Dr. Willars

Question 1

What are the 5 stages of neuronal function

Answer 1

1 - Generate intrinsic activity
2 - Receive inputs from other synapses
3 - Integrate received inputs
4 - Encode patterns for output
5 - Distribute outputs to other neurons

Question 2

Describe the basic features of an electrical synapse

Answer 2

• Direct ionic coupling

– Gap junctions

Question 3

Describe the basic features of a chemical synapse

Answer 3

• Release of a chemical neurotransmitter
• Diffuses across the synapse
• Interacts with a post-synaptic receptor(s)
• FAST & SLOW chemical transmission (receptor-dependent)

Question 4

Describe the basic features of a combined synapse

Answer 4

• Some synapses contain both types (e.g., spinal motor neurones in the frog)

Question 5

What is a gap junction?

Answer 5

• Direct contact between the interior of each cell
• Very small synaptic cleft
• Allows sharing of the cellular contents (ions!)
• Allows very rapid signalling
• Usually (but not always) excitatory
• Present throughout mammalian brain, also retina
• Usually bidirectionality

Question 6

What is a chemical synapse?

Answer 6

Signal propagation across the synapse by chemical neurotransmitter

Question 7

How are small molecule neurotransmitters used in synapses

Answer 7

• Synthesised in situ in the nerve terminal by synthetic enzymes
• Final steps of synthesis take place in the vesicle

Question 8

How are peptide NT (neuropeptides) used in synapses

Answer 8

• Synthesised in the cell body from newly transcribed pre-proproteins by converting enzymes
• Packaged into vesicles in the cell body and transported to the axon terminal

Question 9

What else is used in synapses

Answer 9

Some may also consider gases (e.g. nitric oxide) and metal ions (e.g. Zn2+) to be neurotransmitters

Question 10

What are the purposes of the chemical synapse

Answer 10

Information transfer between cells
Amplification of signals
Integration of multiple inputs
Modulation
Inhibition
Plasticity – learning and memory

Question 11

Describe small molecules and neuropeptide’s role in nerve propagation at synapse

Answer 11

• Synthesised in the neuron and stored in vesicles – requires precursors and enzymes
• Released in response to depolarisation
• Ca2+-dependent release
• Act at post-synaptic receptor(s)
• Removed by degradation or re-uptake

Question 12

How is NO different?

Answer 12

Not stored, generated as required, Ca2+-dependent, acts intracellularly, spontaneous breakdown

Question 13

Name the main small molecule NTs

Answer 13

• acetylcholine, noradrenaline, dopamine, glutamate, GABA etc.
• clear vesicles
• Nerve terminals often contain both types of transmitter
  co-expression

Question 14

Name the main peptide NT

Answer 14

• opioids (endorphins), substance P etc
• Dense core vesicles
• Nerve terminals often contain both types of transmitter
  co-expression

Question 15

Describe small molecule synthesis

Answer 15

Aromatic L-amino acid transporter - tyrosine and Na+ enter - Tyrosine - DOPA via tyrosine hydroxylase - dopamine (DA) via DOPA decarboxylase - noradrenaline (into vesicle via vesicular monoamine transporter (VMAT) via dopamine Beta-hydroxlase

Question 16

Describe peptide neurotransmitter biosynthesis

Answer 16

From the cell body, mRNA leaves the nucleus and travels to the ER then the golgi, it undergoes proteolytic cleavage (post-transcriptional modification) it then travels down the exon and is released as a dense core vesicle from the terminal

Question 17

Give an example of peptide biosynthesis

Answer 17

Pre-pro-peptide -> pro-peptide -> peptide

• Pre-proopiomelanocortin
• Preproenkephalin
• Preprodynorphin

Question 18

Name the opioids and their abreviations

Answer 18

END = endorphin
M = methionine enkephalin
L = leucine enkephalin
NEO = neoendorphin
DYN = dynorphin

Question 19

Describe NO as a neurotransmitter

Answer 19

L-arginine uses Ca+ and nNOS (neuronal nitric oxide
synthase) to change into L-citrulline - releasing NO

This can either be short-lived: rapid spontaneous modification or be used along with guanylate cyclase to convert GTP to cGMP to PKG (protein kinase G)

Used for learning and memory and smooth muscle relaxation

Question 20

Describe Ca2+ dependant vesicular neurotransmitter release

Answer 20

• An action potential arriving at presynaptic terminal causes influx of calcium ions through voltage gated calcium channels
• Calmodium activates which activates protein kinase II
• PKII phyphorylates Synapsin releasing vesicle from actin cage
• Vesicles move to active zone to be released by exocytosis
• SNARE complex brings membranes tightly together to allow membrane fusion

Question 21

Describe the signal termination of Ca2+ vesicular NT synapse (3 ways)

Answer 21

1) uptake into glial cell (noradrenaline)
2) re-uptake via transporter into presynaptic membrane (noradrenaline)
3) Breakdown (e.g. acetylcholine by acetylcholinesterase) and recycling for resynthesis

Question 22

Describe the two major classes of NT action (dependant on receptor type

Answer 22

FAST:
- Opening of ion channels
- Fast; ms time scale
------EPSP (excitatory post synaptic potential) - depolarisation, +ve in like Na+, increased firing rate
------IPSP (inhibitory post synaptic potential) - hyperpolarisation, -ve in like Cl- or +ve out like K+, decresed firing rates
- Ion channels
SLOW:
- G-protein coupled receptors (GPCRs)
- Slow; seconds to minutes time scale
- Modulate ion channel behaviour

Question 23

Give examples of fast and slow

Answer 23

FAST:

• nicotinic acetylcholine
• GABA(little A)
• NMDA (glutamate)

SLOW:

• muscarinic acetylcholine
• adrenoceptors
• GABA(little B)
• metabotropic glutamate
• opioid