Neurotransmitters: Lecture 9

Question 1

What is the function of neurons

Answer 1

Generate intrinsic activity

Recieve input from other synapses

Produce output patterns (action potentials)

Distribute outputs to other neurons

Question 2

What are the different types of synapses

Answer 2

Electrical and Chemical

Question 3

Describe an electrical synapse

Answer 3

• Direct ion coupling (GAP junction)
  
  • Rapid signalling (usually excitatory)
• Low specificity
• Very small synaptic cleft allowing sharing of cellular contents
• Two synaptic plates (upper and lower)
• 2 hemi-channels put together –> bidirectional

Question 4

Describe a chemical synapse

Answer 4

• Releases neurotransmitter which then diffuses across a syanpse to interact with post-synaptic receptors.
  
  • Fast or slow transmission depending on the amount of steps required
• Requires neurotransmitters to be removed
• Structure:
  
  • Presynaptic and post-synaptic cells with a synaptic cleft in the middle
  • Neurotransmitter released from pre-synaptic membrane

Question 5

What types of neurotransmitters are there and what are their specific functions.

Answer 5

• Small molecule
  
  • ​**in situ synthesis –> finalised in the vesicle
    
    • Stored in clear vesicles
  • Ca2+ dependent release
  • E.g. Ach, NA, dopamine
• Neuropeptides:
  
  • pre-proproteins are converted in cell body
  • Then packaged in vesicles for transport to synapse where they undergo ca2+ dependent release
  • Stored in dense vesicles
  • Examples: opoids
• Others:
  
  • Not stored so must be synthesised, still Ca2+ dependent release
  • Examples: NO, metal ions

Question 6

What is the purpose of a chemical synapse?

Answer 6

Information transfer

Signal amplification

Integration of multiple inputs

Modulation or inversion

Inhibition

Plasticity - learning and memory

Question 7

How are neurotransmitters removed

Answer 7

Degradation or re-uptake

Question 8

How are small molecule neurotranmsitters synthesised?

Answer 8

In situ, neurotransmitter packaged in veciles.

Enzymes maybe required for conversion (dopamine –> NA)

Question 9

How are neuropeptides synthesised?

Answer 9

Synthesised in the cell body.

Pre-proproteins are converted by enzymes before.

Pre-pro-protein –> Pro-protein –> Protein

Packaged into vesicles and transport to axon terminal.

Question 10

How are other neurotransmitters synthesised e.g. Nitric Oxide

Answer 10

Question 11

How does synaptic transmission work?

Answer 11

Action potential –> depolarisation –> voltage gated Ca2+ channel opens –> calcium influx –> vesicle priming –> neurotransmitter release –> bind to post-synaptic receptors

Question 12

What is the role of calcium in synaptic transmission

Answer 12

influx through voltage gated calcium channels down the concentration gradient.

Enter close to release mechanisms so that the largest possible increase is created

Ca2+ binds to synaptotagmin –> pulls it down –> release of neurotransmitter

Question 13

How is the signal terminated?

Answer 13

Re-uptake (transporters or glial cells) or degradation

Acetylcholine is degraded

Noradrenaline is uptaken

Question 14

What are the two main classes of neurotransmitter action

Answer 14

FAST

SLOW

depends on the receptor type

Question 15

How does fast neurotransmitter action work?

Answer 15

Opening of ion channels –> post synaptic potential (excitatory (EPSP) or inhibitory (IPSP)

This leads to either depolarisation or hyperpolarisation, through a graded membrane potential change which will decrease over time and distance.

Question 16

How does slow neurotransmitter action work?

Answer 16

G protein coupled receptor facilitated which leads to a longer process compared to ion channel opening.

This can indirectly act on fast action by modulating ion channel behaviour.