Spinal mechanisms of motor control Flashcards
where is the muscle spindle located?
parallel to extrafusal muscle fibers
where is the golgi tendon organ located?
in series with muscle
which type of neuron innervates intrafusal muscle fibers?
group Ia fiber
which neuron is larger - alpha motor neuron or gamma motor neuron?
alpha
what is the function of beta motor neurons?
innervation of both extrafusal and intrafusal fibers
how does coactivation of alpha and gamma motoneurons work?
gamma motor neurons contract intrafusal fibers while extrafusal fibers are contracted - maintains sensitivity to intrafusal fiber stretch
what kind of information is carried by group Ia fibers?
- how fast the muscle length is changing 2. current length of muscle
what kind of information is carried by group II fibers?
only muscle length
how dos the gamma motoneuron control muscle spindle response?
senses sensitivity and provides fusimotor drive to muscle spindles
how does the phasic (DTR) stretch reflex work?
Ia axon from stretch receptor synapses on alpha motor neuron of homonymous muscle as well as an inhibitory interneuron for antagonist muscle
how are phasic stretch reflexes tested?
tendon tap
how are tonic stretch reflexes tested?
passive flexion or extension of a muscle at various speeds
how is reciprocal innervation in the spinal cord related to the stretch reflex?
- group Ia fibers excite homonymous muscle and synergists 2. group Ia fiber collaterals end on Ia inhibitory interneurons, inhibiting alpha motor neurons of antagonist muscles
definition: co-contraction
both the prime mover at a joint and its antagonists are contracted simultaneously - stiffens the joint
when is co-contraction used?
precision movements and joint stabilization
what is the normal group Ib reflex?
innervation of GTO
when does the clasp knife response occur?
hyperactive stretch reflexes of the spastic patient causes increase in resistance to stretch, followed by a sudden decrease
definition: reciprocal innervation
reciprocal innervation causes Ia fiber from muscle spindle of homonymous agonist muscle to inhibit the antagonist muscle via the Ia inhibitory interneuron - yields reciprocal inhibition
what is the sensory organ for the phasic stretch reflex?
muscle spindle
how does the tonic stretch reflex work? what does it measure?
- Ia fibers fires more during lengthening - depends on both primary and secondary endings 2. Ia fibers go to both homonymous muscles and synergist muscles 3. measures muscle tone
what is the GTO (group Ib) reflex arc?
- increased tension on muscle increases Ib firing rate 2. Ib fiber synapses on Ib inhibitory interneuron - inhibits alpha motor neuron of homonymous muscle 3. can be modified by higher brain centers
what are the roles of the Renshaw cell?
- can produce recurrent inhibition in alpha motor neurons of agonist muscle 2. can inhibit Ia inhibitory interneurons to antagonist muscles 3. allows co-contraction at a joint
