The neuromuscular system

Question 1

Neuromuscular system

Answer 1

> includes all the muscles in the body, and the nerves serving them

Question 2

Motor neurone

Answer 2

Specialised cells which transmit signals from the brain to muscles

Question 3

Cell body (soma)

Answer 3

> receives stimuli from the neurones
contains nucleus to control functions of the cell

Question 4

Mitochondria

Answer 4

generates chemical energy needed to power the cell

Question 5

Dendrites

Answer 5

branch-like extensions - receive information from other neurones, and passes it to the cell body

Question 6

Axon

Answer 6

carries the electrical signal away from the cell body, to the axon terminal

Question 7

Myelin sheath

Answer 7

surrounds the axon and electrically insulates it

Question 8

Schwann cell

Answer 8

wraps around the axon, producing the myelin sheath

Question 9

Nodes of Ranvier

Answer 9

gaps in myelin sheath where the action potential jumps from node to node

Question 10

Axon terminal

Answer 10

the end of the axon, forms a synapse with another neurone or muscle motor unit (muscle cell)

Question 11

Neuromuscular junction / motor end plate

Answer 11

> 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

Question 12

Initiation of action potential

Answer 12

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)

Question 13

Transmission of impulse at the neuromuscular junction

Answer 13

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

Question 14

Motor unit:

Answer 14

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)

Question 15

‘All or none’ law

Answer 15

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

Question 16

Depolarisation

Answer 16

cell becomes less negative due to Na+ charges entering

Question 17

Repolarisation

Answer 17

cell becomes more negative and returns to resting potential