Lesson 5

Question 1

How does temperature affect speed of impulse?

Answer 1

• Ions move faster at higher temperatures due to more kinetic energy
• This can be caused by some animals such as birds and mammals to be warm-blooded
• Provides faster responses

Question 2

How does diameter of axon affect speed of neurone?

Answer 2

• Larger diameter means greater volume and surface area
• Less resistance to flow of ions so conduction is faster
• More SA means more exchange of ions occurs across membran

Question 3

What is a nerve net?

Answer 3

• Simplest type of nervous system
• Sense receptors only respond to limited stimuli and small number of effectors
• Consists of simple nerve cells si the short extensions joined to each other, branching in different directions

Question 4

What are Cnidaria?

Answer 4

Phylum containing aquatic animals such as hydra, jellyfish and sea anemone

Question 5

Describe some differences in human and hydra nervous systems

Answer 5

• Hydra uses nerve net and humans have CNS and PND
• Hydra has slow conduction with no myelin sheath but can regenerate neurones

Question 6

What are chemical synapses?

Answer 6

• Gap between neurone that is 20nm
• Branches of axe be lie close to dendrites
• Impulse transmitted across synaptic cleft chemically as a neurotransmitter and then converted back to impulse

Question 7

What are electrical synapses?

Answer 7

3nm gap small enough for electrical impulse to be transmitter directly across

Question 8

What happens when an action potential arrives at an axon terminal?

Answer 8

Voltage-gated Ca2+ ions open and Ca2+ rapidly diffuse into presynaptic knob

Question 9

How does neurotransmitter diffuse across synaptic cleft?

Answer 9

• Influx of Ca2+ cause vesicles with acetylcholine to fuse with presynaptic membrane
• Acetylcholine released into cleft by exocytosis and diffuses

Question 10

How is action potential generated in post-synaptic neurone?

Answer 10

• Acetylcholine binds to specific receptors on post synaptic membrane (PSM)
• So Na+ channels open in PSM and Na+ rapidly diffuses in, causing depolarisation
• If depolarisation reaches threshold, action potential generated in PSM

Question 11

What happens to acetylcholine after action potential generated in PSM?

Answer 11

• Acetylcholine in receptors broken down by acetylcholinesterase into ethanoic acid and choline
• Diffuses back into axon terminal through presynaptic membrane
• ATP package the neurotransmitters back into vesicles