Sodium (Na±) and potassium (K+) are critically important ions in excitable cells for the transmission of impulse. Discuss this statement in an unmyelinated post synaptic neuro beginning with the events at neuronal junction.
At the neuronal junction, the propagation of electrical impulses is crucial for the transmission of information between neurons. In an unmyelinated post-synaptic neuron, this process involves the opening and closing of ion channels, particularly sodium (Na+) and potassium (K+) channels.
When an action potential reaches the presynaptic terminal of the neuron, it triggers the release of neurotransmitters into the synaptic cleft. These neurotransmitters diffuse across the cleft and bind to specific receptors on the post-synaptic membrane. This binding then leads to the opening of ligand-gated ion channels.
In the case of an unmyelinated post-synaptic neuron, these ion channels are predominantly sodium (Na+) and potassium (K+) channels. When neurotransmitters bind to their receptors, the ligand-gated sodium channels open, allowing sodium ions to rush into the post-synaptic neuron. This influx of sodium results in a localized depolarization of the membrane, generating a graded potential called a post-synaptic potential (PSP).
The depolarization caused by the influx of sodium ions spreads along the unmyelinated section of the dendrites and cell body, resulting in the generation of an action potential. This action potential serves as a means of transmitting the electrical impulse along the length of the neuron.
However, the action potential cannot sustain its propagation indefinitely. Therefore, to ensure the successful transmission of the impulse, the neuron employs an antidromic strategy called the action potential regenerative cycle.
As the action potential reaches the initial segment of the axon, a high density of voltage-gated sodium channels becomes active, initiating the regenerative cycle. These channels open, allowing an influx of sodium ions into the axon, resulting in further depolarization and the continuation of the action potential.
During this regenerative cycle, sodium ions are critical in maintaining the depolarization of the membrane. The high concentration of sodium ions inside the neuron and the low concentration outside create a concentration gradient that ensures the continuation of the action potential.
On the other hand, potassium ions play a crucial role in repolarizing the membrane after the action potential has been propagated. As the action potential passes through the neuron, potassium channels open, and potassium ions move outward, following their concentration gradient. This efflux of potassium ions leads to the restoration of the resting membrane potential, bringing the neuron back to its polarized state.
In summary, sodium and potassium ions are critically important in excitable cells, especially in unmyelinated post-synaptic neurons, for the transmission of impulses. Sodium ions initiate and maintain depolarization, ensuring the successful propagation of the action potential. Meanwhile, potassium ions repolarize the membrane after the action potential, bringing the neuron back to its resting state. Without the proper functioning of these ions and their respective channels, the transmission of impulses in the nervous system would be compromised.