Define neurotransmitter the four main categories and their r

Define neurotransmitter, the four main categories, and their role in cell communication. Discuss one of the following synapse types: excitatory cholinergic, inhibitory GABA-ergic, or excitatory adrenergic. ( 2-3 paragraphs)

Solution

Neurotransmitters are the chemical substances released by the nerve terminals. They bind to the receptors present on the presynaptic or the postsynaptic neurons or the effector organs. Depending upon the type of neurotransmitter and the receptor activated, the cellular response is produced. These are known as “chemically regulated channels.”

If the neurotransmitter is excitatory and causes depolarization of post synaptic membrane, then EPSP (excitatory post synaptic potential) is generated. Or if, the released neurotransmitter is inhibitory and causes hyperpolarisation of post synaptic membrane, then IPSP (inhibitory post synaptic potential) is generated.

In the cholinergic neurons, the neurotransmitter at the ganglia and effector is, acetylcholine. Most of the cholinergic neurons belongs to the parasympathetic nervous system. But the cholinergic neurons innervating the adrenal medulla and sweat glands are under the sympathetic nervous system.

In the adrenergic nervous system, the neurotransmitter at the ganglia is, acetylcholine and the neurotransmitter at the effector organ is adrenaline or noradrenaline. Most of the adrenergic neurons are under sympathetic regulation.

The effect of cholinergic and adrenergic neurons on the digestive system and heart:

Organ

Effect of adrenergic stimulation

Effect of cholinergic stimulation

Heart

Sinoatrial node

Increases heart rate (1 receptors)

Decreases heart rate (muscarinic receptors)

Contractility

Increases (1 receptors)

Decreases (muscarinic receptors)

Gastrointestinal tract

Walls of smooth muscles

Relaxes (2 receptors)

Contracts (muscarinic receptors)

Sphincters

Constriction (1 receptors)

Relaxes (muscarinic receptors)

Gastric secretions

Inhibits (2 receptors)

Stimulation (muscarinic receptors)

Myenteric plexus

Inhibits ( receptors)

The GABA (gamma amino butyric acid) is an inhibitory neurotransmitter. Benzodiazepines (BDZ’s) are the sedative-hypnotics that act through the increased transmission of GABA.

Binding of BDZ’s causes chloride ion influx, which causes hyperpolarization of the cell. So, they produce inhibitory responses, they are mainly used as anxiolytics and sedatives.