motor reflex Flashcards
what is the purpose of the myotatic reflex
protect muscle from excessive stretch
what structure initiates the myotatic reflex
muscle spindle/intrafusal fibers
are intrafusal fibers motor or sensory
both
what are the two sensory fibers of the intrafusal fibers/muscle spindle
nuclear bag fiber
nuclear chain fiber
what is the structure of the primary afferent fiber of the muscle spindle
large, myelinated Ia fiber
does the primary afferent fiber of the muscle spindle innervate the nuclear bag or the nuclear chain fiber
both
what does the primary afferent fiber of the muscle spindle detect
length of muscle
rate of change of muscle length
what is the structure of the secondary afferent fiber of the muscle spindle
smaller myelinated group II fiber
does the secondary afferent fiber of the muscle spindle innervate the nuclear bag or the nuclear chain fiber
only nuclear chain
what does the secondary afferent fiber of the muscle spindle detect
length of muscle
what innervated the motor portion of the intrafusal fiber
gamma motor neuron!
what does the motor portion of the intrafusal fiber/muscle spindle do
control the length of the sensory portion of the muscle spindle
when intrafusal muscle contracts, what happens to the sensory intrafusal fibers
they stretch and become more sensitive to further stretch
how do the sensory intrafusal fibers initiate motor reflexes
the IA (primary) afferent fiber synapses on the alpha motor neuron of the stretched muscle
what action does the primary afferent fiber have on the antagonist muscle
it inhibits the motor neuron of the antagonist muscle => relaxation
what is the purpose of the golgi tendon reflex
protect muscle from damage caused by excessive force
where is the structure that initiates the golgi tendon reflex found
golgi tendon organ is found extending from SC => muscle tendon
what is the golgi tendon organ
Ib bare nerve ending with lots of branches
how does the golgi tendon organ protect muscle
it produces APs which increase in intensity with increased tension and activate an inhibitory interneuron
what causes the AP intensity to of the GTO to go back to baseline
relaxation of the muscle
what are the two mechanisms underlying the return of reflexes in spinal shock
- axonal sprouting below transection
- expression of self-activating receptors
what is the cause of rigidity
continual activation of alpha motor neurons by the brainstem => maintained muscle contraction
what is the cause of spasticity
continual activation of gamma motor neurons => hyperactive myotatic reflex
what structure activates gamma motor neurons
brainstem facilitatory region
what does the brainstem inhibitory region do
inhibit gamma motor neurons => muscle spindle is less sensitive to stretch
which of the brainstem regions ((+)/(-) requires activation by the cortex
brainstem inhibitory region
if a pt comes in with their left limb extended and the arm and wrist flexed, what has probably happened to cause them
stroke in the vicinity of the internal capsule => decorticate posturing
