L20 - synapses and neurotransmission Flashcards
synapse
point where electrical signals move from one neurone to another
electrical synapse
pre and post SN directly connected by gap junctions (2nM)
chemical synapse
- pre and post SN physically separated by cleft
- pre SN release chemical transmitter from their axon terminals
- NT binds to receptors on post
gap junctions in electrical synapses
- 2nM
- formed by connexons
- direct passage of ions + small molecules through these channels
- quick signals
features of chemical synapsis
- pre SN
- post SN
- synaptic cleft
- pre S terminal has vesicles with NT
3 types of synapses in CNS
- axo- dendritic
- axo- somatic
- axo- axonal
axo-dendritic synapse
one neuron’s axon sends signals to another neuron’s dendrite
axo-somatic
when one neurones axon sends signals to another cell body
axo-axonal
when one neurones axon sends signals to another neurones axon
describe pre sn
vesicles arranged at active zones
describe post SN
- specialised
- contains clusters of NT receptors and signalling molecules
what is a NT?
chemical messenger
what are NT released by?
- when A.P reaches terminal, there is influx of sodium ions causing depol
- activates calcium channels
- strong electrochemical gradient which moves calcium to terminal
- ca2+ enters cell and interacts with synaptotagmin, which interacts with snare proteins
- vesicles fuse with pre membrane
- exocytosis
- enter cleft
- bind to receptors
what happens to unbound NT or after job is done?
- degradation
- diffusion away from receptor
- reuptake via pre sn
- enzymatically transformed into inactive substances
what can NT’s be classified into?
- amines
- a.a
- peptides
- purines
2 types of NT receptors?
- ionitropic
- metabotopic
describe ionitropic receptors
- ligand (transmitter) gated ion channel- e.g ACh, GABA, dopamine
- transmembrane proteins open for ions like Na+
- excitatory or inhibitory
describe metabotropic receptors
- G protein coupled receptors
- ligand binds
- G protein activates second messenger cascade
cholinergic transmission at neuromuscular junction
- synapse between motor neurone and skeletal muscle
- junction is motor endplate
- uses ACh as NT
suffix -ergic
applies to neurone that release NT (e.g dopaminergic neurone)
synthesis and degradation of ACh
- ACh is synthesised in pre SN by choline acetyltransferase
- metabolised by acetylcholinesterase
what does ACh act on?
nicotinic (ion channels) and muscarinic receptors (GPCR)
glutamate
- main excitatory transmitter in CNS
- activates inotropic and metabotropic receptors
GABA
- main inhibitory transmitter in CNS
- activates small family of ionotropic and metabotropic receptors
what is an excitatory postsynaptic potential?
- EPSP
- makes neurone more likely to generate A.P
what is an inhibitory postsynaptic potential?
- IPSPs
- result of flow of negative ions into cell or positive ions out of cell
- less likely to generate A.P
synaptic integration
- temporal summation: adding up potentials at same synapse but at different times
- spatial summation: adding up potentials that occur at different sites on the neurone
what can happen if excitatory and inhibitory potential of the same size happens at same time and place?
cancel each other out so memb potential may not change
