component 1 - nerves (hard topic) Flashcards
why do the skeletal muscles contract ?
in response to a stimulus from the brain to the muscles via motor nerves
where is the central nervous system ?
brain & spinal cord
what does the motor division of the brain do ?
transmit information from the CNS via efferent motor nerves/neurones to muscles
what are motor neurones a part of ?
the somatic/voluntary NS
what are neurones composed of ?
cell body
dendrites
axon
explain what happens in the motor neurone when a nerve impulse is recieved ?
- 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
what is a motor neurone ?
a neurone innervating muscle fibres
how many muscle fibres does 1 motor neurone stimulate ?
between 15 - 2000
what is a motor unit ?
the motor neurone and the muscle fibres it innervates
what happens to the inactive neurones at resting potential ?
- 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
what is an inactive neurone termed ?
polarised
what happens when the neurones recieve a nerve impulse (action potential ) ?
- 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
what happens if the threshold level is reached when neurones receive a nervous impulse ?-
- 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
what does the chemical neurotransmitter do ?
passes the message to the next motor neurone / muscle fibre across the synapse
how do neurones communicate with each other ?
they release neurotransmitters across synapses
what is a synapse ?
the site where a nerve impulse is transmitted between two neurones
what happens at the synapse ?
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
what is the neuromuscular junction ?
the site where an impulse is transmitted between a motor neurone and a muscle fibre
what happens at the neuromuscular junction ?
- 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
give an example of a neurotransmitter ?
acetycholine
what is the all or none law ?
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
why is there no such thing as a weak contraction ?
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
how do we increase the force of a contraction ?
- we need to recruit more motor units, more fast twitch muscle fibres and the frequency of stimulation
each motor unit stimulates the same type of muscle fibre how many muscle fibres to slow twitch type I motor units stimulate ?
100 per unit
how many muscle fibres do fast twitch type IIb motor units stimulate ?
10000 per unit
what is the ratio of each muscle fibre in an average human muscle ?
50:50
