Question

Once expressed in a neuron in the mouse brain and subjected to a flash of light, how does channelrhodopsin affect the membrane potential?

A. It causes neurotransmitter release, leading to an action potential in the postsynaptic neuron.
B. It increases the membrane permeability to cations and makes the membrane potential more negative.
C. It depolarizes the membrane, leading to the opening of voltage-gated Na⁺ channels.
D. It hyperpolarizes the membrane, leading to the inactivation of voltage-gated K⁺ channels.
E. It changes the membrane potential such that voltage-gated K+ channels but not voltage-gated Na⁺ channels are activated.

Answer 1

Channelrhodopsin activates and increases membrane permeability to cations when subjected to light, causing depolarization of the membrane. Option C.

Step-by-step explanation:

The question concerns how channelrhodopsin, when expressed in a neuron within the mouse brain and activated by light, affects the neuron's membrane potential. When channelrhodopsin, a light-sensitive cation channel, is activated by light, it leads to an increase in the membrane permeability to cations, particularly sodium ions (Na+).

This influx of positive ions results in depolarization of the membrane, reducing the difference in voltage between the inside and outside of the neuron. This depolarization effect brings the membrane potential closer to the threshold for triggering an action potential.

Once the threshold is reached, voltage-gated Na+ channels also open, leading to a further influx of sodium ions and a complete depolarization of the neuron, creating an action potential.

The correct answer to the question is option C. Channelrhodopsin depolarizes the membrane, leading to the opening of voltage-gated Na+ channels and thereby initiating an action potential.

This depolarization is a crucial step in the action potential process as it sets off a cascade of events that lead to nerve signal transmission.

So option C is correct.