What is the resting membrane potential of rods?

What is the resting membrane potential of rods?

• A. -50 mV
• B. -70 mV
• C. -30 mV
• D. -60 mV

Answer: (A)

Photoreceptors in the dark stay depolarized because Na+ channels that are gated by cGMP remain open, allowing a steady Na+ (and some Ca2+) influx—the dark current. This keeps the membrane potential more positive than many other neurons, typically around -50 mV. When light hits the photoreceptors, a signaling cascade lowers cGMP, channels close, and the cell hyperpolarizes toward a more negative value, about -70 mV, reducing neurotransmitter (glutamate) release. So, the resting potential of rods being near -50 mV best matches their dark, depolarized state. Values like -70 mV reflect the light-activated hyperpolarized state, while -60 mV or -30 mV would not accurately represent the typical rod dark-state potential.

Photoreceptors in the dark stay depolarized because Na+ channels that are gated by cGMP remain open, allowing a steady Na+ (and some Ca2+) influx—the dark current. This keeps the membrane potential more positive than many other neurons, typically around -50 mV. When light hits the photoreceptors, a signaling cascade lowers cGMP, channels close, and the cell hyperpolarizes toward a more negative value, about -70 mV, reducing neurotransmitter (glutamate) release. So, the resting potential of rods being near -50 mV best matches their dark, depolarized state. Values like -70 mV reflect the light-activated hyperpolarized state, while -60 mV or -30 mV would not accurately represent the typical rod dark-state potential.