Question

Assertion: The place in retina from which the optic nerve leaves is known as blind spot. Reason: Because this place is devoid of photoreceptor cells.

Short answer

The assertion and the reason are correct. The spot in the retina from which the optic nerve departs is referred to as the 'blind spot' because it lacks photoreceptor cells, and thus, cannot detect any light that hits it.

Step-by-step solution

Understand the Relevant Parts of the Eye

Firstly, note that the retina is the light-sensitive layer at the back of the eye, containing cells that respond to light and relay messages about it to the brain. The optic nerve, meanwhile, is responsible for carrying these messages from the retina to the brain.

Comprehend the Significance of Photoreceptor Cells

Photoreceptor cells are the specific cells in the retina that respond to light. There are two types, rods and cones, which are responsible for detecting different kinds of light. Rods detect light intensity, allowing vision in low-light conditions, while cones discern color.

Understand the Concept of The Blind Spot

The blind spot is the place in the retina where the optic nerve leaves to carry its messages to the brain. This area lacks photoreceptor cells, which is why it's named the 'blind spot' - no light that hits this area can be detected, creating a small area of blindness. Thus, the place in the retina from where the optic nerve leaves is known as the blind spot because this place is devoid of photoreceptor cells.

Key concepts

Optic Nerve

The optic nerve is a crucial part of the human visual system. It acts like a messenger, carrying information from the eye to the brain. This bundle of nerve fibers connects the retina to the brain's visual cortex. When light enters the eye and is captured by the retina, the optic nerve transmits these signals. The brain interprets them as images. Without the optic nerve, our eyes' photoreceptor cells would not be able to communicate visual information to the brain.

• It's composed of over one million nerve fibers.
• The optic nerve begins at the point where the eye meets the brain, passing through the optic canal.

Light reaches the retina and the resulting reaction starts a sequence of events that results in vision. It's like a fiber optic cable, transferring visual cues from your eyes to be turned into actual pictures in your brain.

Photoreceptor Cells

Photoreceptor cells are specialized neurons found in the retina of the eye. They convert light into signals that can be processed by the brain, making them essential for vision. There are two primary types of photoreceptor cells in the human retina:

• Rods: These cells are highly sensitive to light and allow vision in dim lighting conditions. They do not support color vision.
• Cones: These cells require more light and provide the ability to see color. They function best in bright light conditions.

They play a critical role by capturing light photons and initiating the process of sight. When these cells detect light, they change it into electrical signals which are sent via the optic nerve to the brain.

Retina

The retina is a thin layer of tissue located at the back of the eye. It is vital for processing visual information. Light enters the eye through the cornea and lens, focusing on the retina. Once the retina receives light, it uses photoreceptor cells to convert this light into electrical impulses. These impulses carry the information needed to create visual images, which the brain interprets. The retina functions like a camera sensor, capturing the 'images' and setting the stage for the visual perception process.

• The retina has different layers, each designed to process specific tasks of image creation.
• Retinal abnormalities can lead to severe vision problems, highlighting its importance in the visual pathway.

Rods and Cones

Rods and cones are the two types of photoreceptor cells located in the retina. They have different functions but work together to create the complete visual picture. Rods are more numerous than cones and are responsible for vision in low-light environments. They don’t detect color but are very sensitive to light intensity and motion. Cones, on the other hand, enable us to see in detail and in color. There are three types of cones, each sensitive to different light wavelengths corresponding to the colors blue, green, and red.

• Rods help us navigate in the dark by detecting black, white, and shading.
• Cones provide the fine detail and the range of colors necessary during the day.

Together, rods and cones ensure that we can see the world around us in sharp, colorful detail, regardless of the lighting conditions.