Control and Coordination Reflex Action

These notes are based on the chapter Control and Coordination class 10 science of NCERT book and CBSE syllabus

Reflex action is a special case of involuntary movement. When a voluntary organ is in the vicinity of a sudden danger, it is immediately pulled away from the danger to save itself.

For example, when your hand touches a very hot electric iron, you move away your hand in a jerk. All of this happens in flash and your hand is saved from the imminent injury. This is an example of reflex action.

There are many other examples of reflex action, like dilation of pupil on excitement, jaw dropping in surprise, etc.

Reflex Arc

The path through which nerves signals (involved in a reflex action) travel is called the reflex arc. The following flow chart shows the flow of signal in a reflex arc.

Receptor ⇨ Sensory Neuron ⇨ Relay neuron ⇨ Motor neuron ⇨ Effector (muscle)

The receptor is the organ which comes in the danger zone.
The sensory neurons pick signals from the receptor and send them to the relay neuron.
The relay neuron is present in the spinal cord.
The spinal cord sends signals to the effector via the motor neuron.
The effector comes in action and moves the receptor away from the danger.

The reflex arc passes at the level of the spinal cord and the signals involved in reflex action do not travel up to the brain. This is important because sending signals to the brain would involve more time. Although every action is ultimately controlled by the brain, the reflex action is mainly controlled at the level of spinal cord.

Muscular Movements and Nervous Control

Muscle tissues have special filaments, called actin and myosin.
When a muscle receives a nerve signal, a series of events is triggered in the muscle.
Calcium ions enter the muscle cells. It results in actin and myosin filaments sliding towards each other and that is how a muscle contracts.
Contraction in a muscle brings movement in the related organ.
When calcium ions exit from calcium channels, actin and myosin slide away from each other. It results in relaxation of muscles.

Test Your Knowledge

Which part of the brain controls the movements of our hands?
Answer: Cerebrum
Memory is stored in which part of the brain?
Answer: Cerebrum
Which part of the neuron receives signals from an adjacent neuron?
Answer: Dendrites