The Nervous System and the Brain: Lectures 17 - 23

Question 1

What are the two methods of neuron classification?

Answer 1

• Structural classification
• Functional classification

Question 2

What are the 4 structural classifications of a neuron?

Answer 2

• Multipolar: One axon, many dendrites
• Bipolar: One axon, one dendrite
• Unipolar: One neurite
• Anaxonic: No distinguishable axons, only dendrites

Question 3

What is a neurone?

Answer 3

A branch from the body of a neuron that splits into axons and dendrites.

Question 4

What are the there functional classifications of a neurone?

Answer 4

• Afferent: Signals towards the CNS
• Efferent: Signals away from the CNS
  Interneuron: Signals between neurons

Question 5

Define excitable cells:

Answer 5

Cells which react to or can generate action potentials.

Question 6

In what way does the electrical gradient differ to the chemical gradient?

Answer 6

In an electrical gradient, ions move in both directions depending on their charge.

Positive ions move towards the negative end whilst negative ions move towards the positive side.

Question 7

What are leak channels?

Answer 7

Channels open at all times to allow the free passage of a specific molecule.

Question 8

What are the concentrations of K+ and Na+ at RMP inside the cell?

Answer 8

K+: 140mM
Na+: 10-15mM

Question 9

What are the intracellular concentrations of K+ and Na+ at RMP inside the cell

Answer 9

K+: 140mM
Na+: 10-15mM

Question 10

What are the concentrations of K+ and Na+ at RMP outside of the cell?

Answer 10

K+: 4-5mM
Na+: 145mM

Question 11

What are the extracellular concentrations of K+ and Na+ at RMP?

Answer 11

K+: 4-5mM
Na+: 145mM

Question 12

State the intracellular and extracellular concentrations of K+ and Na+ at RMP:

Answer 12

Intracellular -

K+: 140mM
Na+: 10-15mM

Extracellular -

K+: 4-5mM
Na+: 145mM

Question 13

State the concentrations of K+ and Na+ inside and outside of the cell at RMP:

Answer 13

Inside the cell -

K+: 140mM
Na+: 10-15mM

Outside the cell -

K+: 4-5mM
Na+: 145mM

Question 14

What equation is used to calculate the concentrations of charged species on either side of the membrane?

Answer 14

The Nernst equation

Question 15

State and explain the phases of the action potential in order:

Answer 15

Hypopolarisation: Initial increase in membrane potential up to the threshold value due to stimulus

Depolarisation: Increase in membrane potential beyond threshold value

Overshoot: The peak of the AP at 40mV after which the membrane potential decreases

Repolarisation: The decrease in membrane potential towards RMP

Hyper polarisation: The decrease in membrane potential beyond RMP, counteracted by Na+/K+ pump

Question 16

What are the different phases of the action potential (in order)?

Answer 16

Hypopolarisation

Depolarisation

Overshoot

Repolarisation

Hyperpolarisation

Question 17

In what ways are VGKCs and VGNCs the same? In what ways do they differ?

Answer 17

Both VGNCs and VGKCs open and close in response to changes in membrane potential.

However, VGNCs are fast to open and close whereas VGKCs are slow to open and close.

Additionally, VGNCs have an inactive period which VGKCs do not.

Question 18

What is the absolute refractory period? What causes it? Why does it exist?

Answer 18

The period during which a new AP cannot be generated by the neuron membrane.

This is caused by the inactive state of VGNCs which are unable to respond to changes in voltage whilst inactive. As one of the first steps in the AP, they must open in order for the following phases to occur.

It exists in order to prevent the back flow of an AP. By having an inactive state, the VGNCs cannot reopen once the AP they generated has propagated forward and becomes adjacent to their location.