Nerves And Synapses

Question 0

Describe how an action potential is achieved

Answer 0

Sodium ions quickly diffuse into the cell through the sodium ion channels causing depolarisation. Voltage gated sodium ion channels open and more sodium ions flood in causing the cell to become positively charged.

Question 1

Describe the conditions of a resting potential

Answer 1

Sodium/potassium ion pump pumping sodium out and potassium into the cell. Cell membrane polarised, Pd=-60mV

Question 2

What happens directly after an action potential causes the cell to become positively charged

Answer 2

The sodium ion channels close and the potassium channels open and the potassium ions diffuse out of the cell and the potential difference becomes negative again (repolarisation)

Question 3

The potential difference overshoots a little after repolarisation, why is this?

Answer 3

To allow the cell to recover and the ions to return to the testing potential concentrations

Question 4

Describe how local currents happen

Answer 4

When the sodium ion channels open and sodium ions flood in creating an area of increased sodium ion concentration, this causes sodium ions to diffuse sideways away from this area

Question 5

Describe the function of the myelin sheath

Answer 5

To prevent the diffusion of ions in and out of the cell apart from at gaps called ‘nodes of ranvier’. This means action potentials are only formed at these points, extending local currents down the cell. This causes the signal to appear to jump between nodes. This is called saltatory conduction

Question 6

Describe how signals are transmitted across the synapse

Answer 6

Action potential arrives at synaptic knob. Voltage gated calcium ion channels open and calcium ions diffuse in. This causes vesicles full of a neurotransmitter like acetyl choline to move to the membrane and the acetylene choline is released by exocytosis. It diffuses across the cleft and binds to receptors on the sodium ion channels on the post synaptic membrane. The channels open and sodium ions diffuse in creating a generator potential to carry the message on

Question 7

What are the roles of synapses?

Answer 7

Convergence of multiple nerves, divergence of a nerve to multiple nerves, ensure signals travel in only one direction, filter out low level stimuli.