Brain Review

Front 1

Central Nervous System

Back 1

the brain and the spinal cord.

Front 2

Peripheral Nervous System

Back 2

the cranial and spinal nerves with their associated ganglia.

Front 3

Neuron

Back 3

nerve cells; the conducting cells of the nervous system which consist of the soma (containing the nucleus), the dendrites, and the axon.

Front 4

Interneuron

Back 4

a short nerve cell that makes interconnections within one brain region.

Front 5

Gray Matter

Back 5

regions of the CNS that contain aggregations of nerve cells.

Front 6

White Matter

Back 6

regions of the CNS that contain axons (both myelinated and unmyelinated).

Front 7

Afferent Fiber

Back 7

incoming fibers; those fibers that convey information towards a nerve cell body (dendrites) or towards the brain (sensory fibers).

Front 8

Efferent Fiber

Back 8

outgoing fibers; those fibers that convey information away from a neuron (axon) or from the brain (motor fibers).

Front 9

Tract

Back 9

a collection of nerve fibers or axons inside the CNS (also known as a pathway, lemniscus, fasciculus, or peduncle).

Front 10

Ascending Tracts

Back 10

nerve fibers that run towards the brain; the vast majority of these are sensory fibers.

Front 11

Descending Tracts

Back 11

nerve fibers that run away from the brain; the vast majority of these are motor fibers

Front 12

Sensory Neuron

Back 12

a neuron that carries sensory information from the periphery to the spinal cord or brain (CNS

Front 13

First Order Sensory Neuron

Back 13

the first neuron in a chain of sensory neurons that carries a particular sensory modality. This is also called a primary sensory neuron. An example is a dorsal root neuron that carries sensory information from the muscles, skin, etc., into the spinal cord.

Front 14

Second Order Sensory Neuron

Back 14

the second neuron in a chain of sensory neurons that carries a particular sensory modality. This is also called a secondary sensory neuron. An example is a sensory neuron within the spinal cord through which the sensory information reaches the brain.

Front 15

Motor Neuron

Back 15

: a neuron that carries motor information from the CNS to the muscles. These neurons terminate on skeletal, smooth, or cardiac muscles to induce contraction.

Front 16

Upper Motor Neuron

Back 16

a motor neuron that arises and terminates within the CNS. You can think of this as a “first order motor neuron” in that it is the first in the chain of events.

Front 17

Lower Motor Neuron

Back 17

: a peripheral motor neuron or fiber. The cell bodies of these motor neurons originate within the laminar layer of the ventral horn of the spinal cord.

Front 18

Spinal Nerve

Back 18

a nerve that enters or leaves the spinal cord/vertebral column. These nerves can carry both sensory and motor information. There are 31 pairs of spinal nerves (8 cervical; 12 thoracic; 5 lumbar; 5 sacral; 1 coccygeal).

Front 19

Cranial Nerves

Back 19

twelve pairs of nerves that exit directly from the base of the brain. Some are only motor or only sensory while others serve both motor and sensory functions.

Front 20

Ipsilateral

Back 20

nerve fibers that terminate on the same side of the body that the cell body originates (e.g., originate: right; terminate: right).

Front 21

Contralateral

Back 21

nerve fibers that terminate on the opposite side of the body that the cell body originates (e.g., originate: right; terminate: left

Front 22

Decussation

Back 22

the crossing of a neural pathway in the brainstem or spinal cord from one side of the body to the contralateral side.

Front 23

Ganglion

Back 23

a cluster of functionally related neuron cells bodies in the peripheral nervous system (e.g., those that mediate sensory functions).

Front 24

Dorsal Root Ganglion

Back 24

a cluster of primary sensory (afferent) neurons located in the dorsal roots of the spinal cord.

Front 25

Dorsal

Back 25

toward the surface of the back or upper side of the body/section.

Front 26

Ventral

Back 26

toward the surface of the chest, front or lower side of the body/section.

Front 27

Medial

Back 27

toward the midline of the body/section

Front 28

Lateral

Back 28

towards the outside or periphery of the body/section; away from the midline.

Front 29

Rostral

Back 29

towards the head end of an animal (also referred to as anterior).

Front 30

Caudal

Back 30

towards the tail end of an animal (also referred to as posterior).

Front 31

Proximal

Back 31

near the main mass of the body (e.g., thigh).

Front 32

Distal

Back 32

away from the main mass of the body (e.g., toes).

Front 33

The CNS is comprised of two major classes of cells

Back 33

Neurons and Glial Cells.

Front 34

NEURONS

Back 34

The fundamental signaling units of the nervous system; they make
synapses with other neurons to conduct and generate action potentials. Neurons have the unique ability to communicate rapidly with one another over great distances and with great precision.

Front 35

NEURONS CONT

Back 35

•Human brain contains approximately one trillion (1012) neurons
•Typical neuron forms ~ 1,000 synapes and receives even more
•There are three major functional types of neurons: sensory, motor, and interneurons
•All neurons are classified according to their morphology and basic function and are typically named after the individual morphologist who first characterized them

Front 36

Pyramidal Cells

Back 36

cell bodies that look like pyramids “projecting neurons”

Front 37

Purkinje Cells

Back 37

flask-shaped cells in the cerebellum; large cells with extensive dendritic arborizations

Front 38

Basket Cells:

Back 38

cells with dendritic arborizations shaped like baskets – found in the cerebellum

Front 39

Granule Cells

Back 39

small cells in the cortex and cerebellum; responsible for “local activity”

Front 40

Stellate Cells

Back 40

small spiny, sometimes star-shaped cells, in the cortex and cerebellum, also responsible for “local activity”

Front 41

Bipolar Cells

Back 41

the cells in the brain (as well as in the retina), these cells have two poles which are different from the unipolar cells found in invertebrates

Front 42

NEUROGLIA

Back 42

The other major cell in the CNS. These cells are not thought to be essential in processing information in the nervous system, however they function as supporting elements. Glial cells are ~ 10 to 50 times more numerous than neurons in the vertebrate CNS.

Front 43

NEUROGLIA CONT

Back 43

•These cells do not conduct action potentials

•These cells do not make synapses

•Their primary function seems to be as support cells

•They provide the myelin sheath for myelinated neurons in the CNS

•They serve as nutritional cells for neurons

•They act as scavengers of cellular debris following injury or neuronal death

•They act to phagocytize foreign objects (perhaps acting as an immune response)

Front 44

Four Types of Neuroglial Cells in the CNS

Back 44

Astrocytes

Oligodendroglia (oligodendrocytes)

Microglia

Ependymal Cells

Front 45

Astrocytes

Back 45

These are the most numerous of the glial cells

They are spherical / ellipsoidal nuclei with deep indentations which make the cell
look like stars, hence the name “astroglia”

They are found around the external surface of the brain and around the capillaries, thus, they must serve some function in nutrition of primary neurons

They also play a support role since they fill the inter-neuronal spaces

Front 46

Oligodendroglia (oligodendrocytes

Back 46

These cells have small spherical nuclei with very dense cytoplasm

These cells are also found in rows between neurons

Their primary function is to create the myelin sheath surrounding the CNS neurons (one single oligodendrocyte can form sheaths around many axons)

These are analogous to the “Schwann Cells” of the PNS with the exception that only one Schwann Cell myelinates one portion of a PNS axon)

Front 47

Microglia

Back 47

These are small elongated glial cells that are physiologically and embryologically unrelated to the other cell types of the CNS

While their function is not entirely known, they appear to be phagocytes that are mobilized following inflammation/injury, infection, or disease

Front 48

Ependymal Cells

Back 48

three types and all are involved in brain-CSF interactions

Ependymocytes: columnar cells that line the ventricles; may participate in exchange of metabolites between neurons and CSF

Front 49

Ependymal Cells Cont

Back 49

Tanycytes: these look like ependymocytes except that they have long processes that pass through the ventricles; most likely act to transport hormones, etc., into specific regions of the brain

Choroid Epithelial Cells: these line the choroid plexi (which makes CSF) with tight junctions; involved in the partitioning of CSF and plasma proteins.

Front 50

The Three Planes of Orientation for Brain Slices

Back 50

CORONAL (also referred to as Frontal or Transverse sections)

•cut in a plane that is parallel to the face

•cuts from Anterior to Posterior (Front to Back)

•both left and right hemispheres in the section

Front 51

The Three Planes of Orientation for Brain Slices
Cont

Back 51

HORIZONTAL

•cut in a plane parallel to the top of the brain

•cuts from Dorsal to Ventral (Top to Bottom)

•both left and right hemispheres in the section

Front 52

The Three Planes of Orientation for Brain Slices
Cont

Back 52

SAGITTAL

•cut in a plane that is parallel to the side of the brain

•cuts from Medial to Lateral (Middle to Left OR Middle to Right), so you only get one hemisphere in the section

Front 53

TELENCEPHALON

(Forebrain)

Ventricle: Lateral

Back 53

•Includes most of the two symmetrical cerebral hemispheres

•This is the largest division of the human brain: it mediates all of our sensory modalities, most of our motor function, complex thoughts, behaviors, memories and cognitive reasoning

It is important to note that the left side of the brain receives information from and controls the right side of the body and vice versa

Front 54

Telecephalon is comprised of three major divisions:

Back 54

Cerebral Cortex

Basal Ganglia

Limbic System

Front 55

CEREBRAL CORTEX

Back 55

• The cortex is largely made up of neuronal cell bodies (Gray Matter) and their myelinated axons (White Matter)
• The cortex is the “covering” over the cerebral hemispheres
• The left and right hemispheres are separated by the LONGITUDINAL FISSURE and are joined together at the base by the CORPUS CALLOSUM

Front 56

CORPUS CALLOSUM

Back 56

a band of myelinated fibers that provides two basic functions other than holding the left and right hemispheres together:

•allows for neural communication between the two hemispheres

•“unites” the two hemispheres into a “single mind”

Front 57

Layers of the Cortex

Back 57

six layers of the cortex (I – VI) which house various cells that either project information to other regions OR information that is passing through the

Front 58

three main types of fibers of passage that course through the cortex

Back 58

Association

Projection

Commissural

Front 59

Association

Back 59

projects from one region of the cortex to another within the same hemisphere

ties together the front-back or top-bottom of cortex

Front 60

Projection

Back 60

fibers that originate in the cortex and project to subcortical brain structures

ties together the cortex with other brain regions

Front 61

Commissural

Back 61

fibers that project from one hemisphere to another

ties together the right and left hemispheres

Front 62

Gyri

Sulci

Fissures

Back 62

bumps

grooves

deep sulci

Front 63

The cortex is divided up into Four Major Lobes, each separated by defined sulci. These four lobes each serve different functional purposes and are referred to as the

Back 63

Cerebrum

Front 64

4 lobes

Back 64

Frontal, Parietal, Occipital, and Temporal

Front 65

FRONTAL LOBE

Back 65

The largest lobe of the brain

This lobe is divided into Pre-Frontal and Frontal areas:

Front 66

PreFrontal

Back 66

•Most advanced in humans

•Involved in:
a) higher cognitive functions (reasoning, planning, organization),
b) storage of older memories c) ability to inhibit any socially inappropriate responses

Front 67

Frontal

Back 67

•Involved in the execution and control of motor functions (movement, locomotion)

•Most of the generalized motor movement arises from the Primary Motor Cortex: this area is activated when we move.

Front 68

Frotnal cont.

Back 68

•Very specific areas of the Primary Motor Cortex are responsible for very specific areas of the body (“motor homunculus”)

•The Primary Motor Cortex is located in the Precentral Gyrus which lies in front of the Central Sulcus that separates frontal from parietal lobe

Front 69

PARIETAL LOBE

Back 69

•Involved in somatosensory functions (touch, pain, pressure, temperature)

•Also important for body position

•Our perception of somatosensation occurs in the Primary Somatosensory Cortex

Front 70

PARIETAL LOBE CONT.

Back 70

•Very specific areas of Primary Somatosensory Cortex are responsible for very specific areas of the body (“sensory homunculus”).

•The Primary Somatosensory Cortex is located in the Postcentral Gyrus (directly behind the Central Sulcus)

Front 71

OCCIPITAL LOBE

Back 71

•Involved processing visual stimuli and forming perceptions of the processed information

•The Occipital Lobe is separated from the Parietal Lobe by the Parieto-Occipital Sulcus

Front 72

TEMPORAL LOBE

Back 72

•Located on the side of the right and left hemispheres

•The Temporal Lobe is the only “separated” lobe; the right and left lobes do not touch

•The Temporal Lobe is separated from the other lobes by the Lateral Sulcus

•Directly ventral to the Lateral Sulcus is the Superior Temporal Gyrus

Front 73

Superior Temporal Gyrus

Back 73

is responsible for processing and perceiving auditory stimuli

Front 74

Left Temporal Lobe

Back 74

is the main area for language comprehension (our ability to understand and speak/produce speech)

Front 75

TEMPORAL LOBE Cont.

Back 75

• Temporal area is also involved in our ability to form new memories and emotions (specifically because of two internal structures referred to as the hippocampus and the amygdala)

Front 76

Additional Cortical Areas
1.Olfactory Tract
2.Olfactory Bulb
3.Optic Nerve

Back 76

1.sends fiber tract to the Olfactory Bulbs for olfactory processes
2.responsible for olfactory processes
3.nerve that sends information from the eye

Front 77

Additional Cortical Areas
4.Optic Chiasm
5.Optic Tract:
6.Infundibulum

Back 77

4.“X”; crossing of the optic fiber tracts
5.fibers that send visual information back to the Occipital lobe
6.stalk of the pituitary gland

Front 78

Additional Cortical Areas
7.Mammillary Body
8.Uncus
9.Parahippocampal Gyrus

Back 78

7.part of the limbic system, responsible for some aspects of memory (affected in Korsakoff’s Syndrome)
8.houses the amygdala
9.houses the hippocampus

Front 79

Association Areas of the Cerebral Cortex and Their Relation to “Brodmann Areas”

Back 79

• In addition to the main functionality of the four lobes of the brain, each lobe also houses “association areas”. These areas provide support / additional services to the major function of each lobe. Think of them as “relay areas” between the starting point and the ending point.

Front 80

Association Areas of the Cerebral Cortex and Their Relation to “Brodmann Areas”
Cont

Back 80

• The surface of the cortex is divided into localized regions according to each specific function (as we have already studied). This division of the cerebral cortex was first “mapped” out by the neuroanatomist “Brodmann” in 1909. He mapped out specific regions (he used a numbering system of 1-50) which correlated with specific functions and called these areas “Brodmann Areas”.

Front 81

Following Cards are the Brodmann Areas

Back 81

13

Front 82

#1, 2, 3 Primary Somatosensory Cortex

Back 82

•involved in our recognition of pressure, pain, temperature, bodily position, and touch

Front 83

#5, 7 Somatosensory Association Cortex

Back 83

•involved in generalized senses

•“tells us” the significance of sensory information (e.g., “Wow – it’s hot in here!)

•allows us to identify a common object by touch

•gives you a sense of where your limbs are

•lesions produce sensory agnosias : the inability to determine what you are touching

Front 84

#4 Primary Motor Cortex

Back 84

• involved in locomotion and fine motor control

Front 85

#6 Motor Association (Premotor) Cortex

Back 85

•muscle tone

•initiation and execution of motion

•directs primary motor cortex

Front 86

#8 Eye Motor Cortex

Back 86

•volitional eye movements

Front 87

#9,10,11,12,46,47 Prefrontal Cortex

Back 87

•enlarged in the human

•involved in our cognitive skills

•important for judgement, reasoning, thought processes, decision making skills

•vast number of interconnections to other cortical regions

Front 88

#44, 45 Motor Speech Cortex – “Broca’s Area”

Back 88

•usually found on the dominant hemisphere (on left in 75% of people)

•involved in verbalization of language; understanding and producing speech

•lesions produce “Broca’s Aphasia”: slow, laborious but mneaningful speech (sometimes it is faster and easier for the patient to write words down instead of verbalizing them)

Front 89

#41 Primary Auditory Cortex

Back 89

•main area of audition / sense of hearing

•lesions here produce deafness

Front 90

#42 Secondary Auditory Cortex

Back 90

•reacting to what you hear

Front 91

#22 Sensory Language Area / Auditory Association Cortex – “Wernicke’s Area

Back 91

•unique to primates
•found on the left temporal lobe
•comprehension of language and the production of meaningful speech
•association area relates the visual, verbal, and auditory components
•lesions in only the sensory association cortex produce reading disorders: alexia: inability to read and dyslexia: inability to read a few words or sentences together / switching of letters
•more extensive lesions produce “Wernicke’s Aphasia”: production of meaningless speech (“Word Salad”); also have a difficulty understanding language well

Front 92

#17 Primary Visual Cortex

Back 92

• direct and indirect connections from the retina

•lesions in this area produce blindness

Front 93

#18, 19 Visual Association Cortex

Back 93

•provides recognition (knowing what we have seen in the past)

Front 94

#43 Gustatory / Taste Cortex

Back 94

•provides us with our sense of taste

Front 95

Telecephalon (forebrain)
BASAL GANGLIA

Back 95

•Initiation and termination of movement, efficiency of movement, muscle tone, tremor

Front 96

The Basal Ganglia consists of three primary subcortical structures

Back 96

1.Caudate Nucleus

2.Putamen

3.Globus Pallidus

Front 97

Caudate Nucleus

Back 97

•elongated nucleus that is larger anteriorly (head) and thinner posteriorly (tail)

•the tail of the caudate leads to the amygdala

•receives excitatory inputs from primary and accessory motor cortex (corticostriatal projection)

•receives inhibitory dopamine inputs from the substantia nigra (nigro-striatal pathway)

Front 98

Putamen

Back 98

•positioned laterally to the caudate nucleus

•receives excitatory inputs from the cortico-striatal projections and inhibitory inputs from the nigro-striatal dopamine pathway

•both the caudate nucleus and the putamen are afferent nuclei of the basal ganglia

Front 99

Globus Pallidus

Back 99

•positioned ventrally to the head of the caudate and medially from the putamen

•this is the efferent nucleus of the basal ganglia

•sends projections to the ventrolateral thalamus which projects to the accessory motor cortex

•also sends projections to the subthalamus and substantia nigra

Front 100

Lesions of the basal ganglia structures or projections cause neurological deficits:

Back 100

•Dyskinesias: abnormal movements
•Akinesias: loss of or decreased movements
•Bradykinesia: slowed motor movements
•Dystonias: loss of or abnormal muscle tone
•Choreas: jerky movements of arms and legs
•Athetosis: writhing movements of the digits
•Ballismus: uncontrolled flailing of the limbs

Front 101

Damage to Basal Ganglia

Back 101

damage to the caudate nucleus or putamen generally results in either rigidity or excessive, uncontrollable movements while damage to the globus pallidus generally causes akinesias or lack of movements

Thus, the caudate/putamen is inhibitory while the globus pallidus is excitatory in function

Front 102

Damage to Basal Ganglia Cont.

Back 102

• Some of the more common disorders associated with damage to the basal ganglia structures or pathways include Parkinson’s Disease and Huntington’s Chorea

Front 103

LIMBIC SYSTEM
Telecephalon (forebrain)

Back 103

•The Limbic System provides a connection between the higher cortical centers of the Telencephalon and the diencephalon (particularly the hypothalamus) to help govern autonomic and behavioral functions

•The Limbic System is shaped like a sheep’s horn, and contains six main structures:

Front 104

The Limbic System is shaped like a sheep’s horn, and contains six main structures:

Back 104

Hippocampus
Fornix
Mamillary Bodies
Septum
Amygdala
Olfactory Bulb/Tract

Front 105

Hippocampus

Back 105

•located in the temporal lobe; this important structure is housed within the parahippocampal gyrus

•Very important structure for memory, specifically the acquisition and transcription of new material / new experiences

Front 106

Fornix

Back 106

•connects the hippocampus to the mammillary bodies (and thus the hypothalamus)

•main source of efferents from the hippocampus

•seems to serve in aiding the hippocampus with memory processes (i.e., probably transfers our established memories to other areas of the cortex)

Front 107

Mammillary Bodies

Back 107

•connected to the hippocampus via the fornix (described above)

•seem to serve memory function (similar to the hippocampus however this structure may also house some of our older memories as well)

damage to the mammillary bodies results in anterograde and retrograde amnesia

Front 108

Septum

Back 108

•consists of medial and lateral septal nuclei

•involved in temperature regulation, vascular reactivity, smell (due to connections with olfactory areas) and emotions (specifically anger)

•lesions to the septal nuclei result in highly aggressive, dangerously mean behavior

Front 109

Amygdala

Back 109

•located within the temporal lobe; this structure is housed within the Uncus

•found at the end of the caudate nucleus (thus there is connections to basal ganglia regions) and is situated next to the hippocampus

Front 110

Amygdala

Back 110

•involved in behavioral components such as fear (especially the “fight or flight” syndrome), rage, sexual emotions, and smell

•lesions to this regions can result in either intense rage/aggression or placid behavior with no reactions of fear, rage, or aggression

•Thus this structure is highly important for our emotional responses to stimuli

Front 111

Olfactory Bulb/Tract

Back 111

•even though this is considered “older cortex” it is associated with the limbic system due to its fiber connections as well as the role of olfaction in memory

Front 112

LIMBIC SYSTEM
Telecephalon (forebrain)

Back 112

•The Limbic System provides a connection between the higher cortical centers of the Telencephalon and the diencephalon (particularly the hypothalamus) to help govern autonomic and behavioral functions

•The Limbic System is shaped like a sheep’s horn, and contains six main structures:

Front 113

The Limbic System is shaped like a sheep’s horn, and contains six main structures:

Back 113

Hippocampus
Fornix
Mamillary Bodies
Septum
Amygdala
Olfactory Bulb/Tract

Front 114

Hippocampus

Back 114

•located in the temporal lobe; this important structure is housed within the parahippocampal gyrus

•Very important structure for memory, specifically the acquisition and transcription of new material / new experiences

Front 115

Fornix

Back 115

•connects the hippocampus to the mammillary bodies (and thus the hypothalamus)

•main source of efferents from the hippocampus

•seems to serve in aiding the hippocampus with memory processes (i.e., probably transfers our established memories to other areas of the cortex)

Front 116

Mammillary Bodies

Back 116

•connected to the hippocampus via the fornix (described above)

•seem to serve memory function (similar to the hippocampus however this structure may also house some of our older memories as well)

damage to the mammillary bodies results in anterograde and retrograde amnesia

Front 117

Septum

Back 117

•consists of medial and lateral septal nuclei

•involved in temperature regulation, vascular reactivity, smell (due to connections with olfactory areas) and emotions (specifically anger)

•lesions to the septal nuclei result in highly aggressive, dangerously mean behavior

Front 118

Amygdala

Back 118

•located within the temporal lobe; this structure is housed within the Uncus

•found at the end of the caudate nucleus (thus there is connections to basal ganglia regions) and is situated next to the hippocampus

Front 119

Amygdala

Back 119

•involved in behavioral components such as fear (especially the “fight or flight” syndrome), rage, sexual emotions, and smell

•lesions to this regions can result in either intense rage/aggression or placid behavior with no reactions of fear, rage, or aggression

•Thus this structure is highly important for our emotional responses to stimuli

Front 120

Olfactory Bulb/Tract

Back 120

•even though this is considered “older cortex” it is associated with the limbic system due to its fiber connections as well as the role of olfaction in memory

Front 121

DIENCEPHALON

Forebrain

Ventricle: Third

Back 121

Epithalamus

Thalamus

Subthalamic regions

Hypothalamus

optic nerves/tracts

Front 122

Epithalamus

Back 122

•found in the dorsal area of diencephalon

•contains the pineal body: involved in the production of melatonin which may play a role in seasonal reproductive cycles and/or sleep

•also contains the habenula: involved in aspects of olfaction in terms of “food gathering”

Front 123

Thalamus

Back 123

•major “relay center” of the brain; every sensory system sends projections through the Thalamus except olfaction

•the major function of the thalamus is to act as an environmental filter: it categorizes each stimulus and then sends the information to the appropriate region of the cortex

Front 124

Subthalamic regions

Back 124

•located ventrally and posteriorly to the thalamus

•contains both motor and sensory fibers en route to the thalamus

•lesions of this nucleus result in ballistic movements of the limbs

Front 125

Hypothalamus

Back 125

•located just below and slightly anterior to the thalamus

•involved in a number of autonomic functions (both sympathetic and parasympathetic)

Front 126

autonomic functions of hypothalamus

Back 126

1.temperature regulation
2.food and water intake
•medial hypothalamus: “I’m full”
•lateral hypothalamus: “I’m hungry”
3.metabolic center
4.behavior center (from reproduction to emotions)
5.neuroendocrine center: regulates the hormone release from the pituitary gland

Front 127

MESENCEPHALON

Midbrain

Ventricle: C. Aqueduct

Back 127

•surrounds the cerebral aqueduct and consists of two major parts:

Front 128

two major parts of Mesencephalon

Back 128

Tectum

Tegmentum

Front 129

Tectum

Back 129

•the principle structures are: superior colliculi: involved in aspects of the visual system, and the inferior colliculi: involved in aspects of the auditory system

Front 130

Tegmentum

Back 130

•consists of the reticular activating system (important for sleep and arousal, vital reflexes), nuclei that control eye movements, the substantia nigra (important for DA), and the periaqueductal gray (cells bodies that surround the ventricles; important area for modulation of pain)

Front 131

METENCEPHALON

Hindbrain

Ventricle: Fourth

Back 131

• Part of the “Hindbrain” which consists of the metencephalon and myelencephalon

•The Metencephalon consists of two major divisions:
Cerebellum
Pons

Front 132

Cerebellum

Back 132

•cerebellum means “little brain” , resembles a miniature version of the cerebrum

•large structure that operates at the subconscious level to maintain muscle tone, equilibrium, locomotion, posture, and coordinated movements

Front 133

Cerebellum Cont.

Back 133

•Important for our coordinated muscle motor movements (different from Temporal Lobe) such as walking, standing/posture, and our balance/equilibrium (e.g., touching our finger to our nose, throwing a ball, flipping a remote control)

•The cerebellum receives visual, auditory, vestibular, and somatosensory information, as well as individual muscle movements and integrates all this information. It then modifies the motor outflow which results in coordinated, smooth movements

Front 134

Cerebellum Cont.

Back 134

•Cerebellar damage results in jerky, poorly coordinated, exaggerated movements (extensive damage makes it impossible to stand)

•Cerebellum is also responsible for “Motor Memories” (e.g., playing basketball, driving a standard transmission)

Front 135

Pons

Back 135

•large bulge in the brainstem that acts as a bridge between the hemispheres
•involved in efficiency of motor skills, and some aspects of sleep and arousal
•consists of two parts:
A.Dorsal (posterior) portion: contains sensory and motor tracts for the facial region (via the cranial nerves)
B.Ventral (basilar) portion: provides an avenue of communication between the cortex and contralateral cerebellar hemisphere

Front 136

Area Postrema

Back 136

•Lying next to the pons on the wall of the fourth ventricle is a structure known as the Area Postrema: this is our “vomit center”. Whenever we get sick and throw-up, this center is being activated

Front 137

MYELENCEPHALON

Hindbrain

Ventricle: Fourth

Back 137

•The brainstem is responsible for controlling our vital functions such as cardiovascular regulation, circulatory and respiratory functions, as well as playing roles in sleep and arousal

•the myelencephalon contains one major structure: Medulla Oblongata

•consists of a vast number of ascending and descending fiber tracts as well as specific nuclei

Front 138

MYELENCEPHALON

Back 138

•these fiber tracts connect the brain nuclei to the spinal cord

•the most caudal portion of the brainstem (its lower end is the beginning of the spinal cord)

•the medulla oblongata also contains the reticular activating system (as does the mesencephalon and metencephalon since it is a long structure).

Front 139

MOTOR HOMUNCULUS OF CORTEX

Back 139

1.lower limbs occupy the dorsal, medial aspect of the cortex

2.upper limbs and trunk occupy the intermediate (dorsolateral) aspect - hand enlargement

3.face (head) and neck occupy the lateral aspect - 50% of the motor homunculus.

Front 140

Differences in pyramidal and extrapryamidal systems

Back 140

1.pyramidal systems are principally involved in fine motor control and usually involve one or two synapses.

2.extrapyramidal tracts are involved in more ballistic movement (groups of muscles) and are multisynaptic (involve several motor neurons).

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Similarities of the pyramidal and extrapyramidal pathways

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1.both pyramidal and extrapyramidal motor pathways originate from the motor cortex and terminate on motor neurons in the ventral horn of the spinal cord.

2.In fact, pyramidal and extrapyramidal motor pathways terminate upon the same ventral motor neurons, therefore , these two motor systems influence the contraction of the same muscles!!!!!

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PYRAMIDAL SYSTEMS

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Corticospinal Tract

Corticobulbar Tract

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Corticospinal Tract

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•primary motor neurons originate in motor cortex and terminate in the spinal cord ventral horn


•lateral corticospinal tract decussates in the medullary pyramids - contralateral motor pathway

•fine motor control to the digits (hands and feet)

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Corticospinal Tract
Cont.

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•ventral corticospinal tract (15% of fibers) traverses the ventral columns of the spinal cord before crossing over in the region of the cervical/thoracic spinal cord - contralateral motor pathway

•larger coordinated movements of arms and legs, head and neck movements.

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Corticobulbar tract

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•fine motor control to the face, tongue, eye movements

•primary motor neurons arise in the lateral aspects of the motor cortex

•terminate on or near the cranial nerve motor nuclei in the brain stem

•tracts do not enter the spinal cord.

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EXTRAPYRAMIDAL MOTOR PATHWAYS

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Rubrospinal Tract

Reticulospinal Tract

Vestibulospinal Tract

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Rubrospinal Tract

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•multisynaptic motor pathway

•primary motor neurons arise from premotor and motor cortex.

•cortical fibers synapse in the red nucleus.

•rubrospinal fibers traverse the contralateral lateral columns of the spinal cord.

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Rubrospinal Tract Cont.

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•synapse upon ventral motor neurons in the lateral aspects of the ventral horn

•cerebellar inputs for coordinated muscle movement.

•maintenance of muscle tone in the more proximal muscles of the arms (principally) and legs via inputs on gamma motor neurons.

•ballistic movements of extremities (grasp reflex, rotate arm)

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Reticulospinal Tract

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•multisynaptic motor pathway.

•primary motor neurons arise from premotor and motor cortex.

•cortical fibers synapse in nuclei of the pons and medulla of the brainstem.

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Reticulospinal Tract Cont.

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•reticulospinal tract fibers traverse the lateral columns and the ventral columns of the spinal cord.

•reticulospinal tracts terminate on ventral motor neurons in the medial aspects of the ventral horn.

•major function is in control of the large axial muscles involved in walking, running, standing.

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Vestibulospinal Tract

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•multisynaptic motor pathway.

•VOID OF CORTICAL MOTOR INPUTS

•primary motor neurons arise from vestibular nucleus in the brain stem.

•major influence by both the vestibular system and the cerebellum.

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Vestibulospinal Tract Cont.

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•ipsilateral motor pathway course through the ventral columns of the spinal cord and terminates on lower motor neurons in the medial aspects of the ventral horn.

•innervates the musculature of the back, head and neck and proximal limbs that is involved in the maintenance of upright posture... especially in response to turning of the head.

•prominent influence on large extensor muscles.

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Sensory Pathways

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•the sensory tracts are all multisynaptic. order sensory neurons.

•all have a common termination point in the posterior region of the thalamus

•sensory fibers from the posterior thalamic regions project in a topographical fashion to the post central gyrus - primary sensory cortex. AKA Sensory Homunculus

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Sensory Pathways 3

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1. Spinothalamic tract

2. Medial (Dorsal) Lemniscal tract

3. Dorsal Spinocerebellar tract

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Spinothalamic Tract

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•arises from dorsal root fibers all along the spinal column.

•first order sensory neurons synapse in laminar layer 2 (substantia gelatinosa) of the dorsal horn of the spinal cord.

•second order sensory neurons in the substantia gelatinosa immediately cross over and the fibers enter the contralateral lateral and ventral columns and course up the spinal cord towards the brain.

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Spinothalamic Tract Cont.

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•axons from secondary sensory neurons terminate in the ventral/posterior nucleus of the thalamus.

•thalamic sensory neurons (third order sensory neurons) then project to the sensory cortex.

•this sensory pathway is involved in our ability to sense pain, temperature and light touch.

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Spinothalamic Tract Cont.

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•collateral fibers terminate in brain stem regions on descending pain pathways.

•descending pain pathways are most active during periods of chronic or severe pain

•descending pain pathways synapse in the dorsal horn of the spinal cord to modulate pain sensation.

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Medial (Dorsal) Lemniscal tract:

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arises from dorsal root fibers all along the spinal column.

axons from first order sensory neurons enter the spinal cord via the dorsal roots and immediately turn in the dorsal columns and travel towards the brain.

transmit position, pressure, vibration, discriminative touch and conscious position of the upper limbs (cuneate) and the lower limbs (gracile)

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Dorsal Spinocerebellar tract:

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arises from dorsal root fibers along the sacral and lumbar regions of the spinal column.

these fibers are involved in unconscious and conscious proprioception of lower limbs.