MODULE 8- ARPIN STUDY GUIDE Flashcards
what does each lower motor neuron innervate
muscle fibers within a single muscle
motor neuron pool
all the motor neurons innervating a single muscle
somatotopic organization of motor neuron pools in dorsal/ventral horn of SC
ventral
medial ventral horn
-terminates bilaterally
-control of posture + locomotion
lateral ventral horn
-terminates only ipsilatterally
-fine control of distal extremities
2 types of lower motor neurons
-α-motor neurons (striated muscles)
-γ-motor neurons (sensory receptors/muscle spindles)
motor unit
α-motor neuron + all the muscle fibers it innervates
innervation number
number of muscle fibers innervated by one α-motor neuron
size principle
orderly recruitment of motor neurons
S -> FR -> FF
regulation of muscle force (2)
-number of active motor units
-firing rate of active motor units
muscle spindle
intrafusal fibers arranged in PARALLEL
what 3 intrafusal fibers do muscle spindles have
-dynamic nuclear bag fibers
-static nucleus bag fibers
-nuclear chain fibers
3 neurons of muscle spindle
-Ia afferent
-II afferent
-gamma (γ) motor neuron
what does gamma (γ) motor neuron do
contracts intrafusal fibers making Ia afferents more sensitive (gain)
stretch reflex
stretching muscle ->
increased discharge from Ia afferents
stretch reflex increases/decreases alpha motor neurons of agonist
increases
stretch reflex increases/decreases alpha motor neurons of antagonist
decreases
-reciprocal innervation
golgi tendon organs
sense changes in tension
what axons innervate GTOs
Ib axons
positive/negative feedback system for GTOs
negative
negative feedback system of GTOs
increased tension ->
increase in Ib neuron activity ->
inhiits alpha motor neuron of agonist + excites alpha motor neuron of antagonist
flexion reflex
-stimulates cutaneous (nociceptor)
-excites interneuron circuits in SC
what does flexion reflex lead to
withdrawal of limb from painful stimuli
flexion reflex- inhibition/excitation of extensor of stimulated foot
inhibition
flexion reflex- inhibition/excitation of flexor of the stimulated foot
excitation
flexion reflex- what happens to other limb
opposite response
-crossed extension reflex
central pattern generator (CPG)
-rhythmic patterns of movement
-supraspinal commands are not necessary
