Download Chemistry of Neurotransmitters

Chemistry of Neurotransmitters
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Learning Objectives
Define neurotransmitters
Enlist the neurotransmitter of locomotor system. Give their
structure.
Enlist different neurotransmitter receptors
Give the synthesis of these neurotransmitters.
Justify that acetylcholine has sympathetic & parasympathetic
functions.
Explain the mechanism of action of acetylcholine in
modulating muscle contraction.
Definition
• Neurotransmitters are substances that are produced by neurons,
stored in the synapses, and released into the synaptic cleft in
response to a stimulus.
• At the postsynaptic membrane, they bind to special receptors
and affect their activity.
Important neurotransmitters
• Neurotransmitters can be classified into several groups according
to their chemical structure.
Types of Receptors
• Like all signaling substances, neurotransmitters act via receptor
proteins. The receptors for neurotransmitters are integrated into
the membrane of the postsynaptic cell, where they trigger ion
inflow or signal transduction processes
• The receptors for neurotransmitters are divided into two large
groups according to the effect produced by binding of the
transmitter
• Two large groups according to their mode of action.
• 1  Ionotropic receptors
• 2  Metabotropic receptors
Ionotropic receptors
• They are ligand-gated ion channels. The receptors for
stimulatory transmitters mediate the inflow of cations (mainly
Na+). When these open after binding of the transmitter, local
depolarization of the postsynaptic membrane occurs.
• By contrast, inhibitory neurotransmitters (GABA and glycine)
allow Cl– to flow in. This increases the membrane’s negative
resting potential and hinders the action of stimulatory
transmitters (hyperpolarization)
Metabotropic receptors
• They are coupled to G proteins, through which they influence the
synthesis of second messengers. Receptors that work with type
Gs proteins increase the cAMP level in the postsynaptic cell
(cAMP), while those that activate Gi proteins reduce it. Via type
Gq proteins,other receptors increase the intracellular Ca2+
concentration.
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Neurotransmitters of Locomotor System
Acetylcholine (ACh) was the neurotransmitter first discovered,
at the beginning of the last century. It binds to two types of
receptor.
The nicotinic ACh receptor responds to the alkaloid nicotine
contained in tobacco this). The nicotinic receptor is ionotropic
The muscarinic ACh receptors are metabotropic
Neurotransmitters of Locomotor System
Acetylcholine, the acetic acid ester of the cationic alcohol
choline acts at neuromuscular junctions, where it triggers muscle
contraction and in certain parts of the brain and in the
autonomous nervous system.
• The muscarinic ACh receptors influence the cAMP level in the
postsynaptic cells
Acetylcholine receptors
Synthesis
• Acetylcholine is synthesized from acetyl-CoA and choline in the
cytoplasm of the presynaptic axon and is stored in synaptic
vesicles, each of which contains around 1000–10 000 ACh
molecules.
• After it is released by exocytosis, the transmitter travels by
diffusion to the receptors on the postsynaptic membrane.
Catalyzed by acetylcholinesterase, hydrolysis of ACh to acetate
and choline immediately starts in the synaptic cleft and within a
few milliseconds, the ACh released has been eliminated again.
The cleavage products choline and acetate are taken up again by
the presynaptic neuron and reused for acetylcholine synthesis.
Thank You