Neurophysiology

Question 1

What is an action potential

Answer 1

A rapid and temporary electrical signal in the neuron. Which is fundamental to allow neurons to communicate with eachother and other cells

Question 2

What 2 things is a cell membrane made of

Answer 2

1) Phospholipids: each phospholipid molecule has a hydrophilic head and 2 hydrophobic tails
2) Proteins: embedded within the phospholipid layer, allowing certain molecules to pass through

Question 3

What is the membrane potential?

Answer 3

The difference in electrical charge inside vs outside the cell.

The membrane potential can change if the neurons are stimulated which can generate an electric current (mV)

Question 4

What is the resting membrane potential and how many Na / K is there inside or outside

Answer 4

-70 mv (polarised/ negative)

More na outside and K inside

Question 5

When is the neuron hyperpolarized and when is it depolarized

Answer 5

Hyperpolarized when inhibited (rest)
Depolarized when stimulated and the inside of the neuron is more positive.

Question 6

What is the diffusion gradient

Answer 6

Movement of particles from areas of high concentration to low concentration. Then moving around in all directions to reach the Dynamic equilibrium

Question 7

What is the electrical gradient

Answer 7

Where ions create a gradient as they are attracted to areas of the opposite charge.

Question 8

How can ions pass through the membrane

Answer 8

The membrane is semi- permeable so some ions can pass through it.
Others pass through proteins known as channel pores. This is known as selective ionic permeability.

Question 9

What is the equilibrium potential for Potassium

Answer 9

-90mV (hyperpolarised)

Question 10

What is the equilibrium potential for Sodium

Answer 10

+60mV

Question 11

What is a equilibrium potential

Answer 11

The point at which there is no inward or outward flow of particles.

Question 12

How to reach the equilibrium gradient

Answer 12

The diffusion gradient will push ions one way and electrical gradient the other.

Question 13

Explain how the action potential works

Answer 13

• Voltage gated ion channels are closed at rest and open when membrane is depolarised
• Exciting the membrane depolarises it and the channels open allowing sodium in making it more positive
• The action potential is only fired once the threshold of -55mV is reached.
• Once it is reached even more Sodium enters bringing the membrane potential close to the equilibrium potential for sodium but not quite.
• This is because after 1 millisecond ion channels for Potassium open and so sodium ones close. (overshoot)
• The potassium entering leads to the falling phase and the membrane potential gets more negative.
• It then reaches the equilibrium potential of -90mV and the potassium channels close.
• The potential then returns to its resting state of -70 mV. With support of the sodium potassium pump which moves sodium in and potassium out.
• No other action potential can occur until -70mV is reached known as the refractory period
• The nerve impulses travels along the axon as a series of action potentials towards the axon terminal.

Question 14

What are the 2 types of axons

Answer 14

Myelinated axons: Segments wrapped by myelin which is a fatty layer made of glial cells to insulate and prevent current leakage. The myelin sheets are separated by nodes of Ranvier which are non-myelinated areas where action potentials occur and spread. The jumps between the nodes are called Saltatory conduction. This is fast and used in motor and sensory neurons.

Unmyelinated axons: Action potentials are close because current can only travel short distances. So continuous conduction is used it is typically slower and used for autonomic processes.