NEUR 0010 - Chapter5 Flashcards
What do electrical synapses do?
Allow direct transfer of ionic current from one cell to the next through gap junctions
Where do electrical synapses occur?
At gap junctions
What is a gap junction?
Six connexins (special proteins) form a connexon, and a connexon from each of two cells combines to form the gap junction
How do electrical synapses differ from most chemical synapses?
They’re bidirectional; current can pass just as well either way
What does it mean for two cells to be electrically coupled?
That they’re connected by gap junctions through which electrical current can pass
What advantages does electrical coupling offer?
Very fast and reliable signal transmission; almost instantaneous
Electrical synapses are very common in which part of the mammalian nervous system?
CNS: in almost every part
What happens when an action potential occurs in the presynaptic neuron of an electrically coupled pair?
A small amount of ionic current flows across the gap junction channels into the postsynaptic neuron, triggering a small postsynaptic potential
What is a PSP?
Postsynaptic potential: induced by the small amount of current that flows from pre to postsynaptic neuron when the presynaptic neuron experiences an action potential
How do PSPs illustrate bidirectionality of electrical synapses?
An action potential in Neuron 1 induces a PSP in Neuron 2, but when Neuron 2 undergoes its own action potential, it also induces a PSP in Neuron 1
What is the connection between PSPs induced by presynaptic neurons and action potentials in the postsynaptic neuron?
The PSP itself probably isn’t big enough to trigger an action potential in the postsynaptic neuron, but the postsynaptic neuron is often receiving a lot of PSPs from multiple presynaptic neurons, and the cumulative effect can trigger the action potential (synaptic integration)
What function makes gap junctions particularly necessary/prevalent?
Needing the neighboring neuron activity to be highly synchronized; very common during early embryonic stages
What is the majority of synaptic transmission in mature human nervous system, electrical or chemical?
Chemical
What separates the pre and post synaptic membranes at chemical synapses?
Synaptic cleft: filled with matrix of fibrous extracellular protein to bind the two membranes together
What are the two kinds of vesicles usually found in the presynaptic neuron at a chemical synapse?
Synaptic vesicles (smaller, carry neurotransmitters) and secretory granules (also called dense-core vesicles; contain soluble protein; appears dark in electron microscope)
What are secretory granules?
The larger counterpart to synaptic vesicles: carry soluble protein; also called dense-cored vesicles
What are membrane differentiations?
Dense accumulation of protein adjacent to and within pre and postsynaptic membranes of chemical synapses
What are the membrane differentiations on the presynaptic side of a chemical synapse?
Active zones: proteins jutting into cytoplasm of terminal, look like pyramids; actual sites of neurotransmitter release
What is the actual site of neurotransmitter release?
The active zones: little pyramids of protein along the terminal membrane; the presynaptic membrane differentiation
What is the membrane differentiation on the postsynaptic side of a chemical synapse?
Postsynaptic density; contains neurotransmitter receptors (convert intercellular chemical signal to intracellular signal)
What is the postsynaptic density?
The membrane differentiation of the postsynaptic membrane; contains neurotransmitter receptors
How does one distinguish the different types of synapse in the CNS?
Based on what part of the neuron is postsynaptic to the axon terminal, and based on whether the pre and postsynaptic membrane differentiations are symmetrical or not
What is an axodendritic synapse?
When the postsynaptic membrane is on a dendrite
What is an axosomatic synapse?
When the postsynaptic membrane is on the cell body