Synapses (chemical and electrical) Flashcards
Give an example of what can occur when there is synaptic dysfunction in the body?
autism
Where were electrical synapses first discovered?
In the cray fish nervous system
What neurones did the cray fish have?
one for stimulation
2 for recording
Is there a big delay between the pre and post synaptic activity in the cray fish?
no there is little delay
Tell me about the structure of an electrical synapse
Whats more common in nervous systems, an electrical or chemical synapse?
chemical
The junctions in electrical synapses consist of what subunits?
What do these assemble to form?
consist of subunits called connexons
These assemble in hexameric complexes surrounding a central pore
What are the different types of connexons and the channel type associated with them?
roughly, whats the size of the synaptic cleft in electrical synapses?
4 nm
Tell me about electrical synapse transmission properties?
- little attenuation (amplitdude recorded is similar in the pre and post synaptic terminal)
- delay is less than 0.1 ms- this is a fast transmission
What do electrical synapses also permit?
give an example for this?
synchronisation of activity.
This occurs amongst populations of neurons to direct rhythmic and coordinated physiological functions
example; brainstem neurons and breathing hypothalamic neurons and hormone secretion has a synchronised output
Whats located in the retina which also provides fast signalling?
gap junctions
Gap junctions also permit the movement of molecules. Give an example of a moleuce and its role within the body
Example: ATP, second messengers
ATP can also be used by the neuron to synthesise cAMP; cAMP can activate enzyme that target ion channels in the plasma membrane and alters their properties
Rectifying gap junctions only allow ions to move in one direction
Can ion channels be Bi-directional ?
yes
Give an example of an ion channel that can’t be bi-directional?
Rectifying
Label the structure of the synaptic cleft
Roughly what size is this synaptic cleft?
This has a rough size of 20 nm
What type of vesicles are small and large molecules transferred in?
small molecules in small clear vesicles
Large molecules in dense core vesicles
Roughly what size are the small molecules found in small vesicles and give some examples ?
Mw is roughly 100
Examples: Ach, Glutamate, GABA, glycine
What is the rough size of molecules in the large vesicles?
What are the molecules called
Give an example
Mw is roughly ≤ 1000
Example: Substance P
Called: Neuropeptides
The corelease of both the small clear and dense vesicle neurotransmitters can occur in what?
The nociceptor
signalling at the chemical synapse is dependent on what?
Calcium
Tell me about the properties of chemical and electrical synapses
What are the advantages of electrical synapses ?
- No synaptic delay
- Allows synchronisation of many cells quickly
- Can transmit metabolic signals between cells
- Enable repaid reflexive coordination
E.g. Escape response in crayfish
Tell me the disadvantages of electrical synapses ?
- In a neuronal circuit 2 classes of signal are required;
1. Excitation
2. Inhibition - At an electrical synapse a presynaptic depolarisation cannot be converted into a postsynaptic hyperpolarisation
- At an electrical synapse the sign of the signal (pre and post) is always the same
