3.6.2.1 Nerve Impulses

Question 1

What is essential to survive?

Answer 1

Being able to sense changes in the environement or stimulus and respond to these changes

Question 2

What is a sense organ?

Answer 2

An organ which has specialised cells that can detect stimulus called receptor cells

Question 3

What is the 2nd stage of stimulus?

Answer 3

Coordination / processing / thinking

Question 4

What are the steps between the stimulus and response?

Answer 4

Receptor: sensory cells
Co-ordinator: brain or spinal cord, CNS
Effector: muscle or gland

Question 5

What is the purpose of the endocrine system?

Answer 5

It releases hormones in the blood (e.g. insulin)

Question 6

What is the purpose of the exocrine system?

Answer 6

It releases enzymes into specific areas (e.g. saliva)

Question 7

Does the endocrine or exocrine system have a greater effect on the body?

Answer 7

Endocrine (hormones)

Question 8

What does the relay neurone look like?

Answer 8

See card

Question 9

How do you draw a sensory neurone?

Answer 9

See card

Question 10

How do you draw a motor neurone?

Answer 10

See card

Question 11

What are resting potentials created by?

Answer 11

Created by the active transport of Na+ and K+

Question 12

What can a nerve impulse be described as?

Answer 12

A wave of electrical activity

Question 13

What happens to the sodium potassium pump in the axon at rest?

Answer 13

3Na+ ions are pumped out
2K+ ions are pumped in
This makes the neurone polarised at rest
This is known as an electrochemical gradient

Question 14

What is the resting potential helped by?

Answer 14

Faster K+ diffusion caused by carrier proteins

Question 15

How do K+ ions leak out of the axon during rest?

Answer 15

Down their concentration gradient via a carrier protein

Na+ ions do not do this as the membrane is impermeable to Na+

Question 16

What creates an electrochemical gradient?

Answer 16

There are more sodium ions in the tissue fluid than in the axon, thus creating a gradient

Question 17

What causes an action potential to be generated?

Answer 17

When a stimulus above a certain intensity (threshold) arrives at a receptor or nerve ending

Question 18

When an action potential is first generated, what happens to the membrane potential?

Answer 18

There is a rapid switch in membrane potential from -65mV to +40mV

Question 19

What is the process of the refractory period?

Answer 19

A stimulus reaches the threshold
The stimulus causes a local depolarisation of the membrane by Na+ channels opening
The change in membrane potential closes the Na+ channels and opens the K+ channels (voltage-gated)
The diffusion of K+ causes polarisation of the membrane including hyperpolarisation (caused by K+ channels closing more slowly
The resting potential is restored by active transport

Question 20

What is a saltatory conduction?

Answer 20

Where Schwann cells form insulation

Question 21

Where does the ion movement occur along the axon?

Answer 21

In the nodes of ranvier because there is no insulation to prevent ion movement

Question 22

Where does action potential occur?

Answer 22

On adjacent nodes of ranvier

This makes it more rapid because the action potential makes jumps along the axon instead of travelling along it

Question 23

What are the factors affecting the speed of an action potential?

Answer 23

Myeling sheath: is an insulator so forces the action potential to jump which increases the speed
Diameter of the axon: a greater diameter increases the speed of conductance due to less leakage of ions
Temperature: increases the rate of diffusion of ions so speeds up the nerve impulse

Question 24

What is the all or nothing principle?

Answer 24

Any stimulus below the threshold value produces no stimulus

All action potentials are roughly the same size so either there is or isn’t an impulse