Anatomy and physiology of synapses

Question 1

Describe electrical synapses

Answer 1

Symmetrical
Can be uni or bidirectional
Separated by gap junctions
Used for reflexes and to synchronise APs

Question 2

Describe gap junctions

Answer 2

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

Question 3

List the intermediate molecules in noradrenaline synthesis

Answer 3

Tyrosine -> DOPA -> Dopamine -> Noradrenaline

Question 4

Why are neurotransmitters stored in vesicles?

Answer 4

To mediate concentration and to protect from degradation

Question 5

What role does synaptogamin play in synaptic release?

Answer 5

It is a calcium sensor

Question 6

What does nitric oxide synthase do?

Answer 6

Facilitates the reaction of L-arginine and oxygen to form NO and L-citrulline using Fe and calcium

Question 7

What are the different types of nitric oxide synthase and where are they found?

Answer 7

Inducible and neuronal are both soluble and found in the cytosol
Endothelial NOS is found on the membrane

Question 8

What are symmetrical synapses?

Answer 8

Synapses where the pre and post-synaptic densities associated with the synaptic junctions are similar
These synapses are inhibitory in function

Question 9

What is the SNARE complex made of?

Answer 9

4 alpha helices contributed by synaptobrevin, syntaxin and SNAP-25 (x2)

Question 10

What are the different ways neurotransmitters are removed from the synaptic cleft? Give an example for each

Answer 10

Reuptake (GABA, glutamate)
Diffusion (GABA, glutamate)
Enzyme breakdown (ACh)

Question 11

What ions are usually involved with EPSPs and IPSPs?

Answer 11

EPSPs - Sodium and calcium flowing inward

IPSPs - Cl- in and K+ out

Question 12

Chemical synapses can be used to modulate other cells, what is this used for?

Answer 12

Signal amplification
Integration of multiple units
Plasticity

Question 13

What is a metabotropic receptor?

Answer 13

A receptor that activates secondary messengers when a ligand binds rather than allowing ions to pass through

Question 14

What are the three main families of ligand gated ion channels?

Answer 14

Cys-loop receptors
Ionotropic glutamate receptors
P2X receptors

Question 15

Give two examples of cys-loop receptors

Answer 15

Nicotinic ACh receptors
Glycine receptors
GABA receptors

Question 16

Why are EPSPs smaller than APs?

Answer 16

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

Question 17

What is the difference between spatial and temporal summation and what factors affect them?

Answer 17

Spatial - Inputs from several different pre-synaptic neurons simultaneously
Affected by length constant

Temporal - Multiple impulses from the same neuron
Affected by time constant

Question 18

What makes a long length constant?

Answer 18

A high membrane resistance and a low axial resistance

Question 19

Define time constant

Answer 19

The time it takes for an EPSP to decrease by 63% of its maximum amplitude

Question 20

What are the two synapses that GABA binds to and what do they do?

Answer 20

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

Question 21

How is GABA transmission terminated?

Answer 21

GABA transporters move GABA into neurons or glial cells where mitochondrial enzymes break it down