Question

A neural impulse is initiated when a neuron's charge momentarily becomes less negative, or even positive. This event is called: A. an action potential. B. a resting potential. C. impulse facilitation. D. inhibitory.

Short answer

Answer: Action potential.

Step-by-step solution

Understanding the terminologies

To correctly select the answer, let's briefly understand the meanings of each given term: A. Action potential: A rapid rise and subsequent fall in voltage across the membrane of a neuron, resulting in a wave-like electrical impulse transmission along the neuron. B. Resting potential: The stable voltage, typically negative, at which no electrical impulse is being transmitted in a neuron when it is at rest. C. Impulse facilitation: A process in which one neuron enhances the signaling ability of another neuron. D. Inhibitory: A term describing the effect of a neurotransmitter that reduces the likelihood of an action potential in a neuron.

Identifying the correct term

The event described in the exercise is when a neuron's charge momentarily becomes less negative, or even positive. This directly refers to the electrical impulse transmission along the neuron. Therefore, the correct term is: A. an action potential.

Key concepts

Resting Potential

Imagine a neuron as a small but intricate battery, idling and ready to spring into action. This state of readiness is known as the resting potential. Fundamentally, it refers to the electric voltage difference across a neuron's cell membrane when it's not actively sending a signal. Inside the neuron, there is a higher concentration of potassium ions, while outside there are more sodium ions, creating a balance of charges that typically results in a negative internal environment. This negative charge is usually about -70 millivolts (mV).

Within this resting state, the neuron is primed and waiting for a trigger to initiate an action potential, a bit like how a runner crouches at the starting line before a race. If an external event changes the charge to a less negative or even positive state, the neuron responds by 'firing,' resulting in the transmission of an electrical impulse, which is a critical step in neuron communication. This ability to hold a stable, negative voltage is a key feature that sets the stage for the neuron to react swiftly to stimuli.

Neuron Impulse Transmission

Moving from the restful anticipation of resting potential, we journey to the crux of neuronal communication - the neuron impulse transmission. This is likened to the action-packed run of a sprinter following the starting gun. What happens here is a remarkable domino effect, a cascade of ionic movement that we term the action potential.At the heart of this process is the neuron's ability to briefly and rapidly change its membrane potential from negative to positive and back to negative again. This occurs when the neuron is sufficiently stimulated, leading to the opening of voltage-gated sodium channels. The result? A rush of positively charged sodium ions into the neuron, causing the interior to become momentarily positively charged, flipping the resting potential on its head. This spike of positivity is the hallmark of the action potential.As this wave of changing potential travels along the nerve fiber, or axon, it does so without losing strength, thanks to the process of depolarization and repolarization. This all-or-nothing event ensures messages can travel long distances within the nervous system, allowing neurons to communicate rapidly and efficiently across the body. It's worth noting that the integrity of this process is crucial for the accurate and speedy transmission of neural impulses which are essential for everything from reflex actions to complex thoughts.

Neurotransmitter

At the end of the action potential's journey, we reach a critical juncture: the synapse, where one neuron communicates with another neuron or with a target tissue like a muscle. Here, chemicals called neurotransmitters enter the scene to pass the baton in this relay race of neuronal communication.

Neurotransmitters are stored in tiny sacks called synaptic vesicles. When an action potential arrives at the end of an axon—linking the pre-synaptic and post-synaptic cells—it triggers these vesicles to merge with the cell membrane, spilling their contents into the synaptic cleft, which is the gap between the two nerve cells.
Once released, these molecules travel across the cleft and bind to specific receptors on the post-synaptic neuron, like a key fitting into a lock. Depending on the type of neurotransmitter, the effect on the receiving neuron can be either excitatory, moving it closer to firing an action potential, or inhibitory, moving it away from firing. Common neurotransmitters include serotonin, known for mood regulation, and dopamine, which is associated with reward and motivation. This mechanism is fundamental to every move you make, every memory you recall, and even your mood throughout the day. It's through the complex dance of neurotransmitters that our nervous system regulates both voluntary and involuntary functions, orchestrating the symphony that is our experience of life.