The Nervous System

Question 1

What does the nervous system do?

Answer 1

• Detects changes in stimuli
• Processes and stores the information
• Initiates responses

Question 2

What is a stimulus?

Answer 2

-A detectable change in the internal or external environment of an organism that produces a response

Question 3

What is the spinal cord made up of?

Answer 3

• Centre of grey matter, outside of white matter
• Central canal containing cerebrospinal fluid in the centre
• Dorsal and ventral roots on each side

Question 4

Why is grey matter grey and white matter white?

Answer 4

• Grey matter contains the cell bodies of neurones and the nuclei give it a grey colour
• White matter only contains the axons and so doesn’t have a darker colour

Question 5

What is a reflex action?

Answer 5

• An inborn response to a stimulus and is rapid, automatic and beneficial
• The path taken by the nervous impulses in a reflex action is the reflex arc

Question 6

What are the three types of neurones and what are their functions?

Answer 6

• Motor neurone, causes a response in muscles/glands
• Sensory neurone, conducts impulses away from the receptor
• Relay neurone, in between sensory and motor neurones in the spinal cord

Question 7

What is the resting potential of a neurone?

Answer 7

-The potential difference across the membrane of a neurone when no nervous impulse is being conducted

Question 8

How is the resting potential maintained?

Answer 8

-Sodium-potassium ion exchange pumps (maintaining an uneven distribution of ions across the membrane)

Question 9

What is the action potential?

Answer 9

-The rapid rise and fall of the electrical potential across a nerve cell membrane as a nervous impulse passes

Question 10

How is an action potential generated?

Answer 10

• Sodium ion channels are opened by the change in voltage, causing sodium ions to rapidly diffuse into the axon (depolarisation)
• This increases the potential difference up to a peak of +40mV
• Potassium ion channels now open and potassium ions rapidly diffuse out of the axon (repolarisation)
• Resting potential (-70mV) is restored

Question 11

How does the action potential travel along the axon?

Answer 11

• Attraction creates local electrical circuits which act as stimuli
• A wave of depolarisation will spread along the axon as sodium ions repeatedly diffuse further down the axon

Question 12

Why can action potentials only travel in one direction?

Answer 12

• The refractory period means new action potentials can’t be generated while one is currently there
• Therefore it ensures action potentials can’t travel back the direction they came

Question 13

What factors affect the speed of conduction of a nerve impulse?

Answer 13

• Temperature (higher temperature means higher speed)
• Axon diameter (larger the diameter means higher speed)
• Presence of a myelin sheath (conduction happens only at nodes of Ranvier, speeding up the impulse)

Question 14

How do impulses travel between synapses?

Answer 14

• Impulse arrival opens voltage gated calcium ion channels, causing them to diffuse in
• This causes synaptic vesicles to move towards the pre-synaptic membrane
• Vesicles release neurotransmitter (acetylcholine), which diffuses across the synaptic cleft
• Attaches to receptors on the post-synaptic membrane, opening sodium ion channels, initiating an action potential

Question 15

What is meant by:

a) temporal summation?
b) spatial summation?

Answer 15

a) When stimuli arrive in rapid succession causing an action potential to be generated
b) When several stimuli arrive at the same time to cause an action potential to be generated