Action Potentials

Question 1

What ions are inside the cell?

Answer 1

K+ ions and large negative ions

Question 2

What ion is most prominent on the outside of the cell?

Answer 2

Na+

Question 3

What are the three types of membrane channels do we have?

Answer 3

Ligand-gated channels
Voltage-gated channels
Gap junction channels

Question 4

How do ligand-gated channels work?

Answer 4

A ligand, such as a neurotransmitter, binds to a membrane-bound receptor, causing it to open and ions flow into the cell.

Question 5

How does a voltage-gated ion channel work

Answer 5

Voltage-gated ion channels are multisubunit protein complexes that respond to changes in membrane potential with conformational changes that lead to gating, or opening and closing, of an ion-selective transmembrane pore

Question 6

How do gap junctions work

Answer 6

permit direct cell–cell transfer of ions and small molecules

Question 7

How do Sodium-potassium pumps work?

Answer 7

Using ATP since it is against the concentration gradient, Na+ is taken out of the cell, and K+ is taken in.

Question 8

How to measure membrane potential

Answer 8

• Cell membrane potential measured using a voltmeter.
• First microelectrode is impaled through the cell membrane to the interior of the cell.
• Second electrode (indifferent electrode) is then placed in the extracellular fluid.

Question 9

What is the resting membrane potential for a neuron

Answer 9

-70mV

Question 10

What are the events that happen in an action potential?

Answer 10

• Action potential initiated by a rise in the membrane potential from −70 millivolts toward the zero level.
• Rising voltage open voltage-gated sodium channels.
• Rapid inflow of sodium ions cause a further rise in the membrane potential,
• Action potential termination is caused by the rising membrane potential which cause closure of the sodium channels and opening of potassium channels.
• Resting membrane
• Threshold potential
• Depolarization
• Repolarization
• Hyperpolarization

Question 11

What is a threshold potential

Answer 11

A membrane potential that must be reached by the stimulus to trigger an action potential.

Question 12

What is a refractory period

Answer 12

A refractory period is a time in which th membrane does not respond normally to additional depolarizing stimuli from the time an action potential begins until the normal resting potential has stabilized.

Question 13

Distinguish between absolute refractory period and relative refractory period

Answer 13

• During absolute refractory period, the cell cannot respond to any additional stimuli, no matter how strong it is.
• During relative refractory period, the cell can respond to additional stimuli, but the stimulus has to be strong enough in order to trigger an action potential.

Question 14

How is an action potential propagated in unmyelinated vs in myelinated fibres

Answer 14

In unmyelinated fibers, the action potential is propagated slower because the impulses have to move through the whole axon
-In myelinated fibres, the impulses jump from one node of Ranvier to another, thus leading to faster propagation of stimuli. This is called saltatory conduction.

Question 15

Fast and energy efficient movement of stimuli on a myelinated axon

Answer 15

Saltatory conduction