Component 3 - The Nervous System

Question 1

What is the nervous system

Answer 1

The nervous system enables animals to respond to changes in the external or internal environment, also known as stimuli

Question 2

What is the pathway for a nervous pathway

Answer 2

Stimulus → Receptor → Sensory neurone → Co-ordinator → Motor neurone → Effector → Response

Question 3

What part of the nervous system is the coordinator located in

Answer 3

The Central Nervous System

Question 4

What part of the nervous system are the motor and sensry neurone located in

Answer 4

The peripheral nervous system

Question 5

What is a reflex action

Answer 5

A reflex action is a fast, automatic response to a stimulus that has a protective function

Question 6

How do reflex actions occur to protect the body

Answer 6

Receptors detect the harmful stimulus and
send impulses through sensory neurones to a relay neurone in the spinal cord.
This sends an impulse through a motor neurone to an effector,
which responds to protect the body

Question 7

What does grey matter contain

Answer 7

Nuclei and cell bodies

Question 8

What does white matter contain

Answer 8

Myelinated cells

Question 9

What is the spinal cord surrounded by

Answer 9

Membranes called the meninge

Question 10

In a Hydra, what is the CNS

Answer 10

A Nerve Net

Question 11

In a Hydra, in which direction can impulses travel

Answer 11

Both

Question 12

What stimuli can be detected by receptors on Hydra

Answer 12

• Light
• Chemicals
• Physical contact

Question 13

What is the function of a dendrite

Answer 13

Transmits impulses into the cell body

Question 14

What is the funcition of Nodes of Ranvier

Answer 14

Gaps in the myelin sheath that form long local circuits with the next node, speeding up transmission

Question 15

What is the function of schwann cells

Answer 15

wrap around the axon and form the myelin sheath, an electrical insulator

Question 16

What is the function of the Axon

Answer 16

Transmits the impulse to the axon endings away from the cell body

Question 17

Where is the cell body located in a motor neurone

Answer 17

At the dendrites

Question 18

Where is the cell body located in a sensory neurne

Answer 18

On the axon away from the Dendrites

Question 19

Where is the cell body located in a relay neurone

Answer 19

At the dendrites

Question 19

Where is the cell body located in a relay neurone

Answer 19

At the dendrites

Question 20

What is resting potential

Answer 20

-70mV

Question 21

How is resting potential maintained

Answer 21

• The axon is more negative than the outside of the cell
• Na+ channels are closed, K+ channels are open
• A Na+/K+ pump uses ATP to pump 3Na+ out of the axon and 2K+ in
• K+ diffuses out but Na+ can’t diffuse in causing a charge difference

Question 22

How does depolarisation occur

Answer 22

• A stimulus above the threshold (-40mV) causes Na+ channels to open
• Na+ ions diffuse rapidly into the axon
• The membrane depolarises to +40 mV

Question 23

How does repolarisation occur

Answer 23

• Na+ channels close and K+ channels open
• K+ diffuse out rapidly
• Overshoot causes hyperpolarisation
• Resting Potential is restored

Question 24

What is the All or Nothing Law

Answer 24

If the stimulus is below the threshold (-40 mV) then no action potential occurs and the membrane is not depolarised.

Question 25

How does the action potential travel along a neurone in terms of sections

Answer 25

Depolarisation of the membrane sets up a local circuit with the next section. More voltage gated sodium channels open in the next section open causing further depolarisation.

Question 26

What is the refractory period

Answer 26

During repolarisation the membrane can’t form an action potential due to Hyperpolarisation (-90mV)

Question 27

What is the significance of the Refractory period

Answer 27

The impulse only travels foward in one direction

Question 28

What 3 factors affect transmission speed of an impulse in a neurone

Answer 28

• Axon Diameters
• Temperatures
• Myelinated or unmyelinated neurones

Question 29

How do larger axon diameters affect transmission speed

Answer 29

Larger axon diameters increase transmission speed due to less resistance

Question 30

How do higher temperatures affect transmission speed

Answer 30

Higher temperatures increase transmission speed due to an increased rate of diffusion

Question 31

How do myelin sheaths affect rate of transmission

Answer 31

Myelin sheaths speed up transmission because depolarisation can only happen at nodes of Ranvier. The local circuits are longer. Action potentials jump from one node to the next. - Saltatory conduction

Question 32

What is a synapse

Answer 32

The gap between 2 nerve cells. The axon terminals of one neurone meet an effector or another neurone.

Question 33

How does a nerve impulse travel through a synapse

Answer 33

1. Depolarisation of the axon membrane causes Ca²⁺ channels to open
2. Ca²⁺ diffuse into the synaptic knob
3. Ca²⁺ cause vesicles containing neurotransmitter to fuse with the presynaptic membrane
4. Neurotransmitter is released into the synaptic cleft by exocytosis
5. Neurotransmitter diffuses over the synaptic cleft and binds to receptors on the post synaptic membrane.
6. The binding causes Na⁺ channels on the postsynaptic membrane to open
7. The postsynaptic membrane depolarises
8. An enzyme breaks the neurotransmitter down and the products are taken into the synaptic knob and resynthesised and packaged

Question 34

What is the name of a neurotransmitter

Answer 34

acetylcholine

Question 35

What is an Antagonist

Answer 35

Antagonists affect synapses by preventing postsynaptic depolarisations

Question 36

What is an Agonist

Answer 36

Agonists cause more postsynaptic depolarisations

Question 37

What 3 ways could an antagonist work

Answer 37

• preventing Ca2+ channels opening and thus preventing exocytosis
• blocking receptors
• hyperpolarising the post-synaptic membrane so it is harder to reach threshold