Multicellular animals use the nervous system for signal detection and transmissi

Question

Multicellular animals use the nervous system for signal detection and transmission of information. a) The neuron transmits nerve impulses. Identify the subcellular structure of the neuron that forms the basis for the transmission of nerve impulses. Describe how this structure is arranged under resting conditions before a signal is initiated. b) Initiation of an impulse occurs at one end of a neuron. Explain changes in ion concentration and membrane potential that occurs in response to signal initiation.

Explanation / Answer

Please find the answers below:

Answer Part a)

The axon terminal and its nerve endings containing voltage-gated ion channels play the most important and crucial role in nerve impulse transmission. These voltage-gated ion channels on the nerve endings form the basis of transfer of neurotransmitters from one neuron to another by release of the neurotransmitter release from the terminal endings under the inluence of ionic movement across the neuron.

During resting position, the intracellular potassium ion concentration is very high and the extracellular sodium concentration is very high. This causes the membrane of the neuron to achieve a net negative charge of nearly -60 mV and is termed as resting potential. Under the influence of a signal/stress, the ionic concentration changes across the membrane and thus differential movement of these ions across the neuron via the voltage gated channels brings about impulse transmission.

Part b) During rest, the intracellular potassium concentration is very high whereas the extracellular sodium concentration is very high. This gives the neuron a net negative charge at the stage of resting potential nearly -60mV. When the neurons experiences a stress/stiumulus, the voltage-gated ion channels get activated. The potassium channels open up and remove intracellular potassium ions outside the neurons. Simultaneously, the cellular sodium ion channels open up to promote inward movement of sodium ions. Also, long-acting voltage-gated calcium channels also open up to promote intracellular movement of calcium ions. Together, these sequential events change the membrane potential to nearly +40mV at the stage of hyperpolarizationa and then back to nearly -70mV thus leading to transmission of nerve impulse across neurons.

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