Muscular and nervous tissue

Muscular tissue

Muscular tissue is made of long cells called muscle fibres. They can contract, getting shorter, and relax. This moves your limbs, the food in your gut, and the blood in your heart.

Voluntary means you control it, as when you lift your hand. Involuntary means it works by itself, as when your gut moves food or your heart beats. Cardiac muscle beats all through life and does not tire.

Nervous tissue

Nervous tissue receives messages and carries them through the body. Its cells are neurons, which make the brain, the spinal cord and the nerves. A neuron has three parts:

• the cell body, with the nucleus;
• dendrites, short branches that receive the message;
• the axon, a long fibre that carries the message away, ending in nerve endings that pass it on.

A message in a nerve is a nerve impulse. Touch something hot, and an impulse goes to the spinal cord, and another comes back to the muscle that pulls your hand away. The fastest impulses travel at about $100\ \text{m/s}$.

You should find that a 1 m nerve at 100 m/s takes 10 ms, while a slow nerve at 2 m/s takes half a second. That is why the nerves for quick reflexes are the fast, sheathed kind.

Try it in Python

This program finds how many times the heart beats in an hour, a day and a lifetime.

Practise with new numbers

Common mistakes

• Calling heart muscle voluntary. It works by itself.
• Thinking all muscle is striped. Smooth muscle has no stripes.
• Mixing up dendrites and the axon. Dendrites receive; the axon carries the message away.
• Forgetting to change seconds to milliseconds. 1 s = 1000 ms.

Remember these

• Skeletal muscle: striped, many nuclei, voluntary. Smooth muscle: not striped, involuntary. Cardiac muscle: striped, branched, involuntary.
• Nervous tissue is made of neurons: dendrites receive, the axon carries the message away.
• A fast nerve impulse travels at about $100\ \text{m/s}$.

Check yourself

Try each one on your own first. If you are stuck, open a hint. Then check with Show the answer.

1. Which muscle is found in the wall of the heart?

2. Which part of a neuron receives messages?

3. A nerve impulse travels at $100\ \text{m/s}$. How long does it take to go $2\ \text{m}$?

4. Which kind of muscle moves food along the gut?