Neuroanatomy: # 19: Upper/lower Motor Neurons, Block 2

Front 1

what are some types of movement and why are they interesting?

Back 1

reflexes

rhythmic: a little more complicated, involves initiation and termination.

voluntary movement: complex

fine: involves thumb opposition or independent finger movements.

Front 2

list the indirect motor pathways:

Back 2

reticulospinal
rubrospinal
tectospinal
vestibulospinal

note that these are unconscious, involved in reflexes and in keeping posture.

Front 3

where are the upper motor neurons located...in what layer?

Back 3

in layer V pyramidal cells of the precentral gyrus (motor cortex)

Front 4

what are lower motor neuron symptoms if lesioned?

Back 4

atrophy, flacid paralysis

Front 5

what's a motor unit?

Back 5

all the muscle fibers innervated by a single lower motor neuron. this can be a lot of fibers or a few fibers. tend to have small motor units in the hands, large motor units in the legs.

Front 6

corticospinal tract: give a more detailed description of where the upper motor neurons are located:

Back 6

1/3 in premotor

1/3 in motor

1/3 in somatosensory cortex (post-central gyrus)

Front 7

go through the pathway of the corticospinal tract:

Back 7

from the cortex, through the corona radiata, through the posterior internal capsule. through the cerebral peduncles, basalar pons, medullary pyramids, decuastion, spinal cord.

Front 8

what are some upper motor neuron lesion signs?

Back 8

hyper-reflexivia
spasticity
hyper-tonia
babinski sign
eventual atrophy from disuse, not fast.

Front 9

corticospinal tract - how is it somatotopically arranged?

Back 9

this is a little different. here, the medial parts innervate the medial-body (the muscles around the spinal cord, neck, etc). the outer portions of the tract innervate the distal muscles (hands, fingers, etc).

so at the level of the upper limb, the inner ones control the neck. the outer ones control the fingers.

Front 10

in the internal capsule, how is the corticospinal tract somatotopically organized?

Back 10

FATL, starting at the genu and going backwards.

face, arm, trunk, and leg. all in the genu and posterior section of the internal capsule.

Front 11

do lesions commonly affect both the corticospinal and corticobulbar tracts?

Back 11

yes. they travel together in the brain.

Front 12

tongue nerve - how can we tell upper vs. lower motor neuron damage?

Back 12

the 12th nerve decusates. so, if the injury is after the decusation, you lick the wound (toward the side of the lesion).

if it's above the decusation, you deviate contralaterally.

Front 13

what's weird about facial muscle innervation?

Back 13

above the eyes, the muscles get dual innervation from both cortices.

below, it's contralateral and only get one.

Front 14

so how can we use this to diagnose upper vs. lower motor neuron facial injury?

Back 14

if you damage the upper motor neurons, the face experiences paralysis on the contralateral lower side, while the forehead stays fine (dual innervation, afterall).

if you damage the lower motor neuron, get ipsilateral drooping of both the face and forehead, as this is the final common pathway.