The Nerve Impulse

Question 1

How do the charges on the outside and inside of a neuron differ

How do nervous impulses move in the neurons? (3)

Answer 1

the outside and inside of a
Neurons have opposite charges.
——————————————————
1- a nerve impulse is carried when there is a temporary reversal of
the charges across the axon membrane.

2- this reversal is propagated along the axon.

Question 2

The temporary reversal happens in between which two states?

Answer 2

the resting potential
the action potential

Question 3

How is a resting potential produced?

Answer 3

It is because of sodium and potassium ions

the polarity on either side of the
axon membrane can change.
They are constantly ‘hopping’ over
the membrane.

Question 4

What is a resting potential?

What the state of the neuron

What’s the value of it?

in this condition what is the axon said to be?

Answer 4

The neuron is unstimulated

-65 - -70mV
—————–
Polarised

Question 5

what are the steps to resting potential?

Answer 5

1. Na+ are actively pumped out of the axon by sodium-potassium
   pumps.
2. K+ are actively pumped into the axon by sodium-potassium pumps.
3. For every 3 Na+ pumped out, 2 K+ move in. There are therefore more
   Na+ outside, than there are K+ inside (chemical gradient formed)
4. Due to the gradient, Na+ try to move back in and K+ try to move out.
5. However, the Na+ gates are shut, but the K+ gates are open.
6. So only the K+ can move…. and they therefore leave the axon.
7. This causes the outside of the axon to become positively polarised,
   and the inside of the axon to become negatively polarised.
8. But now, due to the massive positive charge outside the axon, some
   K+ are compelled to move back inside!
9. Some of them do move back in, but an equilibrium is formed, where
   there is no more net movement of ions.
10. The electrical gradient becomes balanced, and the resting potential
    is established.

Question 6

What is an action potential?

Whats the state of the neuron

What’s the value of it?

in this condition what is the axon said to be?

Answer 6

When a neuron receives a stimulus, a temporary charge reversal occurs on the axon membrane.

This reversal is passed along the axon, causing a nerve impulse to be sent.

Neuron is stimulated
——————————————
+40 mV
——————————————-
Non-polarised

Question 7

Whats the steps to action potential?

Answer 7

1. STIMULI - exites the neurone membrane, causing Sodium Ion
   channels to open. This causes the membrane to become more
   permeable to Sodium which diffuses in causing the neurone to
   become less negative inside.
2. Depolarisation– if the potential reaches approx. -55mv more
   Sodium channels open and more sodium moves into neurone.
3. REPOLARISATION– at approx. +30mv Sodium channels close
   and Potassium channels open. The membrane is more
   permeable to Potassium which diffuses out. Neurone starts to
   get back to its r.p.
4. HYPERPOLARISTAION– Potassium ion channels are slow to
   close so there is a slight overshootwhen too many potassium
   ions diffuse out. The neurone becomes more negative than its
   r.p.
5. RESTING POTENTIAL - THE ION CHANNELS ARE RESET. The
   sodium potassium pump returns the membrane to its resting
   potential until another stimuli is received.