Synapses + reflexes

Question 1

What is a synapse?

Answer 1

Junction between 2 neurones

Transmit impulses via neurotransmitters.

Question 2

What is an excitatory neurotransmitter?

Answer 2

Acetylcholine
~~>triggers new action potential in postsynaptic neurone

depolarisation

Question 3

What is an inhibitory neurotransmitter?

Answer 3

GABA

~~> does not trigger new AP

hyperpolarisation

Question 4

Describe structure of synapse?

Answer 4

• Synaptic cleft - gap
• Presynaptic neurone -
  where impulse arrives.
• Postsynaptic neurone -
  receives neurotransmitter
• Synaptic knob -
  contains many mitochondria
  + endoplasmic reticulum
  ~~> ability to manufacture
  neurotransmitters
• Synaptic vesicles -
  contains neurotransmitters.
• Neurotransmitter receptors -
  where neurotransmitter binds

Question 5

What is a cholinergic synpase?

Answer 5

Uses neurotransmitter acetylcholine

hydrolysed by enzyme - acetylcholinesterase.
~~>choline + ethanoic acid

Products taken back to presynaptic neurone –> reforms ACh using ATP

Question 6

Describe transmission across a synapse? 6 marks

Answer 6

1. AP arrives at presynaptic neurone –> causes voltage-gated calcium ion channels to open
2. Ca2+ ions diffuse into presynaptic neurone down electrochemical gradient.
3. Ca2+ cause synaptic vesicles with ACh to move and fuse with presynaptic membrane
4. ACh released into synaptic cleft –> diffuses across synapse towards postsynaptic neurone
5. ACh binds to receptor sites on postsynaptic Na+ channels, causing them to open
6. Na+ ions diffuse into postsynaptic neurone = depolarisation of postsynaptic membrane —–> triggers new action potential

Question 7

What is the role of a synapse?

Answer 7

Ensures unidirectional transmission

Can cause multiple responses from 1 stimulus

Can receive multiple stimuli for 1 response

Question 8

What is summation?

Answer 8

Effect of the build up of neurotransmitters in synapse
–> new action potential can only be triggered if neurotransmitter have built up to threshold level.

Question 9

What is spatial summation?

Answer 9

More than 1 presynaptic neurone releases neurotransmitters to trigger new AP in 1 postsynaptic neurone

Question 10

What is temporal summation?

Answer 10

High frequency AP reach presynaptic neurone

—> causes higher conc of NT being released

Trigger new AP in postsynaptic neurone

Question 11

What are reflexes

Answer 11

Involuntary actions
–> prevent overloading of brain

Innate

Extremely fast

Everyday actions

Question 12

Provide overview of reflex arc:

Answer 12

Receptor -> sensory -> relay -> motor -> effector

Question 13

What is the knee-jerk reaction? 6 marks

Answer 13

1. Tap = patellar tendon to stretch –> also stretches extensor muscle
2. Sends reflex arc impulse through sensory neurone
3. Reflex signal goes along 1 motor neurone = extensor muscle to contract
4. Relay neurone inhibits other motor neurone of flexor muscle –> relax
5. Legs kick due to antagonistic muscle action

Involves spinal cord

Question 14

What is the blinking reflex? 6 marks

Answer 14

1. Cornea irritated
2. Triggers impulse along sensory neurone
3. Relay neurone in lower brain stem pass impulse along
4. Signal branches off in motor neurone to eyelid muscle

Both eyes shut as consensual response

Cranial response

Question 15

What is the differences between nervous system and peripheral nervous system?

Answer 15

NS = brain + spinal cord

PS = neurones that connect CS to other parts of the body

Question 15

What is the difference between somatic autonomic systems?

Answer 15

Somatic = conscious

Autonomic = unconscious (constant)

Question 16

What is the autonomic system further branched off into?

Answer 16

Sympathetic = increased activity–> ‘flight-flight’ response

Parasympathetic = lowered activity = relaxing response