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Reflex Action and Reflex Arc: What Happens When You Accidentally Touch a Hot Pot

Updated on August 6, 2017
Reflex action and reflex arc when a cook touched a hot pot by accident
Reflex action and reflex arc when a cook touched a hot pot by accident | Source

Reflex Action and Reflex Arc

Reflex is a special ability that evolution gifted us to facilitate our survival. Whenever part of your body comes in contact with an object capable of causing you harm, you tend to quickly withdraw that part of the body. This happens before your brain gets the time it needs to process the threat.

Reflex Action

If you accidentally touch a hot pot on your stove while cooking, you would involuntarily (and nearly instantaneously) snatch your hand away from the pot. This response is called a ‘reflex action'.

Reflex Arc

Contact with the hot pot triggers the start of a series of events in the body to evoke a response.

At the point of contact with the hot pot, skin receptors quickly send nerve impulses (electrical) to the spinal cord (central nervous system) via sensory neurons. In the spinal cord, the impulses are processed and a response is relayed back.

In the spinal cord, the interneurons (also known as relay neurons) make the connections between the sensory neurons (bringing the message from hand) and the correct motor neurons (taking the response back to the hand). It would be not be useful if the response was sent to the wrong part of the body—in this case, a response sent to the leg wouldn't be too helpful as the stimulus is coming from the hand.

From the interneurons, the response is relayed to the motor neurons which project out of the spinal cord to stimulate your muscles (effector) to contract, causing you to snatch your hand away from the hot pot. This pathway taken by nerve impulses to elicit a response is known as a ‘reflex arc’.

This process happens so fast that the response occurs before the message reaches the brain. This results to a quicker time-to-response as the thinking process of the brain may be relatively time consuming.

Diagram to illustrate a reflex arc
Diagram to illustrate a reflex arc | Source

Components of a Reflex Arc

The stimulus

In the above example, the stimulus is the contact with the hot pot. This contact causes a nerve impulse that will travel to the spinal cord via the sensory neurons. Other examples include an object (e.g. an insert) approaching your eye causing you to blink before you know it.

Sensory neurons

These neurons carry the nerve impulse to the spinal cord. Similar to the interneuron and motor neuron, sensory neurons receive incoming impulses at the dendrites. The impulses move away from the cell body along the axon to the synaptic terminal where the impulse is sent to the next neuron (the interneuron) with the help of a neurotransmitter (acetylcholine).

The spinal cord

Interneurons (also known as relay neurons) are fully contained in the central nervous system (the spinal cord and the brain). The interneuron serves as the connection between the sensory neurons and the motor neurons.

The synapse is a tiny space between two neurons. When an impulse gets to the end of one neuron and has to be sent down the next neuron, the synapse acts as a bridge. The signal arrives at the end of one neuron (close to the synapse) as an electrical signal, crosses the synapse as a chemical signal (with the help of a neurotransmitter known as acetylcholine released by the synaptic vesicles at the synaptic terminal) and continues as an electrical signal in the next neuron.

Motor neurons

In the 'hot pot' example above, motor neurons send nerve impulses away from the central nervous system to effector organs or muscle fibers. This causes the muscle fibers to contract, resulting in you snatching your hand away from the hot pot.

If the stimulus was at the sight an insert flying towards your eye, then the motor neurons would relay the response back to your eyelids (to close) to protect them from the approaching threat.

The response

This occurs when the motor neurons deliver nerve impulses from the spinal cord to the part of the body where a response to the stimulus is needed. In the above example, the response is the muscle contraction to quickly pull the hand away from the hot pot. In the second example, the response is to blink to prevent the insert from making contact with the eye.

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      Debasrita das 2 months ago

      Too nice

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      Bibin 2 months ago

      Why do you immediately remove your hand on touching a very hot object?

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      Pankaj Kumar Thakur 3 months ago

      This is a very helpful

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      Yoram Tumwiine 4 months ago

      Helpful

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      Author

      Edmund Custers 4 months ago

      Hi Arjun, thank you reading and leaving a comment. I'll try to answer your question. Pain that is still detected much later is most likely because there was significant damage done during the contact. In this case nerve fibers would still be sending messages to the brain from the location of the injury. The brain is kind of telling you to treat the affected area with care.

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      Arjun 4 months ago

      Why do we detect pain much later even after removing our hand??

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      Kobi 4 months ago

      This helped so much thank you heaps

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      Pooja 6 months ago

      Thank u. It helped me.

    • profile image

      Gagan Jain 6 months ago

      Really awesome

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      Marryam 6 months ago

      Really helped me in my assignment

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      R.Bala mounika 10 months ago

      This is the one of the best article for this topic

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      vanshita 2 years ago

      if the stimulas is touching the hot vessel then what is the response?

      rply fast

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      Simrat randhawa 2 years ago

      Awsome