Spinal Reflexes

Question 1

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

Answer 1

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

Question 2

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

Answer 2

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

Question 3

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

Answer 3

It’s inside the capsule surrounding the spindle.

Question 4

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

Answer 4

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

Question 5

What do group Ia afferent axons wrap around?

Answer 5

All intrafusal muscle fibers.

Question 6

What do group II afferent axons wrap around?

Answer 6

Only static fibers.

Question 7

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

Answer 7

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

Question 8

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

Answer 8

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.

Question 9

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

Answer 9

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

Question 10

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

Answer 10

Sensory Ib fibers.

Question 11

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

Answer 11

Sensory neuron demyelinates at cpsule and connects to collagen fibers.

Question 12

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

Answer 12

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

Question 13

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

Answer 13

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

Question 14

When are dynamic gamma motor neurons turned on?

Answer 14

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

Question 15

What’s reciprocal innervation?

Answer 15

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

Question 16

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

Answer 16

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

Question 17

What’s the fastest kind of reflex? Why?

Answer 17

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

Question 18

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

Answer 18

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

Question 19

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

Answer 19

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