Nervous system

Question 1

Neurons

Answer 1

Specialised cells that conduct electrical impulses for communication.

Question 2

Properties of neurons

Answer 2

· Respond to stimuli and generate electrical signals
(action potentials) in response to these stimuli =
excitability

. Form new connections or modifying existing ones =
plasticity

. Communicate with each other through specialized
connections = synaptic transmission

· Transmit electrical impulses over long distances,
from dendrites to axon terminals = conductivity

Question 3

Glial cells (functions SINM)

Answer 3

Support, protect and electrically insulate neurons.

Increases the speed of impulse transmission.

Non-conductive.

Mitotic. e.g. Schwann cells (form a myelin sheath).

Question 4

Neurons (functional classification)

Answer 4

Sensory (afferent) neurons:
· conduct impulses from sensory
receptors into CNS.

Motor (efferent) neurons
· conduct impulses away from
CNS to the effector organs
(muscles and glands).

Interneurons (association neurons)
· lie between sensory and motor
neurons or other interneurons.
· most abundant (99%).
· processing and integration of
signals.

Question 5

Sodium potassium pump: process

Answer 5

Initially there is a lower
concentration of Na+ ions
outside versus those inside
the cell.

Three cytoplasmic sodium
(Na+) ions bind to the pump.

This promotes
hydrolysis of ATP into ADP, releasing energy.

The
Na+ / K+ pump changes
shape within the membrane
and releases Na+ outside of the cell.

The new shape of the channel binds two potassium ions.

This triggers release of phosphate and the dephosphorylated pump
resumes its original shape.

K+ is released inside the cell.

Question 6

Action potential

Answer 6

A rapid and transient change in the membrane potential of a neuron, where it briefly becomes positive before returning to its resting state.

Question 7

Absolute refractory period

Answer 7

The neuron cannot generate an action potential because sodium cannot move in through leak channels and potassium continues to move out through
voltage-gated channels. A neuron ‘absolutely’ cannot generate an action
potential during the absolute refractory period, even with a very strong
stimulus.

Question 8

Relative refractory period

Answer 8

The neuron can generate an action potential, but only if it is depolarised to a
value more positive than normal threshold (an exceptionally strong
stimuli would be needed.)

This can occur since some of the sodium channels
are still inactive, but some have reset and returned to their resting state, and
some potassium channels are still open.

Question 9

How does the central nervous system tell the difference between a
weak stimulus and a strong one?

How does the central nervous system control different strengths of
muscle contraction?

Answer 9

Answer = Neurons code the intensity of information by
the frequency of action potentials.

Question 10

Conduction velocity

Answer 10

· the speed that an action potential is propagated along an axon
· Fast:
· essential neural pathways
· Reflexes

· Slow
· Serve internal organs
. Digestive tract, glands and blood vessels

Question 11

Conduction velocity depends on two things

Answer 11

1. The diameter of the axon
2. How well the axon is insulated with myelin