Neuronal signalling

Question 1

What are neurons ?

Answer 1

are nerve cells that send messages all over your body

Question 2

What are neurons at rest ?

Answer 2

Neurones that are ready to conduct impulses – resting potential

Question 3

Is the axon membrane polarised ?

Answer 3

yes

Question 4

How is resting potential established?

Answer 4

1) Neurones have selectively permeable membranes with ion channels and protein pumps.

2) Na+K+ transporter actively transports 3 Na+ ions out of cells and 2 K+ ions in, In addition K+ and Na+ channels

3) Therefore positive ions accumulate outside cells providing a resting potential

Question 5

What are nerve impluses?

Answer 5

an electrical charge that travels along the membrane of a neuron.

Question 6

What is an action potential ?

Answer 6

changes of electrical potential in a cell

Question 7

What are the 3 phases of action potential ?

Answer 7

1.Polarisation
2. Depolarisation
3. Repolarisation

Question 8

What causes during depolarisation ?

Answer 8

1) Stimulus to resting neurone opens Na+ ion channels
Slow movement of Na+ ions into axon down concentration gradient.

2) Increasing depolarisation opens more Na+ channels .

3) Once threshold reached (-50mV) more rapid inrush of Na+ ions triggered

Question 9

What occurs during repolarisation ?

Answer 9

At the peak Na+ gates close and K+ channels open ,
this allows rapid outflow of K+ ions that repolarise the membrane

Question 10

What is the refractory period ?

Answer 10

The refractory period limits frequency and ensures nerve impulses flow in one direction

Question 11

What are the 2 phases of the refractory period ?

Answer 11

1) Absolute refractory period immediately after Na+ channels closed.

2) Relative refractory period - membrane begins to recover, becomes increasingly responsive

Question 12

What are unmyelinated neurones ?

Answer 12

each section of the membrane depolarises the next, so transmission of nerve impulses is relatively slow

Question 13

What are myelinated neurons ?

Answer 13

impulse jumps from one node to the next, so only the membrane of the nodes is depolarised leading to rapid (saltatory conduction)

Question 14

What is the communication between the neurons ?

Answer 14

1) Action potential reaching end of axon terminates in presynaptic terminals.
2) Signals pass to other neurones/effectors
3) Separated by gap/synapse
4) Chemical ‘neurotransmitters released into synapse
5) Diffuses across cleft and binds to postsynaptic membrane
Information transmitted to next cell

Question 15

The role of a synapse ?

Answer 15

has coordinated action of presynaptic and postsynaptic membranes separated by cleft