JC - Motor Neurones and Reflexes

Question 1

What produces a larger voltage nerves or muscles?

Answer 1

Muscles produce a larger voltage than nerves as they are greater in size and move more ions

Question 2

Where do most of the cell bodies reside?

Answer 2

Dorsal Root Ganglia

Question 3

What are some key features of α–Motor Neurones? (4)

Answer 3

• Innervate muscle (no intermediate synapses)
• Soma is located in ventral horn of spinal cord
• Occur in “pools” driving different muscles
• Pools are arranged Topographically

Question 4

What is unique about α–Motor Neurone innervation?

Answer 4

Each muscle fibre/cell is ONLY innervated by ONE α–motor neurone

Each α–motor neurone innervates MANY muscle fibres/cells

Question 5

Describe the concept of a Motor Unit

Answer 5

ONE α–motor neurone PLUS all its muscle fibres

Question 6

How does stimulation rate affect muscle force?

Answer 6

A single motor nerve stimulius produces a twitch (contract and relax)

• Rapidly repeated stimuli lead to increased force as muscle does not fully relax between stimuli leading to smooth sustained contraction – temporal summation

Muscle force increases with stimulation rate

Question 7

What are the characteristics of fast-twitch and slow-twitch muscle fibers?

Answer 7

Fast-twitch

• Strong
• Fatigue quickly
• Glycolytic

Slow-twitch

• Weak
• Fatigue slowly
• Oxidative

Question 8

What are the sensors involved in muscle control and what do they consist of?

Answer 8

MUSCLE SPINDLES

• Sit outside muscle fascicle

Consist of intrafusal fibres (within the spindle)

• Nuclear chain fibres (long)
• Nuclear bag fibres (swelling)

Question 9

What do alpha and gamma motor neurones attatch to?

Answer 9

Alpha motor neurones attach to muscles outside

Gamma motor neurones attach to muscle spindle

Question 10

What are Ia afferents, II afferents and Gamma efferents sensitive to?

Answer 10

Ia afferents primarily bag fibres:

• sensitive to rate of change of length (phasic)

II afferents primarily chain fibres:

• sensitive to length (tonic)

Gamma efferents (motor)

• control sensitivity via stim of INTRAfusal fibres
  Needed when muscles shorten

Question 11

What is the Golgi Tendon Organ, and when does it effectively work in muscle control?

Answer 11

Golgi Tendon Organ is the ending of a nerve cell wrapped in the collagen of a tendon

• It works effectively when the muscle is activated, especially when the muscle shortens

Question 12

Describe the Knee-Jerk Reflex and its feedback loop (5)

Answer 12

1. Applies tension to the muscle
2. Spindle sends a signal of activation
3. Doesn’t use brain
4. Sends signal back to the quadriceps muscle and contracts
5. Communicates with interneurons, inhibitory response inactivates hamstring muscle