Question

In the dark (unstimulated), a rod or cone cell in the retina has open sodium channels and a resting membrane potential of -40 mV. In the dark, there is ______ movement of sodium ions through these channels.

net inward

net outward

no net

Answer 1

In the dark (unstimulated), a rod or cone cell in the retina has open sodium channels and a resting membrane potential of -40 mV. In the dark, there is a net inward movement of sodium ions through these channels. The correct option is a.

Step-by-step explanation:

In the dark, a rod or cone cell in the retina has open sodium channels with a resting membrane potential of -40 mV. In this state, there is a net inward movement of sodium ions through these channels. This movement of sodium ions contributes to maintaining the resting membrane potential.

Normally, the resting membrane potential of a neuron is about -70 mV, and sodium ions (Na+), which have a higher concentration outside the cell, tend to move into the cell down their concentration gradient when sodium channels are open. This movement results in the depolarization of the cell, as the influx of positively charged sodium ions makes the inside less negative relative to the outside.

In the absence of light, photoreceptor cells are slightly depolarized due to the continuous inward flow of sodium ions. This condition changes when light hits the photoreceptors, causing hyperpolarization and a decrease in the release of neurotransmitters, thereby influencing the visual signal that is sent to the brain. Hence, a is the correct option.