B7-017 Spinal Cord Reflexes Flashcards
predominant stretch receptors in muscle
muscle spindles
composed of intrafusal fibers
muscle spindles
muscle spindles lie in […] with extrafusal fibers
parallel
the rapidly adapting (dynamic) component of muscles spindles provides info about
velocity of stretch
the slowly adapting (static) component of muscles spindles provides info about
length
muscle spindle innervation contributes to muscle […]
tone
monitor stresses and forces at the tendon
golgi tendon organs
GTOs lie in […] with extrafusal fibers
series
innervated by Ib afferents only
GTOs
conscious proprioception goes through the […] pathway
DC/ML
unconscious proprioception goes through the […] pathway
spinal cord and cerebellar
pathway the regulates balance and smoothing movements of unconscious proprioception
spinocerebellar
motor units contract the muscle […] a motor neuron fires
every time
have characteristic innervation ratio
motor units
fine control requires lower ratio than coarse control
a lesion in one segment of the ventral horn will result in motor deficits to
several muscles
2 mechanism to increase force to motor neuron
increase firing rate
increase number of motor units firing
order of recruitment
small motor units recruited first, follwed by larger
small slow motor units
type 1
endurance motor units
type 1
large fast motor units
type II
motor units that convey large forces for a short time {sprint}
type 2
oxidative motor unit
lots of mitochondria
type 1
glycolytic motor unit
few mitochondria
type 2
red motor unit
type 1
white motor unit
type 2
afferent coming from one muscle
efferent going into same muscle
homonymous
afferent coming from one muscle
efferent goes to opposing muscle
heteronymous
describe the sequence of events in the stretch reflex
- tendon tapped, muscle is stretched
- muscle spindle is stretched
- Ia and II nerve ending are deformed
- sensory nerve endings depolarized
- increased firing of Ia and II efferents
- excitation of alpha motor neurons
- increased firing of alpha motor neurons
- contraction of the muscle
Ia afferent detects change in velocity/length of muscle and sends quick activation signal to the Ia afferent nerve
dynamic “knee jerk” phase of stretch reflex
[…] phase of reflex is important to maintain muscle tone
tonic
(cutting the Ia afferents would greatly reduce tension)
adjust the gain (length) of the muscle spindles to continuously provide information about the length/stretch to the PNS
gamma motor neurons
activated by stretching a spastic or rigid muscle
contraction, then rigidity “melts away”
inverse stretch reflex
inverse stretch reflex is mediated by
GTO/Ib afferent
stretch reflex is mediated by
muscle spindles
activated by increased stretch
increasing muscle contraction
stretch reflex
initiated from cutaneous stimuli to remove body from potentially damaging stimuli
flexion reflex
contralateral component of the flexion reflex that helps to maintain balance
crossed extensor reflex (crosses the midline)
two stages of reflexes after spinal injury
- hyporeflexive due to spinal shock (1-2 weeks)
- hyperreflexive due to loss of inhibition of LMN
how do muscle spindles send signals to the cerebellum to create balanced, smooth movements?
- muscle spindle afferent synapses at Dorsal Clarke nucleus
- second order axons ascend via dorsal spinocerebellar tract to ipsilateral cerebellum
striking the tendon with a reflex hammer stretches both […] and […] muscle fibers
extrafusal
intrafusal
in the stretch reflex, greater force causes greater stretch, which causes greater activation of […] in the muscle spindle
Ia afferents
results in greater muscle contraction
causes you to extend your contralateral limb after your ipsilateral limb is flexed to try to maintain balance
crossed extensor reflex
DTR is initiated by
stretch
cutaneous afferents in the skin that sense somatosensory stimuli and elicit a protective response
flexor reflex afferents
example: Babinski’s
examples of flexor reflex afferents [3]
Babinski’s
flexion (withdrawal) reflex
corneal blink reflex
sensory component of the inverse stretch reflex
GTOs
the flexor withdrawal reflex is initiated by noxious stimuli carried on what fibers?
C and A-delta fibers
conveys proprioceptive information to the ipsilateral cerebellum to smooth out movements
spinocerebellar
the dorsal spinocerebellar pathway in the spinal cord conveys proprioceptive information to the […] cerebellum
the cerebellum then communicates with the […] motor cortex to correct motor instructions to affected limb
ipsilateral
contralateral
carries pain and temperature information
spinothalamic tract
sudden release of muscle tension when GTOs signal too much stress at the tendon
inverse stretch reflex
maintaining a contraction is stimulated by […] afferents
Ia
[…] afferents inhibit the alpha motor neuron to relax the muscle
Ib
force at the tendon is measured by […] afferents in the GTO
Ib
responsible for altering the length of the muscle spindle intrafusal motor fibers
gamma afferents
[…] fibers mediate pain that stimulates the withdrawal reflex
A-delta
C fibers
number of muscle fibers innervated by a given motor axon
innervation ratio
for imprecise movements requiring large force the innervation ratio is […]
high
(1 motor neuron activates many muscle fibers simultaneously to generate force)
for fine, precise movements the innervation ratio is […]
low
(small groups of muscle fibers controlled individually for greater control)
both firing rate and orderly recruitment by size are mechanisms for
increasing force
inhibition of […] fibers is useful to provide coordinated movements
heteronymous
