Motor Neurons L1-4

Is the basis of voluntary movement lower or upper motor neurons?

Lower motor neurons

What are LMN signs?

decreased muscle tole, flaccid paralysis, decreased reflexes, limp

What are the connections in the spinal cord mediated through? Upper or lower motor neurons?

upper motor neurons

Where do axons project from in upper motor neurons?

Brain

Where do axons exit with upper motor neurons?

white matter

What do axons projecting and exiting affect in upper motor neurons?

lower motor neurons

Where is the cell body in UMN?

brain

What do axons descend through in UMN?

spinal cord and brainstem

What happens when UMNs synapse on LMNs?

initiate and terminate voluntary activity, modulate reflexes

What are Renshaw cells?

inhibitory interneurons in the spinal cord

What do Renshaw cells release?

glycine

What is it called when there is excitation by motor neuron collaterals inhibit the original motor neuron?

recurrent inhibition

What does the tetanus toxin inhibit?

release of glycine

What does lack of inhibition result in?

sustained muscle contraction and hypertonicity

What does the lateral corticospinal tract do?

movement of distal limbs

What does the rubrospinal tract do?

locomotion, controls distal flexors

What do the reticulospinal and vestibulospinal tracts do?

proximal extensor function

does the lateral corticospinal tract decussate?

yes

Does the rubrospinal tract decussate?

yes

Do the reticulospinal tract decussate?

no

Do the vestibulospinal tracts decussate?

No

Does the pontine reticulospinal tract facilitate or inhibit extensors?

facilitates extensors

Does the medullary reticulospinal tract facilitate or inhibit extensors?

inhibits extensors

Which tracts are dorsolateral?

lateral corticospinal tract and rubrospinal tract

Which tracts are ventromedial?

reticulospinal tracts and vestibulospinal tracts

Which neuron is involved when efferents go to extrafusal muscle fiber?

alpha motor neuron

What neuron is involved when efferents go to the intrafusal muscle fiber?

gamma motor neuron

How many neurons are in the lateral corticospinal pathway?

3 neurons

Where is the cell body in the first neuron of the lateral corticospinal pathway?

cerebral cortex

Where does the lateral corticospinal pathwya decussate?

myelencephalon

Is the lateral corticospinal pathway contralateral or ipsilateral?

contralateral

What is the most important pathway upper motor neuron pathway for flexion of the distal limbs in our domestic species?

lateral corticospinal pathway

What are dorsolateral tracts?

controls distal flexors

Where do dorsolateral tracts go?

lateral funiculus

Which tracts are dorsolateral?

lateral corticospinal tract, rubrospinal tract

Where does the rubrospinal pathway decussate?

mesencephalon

What does the rubrospinal pathway do?

controls flexors

What are some inputs to the red nucleus?

motor cortex, cerebellum

What do ventromedial tracts do?

innervate trunk and proximal limb extensors, antigravity

What pathways are in the ventromedial tract?

reticulospinal, vestibulospinal, tectospinal, ventral corticospinal tracts

Where do ventromedial tracts go?

ventral funiculus

What do pontine reticulospinal tracts do?

excites extensors

Where do pontine reticulospinal tracts go? (include ipsilateral or contralateral)

ipsilateral ventrolateral funiculus

What do medullary reticulospinal tracts do?

inhibit extensors

Where does the medullary reticulospinal tract go? (include ipsilateral or contralateral)

ipsilateral ventrolateral funiculus

Where do reticulospinal tracts get input from?

motor cortex

Where do the corticoreticular fibers in the reticulospinal tract decussate?

myelencephalon

What is the primary system for maintaining balance and orientation and the system that provides proprioceptive information for the head?

vestibular system

Where are afferents projected to in the vestibulospinal tract?

vestibular nuclei

Which brain sections are vestibular nuclei in for the vestibulospinal tracts?

metencephalon and myelencephalon

What do UMNs control in vestibulospinal tracts? (ipsilateral or contralateral and to what)

ipsilateral extensor LMNs

When are vestibulospinal tracts active?

always active unless inhibited by other structures

What are so LMN lesion signs?

decreased reflexes, decreased muscle tone, muscle atrophy, paresis/paralysis, flaccid

What are some UMN lesion signs?

spastic paresis/paralysis, increased reflexes, increased muscle tone

Which brain region is the cerebellum in?

metencephalon

What is in the granule cell layer in the cerebellum?

many small neurons

What is in the purkinje cell layer in the cerebellum?

purkinje neurons

What is in the molecular layer in the cerebellum?

fibers from granule and purkinje layers