The neuromuscular system Flashcards
What is the neuromuscular system?
> includes all the muscles in the body, and the nerves serving them
What is a motor neurone?
Specialised cells which transmit signals from the brain to muscles
What is a cell body (soma)?
> receives stimuli from the neurones
contains nucleus to control functions of the cell
What is a mitochondria?
generates chemical energy needed to power the cell
What are dendrites?
branch-like extensions - receive information from other neurones, and passes it to the cell body
What is an axon?
carries the electrical signal away from the cell body, to the axon terminal
What is a myelin sheath?
surrounds the axon and electrically insulates it
What is a schwann cell?
wraps around the axon, producing the myelin sheath
What are Nodes of Ranvier?
gaps in myelin sheath where the action potential jumps from node to node
What is an axon terminal?
the end of the axon, forms a synapse with another neurone or muscle motor unit (muscle cell)
What is a neuromuscular junction / motor end plate?
> synaptic connection where an action potential is transmitted from a motor neurone to a muscle fibre
the synaptic end bulbs form a synapse with the muscle cell membrane
Describe the initiation of an action potential in a neurone
1) Sufficient number of sodium ions (Na+) diffuse into the neurone
2) This depolarises the axon to a critical threshold level (all or none law)
3) This is followed by repolarisation back to resting level
4) This process forms an action potential which is transmitted down the axon
5) The myelin sheath insulates the axon while the action potential travels from node to node
6) The action potential ends at the axon terminal, where the synaptic end bulbs form a synapse with the muscle cell membrane (neuromuscular junction)
Describe the transmission of impulse at the neuromuscular junction
1) When the action potential reaches the axon terminal, voltage gated calcium channels open and calcium ions (Ca2+) rush into the synaptic bulb
2) Synaptic vesicles fuse with pre-synaptic membrane
3) This triggers release of acetylcholine (ach) into the synaptic cleft
4) Ach binds diffuse across synaptic cleft and bind to receptors on the muscle cell membrane (motor end plate)
5) Sodium ion channels open to allow Na+ to flow through (all or none law)
6) This causes the depolarisation of the cell which re-establishes the action potential within the fibre, leading to a contraction
What is a motor unit?
made up of a motor neurone and all of the skeletal muscle fibres supplied by the axon terminals
(when motor neurone is stimulated, all fibres (of the same type) connected are activated)
What is the ‘All or none’ law?
When sufficient sodium ions diffuse into a cell to cause depolarisation (and subsequent depolarisation) to a critical threshold to pass on a neural signal or initiate an action potential
What is depolarisation?
cell becomes less negative due to Na+ charges entering
What is repolarisation?
cell becomes more negative and returns to resting potential
