Reflex Action MCQs Quiz | Class 10

This quiz covers important Multiple Choice Questions (MCQs) on Reflex Action for Class X Science (Code 086), Unit II: World of Living. Specifically, it focuses on concepts like the reflex arc, stimulus-response mechanisms, and various examples of reflexes. Attempt all 10 questions and submit to see your score, then download a PDF of your answers for revision.

Understanding Reflex Actions: A Quick Guide

Reflex actions are fundamental to how our nervous system protects us and helps us respond quickly to environmental changes. These are rapid, involuntary, and automatic responses to stimuli, occurring without conscious thought.

Key Concepts

  • Reflex Action: An automatic, spontaneous, and immediate response to a specific stimulus without involving the brain’s conscious control. It’s a quick way for the body to react to potentially harmful situations.
  • Reflex Arc: The neural pathway that mediates a reflex action. It is the anatomical structure of a reflex.
  • Stimulus: Any detectable change in the internal or external environment that can elicit a response from an organism. Examples include heat, touch, pressure, light, or sound.
  • Response: The reaction of an organism or a part of an organism to a stimulus.

Components of a Reflex Arc

A typical reflex arc consists of five main components that work in a specific sequence to produce a reflex action:

  1. Receptor: Specialized cells or sensory organs that detect the stimulus (e.g., pain receptors in the skin, photoreceptors in the eye).
  2. Sensory Neuron (Afferent Neuron): Transmits nerve impulses from the receptor towards the Central Nervous System (CNS), specifically the spinal cord.
  3. Relay Neuron (Interneuron): Located within the CNS (spinal cord), it connects the sensory neuron to the motor neuron. In some simple reflexes, this neuron might be absent.
  4. Motor Neuron (Efferent Neuron): Carries nerve impulses from the CNS to the effector organ.
  5. Effector: A muscle or gland that carries out the response to the stimulus (e.g., a muscle contracting to withdraw a limb, a gland secreting hormones).

Summary of Reflex Arc Components

Component Role in Reflex Action
Receptor Detects stimulus
Sensory Neuron Transmits signal to CNS
Relay Neuron Processes signal in CNS, links neurons
Motor Neuron Transmits signal from CNS to effector
Effector Carries out the response

Examples of Reflex Actions

Reflex actions are common in our daily lives and demonstrate the body’s efficient defense mechanisms:

  • Withdrawal Reflex: Quickly pulling your hand away from a hot stove or a sharp object.
  • Knee-Jerk Reflex (Patellar Reflex): The sudden extension of the lower leg when the patellar tendon just below the kneecap is tapped.
  • Blinking Reflex: Involuntary closure of the eyelids when an object rapidly approaches the eye or when the eye is irritated.
  • Pupillary Light Reflex: The constriction of the pupil in bright light and dilation in dim light to regulate the amount of light entering the eye.
  • Coughing and Sneezing: Reflexes to clear irritants from the respiratory passages.

Significance of Reflex Actions

Reflex actions are vital for survival because they:

  • Provide Quick Protection: Allow the body to react instantly to dangerous situations, minimizing harm.
  • Reduce Brain Overload: Bypass the brain’s conscious processing, allowing the brain to focus on more complex tasks.
  • Maintain Homeostasis: Help in regulating various body functions involuntarily.

Quick Revision Checklist

  • What is a reflex action? (Involuntary, rapid response)
  • What is a reflex arc? (Neural pathway)
  • Name the five components of a reflex arc. (Receptor, sensory neuron, relay neuron, motor neuron, effector)
  • Which part of the CNS is primarily involved in most simple reflex actions? (Spinal cord)
  • Give two examples of reflex actions. (e.g., hand withdrawal, knee-jerk)

Extra Practice Questions

  1. Which of the following is NOT an example of a reflex action?
    1. Withdrawing hand from a hot plate
    2. Blinking when dust enters the eye
    3. Riding a bicycle
    4. Coughing to clear throat

    Correct Answer: c) Riding a bicycle

  2. The immediate response to touching a very hot object is controlled by the:
    1. Brain
    2. Spinal cord
    3. Cerebellum
    4. Medulla oblongata

    Correct Answer: b) Spinal cord

  3. In a reflex arc, the relay neuron is found in the:
    1. Receptor
    2. Effector
    3. Spinal cord
    4. Motor neuron

    Correct Answer: c) Spinal cord

  4. What is the primary function of the effector in a reflex arc?
    1. To detect the stimulus
    2. To transmit impulses to the CNS
    3. To connect sensory and motor neurons
    4. To carry out the response

    Correct Answer: d) To carry out the response

  5. Which type of neuron carries impulses from the CNS to the effector?
    1. Sensory neuron
    2. Motor neuron
    3. Relay neuron
    4. Interneuron

    Correct Answer: b) Motor neuron