Sodium and potassium are critically important ions in excitable cells for the transmission of impulse. Discuss this statement in an unmyelinated post synaptic neuron , beginning with the events at the neuronal junction.
At the neuronal junction, the transmission of an impulse in an unmyelinated post-synaptic neuron primarily involves the movement of sodium (Na+) and potassium (K+) ions.
When an action potential reaches the pre-synaptic neuron, it triggers the release of neurotransmitters into the synaptic cleft. These neurotransmitters, such as acetylcholine, diffuse across the cleft and bind to specific receptors on the post-synaptic neuron's membrane. This binding initiates a series of events that lead to the generation of an action potential in the post-synaptic neuron.
Once the neurotransmitter binds to the receptor, it causes the opening of ion channels in the post-synaptic neuron's membrane. In the case of sodium and potassium ions, these channels are usually referred to as ionotropic receptors or ligand-gated ion channels.
The binding of the neurotransmitter molecules to these ion channels allows for the entry of sodium ions (Na+) into the post-synaptic neuron's cytoplasm. The sudden influx of sodium ions causes depolarization of the membrane, shifting the membrane potential towards a more positive value.
This depolarization triggers the opening of voltage-gated sodium channels along the post-synaptic neuron's membrane. These channels allow for a rapid influx of sodium ions into the cell, further depolarizing the membrane. This depolarization effect spreads along the entire length of the neuron, creating an action potential.
As the action potential propagates down the neuron, voltage-gated potassium channels are also activated. These channels allow for the efflux of potassium ions (K+) out of the post-synaptic neuron, repolarizing the membrane and restoring it to its resting state.
After repolarization, the sodium-potassium pump, an active transport protein, works to restore the concentration of sodium and potassium ions to their original levels. The pump actively transports sodium ions out of the cell and potassium ions back into the cell. This process consumes energy in the form of ATP.
Overall, the influx of sodium ions and subsequent depolarization, followed by the efflux of potassium ions and repolarization, play crucial roles in the transmission of impulses in unmyelinated post-synaptic neurons. The proper functioning of sodium and potassium ion channels and the sodium-potassium pump ensures the effective transmission of nerve impulses between neurons.