(10) Motor Pathways of the CNS Flashcards
which laminae of gray matter contains LMN
IX
which laminae of gray matter contains intermediate sensory neurons
I-IV
differences in organization of LMN synapses with UMN that control distal extremiteis vs trunk muscualture
Distal:
UMN are from lateral corticospinal tract and synapse on ipsilateral side
Trunk:
UM: are from anterior corticospinal trant and synapse bilaterally
size of LMN cell body is proportional to…
the number of fibers it innervates
type of muscle fibers that tend to be small in size and thus the ration of muscle fibers per neuron is small
slow fatigue resistant fibers
type of muscle fiber that las more mitochondria, myoglobin, and denser capillary beds
slow fatigue resistant fibers
type of metabolism utilized by slow vs fast muscle fibers
slow = aerobic fast = anaerobic/glycolysis
describe muscle stretch reflex
stretched sensed by muscle spindles which send signal to 1a sensory neurons. 1a neurons synapse with LMN and transduce signal to them. LMN sends signal to muscle fibers which contract. 1a sensory neurons also synapse with inhibitor interneurons to inhibit contraction of antagonistic muscle
what type of afferent fibers do muscle spindles give rise to?
Ia and II
what type of afferent fibers do golgi tendon organs give rise to?
IIb
___ motor neuron innervates muscle spindles
gamma
sensory organ that generates the sensory info that triggers a muscle reflex arc
muscle spindle
significance of gamma motor neurons
innervate muscle spindle intrafusal muscle fibers to keep the stretch receptors from becoming relaxed and non-functional. (intrafusal muscle fibers contract with the extrafusal muscle fibers)
type of info carried on type II afferents from muscle spindles
muscle length: inc # APs = inc length and vice versa
type of info carried on type Ia afferents from muscle spindles
muscle length and velocity: inc # APs = inc length and velocity and vice versa
when muscle fibers are static the frequency of APs from type II and Ia afferents reflects …
fiber length
function of golgi tendon organs
prevent generation of excessive (and potentially harmful) force
*generates APs that inhibit contraction and promote relaxation
describe the negative feedback control provided by the GTO
stretch of the GTO causes it to generate an AP which it sends to the 1b inhibitory interneuron which inhibits LMN/contraction of the muscle.
**1b inhibitory interneuron also activate another LMN of the antagonistic muscle to cause it to contract
***they also send signals to descending pathways
What is the flexor reflex
uncomfortable stimulus will produce a reflex withdrawal
Describe the organization/process of reflex withdrawal
stimulus → excitatory interneuron → activate agonist muscle to contract and inhibit contraction of antagonist
Where do the cell bodies of UMN originate
precentral gyrus
Where do UMN decussate?
medulla (aka pyramidal decussation)
Describe the pathway taken by UMN to from the cortex to the spinal cord
precentral gyrus → posterior limb of internal capsule →midbrain and pos → medulla where they decussate → lateral corticospinal tract of spinal cord
large areas of the cortex are dedicated to…
functions that require precise control (i.e. face, tongue, and hands)
location of leg fibers in posterior limb of internal capsule
posterior
arms are anterior and trunk is between them
location of leg fibers in spinal cord
leg is lateral
in the corticospinal tract, not all the fibers decussitate. fibers controlling ___ are do not decussitate
trunk
somatotrophic organization of LMN in spinal cord
in ventral horn:
extremities are lateral and trunk is medial
(flexors posterior and extensors anterior??)
tract that relays fibers from motor cortex to cranial nerve motor nuclei
corticobulbar tract
tract that terminates in cervical and thoracic spinal cord levels to control coordinated movements of trunk and neck muscles
vestibulospinal and recticulospinal tracts
travels closely with lateral corticospinal tract and participates in control of arm mucles
rubrospinal tract
terminates in cervical spinal cord to control movements of the head and eye
colliculospinal (tecto-) tract
lesions in the corticospinal tract would cause pts to develop weakness in (ipsilateral or contralateral) face and limbs
above pt of decussation = contralateral
below pt of decussation = ipsilateral
pt of decussation = caudal medulla, pyramidal decussation
effect of corticospinal tract lesions on local spinal reflexes
they go unchecked and are therefore hyperactive
→ increased muscle tone and reflexes
causes fasciculations (why?)
LMN lesions bc the muscle cell membrane becomes hyperexcitable and may spontaneously discharge → fasciculations
lesion that blocks the release of trophic proteins to the muscle, leading to atrophy
UMN and LMN lesions
Positive Babinski sign looks like… and indicates….
stroking lateral sole of foot will cause extension of big toe and fanning of other toes in a person with a lesion of the UMN in the corticospinal tract
babies will have a positive babinski sign until age…
3 to 6 months
+ Clonus looks like … and indicates…
when the foot is forcefully flexed, the foot will engage in repetitive plantar extension. this indicates and UMN lesion bc it is leaving the muscle stretch reflex unchecked and hyper active
