Difference Between Excitatory and Inhibitory Neurotransmitters

The main difference between excitatory and inhibitory neurotransmitters is that excitatory neurotransmitters increase the trans-membrane ion flow of the post-synaptic neuron, firing an action potential, whereas inhibitory neurotransmitters decrease the trans-membrane ion flow of the post-synaptic neuron, preventing the firing of an action potential. Furthermore, Type I synapses use excitatory neurotransmitters while Type II synapses use inhibitory neurotransmitters. 

Excitatory and inhibitory neurotransmitters are the two types of neurotransmitters or chemical messengers released by the end of the pre-synaptic neurons of the central nervous system. 

Key Areas Covered 

1. What are Excitatory Neurotransmitters
     – Definition, Mechanism of Action, Examples
2. What are Inhibitory Neurotransmitters
     – Definition, Mechanism of Action, Examples
3. What are the Similarities Between Excitatory and Inhibitory Neurotransmitters
     – Outline of Common Features
4. What is the Difference Between Excitatory and Inhibitory Neurotransmitters
     – Comparison of Key Differences

Key Terms 

Action Potential, Excitatory Neurotransmitters, Inhibitory Neurotransmitters, Post-Synaptic Neuron

Difference Between Excitatory and Inhibitory Neurotransmitters - Comparison Summary

What are Excitatory Neurotransmitters  

Excitatory neurotransmitters are a type of neurotransmitters released by the brain. Generally, the pre-synaptic neuron is the neuron responsible for the transmission of an action potential to the post-synaptic neuron. For that, it releases neurotransmitters at its terminus to carry the nerve impulse chemically through the synaptic cleft. Then, these neurotransmitters bind to the receptors on the post-synaptic neuron after diffusing through the synapse. 

Difference Between Excitatory and Inhibitory Neurotransmitters

Figure 1: Ion Movement in Excitatory and Inhibitory Effects

However, excitatory neurons in the brain release excitatory neurotransmitters, which cause the opening of ligand-gated sodium channels on the post-synaptic neuron. Subsequently, this results in the flow of sodium ions into the cytoplasm of the neuron, making it more positive inside. Here, the local increase of permeability to the sodium ions results in a local depolarization known as excitatory post-synaptic potential (EPSP). As ESPS leads to the generation of an action potential on the post-synaptic neuron, excitatory neurotransmitters allow the transmission of the nerve impulse through the post-synaptic neuron. 

What are Inhibitory Neurotransmitters 

Inhibitory neurotransmitters are the other type of neurotransmitters released by the brain. Still, the action potentials on some of the neurons result in the release of inhibitory neurotransmitters. Therefore, these neurons refer to inhibitory neurons. Here, the two main types of inhibitory neurotransmitters are GABA, acting in the brain and glycine, acting in the spinal cord. For instance, they result in the opening of ligand-gated chloride ion channels on the post-synaptic neuron upon binding to the appropriate receptors. Also, in some post-synaptic neurons, they result in the opening of the ligand-gated potassium channels. 

Excitatory vs Inhibitory Neurotransmitters

Figure 2: Membrane Potentials

However, inhibitory neurotransmitters cause the interior of the post-synaptic neuron more negative. So, this leads to hyperpolarization. Thereby, it becomes difficult to generate an action potential on the post-synaptic neuron. Also, the type of potential generated by the inhibitory neurotransmitters on the post-synaptic neuron is known as inhibitory post-synaptic potential (IPSP). Here, the main importance of the inhibitory neurotransmitters is to counterbalance the action of excitatory neurotransmitters. 

Similarities Between Excitatory and Inhibitory Neurotransmitters 

  • Excitatory and inhibitory neurotransmitters are the two types of neurotransmitters released by the pre-synaptic neurons of the central nervous system into the synaptic cleft. 
  • Also, both diffuse through the synaptic cleft to the post-synaptic neuron.  
  • Then, they bind to the specific receptors on the post-synaptic neuron. 
  • Furthermore, they change the trans-membrane ion flow in different ways. 
  • Besides, both types of neurotransmitters play a vital role in the brain, maintaining better cognition and behavior. 

Difference Between Excitatory and Inhibitory Neurotransmitters 

Definition 

Excitatory neurotransmitters refer to the neurotransmitters, which make the post-synaptic neuron to generate an action potential, while inhibitory neurotransmitters refer to the neurotransmitters, which prevent the post-synaptic neurons by generating an action potential. Thus, this is the main difference between excitatory and inhibitory neurotransmitters.

Types of Neurons 

Excitatory neurons such as pyramidal neurons of the cerebral cortex release excitatory neurotransmitters, while inhibitory neurons such as stellate neurons, chandelier neurons, and basket neurons of the cerebral cortex release inhibitory neurotransmitters. 

Range of Action 

Moreover, excitatory neurotransmitters act locally or in a long-range in the cerebral cortex while inhibitory neurotransmitters act locally. Hence, this is another difference between excitatory and inhibitory neurotransmitters.

Main Types 

The two main types of excitatory neurotransmitters are glutamate and acetylcholine while the two main types of inhibitory neurotransmitters are GABA and glycine. 

Other Examples 

Also, some of the other excitatory neurotransmitters are epinephrine, norepinephrine, and nitric oxide while some of the other inhibitory neurotransmitters are serotonin and dopamine.  

Type of Synapses 

Besides, Type I synapses use excitatory neurotransmitters while Type II synapses use inhibitory neurotransmitters. 

Influence on the Trans-Membrane Ion Flow 

Another important difference between excitatory and inhibitory neurotransmitters is their influence on the trans-membrane ion flow. That is; excitatory neurotransmitters increase the trans-membrane ion flow of the post-synaptic neuron while inhibitory neurotransmitters decrease the trans-membrane ion flow of the post-synaptic neuron.

Depolarization 

Furthermore, excitatory neurotransmitters make it easy to depolarize the post-synaptic neuron while inhibitory neurotransmitters make it difficult to depolarize the post-synaptic neuron. 

Type of Opening Channels 

Excitatory neurotransmitters open sodium channels in the post-synaptic neuron while inhibitory neurotransmitters open potassium channels. 

Type of Post-Synaptic Potential 

The post-synaptic potential generated by the excitatory neurotransmitters is called EPSP while the post-synaptic potential generated by the inhibitory neurotransmitters is called IPSP.  

The direction of the Flow 

Also, the excitatory neurotransmitters can either produce a unidirectional and bidirectional flow while inhibitory neurotransmitters produce a bidirectional flow. 

Importance 

Excitatory neurotransmitters allow the flow of information, while inhibitory neurotransmitters counterbalance the action of excitatory neurotransmitters. 

Conclusion 

Excitatory neurotransmitters are a type of neurotransmitters released by the neurons in the brain, making it easy to generate an action potential on the post-synaptic neuron. That means; they open sodium channels on the post-synaptic neuron, depolarizing it. Also, EPSP refers to the type of action potential generated in the post-synaptic neuron by an excitatory neurotransmitter. On the other hand, inhibitory neurotransmitters are the other type of neurotransmitters released by the neurons in the brain. Also, they are responsible for making it difficult to generate an action potential on the post-synaptic neuron. Thereby, they open potassium ion channels on the post-synaptic neuron, preventing depolarization. Here, the type of action potential generated by the inhibitory neurotransmitters is known as IPSP. Therefore, the main difference between excitatory and inhibitory neurotransmitters is the influence on each type of neurotransmitter on the post-synaptic neuron.  

References:

1. Antranik. “Actions of Excitatory and Inhibitory Neurotransmitters.” Antranikorg, Available Here.

Image Courtesy:

1. “Ion channel activity before during and after polarization” By Robert Bear and David Rintoul (CC BY 4.0) via Commons Wikimedia 
2. “1221 Action Potential” By OpenStax (CC BY 4.0) via Commons Wikimedia   

About the Author: Lakna

Lakna, a graduate in Molecular Biology & Biochemistry, is a Molecular Biologist and has a broad and keen interest in the discovery of nature related things

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