8.2.1 Photoreceptors in the Eye

• What are photoreceptors and where are they located?

  Specialized sensory cells in the retina
• Photoreceptors convert light into electrical signals
• There are two main types of photoreceptors: rods and cones
• What is the sensitivity of rods compared to cones?

  High sensitivity
• Match the type of photoreceptor with its function:

  Rods ↔️ Night vision

  Cones ↔️ Color vision
• Rods are primarily located in the peripheral retina.
• Cones have high visual acuity
• What transmits the electrical signals from photoreceptors to the brain?

  Optic nerve
• What conditions are rods responsible for vision in?

  Dim light
• Cones require brighter light to perceive colors
• What is found in the outer segment of photoreceptors?

  Photopigments
• The inner segment of photoreceptors contains the cell's organelles
• Steps in the structure of a photoreceptor (from outer to inner)

  1️⃣ Outer segment with photopigments

  2️⃣ Inner segment with organelles

  3️⃣ Cell body

  4️⃣ Synaptic terminal
• What is the function of the synaptic terminal in photoreceptors?

  Transmit signals
• Rods contain the photopigment rhodopsin.
• Cones have folds of membrane containing opsins in their outer segment
• Why do rods contain many discs with rhodopsin in their outer segment?

  High sensitivity
• Match the type of photoreceptor with its associated photopigment:

  Rods ↔️ Rhodopsin

  Cones ↔️ Opsins
• Cones enable us to see colors in bright light.
• Rods have low visual acuity
• What are photoreceptors and where are they located?

  Specialized cells in retina
• Photoreceptors convert light into electrical signals.
• There are two main types of photoreceptors: rods and cones
• What is the primary function of rods?

  Night vision
• Which photoreceptor has high sensitivity to light?

  Rods
• Cones are primarily responsible for color vision.
• Order the steps of light signal transmission in photoreceptors.

  1️⃣ Light strikes photoreceptors

  2️⃣ Chemical reactions produce electrical impulses

  3️⃣ Signals are transmitted via the optic nerve

  4️⃣ The brain interprets signals as images
• What are the two types of photoreceptors in the retina?

  Rods and cones
• Rods are more sensitive to light and function in dim conditions.
• Cones require brighter light to function effectively.
• In a dimly lit room, which photoreceptor allows you to see shapes?

  Rods
• Match the structure with its function in photoreceptors:

  Outer segment ↔️ Contains photopigments

  Inner segment ↔️ Contains cell organelles

  Synaptic terminal ↔️ Transmits electrical signals
• What photopigment is found in rods?

  Rhodopsin
• Cones contain different types of photopigments called opsins.
• Rods have many discs with rhodopsin for high sensitivity.
• What is the process by which rods convert light into electrical signals called?

  Phototransduction
• Order the steps of phototransduction in rods.

  1️⃣ Light strikes rhodopsin

  2️⃣ Rhodopsin activates transducin

  3️⃣ Transducin activates phosphodiesterase (PDE)

  4️⃣ PDE hydrolyzes cyclic GMP (cGMP) to GMP

  5️⃣ Sodium channels close, hyperpolarizing the cell
• Which wavelengths of light are cones sensitive to?

  Red, green, blue
• Cones require brighter light levels to initiate phototransduction compared to rods.
• In daylight, cones enable us to see colors by detecting different wavelengths of light.