Spinal Cord and Movement 2: Reflexes Lec19 Flashcards
Extrafuscal (normal) muscle fibers are innervated by
α motor neurons
Intrafuscal (muscle spindle / stretch receptors) fibers are innervated by
γ motor neurons
and by Type Ia and Type II sensory neurons
Spindles are arranged in ___ with extrafuscal muscle fibers
parallel
what do γ motor neurons affect?
only spindle stiffness, not contraction
Muscle spindles send stretch signals via
type Ia and type II neurons:
Type ___ central (bag) region
Ia:
type ___ fire intensely at onset of stretch,
! then slows down.
1a
type II firing is at what rate
static, increases linearly with increasing strethc
Stretch reflex?
muscle spindle senses stretch --\> spinal cord --\> original (homonymous) and synergist (heteronymous) muscles excited and anatagonist inhibited to counter perturbation
during stretch reflex, the Antagonist
muscle is___
inhbhited by interneruons
Contraction response:
when extrafuscal muscle contracts,____fire to
shorten intrafuscal fibers
the γ motor neurons
why do the the γ motor neurons fire during contraction response?
to shorten the intrafusal fibers and to keep them sensitive
Golgi Tendon Organs (GTO) only fire when muscle ___
actively contracts
muscle spindle cares about ___
length
golgi tendon cares about ___
tension
holgi tendon organs are receptors are ___ fibers
Type Ib
golgi tendon organ receptors arranged in ____ with extrafuscal muscle fibers
series
muscle spindle is the only afferent that ___
receives a nerve supply
difference between gamma motor neurons and alpha MN?
gamma has a smaller soma and a lower conduction velocity
____ motor.. innervate intrafusal not at center point
but lower down
gamma
____ contraction makes the muscle spindle more sensitive to stim.
intrafusal
sensory receptors on intrafusal fibers
type 1a and II
___ receptor fires with stretch from distal muscle spindle
type II
biceps and brachialis are examples of
agonists
triceps and biceps are
anatagonists
increased load about the elbow causes rotation
–> spindle in biceps are stretched –>
afferents sent to spinal cord activating the
biceps motor neurons
when an anatagonist muscle is inhibited it is by a
1a inhibitory interneuron
correction is ____ perturbation
resisting
if you ___ of a spindle it becomes silent
reduce
when alpha motor neuron is activated without ___ you get silent
gamma MN
golgi tendon reflex involves the ___ interneuron
1b
in golgi tendon reflex action
1b interneuron does what
excites the anatgonist muscle
inhibits the agonist muscle
Flexion-crossed-extension reflex:
if one limb reflexively withdraws, the limb across the midline ____ to keep you balanced.
extends
Central pattern generators are defined as neurons that
produce coordinated movements in the absence of higher inputs
in cats & humans central pattern generators are for ___ movements
stepping
central pattern generators are activated by (2)
- stim of Mesencephalic Locomotor Region
- noradrenergic inputs
if one limb reflexively withdraws, theipsilateral limb ____ to keep you balanced.
flexes
central pattern input can be modified by
training
with emg demonstration Low amplitude action potentials…could mean
lost neurons
its difficult to activate a nerve AP with direct electrical stimulation but easy to
monitor or record
emg – Can only recruit a few motor units…suggests a
partial problem
emg – Spontaneous, non-rhythmic activity…suggests
dennervated muscle
