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159 Cards in this Set

  • Front
  • Back
Central Nervous System
the brain and the spinal cord.
Peripheral Nervous System
the cranial and spinal nerves with their associated ganglia.
Neuron
nerve cells; the conducting cells of the nervous system which consist of the soma (containing the nucleus), the dendrites, and the axon.
Interneuron
a short nerve cell that makes interconnections within one brain region.
Gray Matter
regions of the CNS that contain aggregations of nerve cells.
White Matter
regions of the CNS that contain axons (both myelinated and unmyelinated).
Afferent Fiber
incoming fibers; those fibers that convey information towards a nerve cell body (dendrites) or towards the brain (sensory fibers).
Efferent Fiber
outgoing fibers; those fibers that convey information away from a neuron (axon) or from the brain (motor fibers).
Tract
a collection of nerve fibers or axons inside the CNS (also known as a pathway, lemniscus, fasciculus, or peduncle).
Ascending Tracts
nerve fibers that run towards the brain; the vast majority of these are sensory fibers.
Descending Tracts
nerve fibers that run away from the brain; the vast majority of these are motor fibers
Sensory Neuron
a neuron that carries sensory information from the periphery to the spinal cord or brain (CNS
First Order Sensory Neuron
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.
Second Order Sensory Neuron
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.
Motor Neuron
: a neuron that carries motor information from the CNS to the muscles. These neurons terminate on skeletal, smooth, or cardiac muscles to induce contraction.
Upper Motor Neuron
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.
Lower Motor Neuron
: 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.
Spinal Nerve
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).
Cranial Nerves
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.
Ipsilateral
nerve fibers that terminate on the same side of the body that the cell body originates (e.g., originate: right; terminate: right).
Contralateral
nerve fibers that terminate on the opposite side of the body that the cell body originates (e.g., originate: right; terminate: left
Decussation
the crossing of a neural pathway in the brainstem or spinal cord from one side of the body to the contralateral side.
Ganglion
a cluster of functionally related neuron cells bodies in the peripheral nervous system (e.g., those that mediate sensory functions).
Dorsal Root Ganglion
a cluster of primary sensory (afferent) neurons located in the dorsal roots of the spinal cord.
Dorsal
toward the surface of the back or upper side of the body/section.
Ventral
toward the surface of the chest, front or lower side of the body/section.
Medial
toward the midline of the body/section
Lateral
towards the outside or periphery of the body/section; away from the midline.
Rostral
towards the head end of an animal (also referred to as anterior).
Caudal
towards the tail end of an animal (also referred to as posterior).
Proximal
near the main mass of the body (e.g., thigh).
Distal
away from the main mass of the body (e.g., toes).
The CNS is comprised of two major classes of cells
Neurons and Glial Cells.
NEURONS
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.
NEURONS CONT
•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
Pyramidal Cells
cell bodies that look like pyramids “projecting neurons”
Purkinje Cells
flask-shaped cells in the cerebellum; large cells with extensive dendritic arborizations
Basket Cells:
cells with dendritic arborizations shaped like baskets – found in the cerebellum
Granule Cells
small cells in the cortex and cerebellum; responsible for “local activity”
Stellate Cells
small spiny, sometimes star-shaped cells, in the cortex and cerebellum, also responsible for “local activity”
Bipolar Cells
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
NEUROGLIA
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.
NEUROGLIA CONT
•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)
Four Types of Neuroglial Cells in the CNS
Astrocytes

Oligodendroglia (oligodendrocytes)

Microglia

Ependymal Cells
Astrocytes
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
Oligodendroglia (oligodendrocytes
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)
Microglia
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
Ependymal Cells
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
Ependymal Cells Cont
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.
The Three Planes of Orientation for Brain Slices
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
The Three Planes of Orientation for Brain Slices
Cont
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
The Three Planes of Orientation for Brain Slices
Cont
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
TELENCEPHALON

(Forebrain)

Ventricle: Lateral
•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
Telecephalon is comprised of three major divisions:
Cerebral Cortex

Basal Ganglia

Limbic System
CEREBRAL CORTEX
• 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
CORPUS CALLOSUM
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”
Layers of the Cortex
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
three main types of fibers of passage that course through the cortex
Association

Projection

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

ties together the front-back or top-bottom of cortex
Projection
fibers that originate in the cortex and project to subcortical brain structures

ties together the cortex with other brain regions
Commissural
fibers that project from one hemisphere to another

ties together the right and left hemispheres
Gyri

Sulci

Fissures
bumps

grooves

deep sulci
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
Cerebrum
4 lobes
Frontal, Parietal, Occipital, and Temporal
FRONTAL LOBE
The largest lobe of the brain

This lobe is divided into Pre-Frontal and Frontal areas:
PreFrontal
•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
Frontal
•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.
Frotnal cont.
•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
PARIETAL LOBE
•Involved in somatosensory functions (touch, pain, pressure, temperature)

•Also important for body position

•Our perception of somatosensation occurs in the Primary Somatosensory Cortex
PARIETAL LOBE CONT.
•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)
OCCIPITAL LOBE
•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
TEMPORAL LOBE
•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
Superior Temporal Gyrus
is responsible for processing and perceiving auditory stimuli
Left Temporal Lobe
is the main area for language comprehension (our ability to understand and speak/produce speech)
TEMPORAL LOBE Cont.
• 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)
Additional Cortical Areas
1.Olfactory Tract
2.Olfactory Bulb
3.Optic Nerve
1.sends fiber tract to the Olfactory Bulbs for olfactory processes
2.responsible for olfactory processes
3.nerve that sends information from the eye
Additional Cortical Areas
4.Optic Chiasm
5.Optic Tract:
6.Infundibulum
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
Additional Cortical Areas
7.Mammillary Body
8.Uncus
9.Parahippocampal Gyrus
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
Association Areas of the Cerebral Cortex and Their Relation to “Brodmann Areas”
• 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.
Association Areas of the Cerebral Cortex and Their Relation to “Brodmann Areas”
Cont
• 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”.
Following Cards are the Brodmann Areas
13
#1, 2, 3 Primary Somatosensory Cortex
•involved in our recognition of pressure, pain, temperature, bodily position, and touch
#5, 7 Somatosensory Association Cortex
•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
#4 Primary Motor Cortex
• involved in locomotion and fine motor control
#6 Motor Association (Premotor) Cortex
•muscle tone

•initiation and execution of motion

•directs primary motor cortex
#8 Eye Motor Cortex
•volitional eye movements
#9,10,11,12,46,47 Prefrontal Cortex
•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
#44, 45 Motor Speech Cortex – “Broca’s Area”
•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)
#41 Primary Auditory Cortex
•main area of audition / sense of hearing

•lesions here produce deafness
#42 Secondary Auditory Cortex
•reacting to what you hear
#22 Sensory Language Area / Auditory Association Cortex – “Wernicke’s Area
•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
#17 Primary Visual Cortex
• direct and indirect connections from the retina

•lesions in this area produce blindness
#18, 19 Visual Association Cortex
•provides recognition (knowing what we have seen in the past)
#43 Gustatory / Taste Cortex
•provides us with our sense of taste
Telecephalon (forebrain)
BASAL GANGLIA
•Initiation and termination of movement, efficiency of movement, muscle tone, tremor
The Basal Ganglia consists of three primary subcortical structures
1.Caudate Nucleus

2.Putamen

3.Globus Pallidus
Caudate Nucleus
•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)
Putamen
•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
Globus Pallidus
•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
Lesions of the basal ganglia structures or projections cause neurological deficits:
•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
Damage to Basal Ganglia
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
Damage to Basal Ganglia Cont.
• Some of the more common disorders associated with damage to the basal ganglia structures or pathways include Parkinson’s Disease and Huntington’s Chorea
LIMBIC SYSTEM
Telecephalon (forebrain)
•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:
The Limbic System is shaped like a sheep’s horn, and contains six main structures:
Hippocampus
Fornix
Mamillary Bodies
Septum
Amygdala
Olfactory Bulb/Tract
Hippocampus
•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
Fornix
•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)
Mammillary Bodies
•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
Septum
•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
Amygdala
•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
Amygdala
•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
Olfactory Bulb/Tract
•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
LIMBIC SYSTEM
Telecephalon (forebrain)
•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:
The Limbic System is shaped like a sheep’s horn, and contains six main structures:
Hippocampus
Fornix
Mamillary Bodies
Septum
Amygdala
Olfactory Bulb/Tract
Hippocampus
•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
Fornix
•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)
Mammillary Bodies
•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
Septum
•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
Amygdala
•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
Amygdala
•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
Olfactory Bulb/Tract
•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
DIENCEPHALON

Forebrain

Ventricle: Third
Epithalamus

Thalamus

Subthalamic regions

Hypothalamus

optic nerves/tracts
Epithalamus
•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”
Thalamus
•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
Subthalamic regions
•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
Hypothalamus
•located just below and slightly anterior to the thalamus

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

Midbrain

Ventricle: C. Aqueduct
•surrounds the cerebral aqueduct and consists of two major parts:
two major parts of Mesencephalon
Tectum

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

Hindbrain

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

•The Metencephalon consists of two major divisions:
Cerebellum
Pons
Cerebellum
•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
Cerebellum Cont.
•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
Cerebellum Cont.
•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)
Pons
•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
Area Postrema
•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
MYELENCEPHALON

Hindbrain

Ventricle: Fourth
•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
MYELENCEPHALON
•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).
MOTOR HOMUNCULUS OF CORTEX
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.
Differences in pyramidal and extrapryamidal systems
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).
Similarities of the pyramidal and extrapyramidal pathways
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!!!!!
PYRAMIDAL SYSTEMS
Corticospinal Tract

Corticobulbar Tract
Corticospinal Tract
•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)
Corticospinal Tract
Cont.
•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.
Corticobulbar tract
•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.
EXTRAPYRAMIDAL MOTOR PATHWAYS
Rubrospinal Tract

Reticulospinal Tract

Vestibulospinal Tract
Rubrospinal Tract
•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.
Rubrospinal Tract Cont.
•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)
Reticulospinal Tract
•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.
Reticulospinal Tract Cont.
•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.
Vestibulospinal Tract
•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.
Vestibulospinal Tract Cont.
•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.
Sensory Pathways
•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
Sensory Pathways 3
1. Spinothalamic tract

2. Medial (Dorsal) Lemniscal tract

3. Dorsal Spinocerebellar tract
Spinothalamic Tract
•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.
Spinothalamic Tract Cont.
•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.
Spinothalamic Tract Cont.
•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.
Medial (Dorsal) Lemniscal tract:
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)
Dorsal Spinocerebellar tract:
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.