Neurotransmitters: Types, Fibers, Receptors, and Termination

Q&A flashcards reviewing neurotransmitter classes, cholinergic vs. adrenergic systems, receptor types, and mechanisms of neurotransmitter termination.

What are three examples of amino-acid neurotransmitters that act as the amino acid itself?

GABA, glutamate, and aspartate.

How do amino-acid neurotransmitters differ from amine-based neurotransmitters?

Amino-acid neurotransmitters are the amino acid alone, whereas amine-based neurotransmitters are built from an amino-acid backbone with additional chemical groups.

Serotonin is synthesized from which amino acid?

Tryptophan.

Which three neurotransmitters are collectively called catecholamines?

Dopamine, norepinephrine, and epinephrine.

The catecholamines are derived from which amino-acid precursor?

Tyrosine.

Name two purine molecules that can function as neurotransmitters.

Adenosine triphosphate (ATP) and adenosine monophosphate (AMP).

Give two gaseous neurotransmitters released by neurons.

Nitric oxide (NO) and carbon monoxide (CO).

A neuron whose axon releases acetylcholine is called what type of fiber?

A cholinergic fiber.

What type of receptors bind acetylcholine?

Cholinergic receptors.

On the heart, binding of acetylcholine to muscarinic receptors has what effect on heart rate?

It lowers or diminishes heart rate.

Which two major classes of acetylcholine receptors exist, and what signaling mechanism is each associated with?

Nicotinic receptors—ligand-gated ion channels; Muscarinic receptors—G-protein-coupled receptors.

A neuron that releases norepinephrine (and sometimes epinephrine) is called what?

An adrenergic fiber.

In the United Kingdom, epinephrine is commonly known by what name?

Adrenaline.

What term is used for receptors that bind norepinephrine or epinephrine?

Adrenergic receptors.

Which subtypes of adrenergic receptors exist and what signaling family do they belong to?

Alpha and beta receptors; all are G-protein-coupled receptors.

Binding of norepinephrine to adrenergic receptors on the heart produces what two main effects?

Increases heart rate and increases force of ventricular contraction.

Can a neuron have cholinergic receptors on its dendrites yet release norepinephrine from its axon?

Yes; receptor type on dendrites is independent of the neurotransmitter released by the axon.

Why must neurotransmitters be terminated after release?

To prevent continuous activation or inhibition of the postsynaptic cell and allow on/off signaling.

Which enzyme rapidly terminates acetylcholine in the synaptic cleft?

Acetylcholinesterase (also called cholinesterase).

Into what two molecules does acetylcholinesterase split acetylcholine?

Choline and acetyl coenzyme A.

How is choline returned to the presynaptic neuron after acetylcholine breakdown?

Via a sodium-dependent symporter that co-transports Na+ down its gradient with choline against its gradient.

What does the abbreviation SSRI stand for?

Selective Serotonin Reuptake Inhibitor.

Name three common SSRI medications.

Prozac, Paxil, and Zoloft.

What is the primary pharmacological effect of SSRIs at the synapse?

They block the reuptake of serotonin, keeping it in the synaptic cleft longer to enhance signaling.

Which classic inhibitory amino-acid neurotransmitter works by opening chloride channels to depress neuronal activity?

GABA.