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Flashcards in Lecture 23 Deck (16):

What are the 5 parts of a reflex arc?

1. Receptor that activates sensory nerve
2. Sensory neuron
3. Spinal cord interneuron
4. Motorneuron
5. Effector organ


What is the "final common pathway of the motor system"?

Alpha motor neuron
All behaviors involving muscle must pass along this pathway
Last site for synaptic integration


Is the stretch reflex inhibitory or excitatory?



Describe the stretch reflex.

Stretch muscle --> stretches muscle spindles
Activates 1a and 2 sensory neurons back to spinal cord
Synapse on alpha motorneuron of same muscle
Contract extrafusal fibers to move muscle back to resting length


During the stretch reflex, are synergistic muscles activated or inhibited? Antagonists? Name the specific neurons involved with each.

Synergists activated
- Excite alpha motorneuron
Antagonists silenced
- Inhibit Ia interneuron


What is Ia/reciprocal inhibition?

Sensory feedback from muscle spindles activate inhibitory Ia interneurons which inhibit the motorneurons of antagonist (of the muscle with spindle in it)


What sensory fibers innervate goligi tendon organs?

Ib - convey muscle force


What is Ib inhibition?

↑tension in golgi tendon as muscle contractions
↑Ib sensory nerve firing to spinal cord
Synapses onto an inhibitory interneuron to inhibit the motoneuron of that same muscle and its synergists
Opposite of the stretch reflex - does NOT act to reduce contraction


What is the goal of the flexor reflex?

Withdrawl! Protect against damaging stimuli


What is the crossed-extensor reflex?

See activation of opposite muscle limb from the one stimulate
Via intrasegmental commissural interneurons


What is the mechanism Rhenshaw inhibition?

Stimulation of an alpha motor neuron
That alpha MN sends a collateral branch to a Rhenshaw interneuron
The Rhenshaw will inhibit the alpha motorneuron that stimulated it and others
Via inhibition of Ia inhibitory neuron


What are the 3 goals of Rhenshaw inhibition?

Allows for co-contraction of antagonist and effector muscle
Fine tune motor outputs
Limits motor neuron firing to prevent tremors


Are reflexes always the same? Give an example.

NO - modulated
Walking - modulated with the phase of the step cycle


What is the mechanism of reflex modulation?

Presynaptic inhibition (you know that method) of Ia sensory afferents
No muscle spindle feedback


What is hypertonus?

Abnormally high muscle tone at rest
Becomes spastic with stretching


What is the definition of spacticity?

Involuntary increase in muscle tone with stretching