Question

The electrical potential difference between outside and inside of a nerve axon before excitation is known as (a) resting potential (b) action potential (c) spike potential (d) reaction potential

Short answer

The correct answer is (a) resting potential.

Step-by-step solution

Understanding the Definitions

The exercise involves identifying the correct term that describes the electrical potential difference between the outside and the inside of a nerve axon before excitation.

Identifying Resting Potential

Resting potential is the electrical potential difference across the membrane of a neuron when it is not actively sending a signal. It is the state of the neuron before excitation and subsequent action potentials.

Eliminate Other Options

Action potential, spike potential, and reaction potential are terms associated with the changes in electrical potential during and after a neuron has been stimulated, not the state prior to excitation.

Select the Correct Answer

Given that the question asks for the potential difference before excitation, the correct term is 'resting potential.'

Key concepts

Resting Potential

Resting potential represents the electrical calm before the storm of neuron activity. Imagine a neuron as a watchful sentinel standing at the ready—it's this resting potential state where it awaits its next command. This quiet electrophysical state is characterized by a voltage difference between the neuron's interior and the exterior fluid that surrounds it. This difference typically sits at about -70 millivolts.

Resting potential is maintained by the sodium-potassium pump, a cellular mechanism that pushes sodium ions out and potassium ions in. The result? An environment primed for action, with a higher concentration of positively charged ions outside than inside. Additionally, since neurons contain negatively charged proteins that can't escape, the interior becomes negatively charged relative to the outside. When a neuron is stimulated, it leaps into action — but until then, it remains at rest with its potential.

Action Potential

When a neuron 'fires', it generates an action potential, a rapid and dramatic change in voltage across the neuron's membrane. Think of an action potential as a sudden electrical surge that conveys information along the nerve axon. Initiating this short-lived event is a threshold stimulus; a minimum level of excitation the neuron requires to become active.

Once the threshold is crossed, it's like flipping a switch — sodium channels in the neuron's membrane open, and sodium ions rush in. This influx reverses the voltage differential, momentarily making the inside of the neuron positive in comparison to the outside, a peak typically reaching around +40 millivolts. But what goes up must come down, and so potassium channels open, potassium ions exit, and the neuron returns to its resting state after a brief refractory period. This orchestrated play of ions transmits signals throughout the nervous system, carrying the messages that control everything from muscle contractions to complex thoughts.

Neuron Excitation

Neuron excitation is the catalyst that kicks off a cascade of electrical activity within a nerve axon, leading to the generation of an action potential. It's the spark that begins the complex communication process in the nervous system.

Excitation occurs when a neuron receives sufficient stimuli from its environment or other neurons. This can be chemical, through neurotransmitters binding to receptors, or physical, as in sensory neurons responding to touch, sound, or light. When the sum of these excitatory signals is strong enough to reach a critical threshold, it triggers the action potential, propelling the neuron from its resting state to an activated one. It's through this careful balance of excitation and inhibition that our brains interpret and respond to the world around us.