Difference Between Excitatory and Inhibitory Neurotransmitters

Key Difference – Excitatory vs Inhibitory Neurotransmitters
 

Neurotransmitters are chemicals in the brain which transmits signals across a synapse. They are classified into two groups based on their action; these are called excitatory and inhibitory neurotransmitters. The key difference between excitatory and inhibitory neurotransmitters is their function; excitatory neurotransmitters stimulate the brain whereas inhibitory neurotransmitters balance the excessive simulations without stimulating the brain.

CONTENTS
1. Overview and Key Difference
2. What are Neurotransmitters
3. What is Neuron Action Potential
4. What are Excitatory Neurotransmitters
5. What are Inhibitory Neurotransmitters
6. Side by Side Comparison – Excitatory vs Inhibitory Neurotransmitters
7. Summary

What are Neurotransmitters?

Neurons are specialized cells designated to transmit signals through the nervous system. They are the basic functional units of the nervous system. When one neuron transmits a chemical signal to another neuron, a muscle or gland, they use different chemical substances which carry the signal (message). These chemical substances are known as neurotransmitters. Neurotransmitters carry the chemical signal from one neuron to the adjacent neuron or to target cells and, facilitate the communication between cells as shown in figure 01. Different types of neurotransmitters are found in the body; for example, Acetylcholine, Dopamine, Glycine, Glutamate, Endorphins, GABA, Serotonin, Histamine etc. Neurotransmission occurs via the chemical synapses. Chemical synapse is a biological structure which allows two communicating cells to transmit chemical signals to each other using neurotransmitters. Neurotransmitters can be divided into two main categories known as excitatory neurotransmitters and inhibitory neurotransmitters based on the influence they have on the postsynaptic neuron after binding with its receptors.

What is Neuron Action Potential?

Neurons transmit signals using action potential. Neuron action potential can be defined as a quick rise and fall of the electrical membrane potential (voltage difference across the plasma membrane) of the neuron as shown in figure 02. This happens when the stimulus causes the depolarization of the cell membrane. Action potential is generated when the electrical membrane potential becomes more positive and exceeds the threshold potential. At that moment, the neurons are in the excitable stage. When the electrical membrane potential becomes negative and is not able to generate an action potential, neurons are in the inhibitory state.

What are Excitatory Neurotransmitters?

If the binding of a neurotransmitter causes the depolarization of the membrane and creates a net positive charge exceeding the threshold potential of the membrane and generates an action potential to fire the neuron, these types of neurotransmitters are called excitatory neurotransmitters. They cause the neuron to become excitable and stimulate the brain. This happens when the neurotransmitters bind with ion channels permeable to cations. For, example Glutamate is an excitatory neurotransmitter which binds to a postsynaptic receptor and causes sodium ion channels to open up and allow sodium ions to go inside the cell. Entry of sodium ions increases the concentration of the cations, causing the depolarization of the membrane and creating an action potential. At the same time, potassium ion channels open up and permit the potassium ions to exit the cell with the objective of maintaining the charge within the membrane. Potassium ion efflux and closing of sodium ion channels at the peak of the action potential, hyperpolarize the cell and normalize the membrane potential. However, the action potential generated within the cell will transmit the signal to the presynaptic end and then to the neighboring neuron.

Examples of Excitatory Neurotransmitters

– Glutamate, Acetylcholine (excitatory and inhibitory), Epinephrine, Norepinephrine Nitric oxide, etc.

What are Inhibitory Neurotransmitters?

If the binding of a neurotransmitter to the postsynaptic receptor does not generate an action potential to fire the neuron, the type of neurotransmitter is known as inhibitory neurotransmitters. This follows the production of negative membrane potential below the threshold potential of the membrane. For example, GABA is an inhibitory neurotransmitter which binds with GABA receptors located on the postsynaptic membrane and opens the ion channels permeable to chloride ions. The influx of chloride ions will create more negative membrane potential than the threshold potential. The summation of the signal transmission will happen due to the inhibition caused by hyperpolarization. Inhibitory neurotransmitters are very important in balancing the brain stimulation and keeping the brain functions smoothly.

Examples of Inhibitory Neurotransmitters

– GABA, Glycine, Serotonin, Dopamine, etc.

What is the difference between Excitatory and Inhibitory Neurotransmitters?

Summary –  Excitatory vs Inhibitory Neurotransmitters

Excitatory neurotransmitters will depolarize the membrane potential and generate a net positive voltage that exceeds the threshold potential, creating an action potential. Inhibitory neurotransmitters keep the membrane potential in a negative value farther from threshold value which cannot generate an action potential. This is the main difference between excitatory and inhibitory neurotransmitters.

Reference:
1. Purves, Dale. “Excitatory and Inhibitory Postsynaptic Potentials.” Neuroscience. 2nd edition. U.S. National Library of Medicine, 01 Jan. 1970. Web. 13 Feb. 2017.
2. Adnan, Amna. “Neurotransmitters and its types.” Neurotransmitters and its types. N.p., n.d. Web. 13 Feb. 2017.

Image Courtesy:
1. “Action potential”By Original by en:User:Chris 73, updated by en:User:Diberri, converted to SVG by tiZom – Own work (CC BY-SA 3.0) via Commons Wikimedia 
2. “Reuptake both”By Sabar – self-made, created with Corel Painter and Adobe Photoshop (Public Domain)