Chapter 5 Part II (MT2)

Question 1

Four criteria for identifying neurotransmitters

Answer 1

(1) The transmitter must be synthesized in the neuron or otherwise be present in it

(2) When the neuron is active, the transmitter must be released and produce a response in some target

(3) The same response must be obtained when the transmitter is experimentally placed on the target

(4) A mechanism must exist for removing the transmitter from its site of action after its work is done

Question 2

Putative transmitter

Answer 2

A suspect chemical that has not yet been shown to meet all the criteria (of a neurotransmitter)

Question 3

What chemicals are classified as neurotransmitters?

Answer 3

Chemicals that:

(1) Carry a message from the presynaptic membrane of one neuron to another by influencing postsynaptic membrane voltage

(2) Change the structure of a synapse

(3) Communicate by sending messages in the opposite direction. These retrograde (reverse-direction) messages influence the release or reuptake of transmitters on the presynaptic side

Question 4

Classes of neurotransmitters

Answer 4

(1) Small-molecule transmitters (ACh, DA, Glu)

(2) Peptide transmitters (oxytocin)

(3) Lipid transmitters (endocannabinoids)

(4) Gaseous transmitters (CO, NO)

(5) Ion transmitter (Zn)

Question 5

Small-molecule transmitter

Answer 5

The quick-acting small-molecule transmitters, such as acetylcholine, are typically synthesized from dietary nutrients and packaged ready for use in axon terminals
- diet can influence abundance/activity

• acetylcholine
• amines
• serotonin
• amino acids
• purines

Question 6

What is acetylcholine (small-molecule transmitter) made from?
How is it broken down?

Answer 6

Made from choline (fats in foods, egg yolk, salmon, avocado) and acetate (acidic foods, lemon juice, vinegar)

Broken down by enzyme acetylcholinesterase (AChE)

Question 7

How is amine synthesized?

Answer 7

Tyrosine (precursor, from food like cheese)
[enzyme 1]
L-Dopa
[enzyme 2]
Dopamine
[enzyme 3]
Norepinephrine
[enzyme 4]
Epinephrine

Question 8

Serotonin synthesis and role

Answer 8

Synthesized by amino acid L-tryptophan
Role in mood, aggression, appetite, arousal, respiration, pain

Question 9

Amino acid transmitters (examples)

Answer 9

Glutamate (main excitatory transmitter)
GABA (main inhibitory transmitter)

Question 10

Purine synthesis

Answer 10

Synthesized as nucleotides

Question 11

Neuropeptides (peptide transmitters)

Answer 11

Multifunctional chains of amino acids that act as neurotransmitters
– Synthesized through translation of mRNA from instructions in the neuron’s DNA
– Act slowly and are not replaced quickly

Question 12

Functions of peptide transmitters

Answer 12

Wide range of functions: act as hormones that respond to
stress, enable a mother to bond with her infant, regulate eating and drinking, pleasure and pain, contribute to learning

Question 13

What do opioids (like morphine and heroine) do?

Answer 13

Mimic the actions of natural brain peptides

Question 14

Endocannabinoids (lipid transmitter)

Answer 14

Synthesized at the postsynaptic membrane to act on receptors at the presynaptic membrane
- CB1 receptor is the target of all cannabinoids

Question 15

Anandamide and 2-AG (2-
arachidonoylglycerol)

Answer 15

(Endocannabinoids)
– Both derived from arachidonic acid, an unsaturated fatty acid (found in poultry and eggs)

– Once synthesized, it diffuses across the synaptic cleft and interacts with its receptor on the presynaptic membrane

– Can reduce the amount of small-molecule transmitter being released

Question 16

Gaseous transmitters

Answer 16

Neither stored in synaptic vesicles nor released from them
Synthesized in cell as needed; easily cross the cell membrane

Question 17

Ion transmitters

Answer 17

Actively transported, packaged into vesicles—usually with another transmitter like glutamate—and released into the synaptic cleft

Question 18

Two classes of neurotransmitter receptors

Answer 18

Ionotropic receptor
Metabotropic receptor

Question 19

Ionotropic receptor

Answer 19

Binding site (for neurotransmitter) and pore/channel (for ion) which either opens or closes when the neurotransmitter binds

• rapid changes in membrane volatage, and usually excitatory

Question 20

Metabotropic receptor

Answer 20

Lack their own pore for ions, so they indirectly produce changes in nearby ion channels or in the cell’s metabolic activity

• slower, longer-lasting, and widespread effects

Question 21

What is a metabotropic receptor linked to?

Answer 21

A G protein, which can affect other receptors or act with second messengers to affect other cellular processes

Question 22

What happens to a G protein (guanyl nucleotide-binding protein) when a neurotransmitter binds?

Answer 22

3 subunits of G protein = alpha, beta, and gamma
The alpha subunit detaches

Subunit = a protein that assembles with other proteins

Question 23

Second messenger

Answer 23

Chemical that initiates a biochemical process when activated

Question 24

What can a second messenger do?

Answer 24

(1) Bind to a channel & alter ion flow

(2) Form new ion channels

(3) Bind to DNA to alter protein production

Question 25

Can many transmitters coexist in one synapse?

Answer 25

Yes, more than one type of transmitter is packaged in a single vesicle

Question 26

SNS neurotransmission

Answer 26

Motor (cholinergic) neurons send axons to body
- ACh is main neurotransmitter
- transmitter activated ionotropic channel = nicotine acetylcholine receptor (nAChr)

Question 27

ANS neurotransmission

Answer 27

CNS neurons synapse with parasympathetic neurons
- ACh receptors on the heart are inhibitory
- ACh receptors on the gut are excitatory

CNS neurons synapse with sympathetic neurons
- NE receptors on the heart are excitatory
- NE receptors on the gut are inhibitory

Question 28

ENS neurotransmission

Answer 28

Can act without input from CNS – “the second brain”
Sensory neurons detect mechanical and chemical conditions in GI system
Motor neurons control internal muscles for mixing intestinal
contents & secreting digestive enzymes

Question 29

CNS activating systems

Answer 29

Cholinergic system
Dopaminergic system
Noradrenergic system
Serotonergic system