05.1 Lower Motor Neruones and Muscles Stretch Reflex

Question 1

What is the definition of a lower motor neurone?

Answer 1

Cells whose bodies collect to form a discrete motor nuclei of cranial nerves in the brain stem or LMN in the spinal cord

Question 2

What is an alpha motor neurone?

Answer 2

LMN that innervates the extrafusal fibres (normal muscle fibres) to produce muscle movement

Question 3

What is a gamma motor neurone?

Answer 3

Innervate intrafusal fibres. These keep muscle spindles taught and able to detect muscle stretch.

Question 4

What are muscle spindles?

Answer 4

Connective tissue and intrafusal fibres. Detect change in the length of a muscle.

Question 5

What are golgi tendon organs?

Answer 5

High threshold receptors at the muscle-tendon junction

Cause the antagonising muscle to relax during the stretch reflex

Question 6

What is the stretch (myotatic) relfex?

Answer 6

‘Knee-jerk’ response
Muscle is stretched, muscle spindle detects and fires an action potential
This action potential synapses with alpha motor neurones causing the muscle to contract

Question 7

What is the flexor (withdrawal) reflex?

Answer 7

Nociceptors detect noxious stimuli and fire an AP
AP conducted to the spinal cord and cause alpha motor neurones to fire
Ipsilateral flexors contract

Question 8

How is tone established?

Answer 8

Muscle fibres randomly contract to produce a minimal background contraction without fatigue.