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CONTROL AND COORDINATION : Reflex Action and Reflex Arc

Reflex Action

Definition: It is nerve mediated, automatic, involuntary and spontaneous response to a stimulus acting on a specific receptor without consulting the will.

It was discovered by Marshal Hall(1833)

Reflex action occurs in response to a stimulus where delay can be harmful.

Example: Wider opening of pupil in dimlight, narrowing of pupil in strong light, salivation when food is eaten, jerking of knee when hit below knee cao

Conditioned reflexes: By regular association, Habit or practice, some action can be converted into actions.

Example of conditioned reflexes: Writing, reading, walking, driving, pedalling, salivation at sight or smell of food,
Reflex Arc

It is required a stimulus, a receptor organ , sensory neurons, a part of central nervous system, motor neurons and effector organ.

The pathway taken by a stimulus to travel from receptor organ to effector organ is known as reflex arc.

1) Receptor Organ: It is a tissue or organ which receive the stimulus for initiating nerve impulse, e.g,

2)Sensory Neurons: They conduct impulses from receptor to central nervous system.

3)Part of Central Nervous system: It is spinal cord for most of the apparent reflexes that originate in the trunk and limbs of the body,

e.g , withdrawal of hand or foot on being pricked , knee jerked reaction,

Brain is also used as part of the reflex arc in some cases,

Importance of Reflex Action

  1. Overloading

2.Survival Value

3.Quick Response

4.Condition Reflexes





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