Reflex Action and Reflex Arc

When you touch a hot object or when a pin pricks your finger, what is your immediate reaction? Of course, you remove your hand away from the source of pain, either the hot object or the pin. In situations like these, your reactions are always immediate, involuntary and sudden. They happen without much of a thinking process. In scientific terms, this action is called the reflex action. Here the spinal cord has a major role to play.  The reflex arc shows the pathway through which the reflex action occurs.

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Reflex Action

The whole mechanism of reflex action occurs in such a fashion that there is no conscious control of the brain. Stimulation occurs through the peripheral nervous system and the response to this peripheral nerve stimulation is involuntary. In a reflex action, the spinal cord along with the brain stem is responsible for the reflex movements.

A few examples of reflex action are:

• When light acts as a stimulus, the pupil of the eye changes in size.
• Sudden jerky withdrawal of hand or leg when pricked by a pin.
• Coughing or sneezing, because of irritants in the nasal passages.
• Knees jerk in response to a blow or someone stamping the leg.
• The sudden removal of the hand from a sharp object.
• Sudden blinking when an insect comes very near to the eyes.

The whole process of reflex action involves some important components. They are receptor organs, sensory neurons, nerve center, associated neurons, motor neurons and effector neurons.

The receptor organs perceive the stimuli. They are situated on the sense organs. The afferent neurons or the sensory neurons carry the stimuli from receptors to the spinal cord. The ganglion of the spinal cord has the sensory neurons.

The spinal cord is the nerve center, where synaptic connections are formed. The associated neurons are present in the spinal cord. The ventral horn of spinal cord has the motor neurons. Effector organs are the glands and muscles that behave in response to the stimuli.

Browse more Topics under Neural Control And Coordination

• Nerve Impulse and its Transmission
• Central Nervous System
• Sensory Receptors

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Reflex Arc

The neural pathway that controls the reflexes occurs through the reflex arc. It acts on an impulse even before it reaches the brain. There are some stimuli that require an automatic, instantaneous response without the need of conscious thought. The following diagram shows the reflex arc pathway.

The receptor here is the sense organ that senses danger. The sensory neurons pick up signals from the sensory organ and send them through other neurons which are interconnected. It is then received by the relay neuron which is present in the spinal cord. Immediately, the spinal cord sends back signals to the muscle through the motor neuron. The muscles attached to the sense organ move the organ away from danger. In reflex actions, the signals do not travel up to the brain.

Learn more about Nerve Impulse and its Transmission here in detail.

Solved Question For You

Q. What is the difference between afferent neurons and efferent neurons?

Ans: The difference is as follows,

• Afferent neurons: they conduct the nerve impulses from the receptor organs to the spinal cord.
• Efferent neurons: they conduct the nerve impulses from the brain or spinal cord to the muscles or glands, i.e. the effector organs.

FAQ’s for You

Q1. Describe reflex action and reflex arc.

Answers:

REFLEX ACTION: A reflex, or reflex action, is an involuntary and nearly instantaneous movement in response to a stimulus. A reflex is made possible by neural pathways called reflex arcs which can act on an impulse before that impulse reaches the brain.
Examples include When light acts as a stimulus, the pupil of the eye changes in size. Coughing or sneezing, because of irritants in the nasal passages. Knees jerk in response to a blow or someone stamping the leg

REFLEX ARC: Reflex arc is the nerve pathway involved in a reflex action, including at its simplest a sensory nerve and a motor nerve with a synapse between.
Reflex arc consist of 1)Receptor or sensory organ, 2)Sensory neurine, 3)Reflex centre(brain or spinal cord), 4)Motor neurone and 5)Effector(muscle or gland).

Q2. What is reflex action? Explain pathway of reflex action.

Answers: A reflex, or reflex action, is an involuntary and nearly instantaneous movement in response to a stimulus. Reflex actions happen through the reflex arc, which is a neural pathway that controls the reflexes. The receptor here is the sense organ that senses danger. The sensory neurons pick up signals from the sensory organ and send them through other neurons which are interconnected. It is then received by the relay neuron which is present in the spinal cord. Immediately, the spinal cord sends back signals to the muscle through the motor neuron. The muscles attached to the sense organ move the organ away from danger. In reflex actions, the signals do not travel up to the brain.

Q3. In reflex action, the reflex arc is formed by?

Answers: In reflex actions, a reflex arc is formed by impulses from the receptor reaching the spinal cord and the appropriate reflex impulse then being sent to the muscles by the spinal cord. The impulse is not sent to the brain, to reduce response time.

Q4. Define reflex arc and its component.

Answers: The reflex arc describes the pathway in which the nerve impulse is carried and the response is generated and shown by the effector organ.
The reflex arc typically consists of five components:
1. The receptor is present in the receptor organ.
2. The sensory neuron conducts the nerve impulses towards the central nervous system (CNS). The CNS is comprised of the brain and the spinal cord.
3. The information is transferred from one neuron to other.
4. A motor neuron conducts the response nerve from the CNS to the effector organ.
5. The effector organ shows response by contracting or secreting a product.
The instant movement performed by the individual in response to the stimulus is known as a reflex action.