Pack 8 – The Nervous System and Nerve Impulses

Question 1

What is the CNS made up of?

Answer 1

The brain and spinal chord

Question 2

What does the CNS do?

Answer 2

Controls voluntary (e.g. moving) and involuntary (e.g. breathing) functions

Question 3

How does the CNS work?

Answer 3

The spinal cord receives information from the PNS about a stimulus, this is then interpreted by the brain and a response is sent back

Question 4

What is the PNS?

Answer 4

The rest of your nervous system that isn’t the brain and spinal cord

Question 5

PNS function:

Answer 5

• Responsible for detecting stimuli (e.g. light, sound, temperature, pressure)
• Also responsible for carrying out the response to the stimulus, as directed by the CNS

Question 6

What is the PNS made up of?

Answer 6

Sensory and motor neurones

Question 7

Neurone

Answer 7

• A single cell
• Each one has along nerve fibre
• These carry the nerve impulse

Question 8

A nerve

Answer 8

Bundle of nerve fibres (neurones)

Question 9

Sensory neurones

Answer 9

These carry impulses from sensory cells around the body to the CNS (spinal cord and brain)

Question 10

Motor neurones

Answer 10

• Cell body always based within the CNS and the axon extends out to the body
• Conducts impulses from CNS to effectors (which are muscles or glands)

Question 11

Relay neurones

Answer 11

• Within CNS
• Connect neurons to each other

Question 12

Reflex arcs

Answer 12

Simple nerve pathways

Question 13

Reflexes

Answer 13

• Rapid, involuntary responses to stimuli

Question 14

Action potential process:

Answer 14

Varying the concentration of sodium ions (Na+) and potassium ions (K+) inside and outside the axon creating a difference in charge, through channels for each of these ions in the membrane

Question 15

Resting potential

Answer 15

• At the resting potential (before an impulse), Na+ is being pumped out of the axon and K+ is being pumped into the axon by active transport
• Done by a protein pump in the membrane called the sodium-potassium pump or Na+/K+ pump
• There are more Na+ outside the axon than there are K+ inside the axon meaning the charge across the membrane
• The membrane is polarised

Question 16

3 stages involved in creating an action potential:

Answer 16

1. Depolarisation
2. Repolarisation
3. Restoring the resting potential

Question 17

Depolarisation

Answer 17

• Na+ ions flow into the axon, depolarising the membrane
• Once some Na+ channels are open and the membrane has started to depolarise, the threshold (-55mV) for an action potential to be created is reached.
• These positive ions flowing into the axon reverse membrane polarity from -70mV to +40mV

Question 18

Repolarisation

Answer 18

• Na+ channels close and K+ channels open
• K+ diffuse out of the axon (down a gradient)
• As K+ ions flow out of the axon of the neuron, the inside of the axon returns to being more negative than the outside

Question 19

Restoring resting potential

Answer 19

• K+ keep flowing out of the axon until the potential difference is actually more negative than it is at rest
• Resting potential is then restored to -70mV by closing the K+ channels.

Question 20

A myelin sheath function:

Answer 20

• Protects the nerves from damage
• Speeds up the transmission of the nerve impulse

Question 21

saltatory conduction

Answer 21

As depolarisation occurs in one node, a circuit is set up which reduces the potential difference of the membrane at the next node, triggering an action potential
- The impulse effectively jumps from one node to the next

Question 22

How is a synapse stimulated?

Answer 22

By the arrival of a nerve impulse/action potential

Question 23

What does an action potential trigger?

Answer 23

• A release of neurotransmitter between the two neurons to stimulate the next neuron along
• This is how neurons communicate

Question 24

Neurotransmitter

Answer 24

A chemical that diffuses across a synapse from pre-synaptic to post-synaptic membrane to initiate an action potential in the post-synaptic neurone

Question 25

Synaptic cleft

Answer 25

The gap between the two neurones

Question 26

Synaptic knob

Answer 26

Swelling at the end of the presynaptic neurone containing synaptic vesicles

Question 27

Synaptic vesicles

Answer 27

Membrane bound sacs containing neurotransmitters

Question 28

Function of synpases:

Answer 28

- To transmit information (as action potentials) between neurones - To integrate different nerve pathways - To allow regulation of the progression of the impulse e.g. by filtering out low level stimuli

Question 29

Stage 4-6 of a synaptic transmission:

Answer 29

4. The neurotransmitter is released from the neurone into the synaptic cleft by exocytosis 5. The neurotransmitter then diffuses across the cleft 6. The neurotransmitter binds to receptors on the post-synaptic membrane

Question 30

Stage 1-3 of a synaptic transmission:

Answer 30

1. An impulse travels down the axon of the ¬pre-synaptic neurone and arrives at the synaptic knob 2. This action potential causes calcium ion channels to open and calcium ions (Ca2+) to cross the membrane and enter the pre-synaptic neurone 3. This causes vesicles containing the neurotransmitters to move to and fuse with the presynaptic membrane

Question 31

Stage 7-8 of a synaptic transmission:

Answer 31

7. This causes Na+ channels to open in the post-synaptic membrane 8. The subsequent influx of Na+ causes depolarisation of this membrane

Question 32

Stage 9-10 of a synaptic transmission:

Answer 32

9. This triggers an action potential in the post-synaptic neurone 10. After the impulse had moved on, the neurotransmitter must be removed. It can be a) actively taken up across the presynaptic membrane to be repackaged into vesicles, b) broken down by enzymes within the cleft, or c) diffuse away from the synapse

Question 33

Role of neurotransmitters in synaptic transmission:

Answer 33

- A neurotransmitter is needed to cross synaptic cleft - Released from presynaptic neurone and binds to receptors on postsynaptic neurone - Generating an impulse in the postsynaptic neuron

Question 34

Problem with synaptic transmission:

Answer 34

If there are any problems with the synapses, it has a major impact on how your body works.