Difference Between Inhibitory and Excitatory

Inhibitory vs Excitatory

Ever wonder why we act and react differently to various stimuli? Ever asked about why drugs have certain effects on our bodies; some can suppress certain emotions while others can enhance or stimulate?

The human body is composed of various elements that react differently to various stimuli through the nervous system. The nervous system is composed of the spinal cord, the brain, the peripheral ganglia, and neurons.

Neurons or neurotransmitters are nerve cells that process and transmit information through electrical and chemical signals. There are several types of neurons; one type of which are sensory neurons which respond to touch, light, sound, and other stimuli and send signals to the spinal cord and the brain. Motor neurons then receive signals from the brain and spinal cord and cause muscles to contract and affect the glands. They connect to each other and form networks and communicate through synapses which are contained in the brain.

Synapses are junctions that allow a neuron to electrically or chemically transmit a signal to another cell. Synapses can either be excitatory or inhibitory. Inhibitory synapses decrease the likelihood of the firing action potential of a cell while excitatory synapses increase its likelihood. Excitatory synapses cause a positive action potential in neurons and cells.

For example, in the neurotransmitter Acetylcholine (Ach), its binding to receptors opens up sodium channels and allows an influx of Na+ ions and reduces membrane potential which is referred to as Excitatory Postsynaptic potential(EPSP). An action potential is generated when the polarization of the postsynaptic membrane reaches threshold.

ACh acts on nicotinic receptors which can be found at the neuromuscular junction of skeletal muscles, the parasympathetic nervous system, and the brain. It also acts on muscarinic receptors found at neuromuscular junctions of the smooth muscles, glands, and the sympathetic nervous system.

Inhibitory synapses, on the other hand, cause the neurotransmitters in the postsynaptic membrane to depolarize. An example is the neurotransmitter Gamma Aminobutyric Acid (GABA). The binding of GABA to receptors increases the flow of chloride (CI-) ions in the postsynaptic cells raising its membrane potential and inhibiting it. The binding of GABA to receptors activates a second messenger opening potassium channels.

These bindings result in the increase of membrane potential which is called Inhibitory Postsynaptic Potential (IPSP) which counteracts the excitatory signals. Drugs such as Phenobarbital, Valium, Librium, and other sedatives bind themselves to GABA receptors and enhance its inhibitory effect on the Central Nervous System.

Amino acid such as Glutamic acid is used at excitatory synapses in the Central Nervous System and is helpful in long term potentiation or memory. Serotonin and histamine also stimulate intestinal peristalsis. Neurotransmitters react differently to receptors in different areas of the brain. So while it can cause an excitatory effect in one area, it can cause an inhibitory effect in another.

Summary:

1. Inhibitory synapses decrease the likelihood of the firing action potential of a cell while
excitatory synapses increase its likelihood.
2. Excitatory synapses polarize neurotransmitters in the postsynaptic membrane while
inhibitory synapses depolarize them.
3. Excitatory synapses stimulate neurotransmitters while inhibitory synapses inhibit them.

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