Biology · Neural Control and Coordination · NEET
| Full name | EPSP = Excitatory Post-Synaptic Potential | IPSP = Inhibitory Post-Synaptic Potential |
| Effect on membrane | Depolarises (inside less negative) | Hyperpolarises (inside more negative) |
| Ions involved | Positive ions like Na+ enter | Cl- enters or K+ leaves |
| Effect on neuron | Brings neuron closer to threshold (towards firing) | Pushes neuron away from threshold (away from firing) |
| Outcome | Helps generate an action potential | Prevents/reduces an action potential |
It is decided by which ion channels the neurotransmitter opens on the post-synaptic membrane, NOT by the neurotransmitter alone. If channels let in positive ions (like Na+), the inside becomes less negative (depolarisation) and the potential is excitatory (EPSP). If channels move ions so the inside becomes more negative (like Cl- entering or K+ leaving), the potential is inhibitory (IPSP). NCERT states the new potential 'may be either excitatory or inhibitory'.
No. An EPSP is only a small local potential at the post-synaptic membrane that brings the neuron closer to firing. A single EPSP is usually too weak. Many EPSPs must add up (summation) to reach the threshold before a full action potential is generated in the post-synaptic neuron. So EPSP is a 'push towards' firing, not firing itself.
A single neuron has many synapses on its surface from different neurons. Some release neurotransmitters that cause EPSPs and others cause IPSPs. The neuron adds up all these signals together. If the total effect crosses the threshold, it fires; if IPSPs cancel the EPSPs, it stays silent. This balancing is how the brain controls and fine-tunes responses.
Yes, in simple terms. EPSP is a depolarising change (inside becomes less negative, closer to threshold). IPSP is usually a hyperpolarising change (inside becomes more negative, further from threshold). For NEET, remember EPSP = excitatory = towards firing; IPSP = inhibitory = away from firing.
Receptor sites for neurotransmitters are present on
Try the real previous-year questions from this chapter — each with the answer and a full solution.
EPSP (Excitatory Post-Synaptic Potential) is a depolarising change that brings the post-synaptic neuron closer to firing an action potential. IPSP (Inhibitory Post-Synaptic Potential) is usually a hyperpolarising change that moves the neuron away from firing. Both are 'new potentials' generated on the post-synaptic membrane after neurotransmitter binding.
On the post-synaptic membrane, where the neurotransmitter binds to its specific receptors and opens ion channels. The entry or movement of ions creates the new potential, which is either excitatory or inhibitory.
Yes. Whether the effect is excitatory or inhibitory depends on the receptor type and the ion channel that opens on the post-synaptic membrane, not only on the neurotransmitter chemical itself.
No. A single EPSP is usually too weak. Several EPSPs must add up (summation) to reach the threshold. Only then is a full action potential fired in the post-synaptic neuron.
