Initiation of Muscle Activity & Motor Units

Question 1

What are the two main types of neurons?

Answer 1

• Sensory Neurons
• Motor Neurons

Question 2

How does the brain collect information?

Answer 2

Through sensory neurons

Question 3

How does brain send commands to initiate motion?

Answer 3

Through motor neurons

Question 4

Describe how a nervous message travels from brain to muscle fibres

Answer 4

• Brain releases electrical nervous message
• Travels through spine
• Splits of into motor nerves
• Splits of into motor neurons
• Reaches motor unit

Question 5

Muscle will only stop contracting if…?

2 answers

Answer 5

• Brain stops sending signals
• Energy supply for muscles depletes

Question 6

What are motor units?

Answer 6

Where muscle fibres receive nervous messages from. Contain a bundle of fibres.

Question 7

Describe number of muscle fibres in a motor units

Answer 7

• Small motor units have few muscle fibres (around 10-180)
• Large motor units have many muscle fibres (around 300-800)

Question 8

Describe 2 types of motor units

Answer 8

• Slow-twitch motor units (control slow-twitch muscle fibres)
• Fast-twitch motor units (control fast-twitch muscle fibres)

Question 9

Describe characteristics small motor units

Answer 9

• Slow contracting
• Easily recruitable
• Fatigue resistant
• Utilised for prolonged activities

Question 10

Describe characteristics of large motor units

Answer 10

• Fast contracting
• Less easily recruitable
• Rapidly fatiguable
• Utilised for short-term high force activities

Question 11

What are the two types of body movements and describe them

Answer 11

• Fine movements: Small movements that are delicate/soft/precise
• Gross movements: Large movements involving numerous muscles to produce big/explosive/powerful movement and force

Question 12

What type of motor units are recruited for Fine Movements?

Answer 12

Small motor units

Question 13

What type of motor units are recruited for Gross Movements

Answer 13

Large and Small motor units

Question 14

Amount of force produced by muscle mainly depends on:

Answer 14

• Size of muscle and motor units
• Amount of motor units recruited

Question 15

Explain Henneman Principle

Also known as Size Principle

Answer 15

Recruitment for any kind of movement begins with small motor units before recruiting more and/or larger motor units. For example, when running, body will first activate small motor units before activating more larger motor units to create enough force.

Question 16

Explain ‘All or Nothing Principle’

Answer 16

• Nerve impulses only stimulate a motor unit if that much force is required
• When motor unit is stimulated all muscle fibres will fully contract
• Therefore eitehr all muscle fibres in a motor unit are fully contracting or none of the muscle fibres in a motor unit are contracting at all.