Reflex Action – Class 11 | Chapter – 21 | Biology Short Notes Series PDF

Reflex Action: It is an involuntary response of effectors to the stimulus and it helps us in protecting us from any sudden stimulus which may harm us and thus takes care of the survival of an organism. It is the major point that explains the importance of reflex action.

The importance of reflex action is due to the fact that reflex arcs are composed of different components that are significant to create a reflex. The function of each component is explained below –

  • Receptor – It receives the information and assists in generating impulses. 

  • Sensory Nerve – It carries information from the receptor to the interneurons in the spinal cord. 

  • Interneuron – It processes the information and generates effective responses. 

  • Motor Nerve – It carries the information from the spinal cord to the effector organ. 

  • Effector Organ – It receives information from effector neurons and results in the appropriate response (reflex). 

Benefits of Reflex Action

Reflex actions are common occurrences in an animal’s body. The following are the advantages of reflex action:

  • Animals defend themselves immediately in the face of adversity.
  • The brain is not aware of any type of burden (while thinking) or load.
  • We frequently save ourselves from serious actions by acting reflexively.

Physiology of Reflex Action

The stimulus follows the reflex arc as follows:

  • The receptor detects the stimulus.
  • These stimuli cause nerve impulses to be generated in sensory neurons, and these impulses travel through the axons of these neurons. The sensory afferent nerves leading to the spinal cord are made up of axons.
  • When these impulses enter the spinal cords, they initiate impulses in one or more associations or interneurons.
  • Then, the appropriate motor neurons receive impulses from the association neurons.
  • When impulses travel through motor or efferent nerves to the junction between motor neurons and muscles or glands, effectors are stimulated to perform their functions.

Types of Reflex Action

Reflex actions can be classified into two types.

Inborn or unconditioned reflexes

Simple reflex actions are another term for inborn reflexes. Some of the reflexes are present even before birth. These are known as inborn or unconditioned reflexes. The taste of milk, for example, causes salivation even in a newborn baby who has never tasted the food before, the pupils of the eye constrict even if the eye is illuminated by light at the time of birth, and so on. Inborn reflexes are passed down through families. Inborn reflexes are triggered by specific stimuli. The reflex arcs of unconditioned reflexes are always the same.

Conditioned reflexes

Conditioned reflexes are acquired through learning or experience with stimuli that did not initially elicit a response. Conditioning reflexes involve the formation of new reflex arcs that extend into the cerebral cortex. Conditioned reflexes are transient in nature and may vanish or reappear. For example, if an animal smells food that he has not previously tasted, he does not salivate; however, if the animal sees and smells food several times before eating, saliva is produced. The animal’s nervous system has been conditioned to produce a reflex as a result of seeing and smelling food. The stimulus that causes such a reflex is known as a conditioned stimulus.

Examples of Reflex Action

Reflex Action Examples in Humans Include-

  • Closing of eyes when a bright light hits our eyes

  • Sudden withdrawing hands or legs when they touch something hot or pricking

  • Coughing or sneezing due to irritants in the nasal passage

  • Batting of eyelids frequently

  • Blinking eyes when insects come in contact 

  • Rooting reflex in infants

  • Sucking reflex in infants

  • Grasp reflex in infants

  • The reflex of abdominal muscles to contract upon any force to the abdomen (Muscular defense)

  • Knee-jerk reflex is known as a patellar reflex: when the patellar tendon is stretched, the contraction of quadriceps takes place.

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By Team Learning Mantras