Motor Reflexes Flashcards
The placing and hopping reflexes arise from what part of the CNS?
Cerebral cortex
What are the spinal reflexes?
Stretch (myotactic) reflex
Golgi tendon reflex
Crossed extensor
The suckling, yawning, and righting reflex in children arise from what part of the CNS?
Brainstem - midbrain
What is the difference between a reflex and voluntary movement?
Reflex is faster
What part of the muscle spindle is sensory?
Intrafusal fibers
What is the primary afferent neuron innervating the sensory portion of the intrafusal fiber?
1a fibers
What does the sensory portion of the intrafusal fiber detect?
Length of muscle
How fast length is changing
What part of the intrafusal fiber does the group II fiber innervate? What is it sensitive to?
Innervates only the nuclear chain fiber
Sensitive only to the length of the muscle
What innervates the motor portion of the intrafusal fibers?
Gamma motoneuron
What effect does activity of the intrafusal muscles have on the sensory portion?
Contraction of intrafusal muscles stretches the sensory portion and increases sensitivity of Ia and II fibers to stretch
Activity of which motoneurons in the muscle spindle will directly lead to motion?
Alpha
How does the Golgi tendon reflex present?
Sudden/abrupt relaxation of a contracted muscle
What is the primary afferent fiber innervating the Golgi tendon?
Ib fiber to the spinal cord
Expression of what receptor may allow for recovery of reflexes after spinal shock?
5HTC receptor (Allows Na+ through channel in absence of serotonin)
What reflex is hyperactive in a patient with decerebrate posturing?
Myotatic reflex
What region in the brainstrem is responsible for activating the gamma-motoneurons?
Brainstem facilitatory region
What is the action of the brainstem inhibitory region?
Inhibits gamma motoneurons => less sensitive muscle spindle
Requires activation from cortex
In decerebrate posturing, what brainstem region is dominating?
Brainstem facilitatory region (brainstem inhibitory region is inactive)
What type of posturing is normally seen in a patient who had a stroke in the internal capsule? What structures have been taken out?
Decorticate posturing (Disinhibition of red nucleus, reticulospinal tract, vestibulospinal tract)
