diffuse into nearby neurons or even back into the sending neuron to stimulate a variety of effects; e.g., nitric oxide (NO) and carbon monoxide (CO).

Front 99

Concussion

Back 99

A traumatic injury to an organ, especially the brain, produced by a violent blow and followed by a temporary or prolonged loss of function; some symptoms of a concussion are: persistent low-grade headaches; having more trouble than usual remembering things, concentrating, or making decisions; feeling tired all the time; feeling sad, anxious, or listless; or becoming easily irritated for little or no reason.

Front 100

Contusion

Back 100

A bruise; an injury limited to some disorganization of the subcutaneous tissue and effusion of blood beneath the skin, but without an apparent open wound.

Front 101

Laceration

Back 101

A jagged wound caused by tearing or cutting tissue.

Front 102

Aphasia

Back 102

A partial or total loss of the ability to articulate ideas or comprehend spoken or written language, resulting from damage to the brain caused by injury or disease, although the vocal organs remain intact, and the intellect is preserved.

Front 103

Ischemia

Back 103

A decrease in the blood supply, and, therefore, oxygen and nutrients, to a body organ, tissue, or part caused by constriction or obstruction of the blood vessels.

Front 104

Stroke

Back 104

A sudden loss of brain function resulting when the rupture or occlusion of a blood vessel leads to oxygen starvation in the brain, characterized by loss of muscular control, diminution or loss of sensation or consciousness, dizziness, slurred speech, or other symptoms that vary with the extent and severity of the damage to the brain.

Front 105

Transient ischemic attack

Back 105

A temporary blockage of the blood supply to the brain caused by a blood clot and usually lasting ten minutes or less, during which dizziness, blurring of vision, numbness on one side of the body, and other symptoms of a stroke may occur; nickname ministroke.

Front 106

Alzheimer's disease

Back 106

An organic brain disease marked by the loss of cognitive ability, generally over a period of 10 to 15 years, and associated with the development of abnormal tissues, tangled nerve fiber masses, cortical atrophy and protein deposits in the cerebral cortex; a progressive form of presenile dementia that is similar to senile dementia except that it usually starts in the 40s or 50s; first symptoms are impaired memory which is followed by impaired thought and speech and finally complete helplessness.

Front 107

Parkinson's disease

Back 107

A progressive nervous disease, sometimes with a hereditary component, occurring most often after the age of 50, associated with the destruction of brain cells that produce dopamine and characterized by muscular tremor, slowing of movement, partial facial paralysis, peculiarity of gait and posture, and weakness; nickname shaking palsy.

Front 108

Cerebral palsy

Back 108

A disorder usually caused by motor area brain damage occurring at or before birth and marked by muscular impairment, a loss or deficiency of motor control with involuntary spasms; often accompanied by poor coordination, it sometimes involves speech and learning difficulties; it may congenital, e.g., fetal hypoxia, placental dysfunction, or acquired after birth, e.g., from head injury, jaundice, Rh incompatibility, and rubella (German measles); nickname spastic paralysis.

Front 109

Dyslexia

Back 109

A learning disorder marked by impairment of the ability to recognize and comprehend written words.

Front 110

Reye's syndrome

Back 110

An acute encephalopathy characterized by fever, vomiting, fatty infiltration of the liver, disorientation, and coma, occurring mainly in children and usually following a viral infection, such as chicken pox or influenza; while the cause and cure remain unknown, research has established a link between Reye's Syndrome and the use of aspirin and other salicylate-containing medications.

Front 111

Raynaud's syndrome

Back 111

A circulatory disorder involving improper autonomic regulation of blood flow, which affects the hands and feet, caused by vessel spasms, when exposed to cold, from an emotional upset, smoking cigarettes or working with vibrating machinery, which lead to insufficient blood supply to these parts and resulting in cyanosis, numbness, pain, and, in extreme cases, gangrene.

Front 112

Encephalitis

Back 112

Any inflammation of the brain, usually caused by a virus; symptoms include headache and neck pain and drowsiness and nausea and fever.

Front 113

Poliomyelitis

Back 113

A highly infectious viral disease that chiefly affects children, whose early symptoms include fever, sore throat, headaches and vomiting, often with stiffness of the neck and back; and, in its severe acute form, causes inflammation of somatic motor neurons of the ventral horn of the spinal cord and of brainstem, leading to paralysis, muscular atrophy, and often deformity; through vaccination, the disease is preventable; nickname infantile paralysis.The removal of cerebrospinal fluid from the subarachnoid space of the lumbar region of the spinal cord for diagnostic or therapeutic purposes, e.g., to inject anesthetic drugs.

Front 114

Spinal tap

Back 114

The removal of cerebrospinal fluid from the subarachnoid space of the lumbar region of the spinal cord for diagnostic or therapeutic purposes, e.g., to inject anesthetic drugs.

Front 115

Vertebral column

Back 115

The series of vertebrae forming the axis of the skeleton and protecting the spinal cord; divided into five groups by location: cervical, thoracic, lumbar, sacral and coccygeal groups. aka. spinal column, spine.

Front 116

Vertebral canal

Back 116

The passage formed by the vertebral foramen in the articulated successive vertebrae through which the spinal cord and its membranes pass.

Front 117

Denticulate ligament

Back 117

A band of fibrous pia mater extending along the spinal cord on each side between the dorsal and ventral roots of the spinal nerves; it pierces the arachnoid and is attached to the dura mater at 21 points; this* stabilizes the spinal cord within the vertebral canal and decreases the likelihood of cord damage when physical trauma occurs. (*The filum terminale has a similar function.).

Front 118

Spinal cord

Back 118

The inferior portion of the Central Nervous System; the thick, whitish, cylindrical (slightly flattened dorso-ventrally) mass of nervous tissue that extends from the medulla oblongata down through the upper two-thirds of the spinal canal in the vertebral column to the upper lumbar region and from which the spinal nerves branch off to various parts of the body; the nervous tissue consists of nerve fibers and nerve cells, the latter being confined to the gray matter of the central portions of the cord, while the peripheral white matter is composed of nerve fibers only; the center of the cord is traversed by a slender canal connecting with the ventricles of the brain which contains cerebrospinal fluid.

Front 119

Cervical enlargement

Back 119

An expansion in the mass and diameter of the spinal cord in the region of C3-4 - T1-2 where motor neurons located in prominent ventral horns supply the upper limb muscles and where there are large number of axons entering and leaving the spinal cord to innervate the upper extremity.

Front 120

Lumbar enlargement

Back 120

An expansion in the mass and diameter of the spinal cord in the region of T10-12 - L1-2 where motor neurons located in prominent ventral horns supply the lower limb muscles and where there are large number of axons entering and leaving the spinal cord to innervate the lower extremity.

Front 121

Anterior median fissure

Back 121

The groove along the anterior midline of the spinal cord that incompletely divides it into symmetrical halves; it increases the surface area of the spinal cord for exchange of nutrients and oxygen with the blood stream and the cerebrospinal fluid.

Front 122

Posterior median sulcus

Back 122

The groove along the posterior midline of the spinal cord that incompletely divides it into symmetrical halves; it increases the surface area of the spinal cord for exchange of nutrients and oxygen with the blood stream and the cerebrospinal fluid.

Front 123

Conus medullaris

Back 123

The short tapered end of the spinal cord which is found just inferior to the lumbar enlargement of the cord in the region of L1-2.

Front 124

Cauda equina

Back 124

The spinal nerve roots with a common covering of meninges which extend out from the end of the spinal cord and go down the spinal canal through the lower part of the spine canal in the region of the lower lumbar vertebrae, sacrum and coccyx; it looks somewhat like a horse's tail.

Front 125

Filum terminal

Back 125

The slender threadlike prolongation of the spinal cord below the origin of the lumbar nerves and the last portion of the pia mater; this* stabilizes the spinal cord within the vertebral canal and decreases the likelihood of cord damage when physical trauma occurs. (*The denticulate ligament has a similar function.)

Front 126

Gray commissure

Back 126

The central crossbar of gray matter, observable in every segment of the spinal cord, which encloses the central canal and connects with the masses of gray matter on each side.

Front 127

Central canal

Back 127

The narrow tube originating posteriorly from the fourth ventricle which runs throughout the center of the medulla oblongata and the spinal cord; it is lined by ependymal cells and contains cerebrospinal fluid which is flowing posteriorly.

Front 128

Anterior white commissure

Back 128

The relatively narrow crossbar of white matter, observable in every segment of the spinal cord, which lies anterior/ventral to the gray commissure and posterior/dorsal to the anterior median fissure, and which contains various nerve fibers crossing from one side of the cord to the other.

Front 129

Posterior white commissure

Back 129

The relatively narrow crossbar of white matter, observable in every segment of the spinal cord, which lies posterior/dorsal to the gray commissure and anterior/ventral to the posterior median sulcus, and which contains various nerve fibers crossing from one side of the cord to the other.

Front 130

Anterior gray horn

Back 130

The mass of gray matter, observable in every segment of the spinal cord, which houses the the soma/cell bodies of the somatic motor (efferent) neurons (and various interneurons) and from which motor (efferent) axons emerge, exiting the cord, to form the anterior/ventral root of each spinal nerve.

Front 131

Posterior gray horn

Back 131

The mass of gray matter, observable in every segment of the spinal cord, which houses the soma/cell bodies of the various interneurons which receive sensory (afferent) impulses, which enter the cord via the posterior/dorsal root of each spinal nerve, from the somatic and visceral sensory (afferent) neurons which reside in the posterior/dorsal/sensory root ganglion.

Front 132

Lateral gray horn

Back 132

The masses of gray matter, observable in only the thoracic, lumbar and sacral segments of the spinal cord, which houses the the soma/cell bodies of the autonomic/visceral motor (efferent) neurons (and various interneurons) and from which visceral motor (efferent) axons emerge, exiting the cord, to form the anterior/ventral root of each spinal nerve; this is a major control center for the Autonomic Nervous System (ANS).

Front 133

Colimns (funiculi)

Back 133

The three regional (dorsal/posterior, lateral, ventral/anterior) collections of white matter on each side of the spinal cord which are further subdivided into various specifically named ascending and descending white tracts (fasciculi); they transmit nerve impulses between upper and lower regions of the cord and to and from the brain; they are best observed in cross sections of the spinal cord and brain stem.

Front 134

Tracts (fasciculi)

Back 134

Specific groups of neuron processes (axons and/or dendrites) which carry similar functional types of impulses to and from similar destinations within the central nervous system (CNS); individual ascending and descending white fiber tracts which are grouped into three regional (dorsal/posterior, lateral, ventral/anterior) columns (funiculi) on each side of the spinal cord; in general, their names combine and indicate both their origin and destination; they transmit nerve impulses between upper and lower regions of the cord and to and from the brain; they are best observed in cross sections of the spinal cord and brain stem.

Front 135

Ascending (sensory) tracts

Back 135

The white fiber tracts/fasciculi in the brain stem and spinal cord which carry primarily somatic and visceral sensory (afferent) information superiorly to higher centers with synaptic connections higher in the cord or within the brain.

Front 136

Descending (motor) tracts

Back 136

The white fiber tracts/fasciculi in the brain stem and spinal cord which carry primarily somatic and visceral motor (efferent) information inferiorly to lower centers with synaptic connections lower in the cord.

Front 137

Spinal segment

Back 137

The structural subdivisions of the spinal cord defined by the origin of a pair of spinal nerves from each subdividion or level within the cord (spinal segment); each subdivision is roughly equivalent to the individual vertebrae of the spinal/vertebral column (cervical, thoracic, lumbar and saccral), but in the adult are located somewhat superior to the comparable bone.

Front 138

Spinal nerves

Back 138

The 31 pairs of mixed (m/s) nerves which arise from the various spinal segments of the spinal cord, which originate as dorsal and ventral roots which combine the in the region of the intervertebral foramen and shortly thereafter branch into various rami to innervate various regions of the body, the trunk, arms, legs, and internal organs.

Front 139

Posterior root

Back 139

The collection of afferent sensory processes, emanating from the soma/cell bodies of the somatic and visceral sensory (afferent) neurons which reside in the posterior/dorsal/sensory root ganglion, which merge with the anterior root/ventral/motor root to form the spinal nerve laterally and which emerge from the posterior/dorsal horn at a particular spinal segment.

Front 140

Posterior

Back 140

The enlargement found on each posterior/dorsal/sensory root which houses the soma/cell bodies of the somatic and visceral (afferent) sensory neurons serving a particular spinal segment.

Front 141

Anterior root

Back 141

The collection of efferent motor processes, emanating from the soma/cell bodies of the somatic and autonomic/visceral motor (efferent) neurons which reside in the lateral and anterior/ventral horns of the gray matter, which merge with the posterior root/dorsal/sensory root to form the spinal nerve laterally and which emerge from the anterior/ventral horn at a particular spinal segment.

Front 142

Ramis/rami

Back 142

A general anatomical term for a branch which may be applied to a nerve, a blood vessel, or a region of a bone; in the peripheral nervous system, especially the first branches from each spinal nerve.

Front 143

Sensory modality

Back 143

Any of the various types of sensation, such as cutaneous senses, taste, smell, vision, hearing, equilibrium, proprioception, and visceral sensations.

Front 144

Somatic sensations

Back 144

The perceptions associated with stimulation of exteroreceptors to changes in the external physical environment and routed to the somatosensory cortex for interpretation; modalities include cutaneous senses (touch, pressure, vibration, pain, temperature), taste, smell, vision, hearing, and equilibrium; proprioception is also considered a somatic sensation.

Front 145

Visceral sensations

Back 145

The perceptions associated with stimulation of interoreceptors to changes in the internal physical environment and routed to the hypothalamus and brain stem for interpretation; modalities include chemoreceptors responding to changes in concentration of various molecules, e.g., glucose, O2, electrolytes, etc., mechanoreceptors responding to changes in the dimensions of internal organs, e.g., expansion of a portion of the G.I. tract, urinary bladder, etc., thermoreceptors responding to body temperature, and nociceptors responding to visceral pain.

Front 146

Proprioception

Back 146

The unconscious perception of movement, position, location and spatial orientation of the body and its parts arising from stimuli within the body itself; the sensory modality in which mechanoreceptors respond to stretching of a muscle, tendon, or ligament or responding to the movement of special structures in the inner ear; the mechanism involved in the self-regulation of posture and movement.

Front 147

Adaptation (by sensory receptor)

Back 147

The responsive adjustment of a sensory receptor (or sense organ, such as the ear), to constant condition (constant stimulus strength), such as pressure or noise; the decline in frequency of impulse transmissions of a sensory receptor or sensory neuron under conditions of constant stimulation; this response allows the conscious brain to focus on the more important new or variable sensations which affect the body, while ignoring less important unchanging sensations.

Front 148

Mechanoreceptor

Back 148

A specialized sensory end organ or sensory neuron which responds to mechanical stimuli such as tension (stretching), pressure, or displacement/distortion (bending); they tranduce mechanical energy into nerve impulses (graded potentials).

Front 149

Thermoreceptor

Back 149

A sensory receptor or sensory neuron which responds to changes in temperature (heat and cold); they tranduce heat energy into nerve impulses (graded potentials).

Front 150

Nociceptor

Back 150

A sensory receptor or sensory neuron which responds to injurious or painful stimuli; they tranduce a variety of forms of energy into nerve impulses (graded potentials).

Front 151

Photoreceptor

Back 151

A nerve ending, cell, or group of cells specialized to respond to electromagnetic radiation, typically wavelengths of visible light, but in some organisms to infrared or ultraviolet wavelengths as well; they tranduce light energy into nerve impulses (graded potentials); in humans (and most vertebrates), these are the rods and cones within the deepest layer of the retina of the eye.

Front 152

Chemoreceptor

Back 152

A sensory nerve cell or sense organ which responds to chemical stimuli; they tranduce chemical bond energy into nerve impulses (graded potentials); includes exteroreceptors for smell and taste and enteroreceptors sensitive to concentration changes of a variety of molecules in the blood or other body fluids.

Front 153

Cranial nerves

Back 153

The 12 pairs of nerves (some pure sensory, some motor (with proprioception), and some mixed) which arise from the base of the brain and serve various regions of the head and neck, and, in the case of the Vagus, nerve X, organs and tissues in the thoracic and abdominopelvic cavities.

Front 154

Spinal nerves

Back 154

The 31 pairs of mixed (motor and sensory) nerves which arise from the various spinal segments of the spinal cord, which originate as dorsal and ventral roots which combine the in the region of the intervertebral foramen and shortly thereafter branch into various rami to innervate various regions of the body.

Front 155

Ramus/rami

Back 155

A general anatomical term for a branch which may be applied to a nerve, a blood vessel, or a region of a bone.

Front 156

Dorsal ramus

Back 156

One of the first three branches of each spinal nerve, this small branch supplies the skeletal muscles and skin of the posterior portion of the neck or trunk of the body.

Front 157

Ventral ramus

Back 157

One of the first three branches of each spinal nerve, this thick branch supplies the skeletal muscles and skin of the lateral and anterior portions of the neck or trunk of the body.

Front 158

Meningial branch/ramus

Back 158

One of the first three branches of each spinal nerve, this smallest branch turns back through the intervertebral foramen to supply the spinal meninges and the blood vessels of the spinal meninges.

Front 159

Rami communicantes

Back 159

A fourth branch of the thoracic region spinal nerves, this branch, which is joined to the base of the ventral ramus, contains autonomic (visceral motor) fibers which innervate certain of the thoracic or abdominal organs.

Front 160

Nerve plexuses

Back 160

Interlacing networks of nerve fibers which originate from the ventral rami of spinal nerves (except those in the region T2 - T12) in which individual nerve processes from individual spinal segments become redistributed to that (1) each resulting branch of the plexus contains fibers from several spinal nerves and (2) fibers from each ventral ramus travel to the periphery of the body by several routes; this arrangement permits each skeletal muscle in a limb to be innervated by motor (afferent) fibers from more than one spinal segment -- as a result, an injury to a single spinal segment or spinal motor (ventral) root cannot completely paralyze any limb muscle.

Front 161

Cervical plexus

Back 161

The most superior of the four pairs of plexuses (interlacing branches of the ventral rami of spinal nerves), which provide cutaneous nerves to the skin of the neck, the region of the ear, the back of the head and the shoulder and motor nerves to muscles of the anterior neck and to the diaphragm, is formed from the ventral rami of C1-4.

Front 162

Brachial plexus

Back 162

The large plexus (interlacing branches of the ventral rami of spinal nerves), located in the neck and the axilla, which provides essentially all the innervation to the upper limb, is formed from the ventral rami of C4-5-C8 and T1-2.

Front 163

Lumbar plexus

Back 163

The large plexus (interlacing branches of the ventral rami of spinal nerves), located in the hip, superior and anterior to the ilium within the psoas muscle, which provides the innervation to the abdominal wall muscles, the psoas muscle, and the muscles of the anterior and medial thigh as well as cutaneous sensation from anterior thigh and the medial surface of the lower leg, is formed from the ventral rami of L1-4.

Front 164

Sacral plexus

Back 164

The most inferior of the four pairs of plexuses (interlacing branches of the ventral rami of spinal nerves), located immediately inferior to the lumbar plexus, which provides the innervation to the buttock and lower leg, the pelvic structures and the perineum, is formed from the ventral rami of L4 and S1-4.

Front 165

Intercostal nerves

Back 165

The major branch of each of the ventral rami from spinal nerves T1 - T12, which provides mixed (sensory and motor) innervation to the intercostal muscles between the ribs and the muscles and skin of the anteriolateral thorax and most of the abdominal wall.

Front 166

Dermatome

Back 166

(1) anatomy - The area of skin innervated by the cutaneous branches of a single spinal nerve (this same area of skin will receive some additional innervation from branches of both the spinal nerve of the segment above and the segment below. (2) embryology - The portion of somite mesoderm which forms the dermis of the skin.

Front 167

Myotome

Back 167

embryology - The portion of somite mesoderm which forms the skeletal muscles of the neck, trunk of the body, and via their limb buds, the muscles of the limbs.

Front 168

Fascicles

Back 168

The organizational subunits of peripheral nerves, the bundles of myelinated and unmyelinated processes being routed to and from similar destinations/locations which are bound by a dense fibrous connective tissue liner called the perineurium.

Front 169

Epineurium

Back 169

The outermost dense irregular fibrous connective tissue protective sheath surrounding each peripheral nerve, composed of various nerve fascicles/bundles; this outer layer contains some adipocytes and small blood vessels.

Front 170

Perineurium

Back 170

The intermediate layer of dense irregular fibrous connective tissue protective sheath surrounding each nerve fascicle/bundle within a peripheral nerve, composed of various nerve fascicles/bundles.

Front 171

Endoneurium

Back 171

The innermost loose irregular fibrous connective tissue protective sheath surrounding each nerve fiber (axon or dendrite) within each fascicle/bundle of a peripheral nerve; this layer will be external to the myelin sheath of a myelinated axon; this inner layer contains some mast cells and small blood capillaries.

Front 172

REFLEX-
General

Back 172

(1) general - A relatively rapid and predictable motor response to a stimulus which will be repeated in a similar fashion each time the stimulus is presented; it consists of five general components: the receptor(s) for the stimulus, the sensory neuron(s) transmitting afferent impulses to the CNS, the control/integration center(s) within the CNS, the motor neuron(s) transmitting efferent impulses away from the CNS, and the effector(s) which respond to the afferent impulses with the specific motor response(s)

Front 173

REFLEX-
Learned or acquired reflex

Back 173

(3) learned or acquired reflex - a reflex which is learned through practice or repetition and may involve both a far more complicated set of triggering stimuli and a far more complicated pattern of motor response, e.g., the reflexive motor actions produced after one has learned to ride a bicycle or drive a car; most such reflexes are somatic because they involve complex response patterns from skeletal muscles.

Front 174

REFLEX-
Inborn or intrinsic reflex

Back 174

(2) inborn or intrinsic reflex - a reflex which is unlearned, unpremeditated, involuntary and in which the pathways are built into the neural anatomy of each individual during development; depending on the effectors involved, such reflexes may be termed somatic or autonomic; although unlearned in their original form, they are sometimes subject to modification by learning from experience

Front 175

Spinal reflex

Back 175

The inborn or intrinsic somatic (skeletal muscle response) reflexes (relatively rapid and predictable motor responses to stimuli) mediated by control centers in the spinal cord; although the central pathway(s) involve only spinal cord segment control, some spinal reflexes require the participation of higher brain centers for completion and most spinal reflexes also report information about the reflex having occurred to higher centers in the brain; in many of these reflexes, somatic motor neurons, whose cell bodies (somas) reside in the ventral (anterior) horn of the spinal cord, connect or synapse directly with skeletal muscle cells forming motor units.

Front 176

Cranial reflexes

Back 176

The inborn or intrinsic somatic (skeletal muscle response) and visceral (Autonomic) reflexes (relatively rapid and predictable motor responses to stimuli) mediated by control centers in the brain; the pathway(s) usually involve cranial and, perhaps, cervical spinal nerves; in many of these reflexes, somatic motor neurons, whose cell bodies (somas) reside in gray matter nuclei within the diencephalon or brain stem, connect or synapse directly with skeletal muscle cells forming motor units.

Front 177

Autonomic reflex

Back 177

The inborn or intrinsic visceral (cardiac or smooth muscle or glandular response) reflexes (relatively rapid and predictable motor responses to stimuli) mediated by control centers in the brain, particularly in the hypothalamus and brain stem, and in the spinal cord, particularly in the lateral horns of thoracic and lumbar spinal cord segments; these reflexes are involved in the automatic adjustment or negative feedback control of internal environment = internal homeostasis; in many of these reflexes, visceral motor neurons, whose cell bodies (somas) reside in the lateral horn of the spinal cord, connect to their effectors (smooth or cardiac muscle cells or endocrine or exocrine glands, in two cell efferent pathways; the first cell in the pathway, the preganglionic neuron, synapses with the second cell in the pathway, the postganglionic neuron, within an autonomic ganglion somewhere along the Peripheral Nervous System (PNS); these reflexes control internal environment and homeostasis.

Front 178

Pupillary reflex

Back 178

The variety of autonomic reflexes (relatively rapid and predictable motor responses to stimuli) in which the effectors are the radial and circular muscles of the iris of the eye and the responses are constriction or dilation of the pupil; stimuli are quite variable; responses include components of the light adaptation and dark adaptation processes.

Front 179

Somatic reflex

Back 179

Any reflex (relatively rapid and predictable motor response to a stimulus) in which the effectors are skeletal muscles, e.g., the patellar reflex, the flexor or withdrawal reflex, the crossed extensor reflex, the plantar reflex, the abdominal reflexes, etc.; most named somatic reflexes are inborn/intrinsic, but a variety of more complex learned/acquired reflexes may be included as somatic reflexes.

Front 180

Reflex neural pathway

Back 180

The anatomical route(s) which connect the components: the receptor(s) for the stimulus, the sensory neuron(s) transmitting afferent impulses to the CNS, the control/integration center(s) within the CNS, the motor neuron(s) transmitting efferent impulses away from the CNS, and the effector(s) which respond to the afferent impulses with the specific motor response(s)) of a particular reflex; these pathways control automatic unconscious programmed (hard-wired) responses to particular sensory stimuli.

Front 181

Receptor

Back 181

1.Physiology. A specialized cell or group of nerve endings or a specialized organ which responds to sensory stimuli of some modality. 2. Biochemistry. A molecular structure or site on the surface or interior of a cell that binds with substances such as hormones, antigens, drugs, or neurotransmitters.

Front 182

Sensory neuron

Back 182

A neuron, whose cell body generally is found in a peripheral ganglion such as a dorsal root ganglion, which conducts impulses representing information about an (external or internal) environmental change inwards to the brain or spinal cord.

Front 183

Integrating center

Back 183

Those cells, generally interneurons on the central nervous system, which receive sensory information from the (external or internal) environment, process that information, and, if appropriate, generate motor commands to effector organs in response to the stimulus from the (external or internal) environment.

Front 184

Association neuron

Back 184

A nerve cell found entirely within the central nervous system, often participating in a complex multicellular pathway, that acts as a link between sensory neurons and motor neurons or between other internal linking neurons and integrating or communicating or transmitting information between different parts of the CNS.

Front 185

Monosynaptic

Back 185

Having one neural synapse and referring to direct neural connections between just two neurons, commonly between a primary sensory neuron and a motor neuron in a simple reflex arc where no interneurons are involved.

Front 186

Polysynaptic

Back 186

Of or involving two or more synapses in the central nervous system and referring to direct neural connections between three or more neurons in any neural pathway, often used to describe reflex arcs in which one or more interneurons are involved.

Front 187

Motor neuron

Back 187

A neuron that conveys impulses outward from the central nervous system to a muscle, gland, or other effector tissue that regulates the activity of the effector.

Front 188

Effector

Back 188

A muscle, gland, or other organ capable of responding to a stimulus which has been evaluated by a control center, mediated by a nerve impulse or a hormonal signal.

Front 189

Muscle tone

Back 189

The normal degree of vigor and tension in maintained in skeletal muscles by involuntary spinal reflexes; the resistance of skeletal muscle to passive elongation or stretch.

Front 190

Stretch reflex

Back 190

A (usually) monsynaptic ipsilateral segmental reflex contraction of a muscle in response to stretching of an attached tendon or of the muscle itself; the receptors involved are golgi tendon organs and muscle spindles respectively; the stretch reflex is fast and has a fast onset and offset; it is important in anti-gravity responses; keeping the limbs extended so that one does not fall down; gravity exerts tension on the extensor muscles and they contract and keep the limbs straight.

Front 191

Muscle spindle

Back 191

A special mechanoreceptor organ involved in proprioception consisting of a group of sensory nerve endings wrapped around special muscle cells termed spindle fibers (intrafusal fibers) which have lost the capacity to contract; stretching the spindle fibers initiates nerve impulses in the sensory neurons which are transmitted to the spinal cord where various connections can be made to interneurons or motor neurons and the impulses may be routed to higher centers, e.g., the cerebellum and thalamus.

Front 192

Tendon organ

Back 192

A proprioceptive receptor which is located within the tendons found on each end of a muscle; these organs are composed of skeletal muscle cells (extrafusal muscle fibers) which enter a funnel-like capsule that is filled with collagen fiber bundles; nerve endings are entwined throughout these collagen fibers, and are triggered when tension in the muscle is transferred to the collagen fibers of the Golgi tendon organ; it responds to increased muscle tension or contraction as exerted on the tendon, by inhibiting further muscle contraction; when muscle contraction is excessive, the Golgi tendon organ protects against muscle damage; the proprioceptive sensory neuron of a Golgi tendon organ projects to the motor neurons located within the ventral horn of the spinal cord, where the inhibition occurs; unlike the muscle spindle, Golgi tendon organs do not respond to a change in muscle length, but rather in muscle tension.

Front 193

Ipsilateral

Back 193

Located on or affecting or relating to the same side of the body.

Front 194

Contralateral

Back 194

Located on or affecting or relating to the opposite side of the body.

Front 195

Reciprocal innervation

Back 195

Innervation so that the contraction of a muscle or set of muscles (as of a joint) is accompanied by the simultaneous inhibition of an antagonistic muscle or set of muscles; specific reflex arcs exist so that agonists/prime movers and antagonists do not generally contract simultaneously; the Golgi or Deep Tendon Reflex is an example of reciprocal innervation. aka reciprocal inhibition.

Front 196

Tendon reflex

Back 196

A type of monosynaptic ipsilateral segmental stretch reflex action in which a muscle is made to contract by a blow upon its tendon, e.g., the patellar reflex, the Achilles tendon reflex, the biceps reflex; its absence is generally a sign of disease.

Front 197

Flexor reflex

Back 197

A type of protective polysynaptic ipsilateral segmental reflex in which a painful stimulus triggers the contraction of ipsilateral flexor muscles (and the ipsilateral extensors are inhibited) which takes the limb or structure away from source of the pain; these reflexes have a slower onset and a longer response than the stretch (extensor) reflexes.

Front 198

Intersegmental reflex arc

Back 198

A polysynaptic neuron pathway which involves sensory impulses being received in one segment of the spinal cord and then stimulating interneurons which route the sensory information to motor neurons in both superior and inferior segments of the spinal cord in order to permit innervation of a variety of muscles in the reflex action.

Front 199

Crossed extensor reflex

Back 199

A polysynaptic contralateral segmental reflex that is usually associated with the same painful stimulus which triggered a flexor/withdrawal reflex; in the crossed extensor reflex, the contralateral extensors contract (and the ipsilateral flexors are inhibited) which tends to adjust for any shift in the center of gravity so that balance is maintained and body weight is properly supported.

Front 200

Patellar (knee jerk) reflex

Back 200

A monosynaptic ipsilateral segmental stretch reflex, resulting from a sharp tap on the patellar tendon, in which proprioceptive sensory information from muscle spindles in the quadriceps muscles of the thigh are routed to the appropriate spinal segments where motor impulses to the quadriceps muscle of the thigh cause a reflex extension of the leg.

Front 201

Achilles (ankle jerk) reflex

Back 201

A monosynaptic ipsilateral segmental stretch reflex in which a reflex plantar flexion (downward movement) of the foot is produced by a spasmodic contraction of the gastrocnemius and soleus muscles of the calf in response to sudden extension of the leg or the striking of the Achilles' tendon above the heel.

Front 202

Babinski sign or reflex

Back 202

A ipsilateral segmental reflex in which there is extension upward of the toes and the abduction of the toes when the sole of the foot is stroked firmly on the outer side from the heel to the front; normal in infants under the age of 2 years but a sign of brain or spinal cord injury or disease in older persons.

Front 203

Abdominal reflex

Back 203

The reflex ipsilateral contraction or quivering of the muscles of the abdominal wall and deviation of the umbilicus towards the stimulus in response to stimulation of the overlying skin; babies do not exhibit the abdominal reflex until about 6 months; absence of abdominal reflex is one of the classic criteria used in diagnosing MS.

Front 204

Anesthesia

Back 204

A local or general insensibility to pain and loss of bodily sensation with or without the loss of consciousness, induced by an an appropriate pharmacologic agent = anesthetic.

Front 205

General anesthesia

Back 205

A body-wide (general) insensibility to pain and loss of bodily sensation (anesthesia) characterized by unconsciousness, muscle relaxation, and loss of sensation over the entire body, and resulting from the administration of a general anesthetic or a mix of anesthetics and other supportive drugs.

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Local anesthesia

Back 206

The clinical application of an appropriate (local anesthetic) drug, applied or injected, to produce a regional (local) insensibility to pain and loss of bodily sensation (anesthesia) characterized by the loss of sensation only in the area of the body where a procedure is to be done or pain is to be temporarily alleviated.

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Analgesia

Back 207

A deadening or absence of the sense of pain without loss of consciousness, caused by endogenous endorphins and which can also achieved by a variety of classes of drugs including the opiates/opioids and the NSAIDS (non-steroidal anti-inflammatory drugs).

Front 208

Paresthesia

Back 208

An abnornal skin sensation, such as burning, prickling, itching, tingling, numbness, or hyperesthesia (increased sensitivity), with no apparent physical cause, usually associated with peripheral nerve damage.

Front 209

Neuritis

Back 209

Inflammation of a nerve or group of nerves, characterized by pain and tenderness over the nerves, with anesthesia and paresthesias, and sometimes loss of reflexes, and atrophy (wasting) of the affected muscles; in practice, the term is also used to denote noninflammatory lesions of the PNS.

Front 210

Sciatica

Back 210

Pain along the sciatic nerve usually caused by a herniated disk of the lumbar region of the spine and the pain, often characterized by paroxysmal attacks, radiating to the back or buttocks and to the back of the thigh, or in the leg or foot, following the course of the branches of the sciatic nerve; the name is also popularly applied to various painful affections of the hip and the parts adjoining it.

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Shingles

Back 211

An acute viral infection (herpes/varicella zoster -- the virus causing chicken pox in children) in adults characterized by inflammation of the sensory ganglia of certain spinal or cranial nerves and the eruption of vesicles/blisters along the affected nerve path; it usually strikes only one side of the body and is often accompanied by severe neuralgia; the disease arises by reactivation (usually associated with stress or a decline in cell-mediated immunity) of latent virus particles which persist in spinal or cranial nerve ganglia.

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Somatic senses

Back 212

The perceptions associated with stimulation of exteroreceptors to changes in the external physical environment and routed to the somatosensory cortex for interpretation; the set of five skin senses/modalities (pressure, touch, vibration, cold, warmth), two proprioceptive senses/modalities (sense of position, sense of force), and five kinesthetic (sense of body movements) senses/modalities (angle of joints, activities and tone of muscles, head movements, skin position relative to a touched surface, movements of the person within the environment (visual kinesthesis)); all are detected by mechanoreceptors except for cold and warmth which are detected by thermoreceptors. (Pain may be included but pain reception may be from both somatic and visceral sources.)

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Special senses

Back 213

Modalities of sensation which require complex specialized receptor organs for detection; in humans there are five (or six): sight, hearing, smell, taste, and equilibrium, both static and dynamic. [The so-called five senses are sight, hearing, smell, taste and touch. However, touch is not a special sense.]

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Transduction

Back 214

The conversion of the energy of a stimulus (electrical, mechanical, chemical, radiant, etc.) into another from of energy; in the nervous system, the energy of the stimulus is converted by a receptor into a nerve impulse = action potential for transmission to the central nervous system (CNS).

Front 215

Chemoreceptors

Back 215

Sensory nerve cells or sense organs which respond to chemical stimuli; including exteroreceptors for smell and taste and enteroreceptors sensitive to concentration changes of a variety of molecules in the blood or other body fluids.

Front 216

Fungiform papillae

Back 216

The second most numerous of the papillae of the tongue; small, rounded mushroom-shaped eminences on the upper surface of the tongue, especially at the tip and along the sides; one of the locations for taste buds containing chemoreceptors for taste sensations, particularly to sweet and sour tastes.

Front 217

Circumvallete papillae

Back 217

The third most numerous (about a dozen) and the largest of the papillae of the tongue; rounded mushroom-shaped eminences distributed in a “V”-shaped pattern at the junction of the anterior two-thirds and the posterior one-third of the tongue; one of the locations for taste buds containing chemoreceptors for taste sensations.

Front 218

Gustatory cells

Back 218

The specialized chemoreceptor cells found in taste buds which contain hair-like processes extending to openings in the bud (taste pore) to taste substances; there are five primary tastes: sour, salt, sweet, bitter and umami (beef).

Front 219

Olfactory epithelium

Back 219

The olfactory epithelium of each of the two nasal passages in humans is a 2.5 square centimeter patch of mucous membrane containing about 50 million sensory olfactory receptor cells; the reception of the odorant molecule and the beginning of sensory signal transduction occurs in the olfactory cilia, which are hair-like extensions of the receptor neurons (10-20 cilia per neuron); it is the sensory tissue served by the olfactory nerve, Cranial Nerve I.

Front 220

Olfactory cilia

Back 220

The hair-like extensions of the sensory olfactory receptor neurons (10-20 cilia per neuron) which sample the odorant chemicals from the air which become dissolved in the water of the nasal secretions.

Front 221

Olfactory receptor cells

Back 221

The specialized olfactory chemoreceptor neurons found in the olfactory epithelium which respond to the odorant chemicals from the air which become dissolved in the water of the nasal secretions have a turn-over rate of about 40 days; these cells transduce the stimuli interpreted as the sense of semll; these cells synapse with the olfactory receptor neurons which form axons which penetrate the cribiform plate of the ethmoid bone in bundles and synapse with neurons in the olfactory bulb.

Front 222

Olfactory bulbs

Back 222

The location of the cell bodies of the second order neurons (second in the transmission pathway) which receive nerve impulses carrying olfactory sensory information; they are located on the inferior surface of the frontal lobes of the cerebrum, directly above the cribiform plate of the ethmoid bone.

Front 223

Olfactory tracts

Back 223

The pathway for transmitting olfactory sensory information along the Olfactory nerves (cranial nerve I) to the primary olfactory cortex of the frontal lobes of the cerebrum without first passing through the thalamus; this bypass is unique to olfaction, and is thought to reflect the early development of the olfactory system in the evolution of vertebrates; odor information is widely distributed among other brain areas for conscious recognition of odors.

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Accessory structures of eyes

Back 224

The external protective appendages and supplementary components of the eye, external to the eyeball, which contribute indirectly to vision and image formation; they include the eyebrows, the eyelids and eyelashes, the conjunctiva, the lacrimal apparatus and the extrinsic eye muscles.

Front 225

Conjunctiva

Back 225

The thin, protective, moist mucous membrane lining and lubricating the eyelids and covering the anterior surface of the eye itself, i.e., lining the conjunctival sac.

Front 226

Lacrimal apparatus

Back 226

Those accessory structures of the eye which function in the production of tears including the lacrimal glands which synthesize the tears, and the drainage system for the tears, beginning with the openings, lacrimal puncta, to the lacrimal ducts, and the lacrimal sacs and nasolacrimal ducts; the tears moisten and lubricate the conjunctiva and contain protective compounds to inhibit microbes.

Front 227

Lacrimal gland

Back 227

An acinous exocrine gland about the size and shape of an almond which secretes tears, and is situated laterally and superiorly to the bulb of the eye in a shallow depression on the inner surface of the orbit of the frontal bone; it is regulated by visceral motor commands from the Autonomic Nervous System. aka tear gland.

Front 228

Nasolacrimal duct

Back 228

The major drainage tube (~1 cm) for tears from the nasolacrimal sac into the nasal cavity where the tears mix with nasal mucous secretions and are evaporated.

Front 229

Extrinsic eye muscles

Back 229

The six skeletal muscles (four rectus (inferior, medial, superior, and lateral) and two oblique (superior and inferior) which originate on the bones of the orbit and insert into the sclera of the eye and move each eyeball; they are comprised of many small motor units and are, therefore, capable of very precise control of eyeball movement; they are regulated by the somatic motor commands from the frontal eye fields of the frontal lobes of the cerebrum.

Front 230

Intrinsic eye muscles

Back 230

A set of smooth muscles within the eyeball: (1) The ciliary (smooth) muscle which inserts via the suspensory ligaments on to the periphery of the lens capsule; its state of contraction regulates the shape of the lens; (2) the circular smooth muscle of the iris which constricts the pupil when it contracts; (3) the radial muscle of the iris which dilates the pupil when it contracts; they are controlled by visceral motor commands from the Autonomic Nervous System.

Front 231

Tunics

Back 231

The three coats which form the wall of the eyeball, one inside the other, the outer fibrous, the middle vascular, and the inner sensory layers/coats/tunics.

Front 232

Fibrous tunic

Back 232

The outermost coat of the eyeball consisting of dense collagenous tissue and divided into an anterior transparent cornea and a posterior opaque (white) sclera; this layer provides support, protection and determines the shape of the eye.

Front 233

Sclera

Back 233

White opaque portion of the fibrous tunic of the eyeball, composed of a dense irregular fibrous connective tissue; it is the site of attachment for the extrinsic eye muscles which rotate the eyeball.

Front 234

Cornea

Back 234

Transparent dome-shaped anterior portion of the eyeball; part of the fibrous tunic, composed of a specially formed dense regular fibrous connective tissue covered by a nonkeratinized stratified squamous epithelium; it is a powerful refracting surface, providing 2/3 of the eye's focusing power.

Front 235

Vascular tunic

Back 235

The middle coat of the eyeball consisting of highly vascular and heavily pigmented connective tissue consisting of a posterior choroid layer and an anterior ciliary body and the iris.

Front 236

Choroid

Back 236

The posterior portion of the vascular middle tunic of the eyeball, lined on the inside by a layer of darkly pigmented cells; it provides the main blood supply to the back of the eye and gives rise to the ciliary body and the iris anteriorly.

Front 237

Ciliary body

Back 237

The thickened portion of the vascular tunic of the eye located between the choroid and the iris which contains a circular layer of ciliary muscles, smooth muscle controlled by the ANS, whose contraction causes the lens to thicken, increasing its ability to focus at near objects.

Front 238

Ciliary muscles

Back 238

The circular layer of smooth muscle within the ciliary body of the vascular tunic of the eyeball whose contraction causes the lens to thicken, increasing its ability to focus at near objects; they are regulated by visceral motor commands from the Autonomic Nervous System.

Front 239

Ciliary process

Back 239

A series of ridges or folds of tissue projecting from the crown of the ciliary body, behind the base of the iris, which contains the cells which secrete the aqueous humor into the posterior chamber of the anterior segment of the eye; the ciliary process also forms the anchor for the suspensory ligament which holds the lens in place.

Front 240

Suspensory ligament

Back 240

The delicate fibrous membrane, composed of collagen fibers, which holds the lens of the eye in place; it is anchored to the ciliary process/body.

Front 241

Iris

Back 241

The pigmented, round, contractile membrane of the eye, the anterior portion of the vascular tunic of the eyeball, suspended between the cornea and lens and perforated by the pupil; it contains a radial and a circular layer of smooth muscle innervated by the ANS to regulate the amount of light entering the eye by adjusting the diameter of the pupil.

Front 242

Pupil

Back 242

Opening in the center of the iris through which light enters the eye; it is opened or closed by autonomic reflexes in order to regulate the amount of light entering the eyeball.

Front 243

Sensory tunic

Back 243

Neural tunic of the eyeball; the innermost of the three tunics of the eye; contains photoreceptors (rods, cones) in the deepest layer, bipolar neurons, amacrine cells and horizontal cells in the middle layer, and ganglion cells in the superficial layer.

Front 244

Retina

Back 244

Neural/sensory tunic of the eyeball; contains photoreceptors (rods, cones) in the deepest layer, bipolar neurons, amacrine cells and horizontal cells in the middle layer, and ganglion cells in the superficial laye

Front 245

Photoreceptors

Back 245

Specialized receptor cells that respond to light energy by depolarizing to generate nerve impulses; e.g., the rods and cones within the retina of the eye; transduction occurs when a visual pigment is broken down by light energy and the reaction products trigger a biochemical reaction pathway which leads to an impulse generation and the transmission of a graded potential to the postsynaptic cell, the bipolar neuron.

Front 246

Optic disc

Back 246

The point where the optic nerve enters the retina (neural/sensory tunic of the eye); it is not sensitive to light due to the absence of photoreceptor cells; there are various experiments that may be performed to demonstrate the presence of the blind spot in one's field of vision.

Front 247

Rods

Back 247

One of the two types of photosensitive cells in the retina (neural/sensory tunic of the eye), these cells predominate away from the center of the field of vision (fovea centralis) and are most responsive in low levels of illumination; they are not color sensitive.

Front 248

Cones

Back 248

One of the two types of photoreceptor cells in the retina (neural/sensory tunic of the eye); they provide for color vision; these cells predominate near the center of the field of vision (fovea centralis) and are most responsive in bright levels of illumination; there are three subtypes, red, blue, and green, which are sensitive to certain portions of the spectrum of visible light.

Front 249

Macula densa

Back 249

The small and highly sensitive part of the retina (neural/sensory tunic of the eye), roughly in the center of the retina, lateral to the optic nerve, responsible for detailed central vision; it contains the fovea centralis where cones are concentrated in a region which is a slight depression where the bipolar neurons and ganglion cells and the capillaries are pushed to the side so that light falls on the photoreceptors without as much interference; the macula densa allows one to appreciate detail and perform tasks that require central vision such reading.

Front 250

Fovea centralis

Back 250

A small depression near the center of the retina (neural/sensory tunic of the eye), constituting the area of most acute vision where the bipolar neurons and ganglion cells and the capillaries are pushed to the side so that light falls on the photoreceptors (predominantly cones) without as much interference.

Front 251

Anterior segment

Back 251

That part of the eyeball anterior to the lens, filled with aqueous humor and the location of the iris and ciliary body; it is divided into two parts, the anterior and posterior chambers, which are connected by the opening of the pupil.

Front 252

Anterior chamber

Back 252

The space in the anterior segment of the eye, filled with aqueous humor, bounded anteriorly by the cornea and a small portion of the sclera and posteriorly by a small portion of the ciliary body, the iris, and that part of the crystalline lens which presents through the pupil.

Front 253

Posterior chamber

Back 253

The space in the anterior segment of the eye, filled with aqueous humor, bounded anteriorly by a small portion of the ciliary body, the iris, and by that part of the lens which is distal to the portion which presents through the pupil and bounded posteriorly by the vitreous humor.

Front 254

Aqueous humor

Back 254

The clear, watery fluid which fills the anterior and posterior chambers of the anterior segment of the eye; it surrounds the lens and is involved in the metabolism of the cornea and the lens.

Front 255

Posterior segment

Back 255

That part of the eyeball posterior to the lens, filled with vitreous humor and filling the space above the retina.

Front 256

Vitreous humor

Back 256

The microfibrillar net-like structure which is filled with a very thick, gel-like substance containing mucopolysaccharides and hyaluronate acids; it fills the posterior segment of the eye; it functions to maintain the shape of the eye, keeping the retina pressed against the inner surface of the eye and it also cushions the contents of the eye from shocks such as from running or turning of the head.

Front 257

Lens

Back 257

A unique part of the vascular tunic of the eye; an ovoid mass of specially arranged collagen fibers capable of focusing incident light onto the back of the eye forming an inverted image on the internal photosensitive retina from which nerve impulses are sent to the brain; the lens has an internal nucleus, an outer softer cortex, and a capsule which attaches to the ciliary body by the suspensory ligament; it is a powerful light refracting structure, providing 1/3 of the eye's focusing power.

Front 258

Accommodation

Back 258

The process of increasing the refractive power of the lens of the eye, focusing at a particular point within the depth of field, achieved by appropriate contraction or relaxation of the ciliary muscle which adjusts the shape of the lens; when the ciliary muscle contracts, the lens thickens, increasing its ability to focus at near objects.

Front 259

Photoreception

Back 259

The detection, absorption, and use of light; for vision, special photoreceptor cells (rods and cones) convert light energy into nerve impulses.

Front 260

Visual pigments

Back 260

The light absorbing lipid molecule, retinal, in combination with certain light absorbing proteins called opsins, forms four types of photosensitive molecules, the visual pigments; depending on the form of opsin bound, retinal absorbs different wavelengths of visible light, therefore, different colors can be perceived by photoreceptor cells which rely on different light absorbing molecules; when light of the appropriate wavelength strikes a specific light absorbing molecule, it decomposes, initiating a series of chemical steps which lead to the generation of nerve impulses.

Front 261

Retinal

Back 261

The light absorbing lipid molecule derived from vitamin A, which can combine with proteins called opsins to forms four types of photosensitive molecules, the visual pigments.

Front 262

Opsins

Back 262

Special photosensitive proteins which combine with retinal in cone cells to form a complex, a visual pigment, which will react with a portion of the spectrum of visible light by decomposing to initiate a series of chemical steps which lead to the generation of nerve impulses which will provide color vision.

Front 263

Rhodopsin

Back 263

The visual pigment (a lipid-protein complex) highly sensitive to red light located in the rods of the retinas of the eyes, consisting of an opsin and retinene which will react with a portion of the spectrum of visible light by decomposing to initiate a series of chemical steps which lead to the generation of nerve impulses.

Front 264

Light transduction

Back 264

The conversion of kinetic light energy into the kinetic electrochemical energy of nerve impulses, i.e., action potentials, which is carried out by special photoreceptor cells; in vertebrates, this process occurs in the rods and cones of the retina of the eye.

Front 265

Light adaptation

Back 265

Two processes, one involving constriction of the pupil (a pupillary reflex), by which the eye adapts to an increase in illumination, and the other, a response of the neurons of the retina to changes in the level of illumination such that the ratios of light intensities coming from different parts of the visual field remain constant, i.e., the contrast between lighter and darker objects is maintained.

Front 266

Dark adaptation

Back 266

The physical and chemical adjustments of the eye, including dilation of the pupil (a pupillary reflex) and increased activity of rods in the retina, that make vision possible in relative darkness with an increase in visual sensitivity developing with increasing time in the dark following exposure to light.

Front 267

Optic nerves

Back 267

The second pair of pure sensory cranial nerves (II) which arise from the ganglion cells of the retina, exit at the optic disc, partially decussate at the optic chiasma, and carry visual information to the thalamus and other parts of the brain, especially the primary visual cortex.

Front 268

Optic chiasma

Back 268

A structure at the base of the brain, just anterior to the mamillary body and the infundibulum of the pituitary gland, formed by the partial intersection or crossing of the optic nerve fibers on the underside of the hypothalamus where some (75%), but not all, optic information crosses to the contralateral side of the brain.

Front 269

Optic tracts

Back 269

The portion of the visual system pathway from the optic chiasm to the lateral geniculate nucleus of the thalamus; each optic tract contains axons from ganglion cells in the retinas of both the left and right eyes, but information from only one half (i.e., either left or right) of each eye's visual field.

Front 270

Primary visual cortex

Back 270

he extreme posterior tip of the occipital lobe of the cerebral hemisphere and the tissue deep in the calcarine sulcus; the largest of all cortical sensory areas, it receives visual information which originated at the retinas of the eyes and passed through the (lateral geniculate body of the) thalamus; there is a contralateral map of visual space on the primary visual cortex, with the representation of the image inverted as it was received on the retina.

Front 271

Glaucoma

Back 271

Any of a group of eye diseases, with a diminution of transparency, a bluish or greenish tinge of the refracting media of the eye, in which intraocular pressure increases to levels that cause compression of the retina and optic nerve; results in pain, hardening of the eyeball, and partial to complete loss of vision unless detected early.

Front 272

Cataract

Back 272

Clouding of the lens of the eye; often congenital or age-related; classified by the size, shape and location of the lesion and by the cause and time of occurrence; frequently corrected by surgery.

Front 273

Myopia

Back 273

A condition in which visual images are focused in front of rather than on the retina; it results from the eyeball being too long from front to back or from an increased strength of the media of the eye; it is corrected by the use of a concave lens. nicknames nearsightedness and short sight.

Front 274

Hyperopia

Back 274

An abnormal condition of the eye in which vision is better for distant objects than for near objects; it results from the eyeball being too short from front to back, causing images to be focused behind the retina; this condition is easily corrected with eyeglasses or contact lens. aka farsightedness, hypermetropia.

Front 275

Astigmatism

Back 275

A condition in which unequal curvatures in different parts of the lens (or cornea) of the eye which prevents light rays from focusing clearly at one point on the retina, leading to blurred vision.

Front 276

Outer ear

Back 276

The outer or exterior portion of the ear including the auricle/pinna and the external auditory meatus, the passage leading to the tympanic membrane (eardrum); these structures functions to collect and help focus sound waves on the tympanic membrane.

Front 277

Auricle

Back 277

The outer visible projecting portion of the ear, composed of elastic cartilage covered by skin, which functions to collect and focus sound waves on the tympanic membrane.

Front 278

External auditory meatus

Back 278

The narrow passage way through which sound waves are transmitted from the auricle/pinna to the tympanic membrane; the outer half is supported by cartilage while the inner half is supported by bone (the temporal bone); the opening is protected by small hairs and cerumen.

Front 279

Cerumen

Back 279

The secretion of the ceruminous glands, a yellow or orange sticky, bitter, waxy substance which assists in protecting the external ear canal from invasion by ectoparasites (insects).

Front 280

Tympanic membrane

Back 280

The delicate sheet of skin covered connective tissue which forms the boundary between the outer and middle ear; on its medial surface the malleus (hammer) is attached which responds to sound waves causing vibrations by transmitting those vibrations, in a lever system with the other two ear ossicles, to move the membrane of the oval window in order to transmit pressure vibrations into the perilymph of the cochlea; nickname eardrum.

Front 281

Middle ear

Back 281

The air-filled space in the temporal bone, lined by a mucous membrane, between the tympanic membrane (eardrum) and the inner ear which contains the three auditory ossicles, which convey vibrations through the oval window to the cochlea; it is connected to the nasopharynx by the pharyngotympanic tube which permits equalization of air pressure on either side of the tympanic membrane. aka tympanum and tympanic cavity.

Front 282

Ossicles

Back 282

A small bone, especially any of the three bones of the middle ear: the malleus (hammer), incus (anvil), and stapes (stirrup) which form a lever system for converting the air vibrations (sound) which move the tympanic membrane into movements of the oval window which create pressure waves in the perilymph of the scala vestibuli and scala tympani of the cochlea.

Front 283

Oval window

Back 283

The oval membrane covering and the opening on the medial wall of the middle ear to which the base of the stapes is connected and through which the ossicles of the ear transmit sound vibrations to the perilymph of the scala vestibuli of the cochlea.

Front 284

Round window

Back 284

The round membrane covering and the opening on the medial wall of the middle ear facing the scala tympani which moves to accommodate the pressure waves caused by transmission of sound vibrations into the perilymph of the scala vestibuli and scala tympani of the cochlea.

Front 285

Pharyngotympanic tube

Back 285

A hyaline cartilage tube lined with a mucous membrane which connects the middle ear cavity with the nasopharynx; it aerates the middle ear system and clears mucus from the middle ear into the nasopharynx; opening and closing functions of the tube are physiologically and pathologically important: normal opening of the tube equalizes atmospheric pressure in the middle ear; closing of the tube protects the middle ear from unwanted pressure fluctuations and loud sounds; normal physiological mucociliary clearance drains mucus away from the middle ear into the nasopharynx, thus preventing infection from ascending to the middle ear. aka Eustachian tube.

Front 286

Otitis media

Back 286

Inflammation of the middle ear, occurring commonly in children as a result of infection and often causing pain and temporary hearing loss.

Front 287

Inner ear

Back 287

The portion of the ear, a complex system of interconnecting cavities, located within the petrous part of the temporal bone which is involved in both hearing and balance/equilibrium and includes the semicircular canals, vestibule, and cochlea; structurally it consists of the membranous labyrinth which is housed in the bony labyrinth.

Front 288

Bony landmark

Back 288

The cavity in the petrous part of the temporal bone which houses and protects the membranous labyrinth of the inner ear.

Front 289

Membranous labyrinth

Back 289

The fluid-filled membranous sacs of the inner ear which are associated with the senses of hearing and balance/equilibrium; includes the semicircular canals, vestibule, and cochlea; housed in the bony labyrinth in the petrous part of the temporal bone; pressure waves in the endolymph fluid within this structure are detected by mechanoreceptors in the transduction of sensory stimuli related to hearing (in the cochlea) and to equilibrium (in the vestibule and semicircular canals).

Front 290

Endolymph

Back 290

The fluid, a plasma filtrate, in the membranous labyrinth of the inner ear; pressure waves in this fluid are detected by mechanoreceptors in the transduction of sensory stimuli related to hearing (in the cochlea) and to equilibrium (in the vestibule and semicircular canals).

Front 291

Perilymph

Back 291

The fluid, a plasma filtrate, which surrounds the membranous labyrinth of the internal ear, and separates it from the walls of the chambers in which the labyrinth lies; the scala tympani and scala vestibuli of the cochlea contain perilymph; pressure waves in this fluid are detected by mechanoreceptors in the transduction of sensory stimuli related to hearing (in the cochlea).

Front 292

Cochlea

Back 292

A spiral-shaped cavity of the inner ear that resembles a snail shell (it has 2 1/2 turns) and contains a specialized organ containing mechanoreceptors (hair cells) and nerve endings essential for hearing; a part of the membranous labyrinth anterior to the vestibule where sound vibrations are converted into special sensory nerve impulses by the spiral organ of Corti; these special sensory nerve impulses are transferred to the vestibulocochlear (eighth) cranial nerve.

Front 293

Modiolus

Back 293

The central, conical, bony core of the cochlea; a part of the bony labyrinth.

Front 294

Cochlear duct

Back 294

The middle of the three scalae of the membranous labyrinth of the inner ear; a spiral tube enclosed in the bony canal of the cochlea, which contains a plasma filtrate termed endolymph; bounded by the tectorial membrane and scala vestibuli above and by the basilar membrane and scale tympani below; harmonic vibrations in the endolymph stimulate the hair cells of the spiral organ of Corti for the transduction of sound.

Front 295

Spiral organ of Corti

Back 295

The true organ of hearing, a spiral sensory structure within the cochlea containing hair cells (mechanoreceptors) which are stimulated indirectly by sound vibrations; the hair cells convert the vibrations created in the cochlear duct and basilar membrane into nerve impulses which are transmitted by the cochlear branch of the vestibulocochlear (eighth) cranial nerve to the primary sensory cortex for hearing in the temporal lobes of the brain; high notes are detected at the base and low notes are detected at the apex of the cochlea.

Front 296

Hair cells

Back 296

Specialized mechanoreceptor cells with hairlike processes (stereocilia and kinocilia) found in the sensory epithelium of certain parts of the membranous labyrinth of the internal ear which convert vibrations of the basilar and tectorial membranes into nerve impulses which will be interpreted as sound.

Front 297

Spiral lamina

Back 297

The thin spiral bony ledge, an extension of the modiolus, which serves as the medial support for the basilar membrane.

Front 298

Scala vestibuli

Back 298

The superior compartment of the cochlea within the membranous labyrinth of the inner ear; containing perilymph; it leads from the oval window (point of attachment for the stapes/stirrup) to the apex of the spiral and the helicotrema which is the opening to the scala tympani.

Front 299

Scala tympani

Back 299

The inferior compartment of the cochlea within the membranous labyrinth of the inner ear, containing perilymph; it extends from the apex of the cochlea and the helicotrema which is the opening from the scala vestibuli to a membrane-covered opening in the wall of the inner ear called the round window.

Front 300

Helicotrema

Back 300

The opening by which the two scalae, vestibuli and tympani, connect at the top of the cochlea of the ear.

Front 301

Vestibular membrane

Back 301

The two-squamous-cell-thick membrane that separates scala vestibuli (perilymph) from scala media (endolymph) in the cochlea within the membranous labyrinth of the inner ear; this tissue assists in the transmission of sound vibrations from the perilymph of the scala vestibuli to the endolymp of the scala media (cochlear duct) where the vibrations can stimulate the spiral organ.

Front 302

Basilar membrane

Back 302

A thin, homogeneous layer of connective tissue covered on its surfaces above and below with a layer of epithelium; the spiral organ of Corti rests upon the basilar membrane; differences in the width and flexibility of this membrane determine where within the spiral organ of Corti the hair cells will be stimulated and this difference is a function of the frequency of the sound vibrations so that high notes are detected at the base and low notes are detected at the apex of the cochlea.

Front 303

Tectorial membrane

Back 303

The acellular, gelatinous membrane covering the spiral organ of Corti and resting on the hairlike processes (stereocilia and kinocilia) of its hair cells and bathed in the endolymph of the scala media/cochlear duct within the membranous labyrinth of the inner ear.

Front 304

Cochlear nerve

Back 304

The division of the vestibulocochlear (eighth) cranial nerve which conducts auditory sensory information from the spiral organ of Corti within the membranous labyrinth of the inner ear to the primary sensory cortex for hearing in the temporal lobes of the brain.

Front 305

Sound

Back 305

Vibrations transmitted through an elastic solid or a liquid or gas, with frequencies in the approximate range of 20 to 20,000 hertz, capable of being detected by human organs of hearing.

Front 306

Frequency

Back 306

The number of times a specified periodic phenomenon occurs within a specified interval, e.g., the number of vibrations per second of a particular tone of sound.

Front 307

Wavelength

Back 307

The distance between one peak or crest of a wave of light, heat, sound, or other energy and the next corresponding peak or crest in consecutive cycles of a wave; for electromagnetic waves, the wavelength determines the type (radio, infrared, visible, ultraviolet, X-Ray, gamma-ray) of radiation, in the case of visible light, wavelength determines the color of the light.

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Pitch

Back 308

The distance between one peak or crest of a wave of light, heat, sound, or other energy and the next corresponding peak or crest in consecutive cycles of a wave; for electromagnetic waves, the wavelength determines the type (radio, infrared, visible, ultraviolet, X-Ray, gamma-ray) of radiation, in the case of visible light, wavelength determines the color of the light.

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Amplitude

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The maximum absolute value of a periodically varying quantity; the maximum absolute value of a periodic curve measured along its vertical axis; related to the volume or loudness of a sound.

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Loudness

Back 310

The subjective characterization of a sound by its volume and intensity; measured by its amplitude as a wave form.

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Decibels (dBa)

Back 311

An exponential scale (powers of 10) to measure sound levels; 0 dB is the threshold of hearing, normal conversation is ~60 dB, a large orchestra is ~100 dB, the threshold of pain is ~130 dB, and instant perforation of the eardrum is 160 dB.

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Vestibular apparatus

Back 312

The functional components of the membranous labyrinth involved in the sensations of static and dynamic equilibrium are a system of thin-walled intercommunicating tubes and ducts situated within the petrous part of the temporal bone at the base of the skull; there are five vestibular structures, each containing a specialized mechanoreceptor, a maculae, within the utricle and saccule, and a cristae within the ampullae of the superior, horizontal, and posterior semicircular canals.

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Vestibule

Back 313

The central cavity of the bony labyrinth of the ear containing the functional components of the membranous labyrinth involved in the sensations of static equilibrium which are two vestibular structures, each containing a specialized mechanoreceptor, a maculae, within the utricle and saccule.

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Saccule

Back 314

The smaller of the two membranous sacs in the vestibule of the inner ear; it contains a specialized mechanoreceptor, a maculae, for the detection of static equilibrium.

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Utricle

Back 315

The larger of the two membranous sacs in the vestibule of the inner ear; it contains a specialized mechanoreceptor, a maculae, for the detection of static equilibrium.

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Static equilibrium

Back 316

The special sense which interprets the position of the head permitting the CNS to maintain stability and posture when the head and body are not moving; it is detected by mechanoreceptors in the vestibule of the inner ear, the utricle and saccule, which each contain a macula with the receptors for static equilibrium; when the head moves with reference to gravity, the otolithic membrane shifts and the mechanoreceptors (hair cells) in the macula detect this movement and send the information along the vestibular nerve to the brain for interpretation (which way is up).

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Maculae

Back 317

The specialized mechanoreceptors within the utricle and saccule for the detection of static equilibrium; they make use of hair cells to detect movements of the otolithic membrane; the nerve impulses thus generated are transmitted along the vestibular branch of cranial nerve VIII to the CNS.

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Otolithic membrane

Back 318

The gelatinous covering of macula of the utricle and saccule of the vestibular apparatus which has many crystals of calcium carbonate (otoconia or otoliths); their movements in response to changes in the position of the head with reference to gravity stimulate the hair cells to send nerve impulses to the CNS which are interpreted as information about static equilibrium.

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Dynamic equilibrium

Back 319

The special sense which interprets balance when one is moving, or at least the head is moving; the semicircular canals contain the receptors for dynamic equilibrium; within each semicircular canal is a complex mechanoreceptor called a crista ampullaris which contains the mechanoreceptors (Hair cells) for dynamic equilibrium; when the perilymph in one of the semicircular canals moves, the hair cells in the crista ampullaris are stimulated to send nerve impulses to the brain; this advises the brain of whether or not a person has their balance during body movements or if their body is in motion, e.g, riding in a car or turning one's head from side to side.

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Semicircular canals

Back 320

The functional components of the membranous labyrinth, a series of three interconnected perilymph-filled tubes with enlarged ends, involved in the sensations of dynamic equilibrium; the contain the cristae ampullaris which detect acceleration in the three perpendicular planes (superior, horizontal, and posterior); these accelerometers make use of hair cells similar to those on the organ of Corti, but these hair cells detect movements of the fluid in the canals caused by angular acceleration about an axis perpendicular to the plane of the canal; tiny floating particles aid the process of stimulating the hair cells as they move with the fluid; the nerve impulses thus generated are transmitted along the vestibular branch of cranial nerve eight to the CNS.

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Ampulla

Back 321

The dilation or expanded end of each of the semicircular canals of the vestibular apparatus which contains the specialized mechanoreceptor structure, the crista, which detect acceleration in the planes of the canal; these accelerometers make use of hair cells to detect movements of the fluid in the canals caused by angular acceleration about an axis perpendicular to the plane of the canal; the nerve impulses thus generated are transmitted along the vestibular branch of cranial nerve eight to the CNS.

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Crista ampullaris

Back 322

Within the ampulla of each semicircular canal is a complex mechanoreceptor structure, the crista ampullaris; the ampulla has a ridge covered by neuroepithelium consisting of sensory hair cells and supporting cells; the hair cells attached to a gelatinous mass, the cupula, which rests on top of the crista ampularis; when the perilymph in one of the semicircular canals moves, the hair cells in the crista ampullaris are stimulated to send nerve impulses to the brain; this advises the brain of whether or not a person has their balance during body movements or if their body is in motion, e.g, riding in a car.

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Vestibular nerve

Back 323

The division of the vestibulocochlear (eighth) cranial nerve which conducts sensory information regarding static and dynamic equilibrium from the vetibular apparatus of the inner ear to the various centers of the CNS which process and integrate that information with visual and proprioception.

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Conduction deafness

Back 324

A hearing loss due to problems with the tympanic membrane or the bones of the middle ear.

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Otosclerosis

Back 325

A disease of the ear in which the movement of the stapes, attached to the oval window, becomes impeded by abnormal deposits of spongy bone, leading to a progressive loss of hearing; an example of conduction deafness.

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Sensoneural deafness

Back 326

An irreversible type of hearing loss that occurs when cochlear sensorineural elements (parts of the spiral organ of Corti) or the cochlear nerve is damaged in some way; it can progress to total in the involved ear(s).

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Tinnitus

Back 327

An auditory paresthesia, an imaginary sound in one ear or both ears, such as a buzzing, booming, ringing, roaring, clicking or whistling, occurring without an external stimulus and usually caused by a specific condition, such as an ear infection, the use of certain drugs, a blocked auditory tube or canal, Meniere's disease, or a head injury.