Motor Units And reflexes/Receptors (Fitz)

Question 0

How are the intrafusual and extrafusal fibers innervated?

Answer 0

By gamma and alpha motor neurons respectively

Question 1

What are the components of a muscle intrafusual spindle?

Answer 1

• non contractile center
• two receptors
  1. Ia annulospiral ending
  2. II flower spray

Question 2

What are Golgi tendon organs?

Answer 2

In series with the extrafusal fibers

Question 3

What do muscle spindles responsible for?

Answer 3

Stretch fibers

Mechanoreceptors

Question 4

What do muscle spindles do?

Answer 4

Cause reflexes

Question 5

What is the activity of muscle spindles if the muscle is relaxed?

Answer 5

Almost zero

Question 6

How do Ia receptors respond?

Answer 6

Detect velocity or dynamic movements

Primary response

Question 7

What do II muscle spindles respond to?

Answer 7

Amplitude (static)

Secondary response

Question 8

What is the primary reaction (Ia) to a stretch depolarization?

Answer 8

Phasic stimulation, followed by adaptation

Question 9

Why is there no gap in activity in the Ia receptors after stretch release (during adaptation)?

Answer 9

Because the alpha motorneurons stops “gap”

Question 10

What is the stretch reflex?

Answer 10

Mono synaptic reflex where stretch causes contraction. 5 steps

1. Muscle stretches
2. Depolarization in spindle afferent
3. Activation of both alpha and gamma m neurons
4. Cause contraction of extrafusal muscle fibers(alpha) and intrafusal
5. Contraction of the intrafusal fiber contraction maintains tension in spindle to allow for continued response

Important for muscle tone

Question 11

What is the Golgi tendon flex?

Answer 11

1. Stretch of tendon
2. Depolarization
3. Increase activity of inhibitory interneuron
4. Decrease activity of alpha motor neuron
5. Relaxation

Question 12

What happens normally with the two reflexes?

Answer 12

The spindle fibers and the Golgi tendon organ work together

Question 13

What happens if you eliminate the alpha motor neuron!

Answer 13

Flaccid paralysis

Question 14

What happens of you over activate the gamma motor neurons?

Answer 14

Spastic paralysis

Question 15

What is the final common pathway for spinal reflexes?

Answer 15

Alpha motor neurons

But is it really final?
Really a feedback loop
Muscles are Non linear force generators

Question 16

What are the components of a reflex arc?

Answer 16

1. Sensory receptor
2. Primary afferent
3. 1-3 CNS synapses
4. Motor neuron
5. Muscles

Question 17

What is an example of a complicated or time delayed reflex?

Answer 17

Can have multiple interneurons in series, and also multiple series

Question 18

What is recurrent inhibition?

Answer 18

Has a motor neuron shut off, either motor neuron itself or an afferent

Question 19

How can a motor neuron shut of itself?

Answer 19

By sending a collateral that activates an interneuron called a Rensha cell. The Rensha cell shuts off other motor neurons in the area

Question 20

What is the lengthening reaction?

Answer 20

Light weight –> moderate stretch –> stretch relfex –> contraction (hold weight in place)

Heavy weight –> strong stretch –> inverse stretch –> relaxation

Modulated by gamma-motorneurons –> normal
–> balanced tension

Question 21

What happens if your gamma motor neurons (descending pathway) cannot modulate the system?

Answer 21

Clasp knife reflex

Question 22

How does the withdrawal reflex work?

Answer 22

Contraction of flexors

Relaxation of extensors

Question 23

What is spinal integration?

Answer 23

Motor control builds on underlying circuits

Descending pathways feeding to the first two
Reflexes –> Central pattern generators –> alpha MN

Question 24

What happens when you remove upper motor layers?

Answer 24

Reveals lower forms of controls.

Dicks hallpike) (VOR

Question 25

What is spinal shock?

Answer 25

Shock after cutting the spinal cord

Initial period of no reflexes, however then we get reflexes and maybe clonus