component 1 - nerves (hard topic)

Question 1

why do the skeletal muscles contract ?

Answer 1

in response to a stimulus from the brain to the muscles via motor nerves

Question 2

where is the central nervous system ?

Answer 2

brain & spinal cord

Question 3

what does the motor division of the brain do ?

Answer 3

transmit information from the CNS via efferent motor nerves/neurones to muscles

Question 4

what are motor neurones a part of ?

Answer 4

the somatic/voluntary NS

Question 5

what are neurones composed of ?

Answer 5

cell body
dendrites
axon

Question 6

explain what happens in the motor neurone when a nerve impulse is recieved ?

Answer 6

• dendrites recieve nerve impulses/action potential and conduct them to the cell body
• the impulse is transmitted down the axon to the dendrites of the next neurone

Question 7

what is a motor neurone ?

Answer 7

a neurone innervating muscle fibres

Question 8

how many muscle fibres does 1 motor neurone stimulate ?

Answer 8

between 15 - 2000

Question 9

what is a motor unit ?

Answer 9

the motor neurone and the muscle fibres it innervates

Question 10

what happens to the inactive neurones at resting potential ?

Answer 10

• it has a negative charge inside the cell and a positive charge outside a cell
• the neurone is ready to fire but awaiting the next action potential to be generated

Question 11

what is an inactive neurone termed ?

Answer 11

polarised

Question 12

what happens when the neurones recieve a nerve impulse (action potential ) ?

Answer 12

• a neural impulse causes the release of sodium ions which causes depolarisation
• this causes a positive charge inside the cell and a negative charge outside the cell

Question 13

what happens if the threshold level is reached when neurones receive a nervous impulse ?-

Answer 13

• neurone fires a full action potential
• the impulse passes down the neurone over the myelin sheath
• this continues down the axon to the axon terminal/motor end plates
• here the action potential is turned to a chemical neurotransmitter

Question 14

what does the chemical neurotransmitter do ?

Answer 14

passes the message to the next motor neurone / muscle fibre across the synapse

Question 15

how do neurones communicate with each other ?

Answer 15

they release neurotransmitters across synapses

Question 16

what is a synapse ?

Answer 16

the site where a nerve impulse is transmitted between two neurones

Question 17

what happens at the synapse ?

Answer 17

an impulse travels to a pre-synaptic axon terminal causing synaptic vesicles on the terminal to release chemicals (neurotransmitters) into the synaptic cleft

neurotransmitters bind to the post synaptic receptors on an adjacent neurone

Question 18

what is the neuromuscular junction ?

Answer 18

the site where an impulse is transmitted between a motor neurone and a muscle fibre

Question 19

what happens at the neuromuscular junction ?

Answer 19

• the motor axon terminal releases neurotransmitters which travels across a synaptic cleft and binds to receptors on a muscle fibres
• binding causes depolarisation causing an action potential
• action potential spreads across the sarcolemma into the t tubules causing the muscle fibres to contract

Question 20

give an example of a neurotransmitter ?

Answer 20

acetycholine

Question 21

what is the all or none law ?

Answer 21

if the stimulus is strong enough the depolarisation threshold level is reached and it has to fire off the action potential and all of the muscle fibres are innervated by the motor unit contract maximally with equal force

Question 22

why is there no such thing as a weak contraction ?

Answer 22

if the stimulus isn’t strong enough depolarisation threshold isn’t reached and action potential is not produced so all of the muscle fibres innervated by that motor unit will not contract

Question 23

how do we increase the force of a contraction ?

Answer 23

• we need to recruit more motor units, more fast twitch muscle fibres and the frequency of stimulation

Question 24

each motor unit stimulates the same type of muscle fibre how many muscle fibres to slow twitch type I motor units stimulate ?

Answer 24

100 per unit

Question 25

how many muscle fibres do fast twitch type IIb motor units stimulate ?

Answer 25

10000 per unit

Question 26

what is the ratio of each muscle fibre in an average human muscle ?

Answer 26

50:50