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The Human Body: Nervous System - Reflex actions

Grade 5ICSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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A reflex action is an involuntary, sudden, and automatic response of the body to a stimulus (like heat, cold, or pain) without the involvement of the brain.

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Unlike voluntary actions, reflex actions are controlled primarily by the Spinal Cord\text{Spinal Cord} to ensure a rapid response for protection.

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The pathway followed by a nerve impulse during a reflex action is called the Reflex Arc\text{Reflex Arc}.

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The key components of a reflex arc include the receptor organ (skin/eyes), sensory neuron, spinal cord, motor neuron, and the effector (muscle/gland).

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Reflex actions are essential for survival as they protect the body from immediate harm, such as burning a hand or stepping on a sharp object.

📐Formulae

Stimulus→Receptor→Sensory Neuron→Spinal Cord\text{Stimulus} \rightarrow \text{Receptor} \rightarrow \text{Sensory Neuron} \rightarrow \text{Spinal Cord}

Spinal Cord→Motor Neuron→Effector (Muscle/Gland)→Response\text{Spinal Cord} \rightarrow \text{Motor Neuron} \rightarrow \text{Effector (Muscle/Gland)} \rightarrow \text{Response}

💡Examples

Problem 1:

Explain the reflex action that occurs when you accidentally touch a very hot object.

Solution:

The hand is immediately withdrawn from the hot object.

Explanation:

The heat is the stimulus sensed by receptors in the skin. A message travels via the sensory neuron to the spinal cord. The spinal cord immediately sends a command through the motor neuron to the muscles (effector) of the hand to pull away. This happens in a fraction of a second.

Problem 2:

What is the 'Knee-jerk' reflex?

Solution:

The lower leg kicks forward involuntarily when the tendon below the kneecap is tapped.

Explanation:

Tapping the tendon stretches the muscle, sending a signal to the Spinal Cord\text{Spinal Cord} via sensory neurons. The spinal cord sends an immediate signal back to the leg muscle to contract, causing the kick.