Descending motor systems Flashcards
what part of the brain does the descending upper motor neuron travel through to get to the brain stem
internal capsule of white matter
what is the function of lower motor neurons
directly signals and innervate muscle to contract
what is the function of upper motor neurons
send signal from the motor cortex to the lower motor neuron down an axon
what would be the results of a lesion in a lower motor neuron
- atonia
- areflexia (loss of knee reflex)
- flaccid paralysis
- fasiculations (twitching)
- severe atrophy
what would be the result of a lesion in an upper motor neuron
- spastic paralysis
- hypertonia
- hyperflexia
- mild atrophy
- pathologic reflexes (Babinski sign)
what is the Babinski sign and what causes it ?
big toe dorsoflexion w/fanning of other toes when side of heel it stroked, cause by upper motor neuron lesion
what horn would you find motor neuron cell bodies
anterior horn/ventral horn
what horn would you find somatosensory cell bodies
posterior horn/dorsal horn
nuerons controlling axial muscles tend to stay ____ and those controlling distal muscles tend to stay _____ in the anterior horn
medial, lateral
neurons controlling flexor mm. are located ______ to the extensor muscle neurons in the anterior horn
posterior
what is a motor unit ?
1 motor neuron + all myofibers it innervates
which type of muscle (small or large) demonstrates a very small amount of myofibers innervated by 1 motor unit
small ( extraoccular m. has fine movement so must have small number of myofiber innervated by 1 motor unit)
functionally what are the 3 types of muscle fibers
standing, running, walking
What are the characteristics of type 1 muscle fibers and what is its function
slow twitch, high lipids low sugar, red oxidative (lots of mitochondria)
- used for standing
- dark meat
what are the characteristics of type 2 muscle fibers and what is its function
fast twitch, low lipids high sugar, white glycolytic (little mitochondria
- used for running and jumping
- white meat
what are the 3 regions of the brain that influence (plan/monitor) upper motor neuron output but have NO direct effect on lower motor neurons
basal ganglia
association cortex
cerebellum
what is the difference b/w hierarchial motor control and parallel motor control
Hierarchial - premotor cortex tells motor cortex and the LMN what to do
Parallel - premotor cortex directly talks to LMN what to do
motor nuerons are found on the _____ horn, but terminate or synapse on the _____ horn
anterior/ventral horn
posterior/dorsal horn
what are the 3 main descending motor pathways
- corticospinal tract
- corticobulbar tract
- corticopontine tract
where is the primary motor cortex
precentral gyrus (area 4)
where is the primary somatosensory cortex
postcentral gyrus (3,1,2)
T/F the corticospinal tract originates in the primary motor area only ?
False, originates in the primary motor area, somatosensory area, premotor area, supp. motor area, and superior parietal lobule
what does the primary motor area control
contralateral, voluntary fine digital movements
where is the premotor area and what does it control
lateral aspect of area 6
-plans movements/gives instructions to motor cortex in response to an external stimulus
what would a lesion in the primary motor area cause
complete paralysis of contralateral musculature
what would a lesion in the premotor area cause
- moderate weakness of contralateral musculature
- loss ability to associate hand movements to visual or verbal cues
where is the supplemental motor area and what is its function
medial aspect of area 6 (premotor area is lateral)
-plans movements while thinking, “imagines/visualizes” movements
though the corticospinal tract is a “complex tract”, what movement would be permanently loss if you were to cut it
fine finger movement
where does the corticospinal tract decussate at ?
spinomedullary junction (85 %)
85 % of the lateral corticospinal tract decussates at the spinomedullary junction and descends to where ?
lateral funiculus
the anterior corticospinal tract that does NOT decussate (15%) descends to _________ and controls what muscle activity
anterior funiculus
-axial muscle activity
a lesion in the corticospinal tract in the brain would cause what type of muscle weakness ipsilateral or contralateral
contralateral cuz it decussates at spinomedullary junction
what does the rubrospinal tract control
shoulder and proximal arm mm
what does the reticulospinal tract control
rhythmic motor actions like walking
what does the vestibulospinal tract control
balance (why cats land on feet)
what does the tectospinal tract control
head turning
the corticobulbar pathway ends on what CN nuclei, and specifically what CN recieve no input
V, VII, X, XI, XII
No input - III, IV, VI (all eye muscles)
the corticobulbar path has what type of decussation and what type of input ?
Has No decussation so bilateral input
what CN is the exception to the typical corticobulbar pathway
CN V
- upper face innervate bilaterally
- BUT lower face (lips) innervated ipsilaterally
unilateral damage to CN V of the corticobulbar pathway would result in ?
-inability to smile symmetrically (only lower facial muscles affected cuz upper face can still recieve input from other side since its inervated bilaterally)
