1.8 Motor Neurons Flashcards Preview

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Flashcards in 1.8 Motor Neurons Deck (15)
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1
Q

Explain the route of an upper motor neuron

A

Travels from cortex to the spinal cord

2
Q

Which tract do the upper motor neurons follow?

A

Corticospinal Tract

3
Q

Where do the upper motor neurons decussate?

A

Upper medulla - for the lateral corticospinal tract

spinal level - for the anterior corticospinal tract

4
Q

What is a lower motor neuron, and what else is it known as (which innervate skeletal muscles)?

A

“alpha” motor neuron - synapse and exit from the ventral horn

5
Q

What are the properties of an alpha motor neuron?

A

Cell body in the CNS, thickly myelinated, large diameter and multipolar

6
Q

What is the difference between extrafusal and intrafusal fibers?

A

Extrafusal fubres - normal muscle fibres

Intrafusal fibres - sit on top of extrafusal fibres and monital muscle length

7
Q

Define a motor unit

A

one alpha motor unit, 50-100 extrafusal fibres and 8-10 intrafusal fibres

8
Q

Explain the three types of motor unit

A

Slow - type 1 - continuous extended use
Fast fatigue resistant - type 2a
Fast fatiguable - type 2b

9
Q

Explain the withdrawal reflex…

A
Withdraw from a painful and dangerous stimulus 
Polysynaptic - 4-5 interneurones 
Ipsilateral 
A delta - III 
Higher cortical control 
Interneurones inhibit antagonists
10
Q

Explain the crossed extension reflex…

A
Maintain balance during withdrawal reflex 
Polysynaptic 
Contralateral 
A delta - III 
Inhibits flexor, activates extensor
11
Q

Explain the stretch reflex…

A

Muscle spindle involved in proprioception
Prevents over stretching of muscle - muscle fibre length
Ia - A alpha
Monosynaptic
Negative feedback

12
Q

What is the function of gamma motor neurons?

A

They are special motor neurones - innervate only muscles - 30% fibres going to the muscle - cell bodies in the anterior part of the spinal cord - can adjust muscle spindle sensitivity

13
Q

What triggers the golgi tendon reflex?

A

The stretching of a muscle tendon during muscle flexion
Ib - A alpa
Changes protein shape - AP
Excites extensory and inhibits flexor - prevents from over stretching.

14
Q

Explain what the Renshaw cell is and its function

A

Self inhibiting interneuron

15
Q

What other type of inhibition is there?

A

Reciprocal - inhibits antagonis

Presynaptic