Nerve impulses

Question 1

Threshold value meaning and voltage

Answer 1

Minimum level of stimulus needed to trigger an action potential

-55 mV

Question 2

Mechanisms behind resting potential

Answer 2

ATP used so 3 Na+ ions move out and 2 K+ ions move in to the cell membrane.

Na+ ion channels close so they cannot diffuse back into the cell (impermeable membrane).

K+ ion channels open so facilitated diffusion out of neurone to concentration gradient.

Net movement out of cell then inside cell.

Question 3

Process of a generator potential

Answer 3

Stimulus detected.

Membrane becomes more permeable to Na+.

Causes change in voltage of membrane so the membrane is depolarised.

Bigger stimulus = more Na+ ion movement = larger change in voltage.
If voltage crosses a certain threshold, action potential occurs.

Increasingly postive inside the cell.

Question 4

Action potential process

Answer 4

Once threshold reached, more Na+ ions channels open.

More Na+ ions enter cell which makes it more positive then outside the cell.

Frequency of action potential increases strength of stimulus.

Question 5

Process of repolarisation

Answer 5

Na+ ion chanels close, K+ ion channels open.

More K+ ions diffuse out of the cell down the gradient which creates requirements of resting potential (more negative inside the cell).

Question 6

Where are negative organic ions found? Why is this important?

Answer 6

Found in axon

Cause of negative charge in axon

Question 7

Voltage of resting potential?

Answer 7

-65 - -70 mV

Question 8

What is the ‘all or nothing’ principle

Answer 8

The action potential is the same size regardless of how much it is over the threshold.

Question 9

Voltage of the action potential?

Answer 9

40 mV

Question 10

Properties of resting potential

Answer 10

Receptor is not being stimulated.

Inside of cell more negative then outside the cell.

Voltage across the membrane.

Membrane is polarised.

Question 11

Structure and function of a motor neurone

Answer 11

Cell body - Contains organelles where proteins & neurotransmitters are produces

Dendrites - Carry action potential to surrounding cells

Axon - Carries nervous impulse along the motor neurone

Question 12

What is the cells (+ function) and gaps involved in myelinated motor neurones

Answer 12

Schwann cells
Wrap the axon to form the myelin sheath which is a lipid and disallows charged ions to pass through.

Gaps = nodes of Ranvier

Question 13

What is saltatory conduction

Answer 13

Action potentials jumps from node to node so are transferred quicker

Question 14

Temperature effect on rate of nerve impulses

Answer 14

Higher temp = faster rate

Faster ion diffusion

Enzymes in respiration work faster so more ATP for active transport in pumps

Question 15

Axon diameter effect on rate of nerve impulses

Answer 15

Wider diameter = faster rate

Speed of conduction increases as there is less resistance to the ion flow

Question 16

What is the refractory period and its effect?

Answer 16

Mass movement of positive ions out of the membrane makes it more negative then -70 mV.

Limits action potentials fired as many Na+ ions needed.

Discreet impulses produced which are not continously stimulated and seperate.