13.4 Nervous Transmission

Question 1

What does it mean when a nuerone has resting potential

Answer 1

The neurone is not transmitting an impulse

Outside the membrane it is positively changed - polarised -70mV

Question 2

What ions are involved in the potential of neurones

Answer 2

Sodium ions and potassium ions

Question 3

What is happening with sodium and potassium ions when a neurone is at resting potential

Answer 3

The sodium ions are being actively transported out of the axon
Potassium ions are being actively transported into the axon by a sodium potassium pump
For every 3 sodium ions pumped out , 2 potassium ions are pumped in

Question 4

What is the balance of sodium to potassium ions about a nuerone

Answer 4

There are more sodium ions outside the membrane and more potassium ions inside the membrane so sodium ions will diffuse back in and potassium ions will diffuse back out down the electrochemical gradient

Question 5

What is the movement of sodium ions prevented by

At resting potential

Answer 5

By the gated sodium ion channels being closed

Question 6

Why is there more positively changed ions on the outside of the axon at resting potential

Answer 6

Due to the movement of sodium ions being prevented by the closed gated sodium ion channels
But the potassium ion channnles remaining open so they move out the axon

Question 7

What is the resting potential of a neurone

Answer 7

70mV

Question 8

What is an action potential

Answer 8

When a stimulus is detected by a sensory receptors it causes a temporary change of charge in the axon membrane

Question 9

What happens when the energy of a stimulus effects a nuerone

Answer 9

The energy will trigger some sodium voltage gated ions to open and so sodium can now diffuse into the axon making the inside of the neurone less negative

Question 10

What happens in action potential when the inside of the nuerone becomes less negative after voltage gated sodium ions channels have been opened by the energy of a stimulus

Answer 10

A change in change causes more sodium channels to open so more slimy diffuses into - example Of positive feedback

Question 11

What happens when the potenstial difference reaches +40mV

From sodium ions channels being open

Answer 11

The voltage gated sodium ions channels will close abs the potassium voltage gates channels open
No more sodium enters but potassium will now diffuse out of the axon and reduce the charge causing the inside to become more negative than outside again

Question 12

What happens when after sodium ion channels close again but potassium voltage gated ions open after the potential has reached +40mV

Answer 12

Initially lots of potassium ions diffuse out so the inside becomes more negative than its normal resting state - hyper polarisation
So then voltage gated potassium channels will close and the sodium potassium pumps cause the axon to return to its resting state

Question 13

What is a nerve impulse

Answer 13

When an action potential starts at one end of a neurone and is propagated along to the other end of a neurone

Question 14

What is the first step in the propagation of an action potential

Answer 14

An initial stimulus causes an action potential in sensory receptor causing the first region of an axon membrane to be depolarised - thus acts as a stimulus for the depolarisation of the next region forming a wave of depolarisation

Question 15

How does the wave of depolarisation work in the propagation of an action potential

Answer 15

Sodium ions (when inside the axon) are attracted by the negative charge ahead and the concentration gradient so they cause the next region to be depolarised

Question 16

What is the refractory period and what does it do

Answer 16

After an action potential there is a short amount of time that the axon cannot be excited again
It prevents the propagation of an action potential going backwards and that they don’t overlap - closed sodium ion channels

Question 17

What is saltatory conduction

Answer 17

When an action potential jumps from 1 node to another causing nuerones to transfer electrical impulses much faster because depolarisation of axon only occurs at node of ranvier

Question 18

Why is saltatory conduction more energy efficient

Answer 18

Repolarisation uses ATP so reducing the amount of depolarisation needed is more efficient

Question 19

What are factors that affect action potential speed

Answer 19

Axon diameter - bigger = faster as less resistance

Temperature - higher = faster (up to 40*)

Question 20

What is the all or nothing principle

Answer 20

A threshold value triggers a response, if the threshold isn’t reached then no action potential is triggered