Difference Between EPSP and IPSP

Main Difference – EPSP vs IPSP

Graded potentials and action potentials are two types of electric potentials that occur in the nervous system. The graded potentials arise by the action of ligand-gated ion channel proteins. The action potentials arise by the voltage-gated sodium and potassium channels. The graded potentials differ based on the location and function. The different types of graded potentials are postsynaptic potentials, pacemaker potentials, receptor potentials, end-plate potentials, and slow-wave potentials. The two types of postsynaptic potentials are EPSP and IPSP. EPSP stands for the Excitatory Postsynaptic Potential and IPSP stands for the Inhibitory Postsynaptic Potential. EPSP is a temporary depolarization that is caused by the flow of positively-charged ions into the postsynaptic cell while IPSP is a hyperpolarization caused by the flow of negatively-charged ions into the postsynaptic cell. The main difference between EPSP and IPSP is that EPSP facilitates the firing of an action potential on the postsynaptic membrane whereas IPSP lowers the firing of the action potential.

Key Areas Covered

1. What is EPSP
      – Definition, Characteristics, Role
2. What is IPSP
      – Definition, Characteristics, Role
3. What are the Similarities Between EPSP and IPSP
      – Outline of Common Features
4. What is the Difference Between EPSP and IPSP
      – Comparison of Key Differences

Key Terms: Action Potential, Chloride Ions, Excitatory Postsynaptic Potential (EPSP), GABA, Glutamate, Glycine, Inhibitory Postsynaptic Potential (IPSP), Postsynaptic Potentials (PSP), Sodium Ions

What is EPSP

An Excitatory Postsynaptic Potential (ESPS) refers to an electric charge in the postsynaptic membrane, which makes the postsynaptic membrane to generate an action potential. The EPSP is caused by the binding of the excitatory neurotransmitters, which are released from the presynaptic membrane. The excitatory neurotransmitters are released from the vesicles of the presynaptic nerve. Several EPSPs generating an action potential is shown in figure 1.

Figure 1: EPSPs Generating an Action Potential

The main excitatory neurotransmitter is glutamate. The acetylcholine serves as the excitatory neurotransmitter at the neuromuscular junction. These excitatory neurotransmitters bind to the receptors and open the ligand-gated channels. This causes the flow of the positively-charged sodium ions into the postsynaptic cell. The depolarization of the postsynaptic membrane generates an action potential on the postsynaptic nerve.

What is IPSP

The Inhibitory Postsynaptic Potential (IPSP) refers to an electric charge on the postsynaptic membrane, which makes the postsynaptic membrane less likely to generate an action potential. The IPSP is caused by the flow of negatively-charged chloride ions into the postsynaptic neuron. The inhibitory neurons secret the inhibitory neurotransmitters to the synapses. The most common inhibitory neurotransmitters are glycine and GABA.

The formation of an IPSP is described in the flowchart in figure 2.

Figure 2: Formation of an IPSP

The binding of the inhibitory neurotransmitters to the receptors of the postsynaptic membrane causes the opening of the ligand-gated chloride ion channels. This results in a hyperpolarization of the postsynaptic membrane. The hyperpolarization makes the postsynaptic membrane less likely to generate an action potential.

Similarities Between EPSP and IPSP

Both EPSP and IPSP are two types of postsynaptic potentials.
Both EPSP and IPSP occur on the postsynaptic cell membrane.
Both EPSP and IPSP are mediated by ligand-gated ion channels, which are opened by the binding of neurotransmitters.

Definition

EPSP: An EPSP is an electrical charge on the postsynaptic membrane, which is caused by the binding of excitatory neurotransmitters and makes the postsynaptic membrane generate an action potential.

IPSP: An IPSP is an electric charge on the postsynaptic membrane, which is caused by the binding of inhibitory neurotransmitters and makes the postsynaptic membrane less likely to generate an action potential.

Name

EPSP: EPSP stands for Excitatory Postsynaptic Potential.

IPSP: IPSP stands for Inhibitory Postsynaptic Potential.

Cause

EPSP: EPSP is caused by the flow of positively-charged ions.

IPSP: IPSP is caused by the flow of negatively-charged ions.

Type of Polarization

EPSP: EPSP is a depolarization.

IPSP: IPSP is a hyperpolarization.

To the Threshold

EPSP: EPSP brings the postsynaptic membrane towards the threshold.

IPSP: IPSP takes the postsynaptic membrane away from the threshold.

Excitation

EPSP: EPSP makes the postsynaptic membrane more excited.

IPSP: IPSP makes the postsynaptic membrane less excited.

Firing of an Action Potential

EPSP: EPSP facilitates the firing of an action potential on the postsynaptic membrane.

IPSP: IPSP lowers the firing of an action potential on the postsynaptic membrane.

Results

EPSP: EPSP is the result of the opening of the sodium channels.

IPSP: IPSP is the result of the opening of the potassium or chloride channels.

Types of Ligands

EPSP: EPSP is generated by the flow of glutamate or aspartate ions.

IPSP: IPSP is generated by the flow of glycine or GABA.

Conclusion

EPSP and IPSP are the two types of electric charges found on the membrane of the postsynaptic nerve at the synapse. The EPSP is caused by the flow of positively-charged ions into the postsynaptic nerve whereas, the IPSP is caused by the flow of negatively-charged ions into the postsynaptic nerve. The EPSP facilitates the generation of an action potential on the postsynaptic membrane whereas the IPSP inhibit the generation of an action potential. The main difference between EPSP and IPSP is the effect of each type of electric charges on the postsynaptic membrane.

Reference:

1. “Excitatory postsynaptic potential.” Wikipedia, Wikimedia Foundation, 31 Aug. 2017, Available here. 16 Sept. 2017.
2. “Inhibitory postsynaptic potential.” Wikipedia, Wikimedia Foundation, 30 Aug. 2017, Available here. 16 Sept. 2017.

Image Courtesy:

1. “Synapse diag5” (CC BY-SA 3.0) via Commons Wikimedia
2. “IPSPflowchart” By User:Gth768r – Own work (Public Domain) via Commons Wikimedia