Synapses and the role of neurotransmitters

Question 1

What is the structure of an electrical synapse (gap junction)? Where are they common?

Answer 1

• fastest and most primative
• between adjacent cells or neurites
• direct transfer of ionic curent, also small mlecules
• bi-directional
• allows synchronous activity
• relatively rare between neurons in the CNS, although important in developments
• glia-neuron, glia-glia communicaion

Question 2

What is the structure of a chemical synapse and what happens across it?

Answer 2

1. action potential invades nerve terminal
2. depolarisation triggers Ca2+ channel opening
3. Ca2+ influx
4. neurotransmitter release by exocytosis
5. diffusion across the synapse and receptor binding
6. post synaptic effect
7. rapid termination of signal by -re-uptake of neurotransmitter, or -enzymatic breakdown

Question 3

What is the most abundent NT?

Answer 3

Amino acids: glutamate (major excitatory), gamma-aminobutyric acid (GABA; major inhibitory), glycine

Acetylcholine;

Monoamines: noradrenaline, dopamine, 5-hydroxytryptamine (5-HT; serotonin); Neuroactive peptides:>100 different kinds

Question 4

What is the structure of a neurotransmitter receptor and what happens when a transmitter binds?

Answer 4

• Neurotransmitter receptors are membrane spanning protein molecules
• Transmitter binding causes a conformational change=signal
• receptor are specific to a neurotransmitter
• One neurotransmtter - several receptor subtypes

Question 5

What are the two receptor signalling mechanisms? What is the difference?

Answer 5

ionotropic - receptor operated/ligand gated channels (fast)

Transmitter binding⇒conformational change⇒channel opening⇒ion movement

metabotropic - GPCR, slow

Transmitter binding⇒conformational change⇒activates G protein⇒activates ‘effector systems’⇒’indirect effects’-e.g. open or close ion channels, stimulate or inhibit enzymes, secondary messenger systmes

Question 6

Give examples of each type of receptor signalling mechanism

Answer 6

ionotropic = glutamate, AMPA, NMPA, ACh nicotinic

metabotropic = ACh muscarinic, GABAb

Question 7

What is the electrical effect of ionotropic receptor activation?

Answer 7

Question 8

What is spatial summation?

Answer 8

summing of post synaptic potentials generated at separate synapses

Question 9

What is temporal summation?

Answer 9

summing of post synaptic potentials generated at same synapse, if they occur in rapid succession