Difference Between Excitatory and Inhibitory Neurons

The main difference between excitatory and inhibitory neurons is that the excitatory neurons release neurotransmitters that fire an action potential in the postsynaptic neuron whereas inhibitory neurons release neurotransmitters that inhibit the firing of an action potential. 

Excitatory and inhibitory neurons are the two types of neuron populations in the cerebral cortex. Glutamic acid is the most common excitatory neurotransmitter while GABA (gamma-aminobutyric acid) is the most common inhibitory neurotransmitter.

Key Areas Covered

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

Key Terms

Cerebral Cortex, Excitatory Neurons, GABA (Gamma-Aminobutyric Acid), Glutamic Acid, Inhibitory Neurons, Pyramidal Neurons, Spiny Stellate Cells

What are Excitatory Neurons

Excitatory neurons are the neurons in the cerebral cortex that are involved in the transmission of nerve impulses by means of excitatory neurotransmitters such as glutamic acid. The excitatory neurotransmitters have an important role in the opening of sodium channels on the post-synaptic neuron, which causes the influx of sodium ions, making the interior of the cell less negative. This facilitates the depolarization of the post-synaptic cell. This depolarization is also known as excitatory postsynaptic potential (EPSP).

The two types of excitatory neurons in the brain are made up of pyramidal neurons and spiny stellate cells.

1. Pyramidal neurons – These are a type of multipolar neurons that serve as the primary excitation units of the corticospinal tract and prefrontal cortex of the mammalian brain. These cells also occur in the hippocampus and amygdala apart from the cerebral cortex.
   

   Figure 1: GFP Expressing Pyramidal Cell in Mouse Cortex

2. Spiny stellate cells – They are one of the three types of stellate cells that occur in layer IVC of the V1 region in the visual cortex.

What are Inhibitory Neurons

Inhibitory neurons are the neurons in the cerebral cortex that counterbalance the effect of excitatory neurons. The main form of neurotransmitters released by these neurons is the GABA. The main function of GABA is to open chloride channels on the post-synaptic neuron, increasing the negative charge inside the neuron. This makes the post-synaptic neuron hyperpolarized, making it difficult to generate an action potential. The hyperpolarized potential on the inhibitory neuron is also known as inhibitory postsynaptic potential (IPSP).

Figure 2: Excitation and Inhibition

The three main types of inhibitory neurons in the brain are stellate cells, chandelier cells, and basket cells.

1. Stellate cells – Two of the three types of stellate cells serve as inhibitory neurons. They are the inhibitory interneurons which occur in the molecular layer of the cerebellum and the inhibitory aspiny stellate interneurons.
2. Chandelier cells – They are one of the two types of GABA-ergic cortical interneurons. The two characteristic features of these cells are the containment of parvalbumin and the ability of fast-spiking.
3. Basket cells – The other type of GABA-ergic cortical interneurons is the basket cells. They occur in the cerebellum as well.

Similarities Between Excitatory and Inhibitory Neurons

• Excitatory and inhibitory neurons are the two types of neurons which occur in the cerebral cortex.
• Their effect is generated by means of neurotransmitters, which affect the post-synaptic neuron.
• Both play a vital role in the functioning of the brain.
• The balance between excitation and inhibition is crucial in maintaining better behavior and cognition.

Difference Between Excitatory and Inhibitory Neurons

Definition

Excitatory neurons are neurons that release neurotransmitters to make the post-synaptic neuron generate an action potential while inhibitory neurons are neurons that release neurotransmitters to make the post-synaptic neuron less-likely to generate an action potential. This explains the main difference between excitatory and inhibitory neurons.

Types of Neurons

Another difference between excitatory and inhibitory neurons is the type. The excitatory neurons in the cerebral cortex are pyramidal neurons while the three types of inhibitory neurons in the cerebral cortex are stellate neurons, chandelier neurons, and basket neurons.

Projection

Furthermore, the excitatory neurons project either locally or long-range projections between different cortical areas while the inhibitory neurons project within localized regions that are small.

Type of Neurotransmitters

The type of neurotransmitter is one other difference between excitatory and inhibitory neurons. Glutamic acid is the main excitatory neurotransmitter while GABA is the main inhibitory neurotransmitter.

Other Neurotransmitters

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

Depolarization/Hyperpolarization

Moreover, the excitatory neurons make the post-synaptic neurons depolarize while the inhibitory neurons make the post-synaptic neurons less-likely to depolarize.

Post-Synaptic Potential

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

Information Flow

The information flow of the excitatory neurons can be either unidirectional or bidirectional while inhibitory neurons are responsible for the control of bidirectional excitation.

Role

Excitatory neurons are responsible for the transmission of nerve signals, stimulating the brain while inhibitory neurons counterbalance the action of excitatory neurons.

Importance

Excitatory neurons transmit a flow of information while inhibitory neurons regulate the activation of excitatory neurons. This is also an important difference between excitatory and inhibitory neurons.

Examples of Action

The neurotransmitters of the excitatory neurons cause the opening of sodium channels while the neurotransmitters of the inhibitory neurons cause the opening of the chloride channels.

Conclusion

Excitatory neurons release excitatory neurotransmitters such as glutamic acid to generate an action potential on the post-synaptic neuron. On the other hand, inhibitory neurons release inhibitory neurotransmitters such as GABA to make it less likely to generate an action potential on the post-synaptic neuron. Hence, the main difference between excitatory and inhibitory neurons is the influence of each neuron on its post-synaptic neuron.

Reference:

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

Image Courtesy:

1. “GFPneuron” By Original uploader was Nrets at en.wikipedia – Transferred from en.wikipedia (CC BY 2.5) via Commons Wikimedia  
2. “Neuronactivity” By HgDeviasse – Own work (CC BY-SA 3.0) via Commons Wikimedia