L19 - Synapses And Neurotransmitters Flashcards
What is a synapse?
The point at which electrical signals move from one nervce cell to another
Where are APs generates and what by?
- presynaptic neuron
- graded potentials activated by inputs from other neurons
What is the simple sequence for synaptic transmission?
- AP generated at presynaptic neuron
- invade synaptic terminal after propagation
- release chemical synaptic transmitter
- generate graded potential in postsynaptic neuron
What can postsynaptic potentials be?
- inhibitory
- excitatory
What atre the different types of synapses?
- electrycal synapse
- chemical synapse
What are electrical synapses like?
Pre and post synaptic neurons are directly connected by gap junctions
What are chemical synapses like?
- pre and post synaptic neurones are physically separated by synaptic cleft
- presynaptic neurones release chemical transmitter from their axon terminals
- transmitter binds to receptor on post synaptic neurons
What are the elctrical synapses - gap junctions like?
- formed by connexons in both cell membranes
- direct passage of ions and small molecules through channel
- permit very rapid faithful transfer of signals
What are features of chemical synapses?
- presynaptic neuron
- synaptic cleft
- postsynaptic neuron
What are the types of synapses in the CNS?
- axo-dendritic
- axo-somatic
- axo-axonal
What are presynaptic terminals contain?
Vesicles arranged at active zones
How are postsynaptic membrane is specialised?
Contains clusters of neurotransmitter receptors and signalling molecules
What defines a neurotransmitter?
- neurotransmitter present
- neurotransmitter released
- neurotransmitter receptors activated
- neurotransmitter removed
How are neurotransmitters released?
Exocytosis
What is the sequence of steps in synaptic transmission?
- transmitter synthesised and stored in vesicles
- AP invades presynaptic terminal
- AP depolarises terminal and opens VGCC, Ca2+ enters
- Ca2+ triggers vesicle fusion
- transmitter released by exocytosis
- transmitter binds to receptors
- ion flow causes post response
What is the sequence of steps after synaptic transmission?
- transmitter removed by enzyme breakdown or reuptake
- vesicle retrieved from terminal membrane
What are the 4 key criterias for synaptic transmission?
- substance present within the presynaptic neurone
- substance released in response to presynaptic depolarisation by AP - release must be Ca2+
- specific receptors present on the post cell for postsynaptic response
- mechanism for removal
What are the tyypes of neurotransmitter receptors?
- ionotropic receptor
- metabotropic receptor
What are ionotropic receptors?
Ligand (transmitter) gated ion-channel
What are the metabotropic receptors?
G-protein coupled receptor (GPCR)
Where does cholinergic transmissision occur?
At neuromuscular junction
- synapse between motor neurones and skeletal muscle
What can some motor neurones in CNS be? What is the junction called?
1 metre from terminals in muscles
- motor endplate
What are the transmitters used at cholinergic synapses?
Ach
- act as nicotinic repectors
(Same way as CNS synapses)
Where is ACh synthesised?
In the presynaptic terminal
- by choline acetyltransferase (ChAT) in presynaptic axon
Where is Ach stored and metabolised?
- vesicles
- acetylcholinesterase (AChE) in synaptic cleft
What is a nicotinic acetylcholine receptor?
A neurotransmitter-gated ion channel
What do cholinergic neurones use?
Ach as the neurotransmitter
- both peripheral and CNS
What are the 2 main brain neurotransmitters?
- glutamate
- GABA
What is glutamate? What does it activate?
- main excitatory transmitter in the CNS
- activates both ionotropic and metabotropic receptor
What is GABA? What does it activate?
- main inhibitory transmitter in the CNS
- activates small family of ionotropic and metabotropic receptors
What are EPSPs?
Excitatory PostSynaptic Potentials
What are IPSPs?
Inhibitory PostSynaptic Potentials
What is temporal summation?
Adding together potentials that occur at the same synapse but at different times
What is spatial summation?
Adding together potentials that occur at different sites on the neurone
