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
