Coordination: Q: How many kids of activities are performed by our body?

 

        Explain various types of Reflexes and reflex arc.

 

Ans:- ACTIVITIES PERFORMED by our body

Usually three kinds of activities are performed by our body

1. Involuntary or Automatic Actions

        The responses that occur automatically and without our awareness are called involuntary actions e.g., heart beat, secretions of the gastric glands, peristalsis ete.

2. Voluntary actions

        The responses that are controlled by our will and may not be automatic or immediate are called voluntary actions.

3. Reflexes or Reflex Actions

       The immediate or automatic responses to environmental changes, both internal and external, are called reflexes. They are not intervened by the will.

A reflex arc

TYPES OF REFLEXES

        The reflexes may be divided into two groups:

i)                    Simple reflexes                 ii)          Conditioned reflexes

Simple Reflexes

         They are inborn, inherited or unlearnt responses to stimuli and are immediate and automatic. The structural and functional basis of the simple reflex is called the reflex arc. In the reflex arc impulses are carried from the receptors via sensory neurons to the central nervous system and from here they are passed on via motor neurons to the effectors for the necessary-action.

Example---Touching a hot surface

         On touching a hot surface our hand is automatically withdrawn. When our hand accidently touches a hot surface the receptors of the hand transmit impulses to the sensory neurons which carry them to the associative neurons of the spinal cord. From here impulses are carried by motor neurons to the effectors or muscles of the hand which contract and hand is at once withdrawn.

         It must be pointed out that most reflex actions involve a number of reflex arcs rather than one and secondly there may be other responses such as feeling pain, expression of emotions such as fear or tension bringing the hand to the face to look at and so on.

Other Examples

        There are many other examples of reflex actions such as.

i)      watering of the mouth on the sight or smell of food:

ii)      blinking of the eyes;

iii)     knee jerk; | |

iv)     startling on hearing a loud, unexpected sound;

v)      closing the eye when a flash of light falls across.

Conditioned Reflexes

          They are not inborn or inherited but acquired and dependent on the past experience or training.

Example----Experiment of Pavlov

          A Russian physiologist Pavlov studied the conditioned reflex for the first time in the early part of this century. He performed experiments on dogs. Dogs normally secrete saliva when they see or smell food. This saliva could be collected by microtubes inserted in salivary ducts and this could be measured.

In his experiments Pavlov rang a bell just at the same time or immediately before or after offering meat to the dogs. He repeated this performance many times. He observed that after many repetitions the dogs started associating ring of bell with the presentation of food. So these dogs secreted saliva on simple ringing of the bell even when meat was not offered to them.  Thus natural stimulus (sight of food) was tied up with artificial stimulus (ringing of bell) and in time the latter was enough to produce the same response (secretion of saliva).

Training and learning by experience are also examples of conditioned reflexes.

Palov's observations: (a) the hungry dog responds by salivating to the primary stimulus of food: (b) the dog is subjected to a period in which a second stimulus . a ringing bell. is presented with the primary stimulus to the salivation reflex: (c) eventually the dog salivates where only the secondry stimulus is given. The dog is said to be conditioned.