UBC NSCI 311 Lecture 4 (Motor Systems)

Advanced Neuroanatomy, Midterm 1 Content

two types of neurons in motor pathways

upper and lower motor neurons (multipolar)

do all upper motor neurons cross the midline?

no, but MOST do

how are corticonuclear pathways different from corticospinal pathways

synapses between upper and lower motor neurons occur in the brainstem nuclei for corticonuclear (as opposed to in the spinal cord for corticospinal)

what are lower motor neurons comprised of

nerves (peripheral nervous system)

what are upper motor neurons comprised of

axons (making tracts in CNS)

where are upper motor neuron cell bodies of extrapyramidal pathways

brainstem nuclei

is corticospinal pathway pyramidal or extrapyramidal

pyramidal

how do extrapyramidal pathways receive input

via corticofugal fibers

corticofugal fibers list

• rubrospinal (red nucleus)

• tectospinal (superior colliculi)

• reticulospinal (reticular formation)

• vestibulospinal (vestibular nuclei)

rubrospinal tract does what

archaic motor control pathway (facilitates flexors)

what is decerebrate posturing

extensor posturing (arms straight, wrists bent down), could stop breathing

what causes decerebrate posturing

rubrospinal tracts damage

why do people stop breathing in decerebrate posturing

because damage to the rubrospinal tract means damage to red nucleus, which is very close to the reticular formation, which is a very important breathing centre

what does tectospinal tract do 

reflexive movement related to stimuli (especially visual, eg. SQUIRREL!)

what do reticulospinal and vestibulospinal tracts do

maintenance of muscle tone and postural control

hypotonia

decreased muscle tone

where is the primary motor cortex

precentral gyrus

what percentage of upper motor neurons are in the primary motor cortex

~50%

where are the upper motor neurons that aren’t in the primary motor cortex

premotor and supplementary motor cortices

cortical somatotopic arrangement

• lower limb along longitudinal fissure

• trunk along upper cortex

• upper limb between top and side cortex

• face on the lateral side of cortex

• all in the gray matter

upper motor neurons of corticospinal pathway go through brain how

• cortex in whatever area the lower motor neuron will innervate

• corona radiata

• posterior limb of internal capsule

• cerebral peduncle

genu of internal capsule

• formed by corticonuclear fibers of face

• the corner of the internal capsule

somatotopic arrangement of corticospinal fibers

rostral/medial —> caudal/lateral = cervical, thoracic, lumbar

above (rostral of) internal capsule

caudate nucleus

below (caudal to) internal capsule

thalamus

just lateral of internal capsule

globus pallidus

more lateral of internal capsule (just lateral of globus pallidus)

putamen

where are upper motor neuron axons after entering the brainstem

lateral region

UMN axons of corticospinal pathway location in midbrain

cerebral peduncles (ventral but a little lateral)

UMN axons of corticospinal pathway location in pons

ventral (basilar) pons (pontine nuclei area)

UMN axons of corticospinal pathway location in medulla oblongata

medullary pyramids (completely ventral, medial)

somatotopic arrangement of corticospinal pathway axons

cervical = medial, thoracic, lumbosacral = lateral

where do 90% of upper motor neurons of corticospinal pathways cross the midline

decussation of pyramids

what do the upper motor neurons of corticospinal pathways that have crossed the midline become?

lateral corticospinal tract in spinal cord

what happens to 10% of upper motor neurons of the corticospinal pathways

do not decussate, continue ipsilaterally to form anterior corticospinal tract in spinal cord

where is the decussation of the pyramids

very caudal end of medulla oblongata, near spinomedullary junction

where do UMN of lateral corticospinal tract axons travel through

lateral spinal column (in the nook of the dorsal and ventral horns)

where do UMN of anterior corticospinal tract axons travel through

anterior spinal column (ventral to anterior commissure, medial)

what do neurons of lateral corticospinal tract control

appendicular muscles (voluntary, skilled movements)

what do neurons of anterior corticospinal tract control

axial muscles (postural tone, balance, stability)

where do upper motor neurons synapse with lower motor neurons in the corticospinal pathway

ventral/anterior horns

upper motor neurons of anterior corticospinal tract synapse with lower motor neurons HOW

• ipsilaterally and contralaterally in medial region of ventral horns

• cross anterior commissure to synapse with contralateral LMNs

upper motor neurons of lateral corticospinal tract synapse with lower motor neurons HOW

ipsilaterally in lateral region of ventral horns

somatotopic organization of LMN flexion and extension from ventral horns of both enlargements

• from dorsal ventral horn = flexion

• from ventral ventral horn = extension

• from medial ventral horn = axial/proximal

• from lateral ventral horn = distal/appendicular

lesion on one side of UMNs in anterior corticospinal pathway

little effect

lesions on both sides of UMNs in anterior corticospinal pathway

fucked:)

lesion above decussation on UMNs in lateral corticospinal pathway

contralateral paralysis, hypERreflexia, possible positive Babinski sign, higher muscle tone, below level of lesion

why hyperreflexia in UMN lesions of corticospinal pathway

because there is no inhibitory regulation of lower motor neurons 

lesion below decussation on UMNs in lateral corticospinal pathway

ipsilateral paralysis, hypERreflexia, possible positive Babinski sign, higher muscle tone, below level of lesion

lesion of LMNs in lateral corticospinal tract

ipsilateral damage at the level of the lesion, paralysis, hyPOreflexia, atrophy, fasciculations

why hyporeflexia in LMN lesions of corticospinal pathway

because there is no motor input to muscles by LMNs

fasciculations

persisting, spontaneous firing of LMNs and increased receptor concentration/sensitivity

lesions in S1-S2 spinal levels

calcaneal (achilles) reflex (point toe, buckle my shoe)

lesions in L3-L4 spinal levels

patellar reflex (kick the door)

lesions in C5-C6 spinal levels

biceps brachii + brachialis reflex (pick up sticks)

lesions in C7-C8 spinal levels

triceps brachii reflex (lay them straight)