Nerves (6)

Question 1

What is the basic unit of the nervous system?

Answer 1

A nerve cell or neuron.

Question 2

Bundles of neurons are called ___ in the PNS and ___ in the CNS.

Answer 2

Nerves

Tracts

Question 3

What do nerves consist of?

Answer 3

They consist of the large neuron fibres, which may be or may be not myelinated.

Question 4

Define Neuron fibres.

Answer 4

Cytoplasmic processes that extend from the cell body of all neurons, ie. axons and dendrites.

Question 5

How are neurons bound together?

Answer 5

The neurons are bound together into bundles by connective tissue called the perineurium.

Question 6

What are the neurons surrounded inside the bundles?

Answer 6

They are surrounded by delicate connective tissue called the endoneurium.

Question 7

What is the ENTIRE nerve surrounded by?

Answer 7

It is surrounded by a sheath of connective tissue, the epineurium.

Question 8

Why do an artery and vein occur between bundles in the neurons?

Answer 8

To nourish the fibres and remove waste.

Question 9

What do nerves do?

Answer 9

They carry impulses from receptors to the CNS and from the CNS to effectors to bring about appropriate responses.

Question 10

What is a nerve impulse?

Answer 10

It is a minute electrical signal- wave of depolarisation, which is caused by a stimulus and creates a difference in electrical charges across the membrane of a nerve.

Question 11

What can the stimulus that triggers nerve impulses be? (4)

Answer 11

• Mechanical
• Thermal
• Chemical
• Electrical

Question 12

What are the 3 types of potential that cause nerve impulses to be carried along a nerve fibre?

Answer 12

• Resting potential
• Active potential
• Refractory potential

Question 13

When is a neuron at rest?

Answer 13

It is in resting state when it is not stimulated and its membrane is polarised ie. the outside of the cell membrane is positively charged and the inside is negatively.

Question 14

What is the resting potential?

Answer 14

It is the difference in the charge (voltage) across the cell membrane.

Question 15

What does the active state involve?

Answer 15

It involves the conduction of nerve impulses along a neuron in response to a stimulus.

Question 16

Explain how active potential works? (3)

Answer 16

• When a neuron is stimulated, the distribution of negative and positive ions on either side of the cell membrane changes, resulting in a rapid reversal of charges; the inside of the cell becomes positive and the outside negative. This process is called depolarisation.
• If the stimulus is strong enough, ie above a certain threshold potential, complete depolarisation results in a burst of electrical activity which passes along the length of the neuron as nerve impulses.
• This is known as the all-or-nothing response as, if the threshold potential is not reached, no nerve impulses are generated.

Question 17

What is refractory potential?

Answer 17

This is the recovery stage as the membrane becomes repolarized when an impulses has pass along. This is brought about by carrier molecules that actively transport the ions back through the membrane to their original positions. The membrane is returned to its resting potential, ready for another stimulus.

Question 18

What gives the neurons their special conducting properties?

Answer 18

The difference in the membrane’s permeability to sodium and potassium ions.