Synapses Flashcards
Does mylination or axon diameter have a greater effect on speed of an impulse?
Myelination.
What are the two types of synapse?
Electrical synapses and chemical synapses.
What are the differences between the two types of synapse?
Electrical synapses have pre and post synaptic neurones that are directly connected by gap junctions, whereas chemical synapses are physically separated by a space.
electrical synapses allow local currents from arriving APs to flow directly across the junction, very rapid
What are axodendritic synapses?
Between the axon of one neurone and the dendrites of another.
What are axosomatic synapses?
Between the axon terminals of one and the cell body of another.
What are axoaxonal synapses?
Between two axons.
What are the two types of neurotransmitter receptors?
Ligand-gated ion channels and G-protein coupled receptors.
How are ligand-gated channels opened?
The neurotransmitter binds to the receptor, activated resulting in a conformational change such that it forms an open channel
How are G-protein coupled receptors opened?
A neurotransmitter binding to a receptor that contains and G-protein attached that then binds to an effector protein that sends intracellular messages to a voltage-gated ion channel so that it opens.
Where does Ach act?
Muscarinic or nicotinic receptors. Muscarinic are G-protein coupled and nicotinic receptors are ion channel receptors.
What enzyme synthesises Ach?
Choline acetyl transferase.
What enzyme breaks down Ach?
and where?
acetylcholinesterase, in the cleft
How is ACh formed?
Choline and acetyl CoA combining.
What are the breakdown products of ACh?
Choline and acetic acid.
Why are neuromuscular junctions used as a model synapse?
They are easy to experiment with and study - they are simple as there is only one input and one output.
What is temporal summation?
Adding together of action potentials that occur at the same synapse but at different times.
What is spatial summation?
Adding together of potentials that occur at different sites on the neurone.
How are APs generated in the presynaptic neurone
by graded potentials
common features of all synapses
presynaptic terminals have vesicles arranged in active zones, with the others dispersed
post membrane is specialised and contains clusters of neurotransmitter receptors and signalling molecules
what defines a neurotransmitter
present in axon terminals along with synthetic material for making it
released in response to depolarisation (calcium dependent exocytosis)
specific receptors in post membrane
mechanism for removal
where are nicotinic receptors found?
at neuromuscular junctions of skeletal
process of release of neurotransmitter by exocytosis
- vesicles docked at active sites
- arrival of AP causes VGCC to open, calcium ions flow in and allow docked vesicles to fuse with the membrane (some completely fuse and some are recycled by endocytosis)
a drug might:
increase leakage of neurotransmitter from a vesicle
increase transmitter release into cleft
inhibit transmitter synthesis
block transmitter uptake
bind to receptor on post-synaptic membrane to block neurotransmitter (agonist)
inhibit or stimulate secondary messenger in post synaptic cell
glutamate- excitatory or inhibitory?
generates excitatory postsynaptic potential (EPSP)
GABA
Y-aminobutyric acid
generates inhibitory postsynaptic potential (IPSP)
What is needed for action potentials to occur?
Graded potentials to reach above the threshold.
