Week 2 - topic 2

Question 1

Action potential points

Answer 1

• Axons at rest have a negative electrical charge called the resting potential
• The electrical charge of the axon can change
• Changes in membrane potential determine whether the cell sends a message on to a postsynaptic cell
• Each neuron has a threshold of excitation
• Once there is enough depolarization, an action potential can be produced

Question 2

Hyperpolarisation

Answer 2

When the axon becomes more negatively charged than the resting potential
- less likely to send message to post-synaptic cell

Question 3

Depolarisation

Answer 3

When the inside of the cell becomes more positively charged compared to the outside of the cell
- more likely to send message to post-synaptic cell

Question 4

Threshold of excitation

Answer 4

• the value that the membrane potential has to reach for an action potential to be triggered
• when the cell becomes rapidly depolarised

Question 5

Action potential

Answer 5

a brief electrical impulse that provides the basis for conduction of information along an axon

Question 6

Diffusion

Answer 6

• Diffusion is the movement of molecules from regions of high concentration to regions of low concentration
• molecules will eventually be evenly dispersed in a given medium if there are no barriers to diffusion

Question 7

Electrostatic pressure

Answer 7

Ions: are small charged particles of two basic types
Cations = Positive Charge
Anions = Negative Charge
- Particles with the same kind of charge repel each other, but particles with different charges are attracted together
- The force exerted by attraction and repulsion is called electrostatic pressure. Electrostatic pressure moves ions from place to place.
- Cations move away from regions where there are already cations, towards regions where there are anions.
- Anions move away from regions where there are already anions, towards regions where there are cations

Question 8

Membrane potential

Answer 8

Difference in electrical charge between inside and outside of a cell

Question 9

Cellular fluid and ions

Answer 9

The intracellular fluid (fluid inside a neuron) and extracellular fluid (fluid outside a neuron) have different ions

Question 10

Ions around the cells

Answer 10

organic anions (A-) : only found in intracellular fluid
chloride ions (Cl-): mostly found in extracellular fluid
sodium ions (Na+): mostly found in extracellular fluid
potassium ions (K+): mostly found in intracellular fluid

Question 11

Sodium potassium pump

Answer 11

• Constantly pushes Na+ outside of the cell.

- Made up of protein molecules embedded into the membrane of the cell called sodium-potassium transporters

Question 12

Action potential

Answer 12

• Brief change/increase in the permeability of the cell membrane to Na+ (allowing these ions to rush into the cell), followed by a brief increase in the permeability of the cell membrane to K+ (allowing these ions to rush out of the cell)
• The action potential consists of a series of ion channels opening and closing in the cell membrane

Question 13

First, second third steps action potential

Answer 13

1. Sodium channels open up when the threshold of excitation is reached - sodium ions enter the cell = voltage dependent ion channels.
2. Voltage dependent potassium channels open up - potassium ions exit the cell
3. Sodium channels become blocked and no more sodium ions can enter the cell = refractory.

Question 14

Fourth, fifth and sixth steps action potential

Answer 14

4. Potassium ions continue to leave the cell - membrane becomes more negatively charged
5. Potassium channels close

Na+ channels reset.

6. Cell resets to the resting potential.

Question 15

The all or none law

Answer 15

• The all-or-none law can be used to describe the conduction of the action potential.
• The law states that an action potential either occurs or does not occur, and, once triggered, it is transmitted along the axon to the terminal buttons.
• Furthermore, the strength and duration of an action potential stays the same. This is true, even when the message splits down two or more branches of an axon, on its way to the terminal buttons

Question 16

The rate law

Answer 16

• The rate law is the principle that variations in the intensity of a stimulus or other information being transmitted in an axon are represented by variations in the rate at which an axon fires.
• A high rate of firing = strong muscle contraction
• A low rate of firing = weak muscle contraction

Question 17

The nodes of ranvier and action potentials

Answer 17

• Nodes of Ranvier help the action potential stay the same strength as it travels down the axon.
• the nodes are where the axon comes into direct contact with extra cellular fluid, not shielded by myelin
• action potential regenerated at nodes of ranvier

Question 18

Decremental conduction

Answer 18

• In myelinated areas of an axon, there can be no inflow of sodium through the opening of sodium ion channels.
• Thus, as the message travels along the myelinated axon, it gets smaller and smaller = decremental conduction.

Question 19

Saltatory conduction

Answer 19

• When the message hits a node, it is strong enough to trigger a new action potential.
• The retriggered action potential is then conducted along the axon to the next node.
  = saltatory conduction.
• SC is economic - uses less energy than non-myelinated
• SC is speedy - faster than non-myelinated