Spinal reflexes Flashcards
(21 cards)
which neurons are involved in reflexes?
alpha and gamma motor neurons
what do alpha motor neurons innervate?
skeletal muscle fibers (extrafusal fibers)
what do gamma motor neurons innervate?
contractile (polar) portion of intrafusal fibers of muscle spindles
what forms the sensory (afferent) limb of a reflex arc?
- pseudounipolar (sensory) neuron whose cell body is housed in a DRG 2. peripheral process is in skin / skeletal muscle / tendon / joint capsule; central process synapses in spinal cord gray matter
what forms the motor (efferent) limb of a reflex arc?
- motor neuron whose cell body is usually located in the ventral horn of the spinal cord 2. axon synapses in skeletal muscle
what is the receptor in the muscle stretch reflex?
muscle spindle
what is the receptor in reciprocal inhibition?
muscle spindle at peripheral end of 1a fiber
what is the receptor in autogenic inhibition?
GTO
what is the stimulus in autogenic inhibition?
muscle contraction triggers sensory endings innervating tendons to fire
what does autogenic inhibition inhibit?
muscle over-contraction
what does the autogenic inhibition reflex protect?
tendon
where are the receptors in the flexor reflex (withdrawal reflex, nociceptive reflex)?
cutaneous
what type of fibers make up the afferent limb of the flexor reflex (withdrawal reflex, nociceptive reflex)?
lightly myelinated Ad fibers, or unmyelinated C fibers of pseudounipolar neurons whose cell bodies are in a DRG
where does the central process of a pseudounipolar neuron involved in the flexor reflex enter the spinal cord?
enters the dorsolateral tract of Lissauer and branches into short ascending and descending fibers
what neurons are involved in the crossed extension reflex?
commissural interneurons whose axons cross the midline to synapse with excitatory and inhibitory interneurons located in the ventral horn of the spinal cord on the opposite side
gamma motor neurons are under what type of control?
supraspinal (from the brain)
what do gamma motor neurons stimulate in maintenance of muscle tone?
polar (contractile) portions of intrafusal fibers
what triggers the slight contraction of gross muscle during muscle tone maintenance?
stretch reflex
what does stimulation of gamma motor neurons do to muscle tone? inhibition of gamma motor neurons?
- increase 2. decrease
the gamma loop contains what five components?
- gamma motor neurons 2. intrafusal fibers 3. 1a fibers 4. alpha motor neurons 5. extrafusal fibers
what is the purpose of alpha gamma coactivation?
a way to maintaining sensitivity to stretch during gross muscle contraction
