Problem 59 - Objective Biology for NEET

Question

In reflex action, the reflex arc is formed by (a) Muscle, receptor, brain (b) Brain, spinal cord, muscle (c) Receptor, spinal cord, muscle (d) Receptor, muscle, spinal cord

Step-by-Step Solution

Answer

The correct answer is (c) Receptor, Spinal Cord, Muscle.

Step 1: Understand the Components of a Reflex Arc

A reflex arc involves several components: the sensory receptor, the sensory neuron, the integration center (located in the central nervous system), the motor neuron, and the effector (muscle or gland). The sensory receptor detects the stimulus, and the sensory neuron transmits this information to the integration center. Following this, the motor neuron carries a message from the integration center to the effector, leading to a response.

Step 2: Apply the Knowledge to the Exercise

Looking at the answer choices given, the proper order of a reflex arc can be identified. This order is: sensory receptor detects a stimulus (receptor), signal is sent to the integration center in the central nervous system (which could be the spinal cord in case of a reflex arc), and then a message is sent to lead to a response (muscle).

Step 3: Choose the Correct Answer

With this knowledge, the correct answer can be chosen. The correct order is: Receptor, Spinal Cord, Muscle, which corresponds to option (c).

Key Concepts

Sensory Receptor

Sensory receptors are the initial step in any reflex action. They are specialized structures that detect environmental changes or stimuli. These changes can include temperature, pressure, light, or chemical alterations.
Once a sensory receptor has detected a stimulus, it translates this external input into a nerve impulse. This nerve impulse is then ready to be transmitted to the next component in the reflex arc.

• Types of sensory receptors include mechanoreceptors (for touch or pressure), photoreceptors (for light), chemoreceptors (for taste and smell), and thermoreceptors (for temperature).
• Each receptor is highly specialized for a particular kind of stimulus, ensuring an accurate and efficient response to changes in the environment.

By acting as the first responder to a stimulus, sensory receptors play a crucial role in maintaining balance and adaptability in the body.

Integration Center

The integration center is a critical part of the reflex arc, usually located within the central nervous system (CNS). This is where the nerve impulse, carried by sensory neurons, is processed and interpreted. Depending on the complexity of the reflex, the integration center might just be a single synapse, or it could involve complex networks of neurons.

The primary role of the integration center is to determine the appropriate response to the stimulus. It receives the nerve impulse from the sensory receptor, processes it, and creates a command impulse for the motor neuron to execute.

• For simple reflexes, such as a knee-jerk reaction, the spinal cord often acts as the integration center.
• In more complex reflexes, the brain might be involved to coordinate a more elaborate response.

In essence, the integration center is the decision-making hub of the reflex arc.

Motor Neuron

The motor neuron is responsible for carrying the command from the integration center to the effector, which could be a muscle or a gland. Once the integration center has decided on the appropriate response to a stimulus, it sends a neural signal through the motor neuron.
This neuron travels out of the central nervous system and reaches the peripheral nervous system, eventually connecting to the effector.

• Motor neurons are essential for translating the CNS decision into physical actions.
• They ensure the message reaches the correct effector to produce the necessary action.

In short, the motor neuron acts as the messenger, taking information from the brain or spinal cord to the relevant body part to carry out the response.

Effector

The effector is the final component in the reflex arc. It might be a muscle or a gland, receiving the message from the motor neuron to act in response to the initial stimulus.
When the motor neuron delivers the nerve impulse to the effector, it will either cause a contraction in a muscle or a secretion from a gland. This is the visible or detectable response to the stimulus.

• Muscles working as effectors might contract to pull a limb away from a pain source.
• Glands might secrete hormones or other substances in response to particular signals.

Effectors complete the reflex arc by performing the action needed to protect the body, maintain homeostasis, or facilitate any necessary physiological changes.