Anatomy and physiology of synapses Flashcards
Describe electrical synapses
Symmetrical
Can be uni or bidirectional
Separated by gap junctions
Used for reflexes and to synchronise APs
Describe gap junctions
Gap junctions provide a low resistance way for ions to pass freely between cells
Each channel is made of two hemi channels, each of which are in turn made of 6 connexin subunits
List the intermediate molecules in noradrenaline synthesis
Tyrosine -> DOPA -> Dopamine -> Noradrenaline
Why are neurotransmitters stored in vesicles?
To mediate concentration and to protect from degradation
What role does synaptogamin play in synaptic release?
It is a calcium sensor
What does nitric oxide synthase do?
Facilitates the reaction of L-arginine and oxygen to form NO and L-citrulline using Fe and calcium
What are the different types of nitric oxide synthase and where are they found?
Inducible and neuronal are both soluble and found in the cytosol
Endothelial NOS is found on the membrane
What are symmetrical synapses?
Synapses where the pre and post-synaptic densities associated with the synaptic junctions are similar
These synapses are inhibitory in function
What is the SNARE complex made of?
4 alpha helices contributed by synaptobrevin, syntaxin and SNAP-25 (x2)
What are the different ways neurotransmitters are removed from the synaptic cleft? Give an example for each
Reuptake (GABA, glutamate)
Diffusion (GABA, glutamate)
Enzyme breakdown (ACh)
What ions are usually involved with EPSPs and IPSPs?
EPSPs - Sodium and calcium flowing inward
IPSPs - Cl- in and K+ out
Chemical synapses can be used to modulate other cells, what is this used for?
Signal amplification
Integration of multiple units
Plasticity
What is a metabotropic receptor?
A receptor that activates secondary messengers when a ligand binds rather than allowing ions to pass through
What are the three main families of ligand gated ion channels?
Cys-loop receptors
Ionotropic glutamate receptors
P2X receptors
Give two examples of cys-loop receptors
Nicotinic ACh receptors
Glycine receptors
GABA receptors
Why are EPSPs smaller than APs?
There are fewer synaptic ligand gated ions than axonal VD sodium channels
Ligand gated ions aren’t specific to sodium so potassium can also flow out
What is the difference between spatial and temporal summation and what factors affect them?
Spatial - Inputs from several different pre-synaptic neurons simultaneously
Affected by length constant
Temporal - Multiple impulses from the same neuron
Affected by time constant
What makes a long length constant?
A high membrane resistance and a low axial resistance
Define time constant
The time it takes for an EPSP to decrease by 63% of its maximum amplitude
What are the two synapses that GABA binds to and what do they do?
GABA-a receptors are ionotropic and binding causes the opening of an associated ion channel that allows Cl- to diffuse into the neuron
GABA-b receptors are metabotropic (GPCR coupled) and binding causes the activation of potassium channels causing potassium to leave the neuron
How is GABA transmission terminated?
GABA transporters move GABA into neurons or glial cells where mitochondrial enzymes break it down
