Transmission within a neuron (action potentials)

Question 1

What is a cell membrane made of and what is its function?

Answer 1

Lipid and protein, and it stops things from mixing.

Question 2

Name 6 parts of a neuron.

Answer 2

Soma, dendrites, axon hillock, axon, bouton and synapse.

Question 3

What’s inside the cell membrane?

Answer 3

Organic anions (-)
K+
Water

Question 4

What’s outside the cell membrane?

Answer 4

Na+
Cl-
Water

Question 5

Where are APs generated?

Answer 5

The axon hillock.

Question 6

How are APs transmitted?

Answer 6

By changing electrical charges across the cell membrane.

Question 7

If ions moved passively up and down electric and chemical gradients, which elements would move in and which out and what would this do?

Answer 7

Sodium in, potassium out, would change resting potential to 0mV.

Question 8

What is the resting potential of a neuron?

Answer 8

-70mV - more anions inside and cations outside.

Question 9

What are anions?

Answer 9

Negative ions.

Question 10

What are cations?

Answer 10

Positive ions.

Question 11

How is the resting potential maintained?

Answer 11

Through an active pump - the sodium-potassium pump.

Question 12

What does the sodium-potassium pump do?

Answer 12

Uses energy to move 3 Na+ to the outside and 2 K+ to the inside.

Question 13

What did Hodgkin and Huxley (1952) do?

Answer 13

Found action potentials in a giant squid axon (recorded voltage with electrodes) and developed a mathematical model - won Nobel prize.

Question 14

How does an AP look on a voltage graph?

Answer 14

Resting potential, then goes up (depolarisation) to 40mV (spike), then falling (repolarisation) to -80mV, following which there is a gradual increase back up to -70mV (hyperpolarisation/recovery).

Question 15

What is the firing threshold for an AP?

Answer 15

-55mV.

Question 16

What happens to the cell membrane during depolarisation?

Answer 16

When the membrane reaches the threshold, voltage-gated sodium channels open and sodium rushes into the neuron, increasing the potential to 40mV.

Question 17

What happens to the cell membrane during repolarisation?

Answer 17

Once the membrane reaches 40mV, the sodium channels close and voltage-gated potassium channels open. Potassium rushes out until the potential has decreased to -80mV.

Question 18

What happens to the cell membrane during recovery/hyperpolarisation?

Answer 18

The membrane hyperpolarises - all channels close and the sodium-potassium pump works to restore normal ion balance (swaps 2 K- for 3 Na+). The potential returns to -70mV.

Question 19

What does a Takifugu’s liver contain and how is it lethal?

Answer 19

Tetrodotoxin (TTX), it blocks sodium channels and prevents APs, meaning that about 70 micrograms can kill in 30 mins.

Question 20

How fast does an AP in a regular neuron move?

Answer 20

2 m/s

Question 21

What is myelin?

Answer 21

A fatty layer of insulation generated by Schwann cells and oligodendrocytes. Loss of myelin is seen in MS and it gets harder to produce with age.

Question 22

What is saltatory conduction?

Answer 22

The way in which myelin covers axons with gaps (Nodes of Ranvier) and APs jump across nodes - it’s a fast, efficient method of transmission.

Question 23

How fast can myelin and saltatory conduction make a neuron?

Answer 23

Up to 120 m/s

Question 24

How does the AP encode information?

Answer 24

Spike frequency (firing rate)