**Question:** The only neurons in retina showing action potentials are

A. bipolar cells
B. amacrine cells
C. ganglion cells
D. horizontal cells

**Correct Answer:** C. ganglion cells

**Core Concept:** In the retina, neurons responsible for generating action potentials, which are the primary electrical signals in nervous system, are limited to specific types of cells.

**Why the Correct Answer is Right:** Action potentials are generated in response to light stimulation and are essential for transmitting visual information to the brain. In the retina, these action potentials are generated in ganglion cells. Ganglion cells are the final output neurons of the retina and are responsible for transmitting visual information to the brain, specifically to the optic nerve and further to the visual cortex.

**Why Each Wrong Option is Incorrect:**

A. Bipolar cells are the first-order neurons of the retina, receiving input from photoreceptor cells (rods and cones) and transmitting it to amacrine cells. They do not generate action potentials.

B. Amacrine cells are interneurons in the retina, receiving input from bipolar cells and transmitting it to other amacrine cells, ganglion cells, or horizontal cells. Amacrine cells do not generate action potentials.

C. Photoreceptor cells (rods and cones) do not generate action potentials. They convert light stimuli into electrical signals via the phototransduction cascade, but these signals consist of receptor potential rather than action potentials.

D. Horizontal cells are interneurons in the retina, receiving input from bipolar cells and transmitting it to other horizontal cells or amacrine cells. Horizontal cells do not generate action potentials.

**Clinical Pearl:** Understanding the specific neurons responsible for generating action potentials in the retina is crucial for understanding visual processing and the transmission of visual information to higher visual centers in the brain. This concept is essential for interpreting neuroimaging studies, particularly electroretinography (ERG), which measures electrical activity in the retina and optic nerve head.

**Core Concept:** Ganglion cells are the only neurons in the retina that generate action potentials, which are essential for transmitting visual information to the brain. In the retina, these action potentials are generated in ganglion cells, specifically in their axons that form the optic nerve and further extend to the visual cortex in the brain where visual perception occurs. This process is essential for understanding the visual system and its functioning in humans.