Reflex arc

The idea

A reflex arc connects the nerves that detect an input directly to the nerves that move muscles, in the spinal cord, giving a response quicker than the brain's thinking; the input also goes on to reach the brain.

Too slow to think

If Meena had to think about the pain, decide what to do and then tell her muscles, she might be burnt before her hand moved.

Where do you think the nerves that detect heat are connected to the nerves that move the muscles?

• In the spinal cord, where they first meet
• Only in the brain, after thinking
• At the fingertip itself

Trace the arc

Press Next step to follow the signal.

A short cut

The nerves from the whole body meet in a bundle in the spinal cord on their way to the brain. The first place where input and output nerves meet is the best place for the connection.

A reflex arc connects the nerves that detect an input directly to the nerves that move muscles. It is formed in the spinal cord and gives a response quicker than the brain's thinking. The input also goes on to reach the brain.

Notes

A reflex arc connects the input nerves directly to the output nerves that move muscles, in the spinal cord. The response is quicker than thinking, and the input also goes on to reach the brain.

Check yourself

Where are reflex arcs formed?

What does a reflex arc connect?

Why is a reflex response quicker than a thought-out response?

In a reflex, what also happens to the input information?

• In the muscle. The muscle only carries out the movement. The reflex arc is formed in the spinal cord.
• In the spinal cord — correct. Yes!
• In the hand. The hand holds the receptors. Nerves from all over the body meet in the spinal cord, where the arc is formed.
• The two halves of the brain to each other. A reflex arc joins the input nerves to the output nerves and is formed in the spinal cord.
• One muscle to another muscle. The arc joins the nerves that detect an input to the nerves that move muscles.
• The nerves that detect an input to the nerves that move muscles — correct. Yes!
• The input nerve is connected directly to the output nerve, so the brain's thinking is not needed first — correct. Yes!
• The brain thinks faster during a reflex. The reflex is quicker because the arc skips the brain's slower thinking, not because the brain thinks faster.
• The muscles do not need any signal. The muscles get a signal from the output nerve.
• It is lost completely. The input also goes on to reach the brain.
• It goes on to reach the brain — correct. Yes!
• It stays in the hand. The input travels to the spinal cord and also goes on to the brain.