Problem 61 - Objective Biology for NEET

Question

Which of the following are example of reflexes? (a) Knee-jerk reflex (b) Corneal reflex (c) Papillary reflex (d) All of these

Step-by-Step Solution

Answer

All of these options are considered to be examples of reflexes, so the correct answer is (d) All of these.

Step 1: Analsyis of Knee-jerk reflex

A knee-jerk reflex, also known pathologically as the patellar reflex, is known to be a reflex action. This action involves hitting the patellar tendon with a small mallet which causes the lower leg to jerk forward. Thus, Knee-jerk reflex (option a) is an example of a reflex.

Step 2: Analysis of Corneal reflex

Corneal reflex, also known as the blink reflex, is caused when the cornea of the eye is touched or if a bright light is suddenly shone into the eye. This induces an involuntary blink of the eyelids. Hence, the corneal reflex (option b) is also an example of a reflex.

Step 3: Analysis of Papillary reflex

Papillary reflex is the constriction of the pupil as an immediate response to a high-intensity light. Therefore, the papillary reflex (option c) is another exampe of a reflex.

Key Concepts

Knee-jerk reflex

The knee-jerk reflex, often recognized from doctor visits, is an example of a simple reflex action in the human body. It's a fascinating neurological response that helps test the integrity of the spinal cord. When a doctor taps the patellar tendon—located just below your kneecap—your lower leg kicks out seemingly on its own.
This reflex is classified as a monosynaptic reflex. This means that the signal travels through one synapse—a junction between two nerve cells—in the spinal cord.
The knee-jerk reflex serves an important purpose. It's crucial for maintaining posture and balance while standing. When unexpected force is applied to the knee, such as when starting to fall, this reflex quickly straightens the leg to prevent a fall.

• Key aspect: Quick response does not involve the brain
• Reflex pathway: Plantar tendon -> Spinal cord -> Leg muscles

No thought is required for this reflex, since it bypasses the brain and only involves neurons in the pathway between the tendon and spinal cord.

Corneal reflex

The corneal reflex, or blink reflex, is a protective mechanism for the eye. It happens when the cornea, the clear layer covering the eye, is touched or disturbed by a foreign body.
When you blink, you protect your eyes from potential damage or irritation. The blinking keeps the eyes moist and clean.
This reflex is snappy and essential for eye health. The signal is processed through the brainstem, where sensory neurons detect the disturbance and relay the message to motor neurons, which activate the blink.

• Involuntary action: Designed to protect the eye
• Importance in health: Keeps the eye hydrated and free from dirt

It's similar to closing a curtain right before sun rays could hit your eyes. This reflex involves a slightly more complex pathway compared to the knee-jerk reflex and requires the brain's involvement.

Papillary reflex

The papillary reflex, also known as the pupillary light reflex, is the body's method of protecting the eyes from intense light exposure. When a bright light enters your field of vision, your pupils, the dark circles at the center of your eyes, become smaller.
This reflex helps in regulating the amount of light entering the eye, ensuring your vision is not overwhelmed by brightness which could cause damage. The reflex also adapts vision to different light intensities.
It involves the muscles within the iris and occurs very quickly. It is a part of the autonomic nervous system, which controls involuntary body functions.

• Main function: Adapts eyes to varying light conditions
• Health benefit: Prevents damage to the retina

This reflex showcases the eye's intricate ability to adjust instantaneously to changes in environmental light, maintaining optimal vision.