3b

Question 1

neural communication

Answer 1

Neural and muscle cells => transient and rapid changes in their membrane potentials.
Receive a signal.
Initiate/elaborate a message.
Transmit a message.

Question 2

terms

Answer 2

Depolarization = Reduction in the magnitude of the negative potential <=> The membrane is less polarized
than under resting conditions.

Repolarization = The membrane returns to resting membrane potential value after having been
depolarized

Hyperpolarization = Increase in the magnitude of the negative potential => The membrane is more
polarized than under resting conditions

Question 3

Electrical signals are generated
There are two forms of electrical signals:

Answer 3

The graded potentials (short-distance signals)
 The action potentials (over long distances)

Question 4

Graded potentials

Answer 4

What is a graded potential?
 Local changes in the membrane potential.
 Short distance signals (small areas of a cell membrane change their potential)
 Graded potentials can have various magnitudes and durations

They usually result from a specific triggering that are either chemical (usually a neurotransmitter…see
later) or mechanically gated channels (for example, ‘touch’).
 This starts with an opening of gated Na+ channels => Inward movement of Na+
ions down its
electrochemical gradient.
 Whenever a graded potential occurs, Na+
is typically the first ion to flow between the place of
origin of the potential and adjacent regions of the membrane that are still at the resting potential.

Question 5

the stronger the triggering event

Answer 5

The stronger the triggering event, the more gated channels that open, the greater the positive
charges entering the cell, and the larger the depolarizing graded potential at the point of origin. Also,
the longer the duration of the triggering event, the longer the duration of the graded potential.

The graded potential is decremental
= Its magnitude along the neuron progressively decreases.
Reason? Leaking of charge-carrying ions across parts of the membrane

Question 6

Action potentials

Answer 6

Action potentials
Brief - rapid - large amplitude (100 mV)
The membrane potential REVERSES: The inside becomes more positive than the outside (not simply less negative than the outside as can occur for the graded potential).
The signal is propagated through the entire membrane = NOT DECREMENTAL => Thus, they do not decrease in amplitude. They are long-distance electrical signals. (Example: toe)
A graded potential can generate an action potential if it reaches a sufficient magnitude.

Question 7

deplorization is

Answer 7

Depolarization is slow (graded
potentials) until it reaches the
threshold potential
(-55 to -50 mV)