neurotransmission at synapses

what is a synapse?

specialised junction between two neurons or between a neuron and an effector cell.

what is an excitatory synapse?

when a membrane potential is brought closer to the threshold - depolarisation

what is an inhibitory synapse?

when the membrane potential is hyperpolarised or stabilised at the resting potential

what is convergence?

information from multiple sources influence one cells activity

what is divergence?

one cell affects multiple pathways

what is a chemical synapse?

when the signal is transmitted by a chemical messenger known as a neurotransmitter

what are adjacent cells joined by for electrical synapses?

gap junctions

what is the gap between cells known as for a chemical synapse?

synaptic cleft

where are neurotransmitters stored?

synaptic vesicles in the axon terminal

what enables the release of neurotransmitters from the vesicles?

depolarisation at the pre-synaptic terminal opens calcium channels. calcium ions allow fusion of vesicles.

how do vesicles get docked in active zones?

interaction with SNARE proteins - calcium ions bind to synaptotagmin and there is a conformational change

how can the excess neurotransmitter be removed?

1. actively transported back into the axon terminal for reuptake

2. transported into glial cells where it is degraded

3. diffused away from the receptor site

4. enzymatically broken down and transported back into the axon terminal to be recycled

what is IPSP?

inhibitory postsynaptic potential. post synaptic response is hyperpolarisation. net movement of negative ions into cell.

what is EPSP?

excitatory postsynaptic potential. post synaptic response is depolarisation. net movement of positive ions into cell.

what is temporal summation?

the sum of input signals from the same synapse at different times

what is spatial summation?

the sum of input signals from multiple synapses at different locations on the cell

what are the main neurotransmitters in the PNS?

acetylcholine

noradrenaline

what is the process of noradrenaline synthesis?

tyrosine → DOPA → noradrenaline

what is acetylcholine synthesised from?

acetyl coA + choline in the presynaptic terminal

where are nicotinic acetylcholine receptors found?

NMJ (neuromuscular junction)

give an example of an agent that blocks the nicotinic acetylcholine receptors, and how it is used in practice?

suxamethonium. used in surgical procedures such as intubation.

where are muscarinic acetylcholine receptors found?

smooth muscle

cardiac muscle

give an example of an agent that blocks the muscarinic acetylcholine receptors, and how it is used in practice?

atropine. used in eyedrops - inactivates parasympathetic pathway and causes pupil dilation.