Control and Coordination

When the stimulation of a receptor results in a spontaneous, involuntary reaction, it is called reflex action or simply reflex.

Reflexes are of two types:

• Simple or unconditioned or natural reflex
• Complex or conditioned reflex

Simple or Unconditioned or Natural Reflex

In this type of reflex, the brain is not involved. The receptor is stimulated which is conducted to the spinal cord by the effector. The effector neuron from the spinal cord conducts a response to the muscle or the gland. This causes an immediate reaction. It does not involve any thinking or reasoning. It is a natural response and will occur even in new-born babies. For example, blinking of eyes when strong light falls on the eyes.

Types of Simple Reflex

Simple reflex is also of two types. They are as follows:

In the first type, only the sensory and motor neurons of the spinal nerves are involved.

Jerking of knee when tapped below the kneecap is an example.

In the second type, the interneuron present in the spinal cord is also involved.

The moving away of hand in response to pin-prick or heat is an example of this type.

In the above diagrams, it can be seen that the pathway of conduction is in the form of an arc. Thus, these pathways are also called the reflex arcs.

Know Something

Complex or Conditioned Reflex This type of reflex involves the brain but it is also as fast as the simple reflex. Salivation on smelling one's favourite food is an example of conditional reflex. The individual recognises the smell and based on a previous experience, the response (salivation) occurs. The recognition of the previous experience involves the association centres of the brain. A series of experiments were conducted by Ivan Pavlov, a Russian biologist which demonstrated conditioned reflex. He found that when a bell was rung every time a dog was given food, the dog showed salivation only at the sound of the bell. The ringing of the bell is called the conditioned stimulus. The dog had, thus, 'learnt' to associate the sound of the bell to food and this made it salivate at the sound of the bell. It can be represented as follows: Conditioning is the basis for learning. Learning to cycle or swim can be called a conditional response.