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Biology – Reflex and Voluntary Actions

Biology, SS 3

Topic: Reflex and Voluntary Actions

Reflex Action

Definition: A reflex action is an involuntary or automatic action in response to impulses initiated by a stimulus. A reflex is something that your body does natural. In other words, reflex action is a rapid or quick response to stimuli which are not consciously controlled by the brain. It is fast, inborn (instinctive) and stereo-typed. A given stimulus always produces the same response.

Characteristics of Reflex Action

  1. Reflex action is a response without prior thought or planning.
  2. It is not under the control of the control of the will or it is automatic.
  3. It is a quick response.
  4. It is entirely in stereotyped in nature.
  5. It involves minimum member of nerves cells.
  6. It terminates at the spinal cord.

Examples of Reflex Actions

  1. Blinking of the eyes
  2. Jerking of the kneel
  3. Salivation
  4. Coughing
  5. Peristalsis
  6. Secretion of glands
  7. Beating of the heart

Voluntary Actions

Definition: Voluntary actions are responses to stimuli that are consciously controlled or co-ordinated by the brain. In other words, voluntary actions are actions taken deliberately, involving the exercise of the will or brain.

 Characteristics of Voluntary Actions

  1. It involves prolonged response.
  2. Its response is controlled by the brain.
  3. Its response to a particular stimulus may vary.
  4. It involves many nerves cells.

Example of Voluntary Actions

  1. Writing
  2. Dancing
  3. Eating
  4. Driving
  5. Singing
  6. Walking etc.

Differences Between Reflex and Voluntary Actions

 

Reflex Action

Voluntary Action

1.

Action is initiated by muscle receptor.

Action is initiated in the brain.

2.

It occurs unconsciously.

It occurs consciously.

3.

It is automatic and fast.

It is neither automatic nor fast.

4.

It is inborn.

It can be learnt.

5.

Nerve impulses do not reach the brain.

Nerve impulses always reach the brain.

The Reflex Arc

Reflex reactions in humans are controlled by the reflex arc. When the safety of an organism demands a very quick response, the signals may be passed directly from a sensory neuron, via a relay neurone, to a motor neurone for instant, unthinking action. This is a reflex action.

A reflex arc is a neural pathway that controls an action’s reflex, i.e. it is the nerve pathway which makes such a fast, automatic response possible. It does not matter how brainy you are – you will always pull your hand away from a flame without thinking about it. It is an in-built, or innate, behaviour, and we all behave in the same way.

A reflex arc consists of the following parts:

  1. Sensory cells: These cells receive the stimulus.
  2. Sensory or afferent neurone: This conducts or transmits nerve impulses from the sensory cells to the spinal cord or brain.
  3. Intermediate neurone: This conducts nerve impulses from the afferent to the efferent neurone.
  4. Motor or efferent neurone: This conducts or transmits impulses from the intermediate neurone to the effector.
  5. Effector (muscle or gland): This takes action.

A Simple Reflex Arc

Conditioned Reflex

Conditioned reflex is a learned response or behaviour after birth. Once they are acquired, they can be performed without thinking about them. Most of our behaviours are conditioned reflexes. Examples are walking, driving, reading, writing, swimming etc. It takes a fairly long time to learn each of these skills. But once they have been mastered, they are performed very fast and efficiently without the individual thinking about them. They become habits.

Behaviour conditioning was first described by a Russian scientist, Ivan Pavlov in 1902 from his experiments on dogs. Naturally, a dog’s mouth becomes wet when it is given food due to reflex action. In one experiment, Pavlov rang a bell just before giving the dog its food. After repeating this several times the dog learnt to associate the bell with food. Hence, it salivated as soon as it heard the bell, i.e., before the food appeared. Pavlov called this response a conditioned reflex.

Role of Conditioned Reflex on Behaviour

  1. It helps individuals to acquire new skill through the learning of such habits.
  2. It helps to develop certain behaviour which are not originally shown in the individual.
  3. Unhealthy behaviour like smoking, drinking and drug taking may become bad habits when acquired through conditioned reflex and may be difficult to stop.
  4. The principle is used in the training of dogs for their special role in crime detection and for security.

Differences between Reflex Action and Conditioned Reflex

 

Reflex Action

Conditioned Reflex

1.

It is an inborn behaviour.

It is a learned behaviour.

2.

It takes a short time.

It takes a longer time.

3.

It involves spinal cord and relayed to brain after action is completed.

It is controlled by the brain.

4.

Action starts by muscle receptor cells.

Action starts in the brain.

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