The Brain, Spinal Cord, Pns, And Ans

Front 1

4 Major regions of the Brain

Back 1

• The Cerebral hemispheres include the frontal, parietal, temporal and occipital lobes and the basal nuclei (ganglia).

• The diencephalon includes the thalamus and hypothalamus.

• The brainstem includes the midbrain, pons and medulla oblongata.

The cerebellum

Front 2

Brain Folds

Back 2

• Since the brain grows more rapidly than the skull, the brain forms folds, allowing it to fit inside the skull.

. A raised region is called a gyrus

•A wrinkle towards the interior of the brain is called a sulcus

• A deep wrinkle is called a fissure.

Front 3

Grey Matter

Back 3

The grey matter of the CNS consists of, neuron cell bodies, while the white matter consists of myelinated/nonmyelinated axons.

• CNS has a central cavity surrounded by grey matter, with a layer of white matter externally.

• The brain stem has additional grey matter nuclei scattered within the white matter.

• The cerebral hemispheres and cerebellum have an outer layer of grey matter, called the CorteX

Front 4

Cerebral White Matter

Back 4

Responsible for communication between cerebral areas and the cerebral cortex and lower CNS centres.

Front 5

3 types of fibres that make up cerebral white matter.

Back 5

1. AssoCiatiOn fibres

2. Commissural Fibres

3. Projection Fibres

Front 6

Association Fibres

Back 6

Are tracts of cerebral white matter that run horizontally, connecting different parts of the same hemisphere.

Front 7

Commissural Fibres

Back 7

Run horizontally and connect corresponding areas of grey matter in the two hemispheres, allowing the hemispheres to function together as a whole (includes the corpus callosum).

Front 8

Projection Fibres

Back 8

Run vertically, and connect the cerebral cortex to the lower brain or cord centres, tying together the rest of the nervous system to the body's receptors and effectors.

Front 9

Cerebral Hemispheres

Back 9

The cerebrum is the largest region of the brain, separated into right and left hemispheres

• Each cerebral hemispheres has 3 regions: the superficial cortex of grey matter, internal white matter, and areas of grey matter deep within the white matter, the basal nuclei.

• Each hemisphere is divided into 4 visible lobes: frontal, parietal, temporal and occipital. A 5th region, called the insula, forms part of the floor of the lateral sulcus and is covered by the lobes.

Front 10

Cerebral Cortex

Back 10

• The cerebral cortex is the location of the conscious mind, allowing us to communicate, remember, and understand. It has motor areas, sensory areas, and association areas.

Each hemisphere has contralateral control over sensory and motor functions, meaning that each hemisphere controls the opposite side of the body.

• The hemispheres exhibit lateralization of function, meaning that there is specialization of one side of the brain for certain functions.

Front 11

Motor Areas of the Cerebral Cortex

Back 11

• Motor areas of the cortex are in the posterior of the frontal lobes and control voluntary movement.

• The primary motor cortex (located in the pre-central gyrus) allows conscious control of skilled voluntary movement of skeletal muscles.

• The premotor cortex is the region controlling learned motor skills.

• Broca's area is a motor area that controls muscles involved in making words when speaking or writing.

Front 12

Cortical Homonculus

Back 12

This is an artistic depiction of how the human body would look if the body parts were scaled proportionately to the size of the region of your cerebral cortex that processes sensory information from those body parts.

Front 13

Sensory Areas of Cerebral Cortex

Back 13

• The Primary somatosensory cortex processes sensory information from the body, such as touch and temperature, as well as the location of stimulation. It is located in the postcentral gyrus of the parietal lobe. The somatosensory association cortex integrates sensory information and produces an understanding of the stimulus being felt.

• The primary visual cortex and visual association area in the occipital lobe receive and interpret visual stimuli.

Front 14

Sensory Areas of Cerebral Cortex 2

Back 14

• The primary auditory cortex and auditory association area are in the temporal lobe. They allow detection and recognition of sound

.

• The vestibular cortex is in the parietal lab and the insula. It is responsible for awareness of balance

• The olfactory cortex processes smell and the gustatory cortex perceives taste. They are found at the inferior frontal lobe and insula.

• The visceral sensory areas in the insula are involved in conscious awareness of visceral sensation.

Front 15

Multimodal Association Areas

Back 15

The anterior association area, or prefrontal cortex, is involved with intellect, cognition, recall, and personality. It is closely linked to the limbic system.

• The posterior association area aids in recognition of patterns and faces, as well as understanding of written and spoken language. This includes Wernicke's area, which links words and meanings.

• The limbic association area deals with emotions surrounding situations and includes the cingulate gyrus, parahippocampal gyrus, and hippocampus.

Front 16

Late realization of Cortical functioning

Back 16

• Some medical studies have found varying degrees of lateralization of cortical functioning, in which each cerebral hemisphere has unique control over abilities not shared by the other half.

• In many cases, the left hemisphere dominates language abilities, math and logic, while the right hemisphere dominates visual-spatial skills, ntuition, emotion, and artistic and musical skills.

• Both sides of the brain are involved in virtually all skills and processes.

Front 17

Basal Nuclei

Back 17

• Basal nuclei (sometimes inaccurately called basal ganglia) consist of a group of subcortical nuclei that have overlapping motor control with the cerebellum that regulate cognition and emotion.

They appear to be involved in deciding which action you should take and inhibiting other actions.

• Nuclei are clusters of neuron bodies in the CNS.

Ganglia are clusters of neuron bodies in the PNS.

The brain is part of the CNS, so "basal ganglia" is a misnomer.

Front 18

Thalamus

Back 18

Mediates sensation, motor activities, cortical arousal, learning, and memory. It plays a role in the maintenance of consciousness.

• It acts as a relay station to conduct Sensory impulses to the primary sensory areas of the cerebral cortex and transmits motor information from the cerebellum and basal nuclei to the primary motor area of the cerebral cortex.

Front 19

Hypothalamus

Back 19

The control centre of the body, regulating autonomic nervous system activity.

• It initiates physical responses to emotions, and regulates body temperature, food intake, water balance, thirst, sleep-wake cycles, and endocrine function. It is the integration centre of the autonomic nervous system.

• The hypothalamus also regulates the pituitary. gland and produces oxytocin and antidiuretic hormone.

Front 20

Higher Mental Functions

Back 20

• The interconnected structures of the brain allow higher mental functions.

• The ability to both speak and understand language is produced through coordination of several brain areas, notably Broca's area and Wernicke's area.

• Memory is the storage and retrieval of information and there are different kinds of memory: declarative (fact-based), procectural (skills), motor, and emotional.

Front 21

Declarative Memory

Back 21

Has 2 stages: short-term memory, and long-term memory.

short-term memory, or working memory - allows the memorization of a few units of information for a short period of time.

Long-term memory allows the memorization of potentially limitless amounts of information vor very long periods.

Front 22

More about declarative memory

Back 22

• Transfer of information from short-term to long-term memory can be affected by emotional state (best if alert, motivated, excited or surprised), rehearsal, association of new information with old, or the automatic formation of memory while concentrating on something else.

• Damage to the hippocampus or surrounding temporal lobe structures on either side result in only slight memory loss. Bilateral destruction causes widespread amnesia.

Front 23

Consciousness

Back 23

Can be clinically defined on a continuum that measures behaviour in response to stimuli and ranges through several stages: alertness, drowsiness or lethargy, stupor, and coma.

• Syncopy (fainting) is a brief loss of consciousness, most often due to inadequate cerebral blood flow caused by low blood pressure or sudden, severe emotional stress.

• Coma is unconsciousness for an extended period. Oxygen consumption is lower than during sleep.

Front 24

Sleep

Back 24

• Sleep is a state of partial unconsciousness from which a person can be aroused and has two major types that cycle: non-rapid eye movement (NREM) and rapid eye movement (REM).

NREM sleep is restorative

REM sleep allows the brain to analyze events or eliminate meaningless information. Dreaming occurs & skeletal muscles are inhibited during REM sleep

Front 25

Protecting the CNS

Back 25

The meninges are 3 connective tissue membranes that cover & protect the CNS.

• The Dura mater is the most durable, outermost covering that extends inward in certain areas to limit movement of the brain within the cranium.

• The arachnoid mater is the middle meninx that forms a loose brain covering.

• The Pia mater is the innermost layer that clings tightly to the brain.

Front 26

The blood brain barrier

Back 26

• The blood-brain barrier is a mechanism that helps maintain a protective environment for the brain.

• It contains exceptionally impermeable tight junctions keep brain separated from many bloodborne substances.

• The blood-brain barrier is made up of three layers:

• Continuous endothelium of capillary walls.

• Thick basal lamina around capillaries.

• Feet of astrocytes surrounding neurons.

Front 27

Blood brain barrier 2

Back 27

• Nutrients, essential amino acids, and some electrolytes are allowed to pass into cerebrospinal fluid, but metabolic wastes, proteins, toxins, and most drugs are excluded.

• Lipid-soluble molecules, including alcohol, nicotine, and anaesthetics, can cross the blood-brain barrier.

It is absent in some areas, such as the vomiting centre and the hypothalamus, because these brain areas need to monitor chemical composition and temperature of blood.

Front 28

Cerebrospinal Fluid (CSF)

Back 28

The fluid found w/in ventricles and surrounding the brain and spinal cord.

CSF gives buoyancy to the brain, protects the brain and spinal cord from impact damage, and is a delivery medium for nutrients and chemical signals.

• The four ventricles are lined with ependymal cells and are filled with cerebrospinal fluid. The ventricles of the brain are connected to one another and to the central canal of the spinal cord.

Front 29

CSF 2

Back 29

• The 4 ventricles in the brain are paired lateral ventricles deep within each cerebral hemisphere, a third ventricle within the diencephalon, and a fourth ventricle at the cerebellum.

Ependymal cells are responsible for keeping CS circulating.

• Arachnoid granulation villi are pockets of the arachnoid membrane that extend into the dura mater sinuses, such as the superior sagittal sinus.

This is where CSF can be reabsorbed into venous blood to re-join the circulatory system.

Front 30

Brain stem

Back 30

Midbrain, Pons, Medulla Oblongata

Front 31

Cerebral Peduncles (midbrain)

Back 31

Contain pyramidal motor tracts that descend toward spinal cord

Front 32

Corpora Quadrigemina (midbrain)

Back 32

Control visual & auditory startle behaviours

Front 33

Pons (brain stem)

Back 33

Contains fibre pathways between the brain and spinal cord, as well as giving rise to some cranial nerves, and contains some important nuclei, including one that helps control breathing.

Front 34

Medulla (brain stem)

Back 34

The location of the medullary pyramids, which act as crossover points for corticospinal motor tracts, resulting in the contralateral control of voluntary movements.

It also houses neurons controlling vital functions such as cardiac and respiratory rate

Front 35

Cerebellum

Back 35

The second-largest area of the brain. It adjusts Motor output, ensuring coordination and balance.

Processes inputs from several structures and coordinates skeletal muscle contraction to produce smooth movement.

• The cerebellum may also play a role in thinking, Janguage, and emotion,

Front 36

Structure of Cerebellum

Back 36

Consists of 2 cerebellar hemispheres with 3 lobes each. Anterior and posterior lobes coordinate body movements, and the flocculonodular lobes adjust posture to maintain balance.

Three paired fibre tracts, the cerebellar peduncles, communicate between the cerebellum and the brain stem.

• Grey matter is located in outer cortex (folia) and in deeper nuclei. White matter tracts are called arbor vitae

Front 37

Limbic System

Back 37

Is involved with emotions and is extensively connected throughout the brain, allowing it to integrate and respond to a wide variety of stimuli.

Front 38

Reticular Activating System

Back 38

Extends through the brain stem and keeps the cortex alert while suppressing familiar, repetitive, or weak sensory inputs. 99% of sensory input is not relayed to consciousness.

Front 39

Spinal Cord

Back 39

2 main functions:

1. The spinal cord provides a COnduction pathway.

Each column of white matter in the spinal cord contains bundles of axons (tracts). These tracts have a common origin (or destination) and carry similar information. Tracts are continuous with white matter tracts in the brain.

2. also serves as an integration centre for spinal reflexes.

Front 40

Structure

Back 40

Extends from the foramen magnum of the skull to the level of the first or second lumbar vertebra. It provides a two-way conduction pathway to and from the brain and serves as a reflex centre.

• Fibrous extensions of the Pia mater anchor the spinal cord to the vertebral column and coccyx, preventing excessive movement of the cord.

• The spinal cord has 31 pairs of nerves (part of the PNS) along its length that define the cord segments

Front 41

Anatomy of the Spinal Cord

Back 41

• There are cervical and lumbar enlargements for the nerves that serve the limbs and a collection of nerve roots at the inferior end of the vertebral canal (cauda equina) that travel through the vertebral column to their intervertebral foramina.

The ventral (anterior) median fissure and dorsal (posterior) median sulcus divide the spinal cord into left and right halves. A CSF-filled central canal runs the length of the spinal cord at its centre.

Front 42

Anatomy of the Spinal Cord 2

Back 42

• The grey matter resembles a butterfly or "H" shape n cross section: the dorsal horns contain interneurons; the ventral horns consist most of cell bodies of somatic motor neurons

• In the thoracic and superior lumbar regions, there are also paired lateral horns that extend laterally between the dorsal and ventral horns, and contain cell bodies of autonomic motor neurons.

Front 43

Anatomy if the Spinal Cord 3

Back 43

The grey commissure is a bridge of grey matter that connects masses of grey matter on either side.

Ventral roots exit the spinal cord carrying axons of motor neurons, and join with dorSAl roots entering the spinal cord from peripheral receptors from outside of the spine to form spinal nerves. Dorsal root ganglia are the cell bodies of sensory neurons.

The white matter (myelinated and nonmyelinated nerve fibres) of the spinal cord allows communication between the cord and brain

Front 44

Anatomy of Spinal Cord Diagram

Back 44

Back (Definition)

Front 45

Trauma to Spinal Cord

Back 45

Any localized damage to the spinal cord or its roots leads to paralysis (loss of motor function) × 50 or paresthesias (loss of sensory function).

Severe damage to the ventral root or ventral horn results in flaccid paralysis, since nerve impulses are not transmitted to the skeletal muscles.

When upper motor neurons of the primary motor cortex are damaged, spastic paralysis occurs, in which voluntary control over skeletal muscle is lost.

Front 46

Spinal Cord Trauma

Back 46

If damage to the spinal cord occurs between T1 (first thoracic vertebra) and L1 (first lumbar vertebra), lower limbs are affected, resulting in paraplesia. Further down

If the damage occurs in the cervical region, all four limbs are affected, resulting in quadriplegia.

Spinal shock is a transient loss of function caudal to the trauma.

Front 47

Neuronal Pathways

Back 47

Carry sensory and motor information to and from the brain.

Major spinal tracts are part of paired multineuron pathways that mostly:

• Cross from one side to the other (decussate)

• Consist of a chain of 2 or 3 neurons

•Exhibit somatotopy (a point-for-point relationship between an area of the body and a specific point in the central nervous system).

Front 48

Examples of conduction pathways

Back 48

Back (Definition)

Front 49

Ascending Sensory Pathways

Back 49

Ascending pathways conduct sensory impuises upward through a chain of three neurons.

1. First-order neuron conducts the sensory info from the receptor to the spinal cord or brain stem.

2. Second -order neuron conducts the impulse to the thalamus.

Third -order neuron conducts the impulse to the primary somatosensory cortex of the cerebrum.

Front 50

Ascending Sensory Pathways

Back 50

Nonspecific ascending pathways receive input from many different types of sensory receptors, and make multiple synapses in the brain.

Specific ascending pathways mediate precise input from a single type of sensory receptor.

•Spinocerebellar tracts convey information about muscle and tendon stretch to the cerebellum. They are ipsilateral (don't cross over) and only involve two neurons, not three.

Front 51

Descending Motor Pathways

Back 51

Descending pathways involve two neurons: upper motor neurons and lower motor neurons that innervate skeletal muscle.

• In the direct or pyramidal, system, upper motor neurons from the cerebral cortex regulates fast, finely controlled or skilled movements.

• In the indirect or extrapyramidal system, upper motor neurons from the brainstem regulate muscles for balance and coarse movements and head, neck, and eye movements for visual tracking.

Front 52

Descending Motor Pathways

Back 52

Back (Definition)

Front 53

Peripheral Nervous System

Back 53

Includes all neural structures outside the brain and spinal cord: sensory receptors, peripheral nerves and their associated ganglia, and efferent motor endings.

Front 54

PNS Sensory Receptors

Back 54

Sensory receptors are specialized'to respond to changes in their environment called stimuli.

Activation of sensory receptors by a strong enough stimulus causes the production of graded potentials that trigger nerve impulses along afferent pathways to the central nervous system (CNS).

Front 55

Receptor Structure

Back 55

•Simple receptors are general senses and endings may be free (non-encapsulated) or encapsulated.

• Non-encapsulated dendritic endings are free nerve endings that detect temperature, pain, itch, light touch, or are located at the base of hair follicles.

Encapsulated dendritic endings consist of a dendrite enclosed in a connective tissue capsule and detect discriminatory touch, initial, continuous, and deep pressure, and stretch of muscles, tendons, and joint capsules.

Front 56

First Order Sensory Neurons

Back 56

• Graded receptor potentials can trigger action potentials that travel along the axon to the CNS

Front 57

Types of Stimulus

Back 57

Mechanoreceptors are stimulated by mechanical force, such as touch, pressure, vibration, and stretch.

Thermoreceptors detect changes in temperature

Photoreceptors detect light.

Chemoreceptors are stimulated by chemicals, such as odours, tastes, or chemical components of body fluids.

Nociceptors respond to painful stimuli.

Front 58

Location of Stimulus or Sensor

Back 58

Exteroceptors are located at or near the body surface and detect stimuli from outside the body, such as touch, pressure, pain, skin temperature receptors, and most of the special senses.

• Interceptors, associated with internal organs and vessels, monitor chemical changes, stretch, or temperature.

• Proprioreceptors are found within skeletal muscles, joints, and associated connective tissues and relay information about body movements.

Front 59

Sensation & Perception

Back 59

Sensation is the awareness of changes in the internal and external environment.

Perception is the conscious interpretation of those stimuli.

First-order sensory neurons carry impulses from receptors.

Second-order neurons transmit to the cerebellum or third-order neurons, which carry impulses to the postfrontal gyrus.

Front 60

Pain

Back 60

The perception of pain protects the body from damage and is stimulated by extremes of pressure and temperature, as well as chemicals released from damaged tissues.

• The pain threshold is the stimulus intensity at which we begin to perceive pain and is the same for most people. Pain tolerance is a genetically determined trait with learned aspects that varies from person to person. Like any other perception, perceived pain can be affected by the environment.

Front 61

Visceral Pain

Back 61

Visceral pain results from stimulation of receptors within internal organs from stimuli such as extreme stretch, ischemia (lack of blood flow), chemical irritation, and muscle spasms.

Visceral pain travels along the same fibre tracts as somatic pain impulses, giving rise to reFerred pain that feels as though it is located in an area different from the affected body region.

Front 62

Peripheral Nerves

Back 62

• Peripheral nerves, either cranial or spinal, are classified according to the direction in which they transmit impulses.

• Mixed nerves contain both sensory and motor fibres. Most nerves are mixed nerves.

• Sensory, or afferent, nerves carry impulses only toward the CNS.

• Motor, or efferent, nerves only carry impulses away from the CNS.

Front 63

Nerve Structure

Back 63

A nerve is a cord-like organ consisting of parallel bundles of peripheral axons enclosed by connective tissue wrappings.

Each axon within a nerve is surrounded by a thin layer of loose connective tissue, the endoneurium.

A perineurium is a connective tissue wrapping that bundles groups of fibres into fascicles.

An Epíneurium bundles all fascicles into a nerve.

Front 64

Structure of peripheral nerve diagram

Back 64

Back (Definition)

Front 65

Motor Endings & Motor Activity

Back 65

• All ventral branches except T2-T12 form interlacing networks called nerve plexuses. Within each plexus, fibres crisscross so that each branch contains fibres from several different spinal nerves. Fibres go to the body periphery via several routes, so that each limb muscle is innervated by more than one spinal nerve and damage to one does not cause paralysis

Dermatomes are areas of skin innervated by cutaneous branches of a single spinal nerve. Most dermatomes overlap, so destruction of a single spinal nerve will not cause complete numbness.

Front 66

Motor Endings & Motor Activity

Back 66

The terminals of the somatic motor fibres that innervate voluntary muscles form neuromuscular junctions with their effector cells and they release the neurotransmitter acetylcholine.

The junctions between autonomic motor endings and the visceral effectors form synapses en passant ("synapses in passing") involving varicosities and release either acetylcholine or epinephrine as their neurotransmitter.

Front 67

Varicosities

Back 67

• Autonomic nerve fibres innervate most smooth muscle. These muscle contractions tend to be a bit slower than the reactions of skeletal muscles.

• Vesicles release neurotransmitters into a wide synaptic cleft (a diffuse junction).

Front 68

Peripheral Nerve Repair

Back 68

Ganglia are collections of neuron cell bodies associated with nerves in the PNS.

Damaged CNS nerve fibres almost never regenerate, but if a PNS nerve fibre is cut or compressed, and the cell body remains intact, axons can regenerate.

• Schwann cells participate in regenerating PNS axons, but in the CNS, oligodendrocytes have growth-inhibiting proteins that do not support regrowth of axons.

Front 69

Neuroregeneration

Back 69

Chromatolysis is the breakdown of Nissl bodies after nerve damage.

Wallerian degeneration is the breakdown of the distal portion of the axon and myelin sheath.

Nerves within a regeneration tube grow at a rate of 1mm per day

Front 70

Autonomic Nervous System

Back 70

Lecture 35

Front 71

Reflexes

Back 71

• Reflexes are unlearned, rapid, predictable motor responses to a stimulus and occur over highly specific neural pathways called reflex arcs. The spinal cord is the integration centre for these arcs.

• Inborn, or intrinsic, reflexes are unlearned, unpremeditated, and involuntary.

Learned, or acquired, reflexes result from practice, or repetition.

Front 72

Reflex Arc

Back 72

• A reflex arc is a very specific neural path that controls reflexes and has 5 components: a receptor, a sensory neuron, an integration centre, a motor neuron, and an effector.

• Somatic reflexes activate skeletal muscle.

• Autonomic reflexes involve smooth muscle, cardiac muscle and/or glands.

Front 73

Reflex Arc

Back 73

• A reflex arc is a very specific neural path that controls reflexes and has 5 components: a receptor, a sensory neuron, an integration centre, a motor neuron, and an effector.

• Somatic reflexes activate skeletal muscle.

• Autonomic reflexes involve smooth muscle, cardiac muscle and/or glands.

Front 74

Stretch Reflex

Back 74

The stretch reflex causes contraction of a muscle that has been stretched.

muscle spindle is stretched and excited by either an external stretch or an internal stretch.

This stretch can trigger a reflex to protect the muscle by contracting to oppose the stretch.

Front 75

Reflex Arc

Back 75

• A reflex arc is a very specific neural path that controls reflexes and has 5 components: a receptor, a sensory neuron, an integration centre, a motor neuron, and an effector.

• Somatic reflexes activate skeletal muscle.

• Autonomic reflexes involve smooth muscle, cardiac muscle and/or glands.

Front 76

Stretch Reflex

Back 76

The stretch reflex causes contraction of a muscle that has been stretched.

muscle spindle is stretched and excited by either an external stretch or an internal stretch.

This stretch can trigger a reflex to protect the muscle by contracting to oppose the stretch.

Front 77

The Autonomic Nervous System

Back 77

The peripheral nervous system can be divided into a somatic nervous system, which innervates skeletal muscle, and an Autonomic nervous system (ANS).

• The autonomic nervous system is also called the involuntary nervous system. It helps to maintain homeostasis by controlling smooth muscle, cardiac muscle and glands.

• The ANS has parasympathetic and sympathetic divisions. Both divisions usually serve the same visceral organs, but cause opposite effects.

Front 78

Reflex Arc

Back 78

• A reflex arc is a very specific neural path that controls reflexes and has 5 components: a receptor, a sensory neuron, an integration centre, a motor neuron, and an effector.

• Somatic reflexes activate skeletal muscle.

• Autonomic reflexes involve smooth muscle, cardiac muscle and/or glands.

Front 79

Stretch Reflex

Back 79

The stretch reflex causes contraction of a muscle that has been stretched.

muscle spindle is stretched and excited by either an external stretch or an internal stretch.

This stretch can trigger a reflex to protect the muscle by contracting to oppose the stretch.

Front 80

The Autonomic Nervous System

Back 80

The peripheral nervous system can be divided into a somatic nervous system, which innervates skeletal muscle, and an Autonomic nervous system (ANS).

• The autonomic nervous system is also called the involuntary nervous system. It helps to maintain homeostasis by controlling smooth muscle, cardiac muscle and glands.

• The ANS has parasympathetic and sympathetic divisions. Both divisions usually serve the same visceral organs, but cause opposite effects.

Front 81

Somatic VS Autonomic

Back 81

• In the somatic motor pathway, motor neuron bodies are in the CNS. Axons extend to skeletal muscles via cranial or spinal nerves.

In the autonomic motor pathway, there are 2 neurons in sequence

• The first neuron has its cell body in the CNS and is referred to as a preganalionic neuron. This neuron terminates in a ganglion (outside of the CNS) where it synapses with the postganglionic neuron.

* the postganglionic neuron has an unmyelinated axon & Carries the signal to an effector organ (smooth muscle, cardiac muscle or glands).

Front 82

Sympathetic Division

Back 82

The "fight-or-flight" system, enables the body to cope with potential threats to homeostasis, by stimulating heart rate and force of contraction, increasing breathing, sweat production, pupil dilation, and glucose release from the liver, while inhibiting nonessential tasks, such as digestion.

Front 83

Parasympathetic Division

Back 83

rest-and-digest" system, keeps body energy use as low as possible, stimulates the gastrointestinal tract and directs digestion and waste elimination.

Front 84

Parasympathetic Division

Back 84

rest-and-digest" system, keeps body energy use as low as possible, stimulates the gastrointestinal tract and directs digestion and waste elimination.

Front 85

Autonomic Neurotransmitters

Back 85

• The neurotransmitter released by the somatic motor neurons is acetvlcholine, which always has an excitatory effect (contraction) on skeletal muscle.

• The neurotransmitters released by the ANS are epinephrine and acetylcholine, and both can have either an excitatory or an inhibitory effect.

Higher brain centres (specifically the hypothalamus) coordinate the somatic and autonomic nervous systems, so that there is cooperation between skeletal muscle and visceral organ functions.

Front 86

Differences in Neurotransmitters

Back 86

The preganglionic neurons of both divisions release acetylcholine (Ach)

The postganglionic neurons differ, with most postganglionic sympathetic neurons releasing norepinephrine (NE) and most postganglionic parasympathetic neurons releasing Ach.

Sampathetic division effects tends to be longer-lasting with body-wide effects because NE is inactivated more slowly than Ach and because hormones from the adrenal medulla can persist.

Front 87

Differences in Receptors Used

Back 87

• Autonomic neurons can be classified by the neurotransmitter they produce and release.

• Cholinergic neurons release acetylcholine.

There are 2 different types of cholinergic receptors. In addition to responding to acetylcholine, we have found drugs that can also activate these receptors, so they are described as either nicotinic (stimulated by nicotine, an anti-herbivore chemical) or muscarinic (stimulated by muscarine, a mushroom poison) receptors.

Front 88

Nicotinic Cholinergic Receptors

Back 88

Found on all postganglionic neurons, hormone-producing cells of the adrenal medulla, and skeletal muscle cells at the neuromuscular junction, and are always excitatory.

Front 89

Nicotinic Cholinergic Receptors

Back 89

Found on all postganglionic neurons, hormone-producing cells of the adrenal medulla, and skeletal muscle cells at the neuromuscular junction, and are always excitatory.

Front 90

Muscarinic cholinergic receptors

Back 90

Occur on all parasympathetic target organs and a few sympathetic targets, such as eccrine sweat glands, and may be excitatory or inhibitory.

Front 91

Adrenergic Receptors

Back 91

(adrenalin-related, responding to norepinephrine and epinephrine).

Adrenergic a, and B, receptors cause excitation and a, and B, cause inhibition of the sympathetic division.

Front 92

Adrenergic Receptors

Back 92

(adrenalin-related, responding to norepinephrine and epinephrine).

Adrenergic a, and B, receptors cause excitation and a, and B, cause inhibition of the sympathetic division.

Front 93

ANS Physiology

Back 93

• Sympathetic and parasympathetic tone are the result of having both divisions active.

• Sympathetic tone throughout the vascular system allows the firing rate of sympathetic neurons to control the diameter of blood vessels, regulating systemic blood pressure.

• Parasmpathetic, tone is usually dominant in the heart, digestive system and urinary tracts, maintaining normal levels of function unless overridden by the sympathetic system during stress,

Front 94

Differences in effects on organs

Back 94

, Most visceral organs receive dual innervation by both autonomic divisions, allowing for a dynamic antagonism to exist between the divisions and precise control of visceral activity (example: heartrate).

• The sympathetic is dominant during vigorous activity while the parasympathetic is dominant during resting periods. The two divisions can also show a cooperative effect, such as in the external genitalia during sexual excitement and release.