synapses Flashcards
What are synapses?
Specialized sites of communication between neurons (or between a neuron and target organ)
Synapses can happen at different locations and are crucial for neural communication.
What are the two main types of synapses?
Electrical and chemical
These types differ in their mechanisms and characteristics.
What defines chemical synapses?
Neurotransmitters (NT) are released from presynaptic neuron + receptors
Chemical synapses are Ca2+-dependent, unidirectional, and slower.
What defines electrical synapses?
Gap junctions as ion channels
Electrical synapses are bidirectional and faster due to direct connections between neurons.
What is a gap junction?
Made of ion channels allowing ions + small signaling molecules to pass
It consists of connexons formed by connexin subunits.
What is a connexon?
6 connexin subunits = 1 connexon
Two connexons form one intercellular channel (gap junction channel).
What are the main features of electrical synapses?
During development, crucial for neural circuit formation
They synchronize action potentials and are involved in processes like hormone secretion.
What is the presynaptic terminal?
Contains active zone with synaptic vesicles ready for exocytosis
This structure is involved in neurotransmitter release.
What is the synaptic cleft?
Extracellular space between presynaptic and postsynaptic neurons
It is where neurotransmitters diffuse after release.
What is the postsynaptic density (PSD)?
Region in plasma membrane of postsynaptic neuron with anchored neurotransmitter receptors
It enhances the efficiency of neurotransmitter binding.
What initiates excitatory or inhibitory postsynaptic currents?
Activation of receptors on the postsynaptic membrane by neurotransmitters
This process occurs after neurotransmitter release.
What is the role of Ca²⁺ in neurotransmitter release?
Ca²⁺ entry through presynaptic voltage-gated channels causes transmitter release
Free Ca²⁺ concentration is typically 10–100 nM at rest.
What happens when an action potential arrives at the presynaptic terminal?
Membrane depolarizes, VGCC opens, Ca²⁺ rushes in
This influx of Ca²⁺ triggers neurotransmitter release into the synapse.
What effect does incubation with Cd have on postsynaptic response?
No postsynaptic response
Cd is a Ca²⁺ channel blocker that prevents neurotransmitter release.
Fill in the blank: Each cell contributes ______ of the ion channel in a gap junction.
½
This forms a complete channel when paired with another cell’s contribution.
