Electrical Synapse

What are electrical synapses made of?

Gap junctions.

What is the structure of gap junctions?

Two closely apposed membranes with ion channels (gap junction channels) made of two connexons, each with six connexins.

What do gap junction channels allow to pass?

Ions and small organic molecules.

What factors open gap junction channels?

1. Cytoplasmic pH,

2. Ca²⁺ levels,

3. voltage,

4. neurotransmitters.

Why do gap junction channels close under high Ca²⁺ or low pH?

To prevent death signals causing apoptosis from spreading from dying cells.

How does current flow in electrical synapses?

Directly through gap junctions, causing instantaneous postsynaptic potentials.

Are electrical synapses bidirectional?

Yes, current flows both ways.

How does the postsynaptic potential compare to the presynaptic in electrical synapses?

Smaller in amplitude but same type (hyper or de)

Where are electrical synapses found?

In neurons and glial cells, more common in early development and glial function in adults.

What are the main connexins in neurons and glia?

Neurons: Cx36, Cx45; Glia: Cx43, Cx30.

How many human genes code for connexins?

21.

What are uses of gap junctions?

Motor coordination,

synaptogenesis,

circadian rhythms,

learning,

memory,

calcium waves in astrocytes.

What conditions will lead to a junction channel opening and a junction channel closing

high calcium conc + low pH = close

low calcium conc + high pH = open