neurotransmission

What is a neurotransmitter?

A chemical messenger that transmits signals across a synapse from one neuron to another, a muscle cell, or a gland.

How are neurotransmitters released into the synapse?

Action potential arrival leads to depolarization that opens voltage-gated calcium channels, allowing calcium to enter the presynaptic terminal, facilitating docking and fusion of synaptic vesicles.

What triggers the release of small neurotransmitters in the synapse?

Small neurotransmitters are predocked close to the presynaptic membrane for rapid release through exocytosis.

What is the role of voltage-gated calcium channels in neurotransmitter release?

They allow calcium to enter the presynaptic terminal, triggering the SNARE complex to mediate vesicle fusion and neurotransmitter release.

What are the effects of neurotransmitter release on the postsynaptic membrane?

They bind to receptors, causing either excitatory postsynaptic potential (EPSP) or inhibitory postsynaptic potential (IPSP).

What is an excitatory postsynaptic potential (EPSP)?

A change in the postsynaptic membrane potential that increases the likelihood of an action potential, typically involving sodium influx.

What is an inhibitory postsynaptic potential (IPSP)?

A change in the postsynaptic membrane potential that decreases the likelihood of an action potential, typically involving chloride influx or potassium efflux.

What happens to neurotransmitters after they bind to a receptor?

They can be enzymatically degraded, reabsorbed by the presynaptic terminal via reuptake, or diffuse away from the synaptic cleft.

What is the significance of reuptake in neurotransmitter action?

It allows neurotransmitters to be transported back into the presynaptic terminal for reuse, maintaining their availability.

What are the conditions for a substance to be classified as a neurotransmitter?

It must be synthesized and stored in presynaptic neurons, released upon stimulation, and elicit a response at the postsynaptic receptor.

What are ionotropic receptors?

Ligand-gated ion channels that directly alter membrane potential, providing fast and short-lasting effects.

What are metabotropic receptors?

G-protein-coupled receptors that initiate intracellular signaling cascades, leading to slower but longer-lasting effects.

What is the difference between EPSP and IPSP events?

EPSP results from opening Na⁺ or Ca²⁺ channels causing depolarization, while IPSP results from opening Cl⁻ or K⁺ channels causing hyperpolarization.

How is acetylcholine degraded?

Acetylcholine is broken down by the enzyme acetylcholinesterase.

How are serotonin, dopamine, and norepinephrine reabsorbed?

They are reabsorbed by specific transport proteins, such as SERT for serotonin, DAT for dopamine, and NET for norepinephrine.

What is the role of neuropeptides in neurotransmission?

Neuropeptides are synthesized from larger precursors in the cell body and require prolonged calcium signaling for release.

What distinguishes small neurotransmitters from neuropeptides?

Small neurotransmitters are released rapidly with low-frequency stimulation, while neuropeptides require higher calcium levels and higher-frequency stimulation.