Reflex and Reflex Action

HUMAN BRAIN:-

Involuntary actions:-

Actions that donot require thinking and occour without the concious choice of an organism are known as involuntary actions.

Reflex actions are a part of involuntary action as these actions occur rapidly as a responce to the external stimulus and are known as reflex involuntary actions.

• Simple reflex actions like change in the size of the pupil, and the thought out actions such as moving a chair, there is another set of muscle movements over which we do not have any thinking control.
• Many of these involuntary actions are controlled by the mid-brain and hind-brain.
• All the involuntary actions including blood pressure, salivation and vomiting are controlled by the medulla in the hind-brain. 

HUMAN BRAIN:-

• Voluntary actions  are based on deciding what to do next.  So, the brain also has to send messages to muscles.
• The fore-brain is the main thinking part of the brain. It has regions which receive sensory impulses from various receptors.
• Separate areas of the fore-brain are specialised for hearing, smell, sight and so on.  There are separate areas of association where this sensory information is interpreted by putting it together with information from other receptors as well as with information that is already stored in the brain.
• Based on all this, a decision is made about how to respond and the information is passed on to the motor areas which control the movement of voluntary muscles, for example, our leg muscles.
• Activities like walking in a straight line, riding a bicycle, picking up a pencil. These are possible due to a part of the hind-brain called the cerebellum. It is responsible for precision of voluntary actions and maintaining the posture and balance of the body.

REFLEX ACTIONS:-

‘Reflex’ is a word we use very commonly when we talk about some sudden action in response to something in the environment.

Reflex action is the extremely quick, automatic, sudden action in response to something in the environment.

Example-

i) Immediately pulling back of fingers after touching a hot plate.

ii) Closing of eyes when flashed with high intensity light.

iii) Salivation when hungry.

Reflex arc is the pathway of nerve involved in reflex action. Reflex arc involves-

• Receptors- receive the message from external environment.

• Sensory neuron- carries the message from the receptor to the central nervous system.

• Central nervous system- processes the message and sends impulses to the concerned part of the body in the form of response.

• Motor neuron- carries the message from the central nervous system to the effector.

• Effector- responses against the stimulus.