2

Question 1

They are endogenous substances responsible for
signal transmission between individual neurons
across a synapse .

Answer 1

NEUROTRANSMITTERS

Question 2

Neurotransmitters are stored in

Answer 2

synaptic vesicles
beneath the membrane on the presynaptic side of
a synapse.

Question 3

Chemical Classification of Neurotransmitters:

Answer 3

1. Acetylcholine
2. Biogenic Amines,formed by decarboxylation of amino acids as:
   - Catecholamines: Dopamine, epinephrine & norepinephrine.
   - Indolamines.
   - Serotonin (5-Hydroxytryptamine or 5-HT).
   - Histamine.
   - GABA (Gamma-aminobutyric acid).
   (All of them act as both neurotransmitters & as hormones or mediators).
3. Amino Acids:
   - Glycine.
   - Aspartate.
   - Glutamate
4. Purine derivatives: ATP, ADP, AMP & adenosine.
5. Neuropeptides:
   - Substance P.
   - Endorphins, enkephalins & others.
   - Somatostatin, gastrin, cholecystokinin, oxytocin, vasopressin.
   - Leutinizing hormone releasing hormone (LHRH) 6. Others.

Question 4

Functional Classification of Neurotransmitters

Answer 4

excitatory: glutamate, Histamine, norepinephrine, Aspartate

inhibitory: GABA, Glycine, enkephalins

inhibitory, excitatory: Acetylcholine, Serotonin, Dopamine

Question 5

Biosynthesis of Catecholamines

Sites of synthesis

Answer 5

Sites of synthesis ; adrenal medulla & CNS from tyrosine as follows:
1. Hydroxylation of the aromatic ring → DOPA (3,4 dihydroxyphenyl-alanine) by tyrosine hydroxylase in the presence of the coenzyme tetrahydro-biopterin (THB).
2. Decarboxylation of DOPA → Dopamine (important transmitter in the CNS).
3. In adrenal gland and adrenergic neurons, hydroxylation of dopamine → norepinephrine, in presence of vitamin-C as a coenzyme.
4. Finally, N-methylation of norepinephrine → epinephrine. The methyl donor is S-adenosyl-methionine (SAM).

Question 6

ACETYLCHOLINE

Released at

Answer 6

Released at neuromuscular junctions and some neurons of ANS

Question 7

ACETYLCHOLINE Degraded by the enzyme

Answer 7

Degraded by the enzyme acetylcholinesterase (AChE).

Question 8

ACETYLCHOLINE ACh is synthesized from

Answer 8

choline & Acetyl-CoA by the enzyme Choline
Acetyl Transferase (CAT).

Question 9

• Free choline from

Answer 9

• Free choline circulating in blood crosses BBB and is taken up by cholinergic nerve terminals , mainly by a high-affinity choline uptake (HACU) system, which is thought to act as a rate-limiting step in the production of Ach.

About 35-50% of the choline released from the breakdown of ACh in the synaptic cleft is taken up again by the presynaptic neuron .

Question 10

Glutamate (Glu) controls ………&……..
. • GABA is involved in regulating ………..&…….&

Answer 10

memory & emotion

anxiety & may be related to eating or
sleep disorders.

Question 11

Glutamate, Glutamine & GABA

Answer 11

GABA neurons & glutamate neurons initially hydrolyze glutamine to glutamate (Glu) by glutaminase enzyme.

Glutamate neurons store this Glu in vesicles and release it when stimulated

GABA neurons continue the degradation process by using glutamate decarboxylase to convert glutamate to the transmitter GABA.

Question 12

GABA Shunt is a Characteristic of the CNS:

Answer 12

GABA + ⍺-Ketoglutarate=succinat semi aldehyde + Glutamate

Question 13

Biogenic Amines, formed by

Answer 13

decarboxylation of amino acids

Question 14

Dopamine is involved in

Answer 14

Dopamine is involved in addiction pathway.