Question

What do you mean by reflex arc? Draw a simple reflex arc and label the following parts: (i) Receptor (ii) Sensory nerve (iii) Motor nerve (iv) Effector.

Hint:

In a drawing, the Sensory nerve always enters the spinal cord through the \textbf{Dorsal} root, and the Motor nerve exits through the \textbf{Ventral} root.

Answer 1

Step 1: Understanding the Concept:
A reflex action is a rapid, automatic, and involuntary response to a stimulus, handled primarily by the spinal cord rather than the brain to ensure speed.

Step 2: Detailed Explanation:
Definition: The anatomical pathway over which nerve impulses travel during a reflex action is called a reflex arc.
Components (for drawing/labeling):
1. Receptor: A specialized cell or organ (like skin receptors) that detects the external stimulus (e.g., heat or pain) and initiates a nerve impulse.
2. Sensory Nerve (Afferent Neuron): This nerve carries the electrical impulse from the receptor towards the central nervous system (specifically, the spinal cord).
3. Relay Neuron (Interneuron): Located inside the spinal cord, it links the sensory neuron to the motor neuron.
4. Motor Nerve (Efferent Neuron): This nerve carries the response impulse away from the spinal cord to the target organ.
5. Effector: The muscle or gland that executes the response (e.g., pulling the hand away).

Step 3: Final Answer:
The student should draw a cross-section of the spinal cord showing the dorsal root ganglion, sensory neuron entering, synapsing with an interneuron, and a motor neuron exiting to a muscle (effector).