Autonomic Nervous System (ANS)

The autonomic nervous system (ANS), also known as the visceral or vegetative nervous system, is a part of the nervous system that controls internal organs, smooth muscles, and glands. It functions automatically, without conscious effort, to regulate vital bodily functions such as heart rate, the force of heart contractions, digestion, breathing rate, pupil dilation, urination, and sexual arousal. The ANS is also responsible for triggering the fight-or-flight response, which is the body's immediate reaction to stress. The ANS consists of the nerves of involuntary organs like the heart, lungs, stomach, etc. It is not under the control of our will.

Reflex Action

A reflex action is an automatic and immediate response to a stimulus from the environment. It happens without any conscious thought or control. For example, when you touch a hot object, your hand pulls back instantly. Reflex actions occur without the involvement of the brain, as the response is coordinated by the spinal cord. This ensures quick and efficient control to protect the body from harm.

Reflex action

Observe the above figure carefully and as per the numbers in that figure, answer the following questions:
a. What is happening at 1 and 2?

• 1: The finger touches a hot object (stimulus), triggering a sensory impulse.
• 2: The sensory neuron sends the impulse to the spinal cord, and the hand begins to withdraw.

b. Which nerve carried the impulse to the point marked 3? In which direction is it conducting the impulse?

• Nerve: Sensory nerve (afferent nerve).
• Direction: It conducts the impulse from the sensory organ (finger) towards the spinal cord.

c. Which is the nerve shown by 4?

• Nerve: Interneuron (relay neuron) in the spinal cord.

d. Which is the organ marked as 5?

• Organ: Spinal cord.

e. At 6, which nerve is conducting the response impulse?

• Nerve: Motor nerve (efferent nerve).

f. At 7, where has the impulse reached? What is its effect?

• Location: The impulse has reached the muscle.
• Effect: The muscle contracts, causing the hand to move away from the hot object (reflex action).