structure of neuronal synapses

what is a synapse

point of connection between 2 neurones

what is a neurotransmitter

endogenous chemical that transmits signals across synapse from one neurone to another ‘target neurone, muscle cell or effector cells

what is a neuromodulator

endogenous chemical that is released from one neurone but if affects groups of neurones or effector cells that have appropriate receptor

differences between neurotransmitters (NT) and neuromodulators (NM)

• NM acts through second messengers vs NT act directly on postsynaptic cells

• NM produces long lasting effects vs NT have fast immediate response

• NT is released at synapses vs NM not always released at synapses

• NT = rapid, localised communication at synapses vs NM more longer duration responses

name if these are NT and/or NM:

• acetylcholine

• monoamines 

  • catecholamines (dopamine, noradrenaline)

  • indolamines (serotonin)

• amino acids - glutamate, GABA, glycine

• peptides - endorphins

• lipid substances 

• nucleosides - adenosine

• acetylcholine = NT

• monoamines = NT and NM

  • catecholamines (dopamine, noradrenaline)

  • indolamines (serotonin)

• amino acids - glutamate, GABA, glycine = NT and NM

• peptides - endorphins = NT and NM

• lipid substances = NT

• nucleosides - adenosine = NM

summary of the different ways drugs can modify neurotransmitter system in brain

what is a presynaptic autoreceptor

Receptor on a neuron that binds the same neurotransmitter it releases → typically inhibits further release

what is presynaptic heteroreceptor

receptor on a presynaptic neuron that binds a different neurotransmitter → can inhibit or facilitate release of the main neurotransmitter

how can drugs affect presynaptic receptors

they can block or enhance autoreceptors or heteroreceptors to modify neurotransmitter release

how can presynaptic heteroreceptors produce presynaptic inhibition

inhibit release of neurotransmitter e.g. glutamate release by GABA b receptors so this causes reduction in postsynaptic activity