WEEK 2 (Neural communication)

Question 1

What are leak channels?

Answer 1

Passive membrane channels that are always open

Question 2

What are the properties of leak channels?

Answer 2

• Main reason membrane potential exists
• Size/shape/structure determine which ions can diffuse through

Question 3

What are the changes in membrane potential?

Answer 3

• Depolarisation (decrease in potential; membrane is less negative)
• Repolarisation (Return to resting potential after depolarisation)
• Hyperpolarisation ( Increase in potential; membrane is more negative)
• Resting potential

Question 4

What are the different gated channels?

Answer 4

Voltage-gated channels
Ligand-gated channels
Mechanically-gated channels

Question 5

Describe the stages of a nerve impulse

Answer 5

1. Unbalanced charges are distributed across the plasma membrane that are responsible for membrane potential; membrane is at resting potential and all voltage-gated channels are closed
2. Triggering event opens ion channels which permits net entry of Na+; inward entry of Na+ depolarises membrane producing a graded/action potential
3. Depolarisation spreads by local current flow to adjacent inactive areas away from point of origin
4. At peak of action potential, Na+ inactivation gate closes and Na+ falls ending net movement of Na+ into cell. Simultaneously, K+ activation gate opens a K+ rises
5. K+ leaves cell, causing repolarisation and generates falling phase of action potential
6. On return to resting potential, Na+ activation gate closes and inactivation gate opens which resets the channel
7. Further outward movement of K+ causes hyper polarisation
8. K+ activation gate closes and membrane returns to resting potential

Question 6

Is resting potential +ve or -ve?

Answer 6

Negative

This means that there are less -ve ions inside the membrane than there are +ve ions

Question 7

What is the reason for current loss across the plasma membrane leading to decremental spread of a graded potential?

Answer 7

• Leakage of charge-carrying ions across the plasma membrane results in progressive loss of current with increasing distance from the initial site of the change in potential.
• Leaks in current cause the magnitude of a graded potential to continue to decrease as it passively spreads from the initial active area

Question 8

What are the differences between Graded potentials and Action potentials?

Answer 8

• TRIGGERING EVENTS: GP is triggered by stimulus, combination of neurotransmitter with receptor or self-induced changes in cell permeability & AP is triggered by depolarisation
• ION MOVEMENT PRODUCING A CHANGE IN POTENTIAL: GP is net movement of Na+, K+, Cl- or Ca2+ across membrane by various means, AP is sequential movement of Na+ into and K+ out through voltage-gated channels
• CODING OF MAGNITUDE OF TRIGGERING EVENT: GP magnitude varies with magnitude of triggering event, AP is an all-or-nothing response
• DURATION: GP varies with duration of triggering event, AP is constant
• MAGNITUDE OF THE POTENTIAL CHANGE WITH DISTANCE FROM THE INITIAL SITE: GP magnitude diminishes with distance from initial site, AP Self-regenerates so is constant in an undiminishing fashion
• REFRACTORY PERIOD: GP has none, AP is relative/absolute
• SUMMATION: GP is temporal/spatial, AP has none
• DIRECTION OF POTENTIAL CHANGE: GP depolarises/hyperpolarises, AP always depolarises
• LOCATION: GP is in specialised regions of the membrane designed to respond to triggering event, AP is in regions with an abundance of voltage-gated channels

Question 9

What is the location of K+ and Na+ ions regarding the membrane at resting potential?

Answer 9

Na+ are outside and K+ are inside

Question 10

What is the anatomy of the neuron?

Answer 10

• Dendrites
• Cell body (organelles)
• Axon
• Terminals

Question 11

What is the direction of Action potential in the neuron?

Answer 11

From the Dendrites towards the Axon terminals