the motor unit

Question 1

motor unit

Answer 1

a motor neurone and its muscle fibres

- only one type of muscle fibre can be found in a particular motor unit

Question 2

motor neurones

Answer 2

nerve cells which transmit the brains instructions as electrical impulses to the muscles

Question 3

neuromuscular junction

Answer 3

where the motor neurone and the muscle fibre meet

Question 4

muscle is made up of

Answer 4

many motor units and they vary in size

Question 5

all or none law

Answer 5

once the motor neurone stimulates the muscle fibres, either all of them contract or none of them contract. It is not possible for a motor unit to partially contract

• a minimum amount of stimulation called the threshold is required to start a contraction, If the sequence of impulses is equal to or more than the threshold, all the muscle fibres in a motor unit will contract
• if the sequence of impulse is less than the threshold then no muscle action will occur.

Question 6

how to increase the strength on contraction

Answer 6

wave summation
spatial summation
tetanic contraction

Question 7

wave summation

Answer 7

• the greater the frequency of stimuli, the greater the tension developed by the muscle
• it is when repeated activation of a motor neurone stimulating a given muscle fibre results in a greater force of contraction as muscle becomes stimulated before it can completely relax

e.g. high jumper suddenly requiring a powerful contraction to jump over the bar

Question 8

spatial summation

Answer 8

when the strength of a contraction changes by altering the number and size of the muscles motor units

• occurs when impulses are received at the same time at different places on the neurone.
• it is the recruitment of additional and bigger motor units within a muscle to develop more force

e.g. basketball player will use lots of large, fast twitch motor units in quads to try and achieve as much height as possible.

Question 9

tetanic contraction

Answer 9

occurs when the stimulation of the muscle happens too quickly for relaxation to occur resulting in a sustained contraction

• each time the nerve impulse reaches the muscle cell, calcium is released (calcium needs to be present for a muscle to contract)
• if there are repeated nerve impulses with no time to relax, calcium will build up in the muscle cell and produces a a forceful, sustained, smooth contraction which is a tetanic contraction

Question 10

muscle spindles

Answer 10

these detect how far and how fast a muscle is being stretched an produce the stretch reflex

• provide info the the CNS about how fast and far a muscle is being stretched
• the CNS sends an impulse back to the muscle telling it to contract, which triggers the stretch reflex
• This reflex action that causes the muscle to contract to prevent over-stretching reduces the risk of injury

Question 11

proprioceptors

Answer 11

sensory organs in muscles, tendons and joints that inform the body about movement that has taken place

Question 12

types of proprioceptors

Answer 12

muscle spindles

golgi tendon organs

Question 13

golgi tendon organs

Answer 13

these are activated when there is tension in a muscle

• when the muscle is contracted isometrically in PNF they sense the increase in muscle tension and send inhibitory signals to the brain which allows the antagonist muscle to relax and lengthen AKA autogenic inhibition

Question 14

isometric contraction

Answer 14

where there is tension in a muscle but no visible movement

Question 15

autogenic inhibition

Answer 15

where there is a sudden relaxation of the muscle in response to high tension.

Question 16

PNF

Answer 16

advanced stretching technique

- effective forms of flexibility training for increasing range of motion