basics of neurotransmitter

 INTRODUCTION 

Neurotransmitters are chemical substance that acts as a mediator for impulse transmission from one neuron to the other. 

FUN FACT: they were found by otto Loewi while experimenting on the vagus nerve of frog heart kept in saline solution

• Proteins needed for the synthesis of neurotransmitter are found in the cell body and are transferred through axoplasmic flow

• Neurotransmitters are capable of acting on multiple neurons 

• Neurotransmitters and the enzyme required for their synthesis are identified by immunohistochemistry and hybridization histochemistry

Neurotransmitters are classified based on chemical nature and function

TYPES OF NEUROTRANSMITTER

As mentioned before they are classified under two categories 

1. Based on the chemical nature

2. Based on function 

BASED ON THE CHEMICAL NATURE

1. THE AMINES

1. Involved in fast synaptic transmission 

2. They are both inhibitory and excitatory in nature

3. eg :

1. GABA

2. Glycine 

3. Glutamate

4. aspartate

MNEMONICS: google good girl audacity

2. AMINES

1. Involved in slow synaptic transmission

2. Both inhibitory and excitatory nature

3. Eg

1. Adrenaline

2. Noradrenaline

3. Dopamine

4. Serotonin

5. histamine

3. OTHER

1. Acetylcholine

2. Nitric  oxide

DEPENDING ON FUNCTION

EXCITATORY NEUROTRANSMITTER

• Allows the conduction of neurotransmitter from presynaptic to the postsynaptic membrane

• It doesn’t directly act on the postsynaptic membrane

• it causes slight depolarization by the opening of sodium channels in the postsynaptic membrane and the influx of sodium ions from ECF.

•  This slight depolarization is called excitatory postsynaptic potential (EPSP). 

• Epsp in turn stimulates the postsynaptic neuron

• Eg:

• Glutamate 

• Aspartate

• Noradrenaline 

• Histamine

• Nitric oxide 

• Acetylcholine

INHIBITORY NEUROTRANSMITTER

• Inhibits the conduction of impulse from the presynaptic neuron to the postsynaptic neuron

• At release from the presynaptic membrane, it causes opening of potassium channels in the postsynaptic membrane and efflux of potassium ions

• This leads to hyperpolarization, which is called the inhibitory postsynaptic potential (IPSP)

• When IPSP is developed, the action potential is not generated in the postsynaptic neuron

• Eg:

• GABA 

• Noradrenaline 

• Adrenaline

• Dopamine 

• Serotonin

MECHANISM OF ACTION OF NEUROTRANSMITTER

PRESYNAPTIC

• Neurotransmitter gets transported from cell body to axon through axoplasmic movement

• They get stored in vesicles in the axon terminal

 

SYNAPTIC

• Neurotransmitter vesicles release transmitter in the synaptic cleft 

• The neurotransmitter binds to specific receptors on pot synaptic membrane

• Receptors are G proteins, protein kinase or ligand-gated receptors

INACTIVATION OF NEUROTRANSMITTERS 

After the execution of the action, the neurotransmitter is inactivated by four different mechanisms: 

1. It diffuses out of the synaptic cleft to the area where it has no action.

 2. It is destroyed or disintegrated by specific enzymes.

 3. It is engulfed and removed by astrocytes (macrophages) 

4. It is removed through fibres for reuptake into the axon terminal.

REUPTAKE OF NEUROTRANSMITTER 

Reuptake is a process by which the neurotransmitter is taken back from the synaptic cleft into the axon terminal after execution of its action. 

Norepinephrine transporter transports norepinephrine from synaptic cleft to presynaptic terminal. part of norepinephrine entering the terminal is transported into the vesicle by vesicular monoamine transporter (VMAT)

Transporters are present at the synapse for the reuptake of neurotransmitters