3e

Question 1

Refractory period

Answer 1

During the action potential, a second stimulus, no matter how strong it is, will NOT generate a second
action potential => This region of the plasma membrane is in its absolute refractory period. (Voltage-gated Na+ channels are open or just recently inactivated).

Relative refractory period: A
a second action potential can be
generated if the stimulus is
stronger than usual (occurs
during hyperpolarization).

Question 2

Restoration of concentration gradients

Answer 2

Restoring the original concentration of Na+ and K+ occurs through the Na+
/K+ ATPase pump.

When 2 K+ are pumped back into the cell, 3 Na+ are pumped out.
Concentration gradients are maintained.
 This is a primary active transport = Requires energy (ATP) to provide the energy required for the conformational change of the
transporter (‘ATPase’ pump)

 This active movement of ions also results in 2 positive charges sent
back into the cell vs 3 positive charges sent out. This transport is not
electrically neutral since there is a net transfer of 1 positive charge out
of the cell for each molecule of ATP hydrolyzed.
 The pump is therefore critical for restoring the normal chemical
concentration

Question 3

propagation of Action potential

Answer 3

1: input zone dendrites and cell body: where incoming signals are received (gated potential)
2 trigger zone Axon Hillock: the part where the action potential is initiated (action potential)
3: conducting zone Axon: conducts action potential
4: Output zone: axon terminals, which are the parts that release a neurotransmitter that influences other cells.

Question 4

Once generated at the axon hillock, the action potential will be conducted without further stimulation by
one of two methods

Answer 4

Contiguous conduction
Saltatory conduction

Question 5

Contiguous conduction

Answer 5

= Propagation of the action potential along every membrane patch down the axon’s length.
- Once an action potential is initiated in one part of a nerve cell membrane, a self-perpetuating cycle is
initiated so that the action potential is automatically propagated along the rest of the fibre.

-The action potential does not ‘travel’ along the membrane; instead, it triggers an identical new action
potential in the adjacent area of the membrane.
explain using picture

Question 6

Saltatory conduction

Answer 6

Relevant to myelinated fibres
Myelin: 80% Phospholipids + 20
% proteins = Insulator
Covered by myelin at regular intervals along the length of the axon.
The distance between two nodes of Ranvier is short enough so local current can take place between
an active node and the adjacent one.
=> the electrical impulse jumps from node to node = Saltatory conduction
= Rapid conduction compared to non-myelinated fibres (50 times faster for fibres of similar diameters).

Question 7

Fibre diameter and the velocity of action potentials

Answer 7

the amount of charges that are in movement (= magnitude) depends on the difference in potential
between two electrically charged adjacent areas, AND on the resistance to electrical charge movement
between the two regions.
The larger the diameter of the fibre, the higher the velocity.