Synaptic transmission

Question 1

What is the somatic nervous system?

Answer 1

• Voluntary control
• Sensory and motor supply to skin, muscles & joints.
• Common neurotransmitter: acetylcholine

Question 2

What is the autonomic nervous system?

Answer 2

• Involuntary control
• Smooth muscle, glands & specialised effector cells e.g. pacemaker cells in heart.
• E.g. heart rate, blood pressure

Includes Sympathetic & parasympathetic nervous system

Question 3

Sympathetic nervous system - what is it? what are the actions? Name the neurotransmitter and receptor for the neurons.

Answer 3

Flight or fight”

Activated when we come across stressful situations that are a threat to survival, or exercise

Increases energy expenditure and inhibits digestion.

Actions include:
- ↑ heart rate
- Dilation of pupils
- Inhibits salivation and peristalsis
- Increased glucose production.

1. Pre-synaptic neurone
   - Neurotransmitter- acetylcholine
   - Receptor- nicotinic
   - receptor is on post synaptic neurone
2. Post-synaptic neurone
   - Neurotransmitter- adrenaline & noradrenaline
   - receptor- adrenergic
   - receptor is on target site e.g. muscle
3. Post synaptic neurones of sweat glands:
   - Neurotransmitter- acetycholine
   - receptor- muscarinic receptors
   - receptor is on sweat glands

Question 4

Parasympathetic nervous system: what is it? what are the actions? Name the neurotransmitter and receptor for the neurons.

Answer 4

“Rest and digest”

Neurons involved in this system are called the “cranial nerves” but only III, VII, IX, and X.

Actions include:
- Decrease in heart rate
- Constriction of pupils
- Stimulates saliva flow and peristalsis
- Stimulates bile release instead of glucose.

1. Pre-synaptic neurones
   - Neurotransmitter- acetylcholine
   - receptor- Nicotinic
   - receptor is on post synaptic neurone
2. Post-synaptic neurones
   - neurotransmitter- acetylcholine
   - receptor- Muscarinic
   - receptor is on target site

Question 5

What is a neuromuscular junction?

Answer 5

• The synapse btw the end of the motor neurone & muscle.
• Each branch links to the muscle fibres and forms part of a motor unit.

Question 6

How does synaptic transmission occur at a neuromuscular junction?

Answer 6

Function of synapse depends on movement of Ca ions

Arrival of impulse to synaptic knob opens Ca channels:
- increases permeability of presynaptic membrane to Ca ions

Ca ions move into synaptic knob down their conc gradient

Influx of Ca ions cause synaptic vesicles, which contain neurotransmitters e.g. acetylcholine, to move to presynaptic membrane

Vesicle fuse w/ presynaptic membrane & release neurotransmitters into synaptic cleft via exocytosis

Molecules diffuse across gap & attach to protein receptor sites (e.g. nicotinic) on Na channels of post synaptic membrane

Na ion channels open & Na enter- causes membrane to depolarise
- excitatory post-synaptic potential set up

If there’s sufficient excitatory post-synaptic potential, +ve charge in post-synaptic cell exceeds threshold level & action potential is set up- moved along post-synaptic neutron

Question 7

What other effect can neurotransmitters have?

Answer 7

Opposite effect- inhibit impulse

• Different ion channels open up- allow movement of -ve ions- makes inside more -ve than normal resting potential
• An inhibitory post-synaptic potential results- makes it less likely that action potential will occur in spot- synaptic neurone