Selina Solutions Class 8 Biology Solutions for Exercise Long Answer Questions (LA) in Chapter 7 - Nervous System

Question 4 Long Answer Questions (LA)

Q4) With the help of suitable example, describe reflex action.


Solution :

The peripheral nervous system and spinal cord together control certain actions where the brain is not involved,e.g.when we touch a hot object or get pricked by a pointed object,we instantly remove your hand,without thinking about it. Such an action is called a reflex action.

Reflex action is the quick immediate and automatic response to a stimulus without the involvement of the brain.

The shortest pathway of the nerve impulse from a receptor to the effector which makes a reflex action is called a reflex arc.

Reflexes are of two types-

(1) Natural (inborn) reflex:-Is one in which no previous experience or learning is required.These reflexes are inborn ,i.e.inherited from the parents.Example

  • Blinking and watering of eyes coughing,sneezing,vomiting
  • Salviation (when hungry),swallowing.

(2) Conditioned (or acquired) reflex: Is one which develops during the lifetime due to experience or learning.Examples are :

  • Watering of mouth (salivation) at the sight of a favourite or tasty food.Here,as an acquired reflex,salivation occurs because our brain remembers the taste of the food due to a previous experience
  • Typing on the keyboard of a computer
  • Playing a musical instrument.
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