Coordination and Control – JSS3 Intermediate Science Lesson Note (Second Term)

Coordination and control is the way the body parts work together, using the nervous system and hormones, so that the body responds correctly to changes.

Behavioural objectives

1. Define coordination, control, hormone, reflex action and homeostasis.
2. Compare the nervous system and the hormonal system.
3. State the location and function of the main endocrine glands.
4. Distinguish between voluntary and involuntary actions with examples.
5. Describe the steps of a reflex arc.

What is coordination and control?

Coordination is the working together of different body parts so that they act as one system.

• Control: the way the body adjusts its activities, such as heartbeat and blood sugar level, to suit changing conditions.
• Stimulus: any change inside or outside the body that causes a response, such as heat, light or fear.
• Response: the action the body takes after a stimulus, such as pulling your hand away from a hot iron.
• Everyday comparison: a traffic warden directs cars so that there is no accident, and the control systems direct body activities in the same way.

What are the two control systems of the body?

There are two control systems in the body: the nervous system and the hormonal system.

The nervous system

• Message carrier: nerves carry fast electrical messages called impulses.
• Parts: the brain, the spinal cord and the nerves.
• Comparison: it works like a phone call.

The hormonal system

• Message carrier: hormones, which are chemical messages carried in the blood.
• Parts: the endocrine glands.
• Comparison: it works like sending a letter.

Comparison of the two systems

What are the main parts of the nervous system?

The nervous system is made up of the brain, the spinal cord and the nerves, which are made of nerve cells called neurons.

• Brain: the control centre that thinks, remembers and sends out messages.
• Spinal cord: a cord of nerve tissue inside the backbone that links the brain to the nerves.
• Nerves: bundles of neurons that carry impulses to and from the body.
• Receptor: a cell or organ that detects a stimulus, such as the skin, eye or ear.
• Effector: a muscle or gland that carries out the response.
• Sensory neuron: carries impulses from the receptor to the spinal cord or brain.
• Relay neuron: passes impulses across the spinal cord from sensory to motor neurons.
• Motor neuron: carries impulses from the spinal cord or brain to the effector.

What are hormones and endocrine glands?

Hormones are chemicals made by endocrine glands and carried by the blood to specific parts of the body.

• Endocrine glands: ductless glands that pour hormones straight into the blood.
• Target organ: the part of the body that a hormone acts on, to make it grow or change.

Key endocrine glands and their jobs

What is the fight or flight response?

• Cause: sudden fear or excitement, such as meeting a dog on the road.
• Hormone: the adrenal glands release adrenaline into the blood.
• Effects: the heart beats faster and breathing quickens.
• Result: more energy reaches the muscles so you can fight or run away.

What are voluntary and involuntary actions?

Voluntary actions are actions we choose to do, while involuntary actions happen automatically without our choice.

Voluntary actions

• Control: the brain thinks first, then sends a message to the muscles.
• Examples: walking to the chalkboard, eating lunch and waving at a friend.

Involuntary actions

• Control: they happen without thinking and are hard to stop.
• Examples: the heart beating, breathing and the stomach digesting food.

Comparison

What is a reflex action?

A reflex action is a very fast, automatic response to a stimulus, often one that could cause harm.

• Speed: it is quick because the message goes through the spinal cord without waiting for the thinking part of the brain.
• Purpose: it protects the body from injury.
• Reflex arc: the path followed by the impulse during a reflex action.

What are the steps of a reflex arc?

1. Stimulus: you step on a sharp nail.
2. Receptor: pain receptors in the skin of your foot detect the nail.
3. Sensory neuron: carries the impulse to the spinal cord.
4. Relay neuron: passes the impulse across the spinal cord.
5. Motor neuron: carries the impulse from the spinal cord to the leg muscles.
6. Response: the leg muscles (effector) pull your foot up at once.

Other examples of reflex actions

• Blinking: the eyelids close when something flies towards the eye.
• Knee jerk: the leg kicks forward when a doctor taps below the knee.
• Pupil reflex: the pupils get smaller in bright sunlight.
• Withdrawal reflex: the hand jumps away from a hot iron.

What is homeostasis?

Homeostasis is the keeping of steady conditions inside the body, even when conditions outside change.

• Blood sugar: insulin from the pancreas keeps the sugar level in the blood steady.
• Body temperature: the body sweats to cool down when it is too hot.
• Role of the control systems: the nervous and hormonal systems work together to keep these conditions balanced.

Why does coordination matter?

Coordination matters because it keeps the body parts working together, safely and in balance.

• Hormones: make sure you grow properly and keep blood sugar steady.
• Reflexes: keep you safe from injury.
• Voluntary actions: allow you to deal with the world around you.

Evaluation

1. What is the difference between a voluntary and an involuntary action?
2. Which hormone is produced when you are suddenly frightened by a dog, and which gland makes it?
3. Why is the spinal cord important in reflex actions?
4. State two differences between the nervous system and the hormonal system.
5. Which gland makes insulin, and what does insulin do?

Assignment

Draw a reflex arc for touching a hot pot, label each part in order, and give one more example of a reflex action.