GCSE Biology: Nervous coordination

Justina: Your body contains billions and billions of nerve cells, or neurons.

Georgina: There are around 100 billion in your brain and over 13.5 billion in your spinal cord alone.

Justina: Your brain is the control centre for your whole body.It communicates with the rest of your body through a network of nerve cells, known as the nervous system.

Georgina: Shall we take a closer look?

Justina: Your brain is connected to the spinal cord, which is made up of nervous tissue that runs down your spine.Thirty one pairs of spinal nerves branch off into a wider network of nerves that spread throughout your body.

Georgina: The brain and spinal cord form the central nervous system.The nerves that go to other parts of your body are called the peripheral nervous system, because they go to the periphery, or edges.

Justina: You’ve got a lot of nerves.

Georgina: True!If you laid all your nerves end to end, they’d be nearly a thousand kilometres!Inside each nerve are nerve cells, called neurons.There are billions of neurons; most of them inside your brain.

Justina: Neurons generate electrical impulses that travel along the axon; a thin fibre on a neuron, to communicate with the brain.
Different parts of the brain do different things and scientists have discovered what some parts do by using scanning methods, like magnetic resonance imaging, or by studying the brains of people who have died.Broca’s area was discovered when a patient who had lost the power of speech, died.One examining his brain, Paul Broca found the left frontal lobe was damaged through disease, suggesting this part was responsible for language.

Georgina: The cerebrum (the largest part of the brain) is divided into two halves called hemispheres.It controls things like personality, thought, language, memory and more.Its’ folded outer layer is called the cerebral cortex and contains over 15 billion neurons.

Justina: The cerebellum controls balance, coordination of movement and muscular activity.

Georgina: And the hypothalamus links the brain with the endocrine system, which regulates hormones that control body temperature, water levels, hunger and sleep.

Justina: The brain stem connects the brain to the spinal cord.An important part of the brain stem is the medulla oblongata.It coordinates and controls unconscious activities and involuntary movements like breathing, swallowing and sneezing.For a voluntary action, there are three main stages in the nervous system.Firstly, your sensory receptors, located in your sense organs: your eyes, ears, nose, tongue or skin, respond to a stimulus such as light, sound or touch.

Georgina: The sensory receptor generates and sends an electrical impulse along your sensory neurons to relay neurons in your brain.

Justina: Secondly, the brain interprets the signal, depending on where it’s come from.

Georgina: For example, sight if it’s come from the eyes or sound if it’s come from the ears.

Justina: Then thirdly, the brain sends electrical impulses via a motor neuron, telling your muscles to contract or your glands to release hormones.This all happens very fast.Nerve impulses travel at up to 100 metres per second.

Georgina: If your body is in danger of being hurt, you can respond even more quickly and can bypass the brain with a reflex action.Instead of sending the electrical impulse to the brain, it is sent along the sensory neuron to a relay neuron in the spinal cord.The impulse passes straight to a motor neuron, to get your muscles to contract quickly.That’s how you snatched your hand away so fast if you touched something hot or sharp.

Justina: It’s amazing to think that there’s so much going on in the nervous system right now.

Georgina: Yeah, the brain and the nervous system work all the time, even when you’re asleep.

Justina: Our neurons are always kept busy.