Neuroanatomy IRF Block 2

Three functions of the motor system

1.) help support the body against the pull of gravity

2.) help establish posture/maintain upright position

3.) produces/coordinates movement of the body

Two divisions of the motor system:

1.) upper motor system

2.) lower motor system

Upper motor neuron

cell body in the brain; axons are in the spinal cord and synapse with an interneuron to exert influence on a lower motor neuron

Upper motor neurons regulate ______ ______ ________

lower motor neurons

Upper motor neurons are entirely contain in the ________ nervous system

central

Lower motor neuron

cell body in the spinal cord; axons travel to the PNS and extend out to the muscle to cause contraction

The lower motor neuron controls the _______ ______

reflex arc

reflex arc

lower motor neuron will cause a stimulus in periphery, and a sensory neuron takes that info and transfer it onto a motor neuron to cause contraction

Two divisions of the upper motor neuron system

1.) pyramidal system

2.) extrapyramidal system

pyramidal system

cerebral cortical system; motor neuron cell bodies are located in the cerebral cortex

What type of LMNs do pyramidal motor neurons regulate?

LMNs that result in highly skilled motor activities

Where do the axons of a pyramidal motor neuron travel?

from the cerebral cortex through the brain stem and spinal cord and pass through the pyramids

Extrapyramidal system

non-cortical system; motor neuron cell bodies are located all over the place

What type of LMNs do extrapyramidal motor neurons regulate?

LMNs responsible for maintaining muscle tone, coarse/stereotype movements, and subconscious motor activity

Where do the axons of an extrapyramidal motor neuron travel?

do not contribute to the formation of pyramids; multiple synapses occur prior to the synapse with LMN

Pyramidal cell bodies are located in an area of the cerebrum called the _________ cortex

motor cortex

Two gyri part of the motor cortex

1.) precruciate gyri

2.) postcruciate gyri

The axons of the pyramidal motor system travel through the brain stem and spinal cord and create identifiable bundles of...

white matter

Six white matter structures of the pyramidal motor system:

1.) corona radiata

2.) internal capsule

3.) crus cerebri

4.) longitudinal fibers of pons

5.) pyramids

6.) lateral and ventral corticospinal tracts

corona radiata location

telencephalon

internal capsule location

diencephalon

crus cerebri location

mesencephalon

longitudinal fibers of pons location

metencephalon

pyramids location

mylencephalon

lateral and ventral corticospinal tracts location

spinal cord

The tracts of the pyramidal motor system are named based on their ____________

destination (LMNs)

When pyramidal motor system tracts target LMNs in the brainstem they are called...

corticonuclear tracts

Where do axons of corticonuclear tracts go?

from the pyramidal motor cortex to motor nuclei of cranial nerves in the brainstem

What cranial nerves do corticonuclear tracts target?

3-7 and 9-12

When pyramidal motor system tracts target LMNs in the spinal cord they are called...

corticospinal tracts

Two corticospinal tracts

1.) lateral corticospinal tract

2.) ventral corticospinal tract

lateral corticospinal tract

75% of axons that will cross over and descend contralaterally to find the appropiate motor neuron on the spinal cord

ventral corticospinal tract

25% of axons that will descend ipsolaterally down the spinal cord from the side of the brain they originated from until they find the appropriate motor neuron on the spinal cord, then they will cross

location of the lateral corticospinal tract

lateral funiculus of spinal cord

location of the ventral corticospinal tract

ventral funiculus of spinal cord

Cerebellum function

creates smooth, coordinated movement

The cerebellum has input from both ______ and _______ neurons

motor; sensory

How does the cerebellum have input from both motor and sensory neurons?

the pyramidal motor system sends input to let cerebellum know what limbs need to be moved, and the cerebellum combines that information with sensory info to move smoothly

What is the tract from the pyramidal motor system that communicates with the cerebellum called?

corticopontocerebellar tract

corticopontocerebellar tract

two step tract that communicates with the cerebellum; includes the corticopontine tract and pontocerebellar tract

corticopontine tract

pyramidal motor cells in the cortex go the pontine nucleus located in longitundal fibers of pons

pontocerebellar tract

cells located at the pons continue on through the cerebellar peduncles to reach level of the cerebellum

Extrapyramidal system

non-cortical system; motor neuron cell bodies are located all over the place

Function of the extrapyramidal system

regulates muscle tone, posture, and subconscious movement (stereotype movement)

The axons of the extrapyramidal system do not contribute to the formation of the ____________

pyramids

Where do axons of extrapyramidal system travel to?

LMNs in the brain stem and spinal cord

Where are cell bodies of the extrapyramidal system located?

in all five divisions of the brain (unlike pyramidal system where cell bodies are located in the pre and post cruciate gyri)

Each of the five adult centers of the brain contain extrapyramidal system ___________ ________

cell bodies

Telencephalon extrapyramidal cell bodies location

corpus striatum

corpus striatum

structure buried underneath the cerebrum (telencephalon); formed by alternating bundles of white matter and extrapyramidal nuclei

Four structures of the corpus striatum

1.) external capsule

2.) lentiform nucleus

3.) internal capsule

4.) caudate nucleus

external capsule

white matter fibers of the corpus striatum passing through the cerebrum

lentiform nucleus

gray matter nucleus of the extrapyramidal system in the telencephalon; further divided into the putamen and pallidum nuclei

internal capsule

white matter fibers of the corpus striatum passing through the cerebrum and brain stem

caudate nucleus

gray matter nucleus of the extrapyramidal system in the telencephalon

Diencephalon extrapyramidal cell bodies location

multiple nuclei, with those in the thalamus most prominent

Mesencephalon extrapyramidal cell bodies location

red nucleus

red nucleus

gray matter nucleus of the extrapyramidal system in the mesencephalon that is the origin of the rubrospinal tract

rubrospinal tract

extrapyramidal tract originating from the red nucleus in the mesencephalon that is the most important extrapyramidal tract!

Where do rubrospinal tract fibers travel?

they cross to opposite side of the brain stem to reach the LMN in the spinal cord (lateral funiculus)

Metencephalon extrapyramidal cell bodies location

pontine reticular formation

pontine reticular formation

The portion of the reticular formation that is located in the pons; origin on the pontine reticulospinal tract

pontine reticulospinal tract

provides excitatory impulse to extensor muscles; aka as ventral reticulospinal tract

Mylencephalon extrapyramidal cell bodies location

medullary reticular formation

medullary reticular formation

The portion of the reticular formation that is located in the medulla oblongata; gives rise to the medullary reticulospinal tract

medullary reticulospinal tract

sends inhibitory stimulus to the extensor muscles; aka lateral reticulospinal tract

Three main paths of the extrapyramidal system that have major influence on LMNs in spinal cord:

1.) ruprospinal tract

2.) pontine reticulospinal tract/ventral reticulospinal tract

3.) medullary reticulospinal tract/lateral reticulospinal tract

Olivocerebellar tract

axons that synapse with the police form pathway going form the olive to the cerebellum; part of extrapyramidal motor system

Clinical signs of UMN disease

1.) hyperreflexia

2.) hypertonus

3.) spastic paralysis

4.) slow muscular atrophy

Lower motor system

located in the spinal cord and brain stem and are assigned by functional classification

Lower motor neurons are regulated by the...

upper motor neuron system

Lower motor neurons can be _______ or __________

excitatory or inhibitory

Convergence

all of the processes of upper motor neurons converging with the lower motor neurons

summation

combination of excitatory and inhhaotiry regulations from the upper motor neuron to determine the set sum of the response of the lower motor neuron

Lower motor neurons are located in two places:

1.) spinal cord

2.) brain stem

lower motor neurons of the spinal cord

cell bodies located in the ventral horn and axons become spinal nerves

lower motor neurons of the brain stem

cell bodies scattered in different areas and axons become cranial nerves

Three functional classifications of the lower motor system:

1.) GSE

2.) SVE

3.) GVE

The cell body for the GSE spinal lower motor neuron is located where?

the ventral horn

Function of the spinal GSE LMN

innervates skeletal muscle

There are two populations of GSE neurons in the ventral horn classified by _______

size

Two types of skeletal muscle

1.) extrafusal fiber

2.) intrafusal fiber

extrafusal fiber

majority of skeletal muscle; innervated by large LMN from the spinal cord (alpha)

intrafusal fiber

receptor for stretch; determines muscle tone and innervated by small LMN from spinal cord (gamma)

In the limbs of the body, reflexes are transmitted by spinal nerves with LMNs located from the ________ __________

ventral horn

Reflex arc

in the periphery, a sensory receptor sends info into the spinal cord through an afferent fiber; an interneuron communicates with the GSE cell body in the ventral horn whose efferent fibers transmit a signal back to the periphery in skeletal muscle

Monosynaptic arc

rare, no interneuron present in the reflex arc

Polysynaptic arc

common, interneuron is present in the reflex arc

Lesion sites can occur ________ along the extent of the LMN

anywhere

What happens if a LMN is damaged?

muscles won't contract

Clinical signs of LMN disease

1.) Hyporeflexia

2.) Hypotonus

3.) Flaccid paralysis

4.) Relatively quick muscular atrophy

for cranial nerve reflexes, the LMN is located in the _______ _________

brain stem

Cranial nerves are classified by their __________ ___________

target structure

Three types of cranial LMNs:

1.) GSE

2.) SVE

3.) GVE

GSE targets...

voluntary skeletal muscle

SVE targets...

skeletal muscle that came from branchial arches (develop from neck area in embryo)

GVE targets...

cardiac muscle, smooth muscle, and glands

Which classifications of LMNs are found in both the spinal cord and cranial nerves?

GSE and GVE (general)

Which classifications of LMNs are found in only the cranial nerves?

SVE (special)

Neurobiotaxis

the idea that the cell body wants to be close to the target it innervates; causes pockets of collections of cell bodies that form cranial nerve nuclei (so that there will be multiple GSE nuclei, for example)