Neuronal Signaling (3)

Question 1

What is the main purpose of synaptic transmission?

Answer 1

To allow neurons to communicate with other cells by converting electrical signals (APs) into chemical signals (neurotransmitters) that affect postsynaptic cells.

Question 2

What are the five key aspects of synaptic transmission?

Answer 2

1. Structure of synapses
2. Synthesis, packaging, and transport of neurotransmitters
3. Release of neurotransmitters
4. Activation of receptors by neurotransmitters
5. Reuptake, enzymatic degradation, and recycling of neurotransmitters.

Question 3

What is an axodendritic synapse?

Answer 3

A synapse where an axon terminal button connects to a dendrite of another neuron, often on dendritic spines.

Question 4

What is an axosomatic synapse?

Answer 4

A synapse where an axon terminal button connects directly to the soma (cell body) of a neuron.

Question 5

What is a tripartite synapse?

Answer 5

A synapse involving two neurons and an astroglial cell, where all three cells communicate via synaptic transmission.

Question 6

What is a dendrodendritic synapse?

Answer 6

A synapse between dendrites, capable of bidirectional transmission.

Question 7

What is an axoaxonic synapse?

Answer 7

A synapse on or near a terminal button that can mediate presynaptic facilitation or inhibition, selectively influencing one synapse rather than the entire neuron.

Question 8

What is an axomyelenic synapse?

Answer 8

A synapse where an axon connects to the myelin sheath of an oligodendrocyte, allowing neuron–glia communication.

Question 9

What is the difference between directed and nondirected synapses?

Answer 9

• Directed synapses: Release and reception sites are close together.

Nondirected synapses: Neurotransmitters are released at a distance, often from varicosities, dispersing widely.

Question 10

What are ‘string-of-beads’ synapses?

Answer 10

A type of nondirected synapse where neurotransmitters are released from multiple swellings (varicosities) along an axon, dispersing to surrounding targets.

Question 11

What are the five main aspects of synaptic transmission?

Answer 11

1. Structure of synapses
2. Synthesis, packaging, and transport of neurotransmitter molecules
3. Release of neurotransmitter molecules
4. Activation of receptors by neurotransmitter molecules
5. Reuptake, enzymatic degradation, and recycling of neurotransmitter molecules

Question 12

What is an axodendritic synapse?

Answer 12

A synapse where an axon terminal button synapses onto a dendrite, often on dendritic spines, forming part of a tripartite synapse with an astrocyte.

Question 13

What is an axosomatic synapse?

Answer 13

A synapse where an axon terminal button synapses directly on a soma (cell body) of a neuron.

Question 14

What is a dendrodendritic synapse?

Answer 14

A synapse between dendrites, capable of bidirectional transmission.

Question 15

What is an axoaxonic synapse?

Answer 15

A synapse where an axon synapses on another axon’s terminal button, allowing presynaptic facilitation or inhibition of that synapse.

Question 16

What is an axomyelenic synapse?

Answer 16

A synapse where an axon synapses on the myelin sheath of an oligodendrocyte, representing neuron–glia communication.

Question 17

What are directed vs nondirected synapses?

Answer 17

Directed: neurotransmitter release site close to receptor site (common).
Nondirected: neurotransmitter released from varicosities along axon branches, affecting multiple targets (string-of-beads synapses).

Question 18

What are the two main categories of neurotransmitter molecules?

Answer 18

1. Small-molecule neurotransmitters
2. Large neurotransmitters (neuropeptides)

Question 19

How are small-molecule neurotransmitters synthesized and packaged?

Answer 19

Synthesized in the terminal button cytoplasm, packaged into vesicles by the Golgi complex, stored near the presynaptic membrane.

Question 20

How are neuropeptides synthesized and transported?

Answer 20

Assembled in the cell body on ribosomes, packaged by Golgi complex, transported along microtubules to terminal buttons (~40 cm/day). Vesicles are larger and less concentrated near the presynaptic membrane.

Question 21

What is coexistence in neurotransmission?

Answer 21

Many neurons contain and release two or more neurotransmitters, such as a neuropeptide and a small-molecule neurotransmitter, or multiple small-molecule neurotransmitters.

Question 22

How does exocytosis release neurotransmitters?

Answer 22

APs trigger Ca²⁺ influx via voltage-gated channels → vesicles fuse with presynaptic membrane → neurotransmitters released into synaptic cleft.

Question 23

How do small-molecule vs neuropeptide neurotransmitters differ in release?

Answer 23

Small-molecule: released in pulses with each AP.
Neuropeptides: released gradually in response to general Ca²⁺ increases.

Question 24

What is a ligand in synaptic transmission?

Answer 24

A molecule that binds to a receptor; neurotransmitters act as ligands for their specific receptors.

Question 25

What is the difference between ionotropic and metabotropic receptors?

Answer 25

Ionotropic: ligand-gated ion channels → rapid, brief postsynaptic potentials. Metabotropic: coupled to G-proteins → slower, longer-lasting, diffuse effects through second messengers.

Question 26

What are autoreceptors?

Answer 26

Metabotropic receptors on presynaptic membranes that monitor neurotransmitter levels and adjust release accordingly.

Question 27

General functional differences between small-molecule and peptide neurotransmitters?

Answer 27

Small-molecule: rapid, brief, directed signals. Neuropeptides: slow, diffuse, long-lasting signals via metabotropic receptors.

Question 28

How do metabotropic receptors work?

Answer 28

Neurotransmitter binds → G-protein subunit detaches → either opens ion channel or triggers second messenger synthesis → modulates neuronal activity.