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Flashcards in Spinal Reflexes Deck (19):

Where are Golgi tendon organs located? What do they detect?

At the musculo-tendon junction. They detect changes in tension in the muscle.


Where are muscle spindle organs located? How are they oriented? What do they detect?

Located centrally, in among the muscle fibers. They're oriented in parallel to the fibers. They detect small changes in muscle length.


What does it mean for a muscle fiber to be intrafusal?

It's inside the capsule surrounding the spindle.


Are alpha motor neurons intra or extrafusal? What about gamma motor neurons? Spindles?

Alpha motor neurons are extrafusal. Gamma motor neurons and spindles are intrafusal,


What do group Ia afferent axons wrap around?

All intrafusal muscle fibers.


What do group II afferent axons wrap around?

Only static fibers.


What are the striations at the ends of intrafusal muscle fibers? What's the significance of this?

Contractile elements. The middle of the spindle doesn't contract -> increased tension in the middle.


How is the stretch in the middle membrane transferred to the afferent axons?

The tips of the nerves are in tight association with the spindle membrane. When stretched, the nerves stretch, opening stretch-sensitive ion channels, causing an action potential.


Are all the skeletal muscle fibers contributing to a Golgi organ innervated by the same alpha neuron? Signficance?

No. This allows the Golgi organ to detect graded levels of contraction in the muscle.


What kinds of nerve fibers get afferent signals from the Golgi tendon organ?

Sensory Ib fibers.


What happens when the sensory neuron enters the Golgi tendon organ?

Sensory neuron demyelinates at cpsule and connects to collagen fibers.


Which responds more to passive stretching: spindle or Golgi organ?

Spindle, because the stetching is more prominent in the middle of the muscle...


What would happen is spindles didn't have gamma motor neurons?

If a muscle shortened while bearing weight, you wouldn't know it was still bearing weight because there would be slack in the spindle.


When are dynamic gamma motor neurons turned on?

When the kitty is experiencing imposed movements or executing more complex movements. (the diagram had a cat on it...)


What's reciprocal innervation?

Excitatory innervation to muscles on one side of the joint, inhibitory to those muscles' antagonists.


What's a myotactic reflex? What kind of nerve fibers does it involve?

It opposes muscle stretch. 1a sensory (proprioception), alpha motor neurons.


What's the fastest kind of reflex? Why?

Myotactic reflex, because it only involves one synapse: sensory neuron directly to motor neuron.


What happens when you step on a lego? Describe the path.

Ipsilateral activation of flexors, contralateral activation of extensorts. Cutaneous nociceptor (A delta fibers) -> ipsilateral synapse with the first interneuron -> second interneuron -> Alpha motor neurons.


Where does descending control of spinal reflexes come from? How does it get there? Where does it act?

Primary motor, premotor, and somatosensory cortices -> cortico-spinal tract -> axo-axonic modification of the signals from the sensory fibers.

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