Neuronal signaling (4)

Question 1

Why must neurotransmitters be removed from the synapse?

Answer 1

If neurotransmitters remain active, they could clog the synapse and prevent new signals from being transmitted.

Question 2

What are the two main mechanisms that terminate synaptic messages?

Answer 2

1. Reuptake by transporters
2. Enzymatic degradation

Question 3

What is reuptake?

Answer 3

The process where neurotransmitters are drawn back into the presynaptic terminal by transporter mechanisms after being released.

Question 4

What is enzymatic degradation in the synapse?

Answer 4

The breakdown of neurotransmitters by enzymes in the synapse; e.g., acetylcholine is broken down by acetylcholinesterase.

Question 5

What happens to neurotransmitter molecules and vesicles after deactivation?

Answer 5

They are recycled: neurotransmitters or their breakdown products are drawn back into the terminal, and vesicles are reused to create new vesicles.

Question 6

What roles do glial cells play in synaptic transmission?

Answer 6

Glial cells, especially astrocytes, release chemical transmitters, contain neurotransmitter receptors, conduct signals, and influence neuron-to-neuron synaptic transmission.

Question 7

What are gap junctions?

Answer 7

Narrow spaces between adjacent cells bridged by connexins, connecting the cytoplasm of two cells and allowing electrical signals and small molecules to pass directly.

Question 8

What is the function of gap junctions in the brain?

Answer 8

They synchronize the activity of like cells (e.g., inhibitory interneurons or astrocytes) and enable rapid electrical communication via electrical synapses.

Question 9

Where do gap junctions occur on astrocytes?

Answer 9

At the end of astrocytic processes, where they contact adjacent astrocytes’ processes.

Question 10

Why are glial cells and gap junctions important in modern neuroscience?

Answer 10

They play major roles in brain function, including synaptic coordination, rapid communication, and regulation of neuronal activity, challenging the traditional neuron-centric view.

Question 11

What are the four major classes of neurotransmitters?

Answer 11

1. Amino acids (small-molecule)
2. Monoamines (small-molecule)
3. Acetylcholine (small-molecule, in its own class)
4. Neuropeptides (large-molecule)

Unconventional small-molecule neurotransmitters are sometimes treated separately.

Question 12

Name the four most widely studied amino acid neurotransmitters.

Answer 12

Glutamate, aspartate, glycine, GABA

Question 13

Which amino acid neurotransmitter is the most prevalent excitatory neurotransmitter in the mammalian CNS?

Answer 13

Glutamate

Question 14

Which amino acid neurotransmitter is the most prevalent inhibitory neurotransmitter?

Answer 14

GABA (but it can be excitatory at some synapses)

Question 15

What are monoamine neurotransmitters, and how are they synthesized?

Answer 15

Small-molecule neurotransmitters synthesized from a single amino acid. They include dopamine, norepinephrine, epinephrine (catecholamines from tyrosine) and serotonin (indolamine from tryptophan).

Question 16

What are the differences between catecholamines and indolamines?

Answer 16

Catecholamines (dopamine, norepinephrine, epinephrine) are synthesized from tyrosine. Indolamines (serotonin) are synthesized from tryptophan.

Question 17

What neurons are called noradrenergic, adrenergic, and cholinergic?

Answer 17

• Noradrenergic: release norepinephrine
• Adrenergic: release epinephrine
• Cholinergic: release acetylcholine

Question 18

How is acetylcholine synthesized and deactivated?

Answer 18

Synthesized by adding an acetyl group to choline. Deactivated by acetylcholinesterase.

Question 19

What are unconventional neurotransmitters?

Answer 19

Neurotransmitters with unusual mechanisms, such as soluble-gas neurotransmitters (nitric oxide, carbon monoxide) and endocannabinoids (like anandamide).

Question 20

How do soluble-gas neurotransmitters function?

Answer 20

Produced in the cytoplasm, diffuse through cell membranes, act quickly to stimulate second messengers, then are rapidly deactivated. They can act retrogradely from postsynaptic to presynaptic neurons.

Question 21

What are endocannabinoids, and how are they released?

Answer 21

Neurotransmitters similar to THC, synthesized from fatty compounds in the cell membrane, released from dendrites and cell bodies, mainly inhibiting presynaptic neurons.

Question 22

How are neuropeptides categorized?

Answer 22

1. Pituitary peptides (first identified as pituitary hormones)
2. Hypothalamic peptides (first identified as hypothalamus hormones)
3. Brain–gut peptides (first discovered in the gut)
4. Opioid peptides (similar to opium compounds)
5. Miscellaneous peptides (not in other categories)

Question 23

What is the general function difference between small-molecule neurotransmitters and neuropeptides?

Answer 23

• Small-molecule neurotransmitters: rapid, brief, localized signals
• Neuropeptides: slow, long-lasting, diffuse signals

Question 24

What are the two fundamental effects drugs can have on synaptic transmission?

Answer 24

• Agonists: facilitate the effects of a neurotransmitter
• Antagonists: inhibit the effects of a neurotransmitter

Question 25

What are the seven general steps common to most neurotransmitters in synaptic transmission?

Answer 25

1. Synthesis of the neurotransmitter 2. Storage in vesicles 3. Breakdown of leaked neurotransmitter in the cytoplasm 4. Exocytosis (release) 5. Inhibitory feedback via autoreceptors 6. Activation of postsynaptic receptors 7. Deactivation

Question 26

How do agonistic and antagonistic drugs influence synaptic transmission?

Answer 26

- Agonists can bind to and activate postsynaptic receptors. - Antagonists (receptor blockers) bind to postsynaptic receptors without activating them, blocking the normal neurotransmitter.

Question 27

What is atropine, and how does it act as a drug?

Answer 27

- Main active ingredient of belladonna - Receptor blocker (antagonist) of muscarinic receptors - Pupillary dilation via ANS; high doses disrupt memory via CNS

Question 28

What is curare, and how does it affect synaptic transmission?

Answer 28

- Nicotinic receptor antagonist - Blocks transmission at neuromuscular junctions, causing paralysis - Used in small doses in surgery to prevent muscle contraction

Question 29

What is Botox, and how does it affect neurotransmission?

Answer 29

- Nicotinic antagonist - Blocks release of acetylcholine at neuromuscular junctions - Toxic in large doses, but used medically (tremor reduction) and cosmetically (wrinkle reduction) in small doses