tema 15

Question 1

what is an electrical synapse

Answer 1

They are rare.
A direct current flow is established from the presynaptic neuron to the postsynaptic neuron

There are special ion channels; intimate junction cells or gap junctions, that serve as a bridge to the cytoplasm of the two cells.

These channels have low resistance and high conductance: they provide an instantaneous transmission of the signal.

Question 2

how are the channels of electrical signals formed?

Answer 2

CONNEXON: Proteic hemichannel (channel= 2 connexons)
* CONNEXINS: proteins integrated in the membrane (1 connexon = 6 connexins)
* ELECTRICAL CONNECTIONS (gap junction channel)
20 nm → 3,5 nm

Question 3

Functioning of chemical synapse

Answer 3

The movement of small ions makes the two cells have the same potential.
A depolarization in the presynaptic neuron will be conducted directly to the postsynaptic neuron.

Excitable cells allow the diffusion of electrical signals with speed and synchronization (electrical synapses), as if the cells formed an electrical syncytium.

Question 4

how are the electrical signals controlled

Answer 4

The gap junctions are adjustable, since they can change the diameter of the channel:
- by changes in osmolarity
– by increase of H + or intracellular Ca2 +
– in response to some hormones:
* glucagon in the liver.
* dopamine in the retina.

Question 5

electrical synapse characteristics (summary)

Answer 5

• 3.5 nm pre-post distance
• Cytoplasmic continuity
• Bidirectional conduction possible
• Independent of Ca2 +
• Very fast
• Ion currents