How Nerves Work 4

Question 1

What does a diagram of an action potential look like?

Question 2

What is the threshold to fire an action potential?

Answer 2

-55mV

Question 3

Explain the ionic basis of the firing of an action potential?

Answer 3

1. Leaky K⁺ channels bring the cell to threshold (graded potential)
2. Voltage gated channels open allowing Na⁺ to flow in and bring the cell to +40mV
3. More K⁺ channels open and bring the cell down to -90mV

Question 4

What channel is faster, and which is slower, out of Na⁺ and K⁺?

Answer 4

Na⁺ channels open faster and K⁺ stay open for longer

Question 5

Explain how the excitability of a cell changes?

Answer 5

The greater the membrane potential, the greater the excitability of a cell

Question 6

What does excitability of a cell mean?

Answer 6

How easy it is to fire an action potential

Question 7

What is the absolute refractory period?

Answer 7

When all gates are opened and the action potential fires (low excitability)

Question 8

What is the relative refractory period?

Answer 8

Gates are closing and recovering (excitability increasing)

Question 9

Is the size of an action potential proportional to the size of the stimulis?

Answer 9

No, they are all the same size

Question 10

How does the size of a stimulis impact an action potential?

Answer 10

The bigger the stimulis, the more action potentials are fired (increased frequency) but the size is the same (same amplitude)

Question 11

Are action potentials self-propogating or decremental?

Answer 11

Self propogating

Question 12

What does self propogating mean?

Answer 12

Keep making new ones for themselves

Question 13

How does the self propogation of action potentials work?

Answer 13

Depolarisation spreads across a membrane decrementally, opening more channels

Question 14

Why do action potentials technically not spread backwards?

Answer 14

They do, but the gates are not opened so nothing happens and it decremenates into nothing

Question 15

How can you increase conduction velocity?

Answer 15

Larger axons

Myelination

Question 16

Why do larger axons increase conduction velocity?

Answer 16

They decrease conduction resistance

Question 17

What two cells form myelin sheath?

Answer 17

Schann cells (PNS)

Oligodendrocytes (CNS)

Question 18

Where are the voltage gates on a myelinated axon?

Answer 18

Not in the myelinated section, but in the gaps between (nodes)

Question 19

How does depolarisation spread along a myelinated axon?

Answer 19

Spreads from node to node without decaying much to to the high insulation

Question 20

What are some diseases that de-myelination causes?

Answer 20

Multiple scerosis

Gwillain-Barre syndrome

Question 21

Why does de-myelination cause disease?

Answer 21

Signal decays quicker and doesn’t reach threshold at the next node

Question 22

What is a nerve?

Answer 22

A bundle of axons

Question 23

What varies within the axons of a nerve?

Answer 23

The size and extent of myelination

Question 24

What is the compound action potential?

Answer 24

Signal recorded extracellularly from large populations of axons

Question 25

What does each bump in the graph of a compound action potential represent?

Answer 25

An action potential going past at that point in time, each one being from the same stimuli

Question 26

What are the different waves and speeds in a compount action potential?

Question 27

Which end of the spectrum of waves is most sensitive to anoxia and local anaesthetic?

Answer 27

Aa is most sensitive to anoxia

C is most sensitive to local anaesthetic

Question 28

What is anoxia?

Answer 28

An absence of oxygen