Neuronal Communication and Synaptic Mechanisms

Vocabulary terms covering neuronal communication, including synapse structures, receptor types, and mechanisms of neurotransmission as described in the lecture notes.

Synapsis

The method of intraneuronal communication involving the release of neurotransmitters from presynaptic terminal buttons to postsynaptic receptors.

Chemical Synapses

The most common and abundant type of synapse, based on the release of neurotransmitters that activate specific receptor molecules to alter membrane potential.

Electrical Synapses

Uncommon, bidirectional synapses that use gap junctions to directly connect the cytoplasm of two neurons for rapid and coordinated responses.

Gap Junctions

Communicating transmembrane channels that directly transmit action potentials between neurons in electrical synapses.

Synaptic Vesicles

Small membrane-bound sacs containing neurotransmitters and neuromodulators; some are produced in the soma by the Golgi apparatus.

Neuromodulators

Chemicals stored in synaptic vesicles that adjust the strength or properties of the synapse rather than directly exciting or inhibiting the postsynaptic neuron.

Anterograde Transport

The process of transporting synaptic vesicles from the cell body (soma) down the axon to the presynaptic terminal using kinesin motors.

Exocytosis

The energy-dependent process where vesicles move, fuse with the presynaptic membrane at the active zone, and release neurotransmitters into the synaptic cleft.

Synaptic Cleft

The space between the pre- and postsynaptic elements, measuring $20-50\,nm$, composed of extracellular fluid.

Postsynaptic Density

A protein-rich layer attached firmly to the postsynaptic membrane containing receptors and several specialized proteins.

Ligand

Any molecule, such as a neurotransmitter or neuromodulator, that binds specifically to a receptor to produce a specific effect.

Autoreceptors

Presynaptic metabotropic receptors that regulate the synthesis and release of neurotransmitters from the neuron that releases them, having no effect on ion channels.

Ionotropic Receptors

Receptors that function as ion channels, opening immediately (within approximately $10\,ms$) upon neurotransmitter binding to allow fast, short-duration ion flow.

Metabotropic Receptors

Common modulatory receptors that initiate metabolic reactions via G-proteins and second messengers like $\text{cAMP}$, resulting in slow, long-lasting, and diffuse effects.

Axodendritic

A type of synapse forming a connection between the presynaptic neuron's terminal buttons and the postsynaptic neuron's dendrites.

Axosomatic

A type of synapse forming a connection between the presynaptic neuron's terminal buttons and the postsynaptic neuron's soma.

Axoaxonic Synapse

A connection between terminal buttons of two neurons that controls $Ca^{2+}$ entry to mediate presynaptic inhibition or presynaptic facilitation.

Dendrodendritic Synapse

A connection between the dendrites of two neurons that acts as local modulators to coordinate activity within groups of nearby neurons.

Directed Synapse

A precise form of communication where neurotransmitters are released directly at the postsynaptic receptor.

Non-directed Synapse

A synapse where the release zone is distant from the receptor, requiring neurotransmitters to diffuse, resulting in diffuse modulation.

Endocytosis

The process of vesicle recycling where excess membrane is pulled back into the neuron to form new vesicles.

Spatial Summation

The additive effect of EPSPs or IPSPs produced when several presynaptic neurons or multiple terminals fire at the same time.

Temporal Summation

The additive effect of multiple EPSPs arriving consecutively in a short time from the same presynaptic terminal.

Reuptake

The energy-requiring process where neurotransmitters are taken back into the presynaptic neuron by special transporter proteins.

Enzymatic Inactivation

The process where neurotransmitters are broken down by enzymes within the synaptic cleft to terminate the postsynaptic potential.