The nervous system

Your nervous system allows you to respond to your surroundings and to coordinate your behaviour. It helps you to avoid danger, find food, catch the bus. It works through a system of receptors, processing centres and effectors, all linked up by nerve cells.
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Components of the nervous system
The nervous system is divided into 2 main sections
  • the central nervous system (CNS) - brain and spinal cord
  • the peripheral nervous system (PNS) - motor and sensory nerves

The CNS is enclosed within a boney casing to protect it. This is the skull and the vertebral column.
The peripheral nerves branch off from the spinal cord.

The nervous system processes information by using a simple series of steps:
KEY WORDS
Stimulus - a change in the environment
Receptors - detect changes in the environment
Effectors - carry out the response (muscles and glands)
Neurone - a nerve cell
Impulse - electrical signal
Sense organs
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Neurones

Neurone is another word for a nerve cell. There are 4 main principles of neurones
  1. they are single cells and can sometimes be feet long, even though you need a microscope to see them!
  2. they carry electrical signals called impulses. This is how information can be moved so quickly
  3. when they join another neurone, the impulse is converted to a chemical signal which diffuses across the minute gap between the cells. This gap is called a synapse (more about this later)
  4. there are 2 major types of neurone: sensory and motor neurones

This is a motor neurone showing the main features of an axon, dendrites and a cell body. In addition to this, neurones also have all of the usual features of an animal cell, including a nucleus, cytoplasm, ribosomes, mitochondria and cell membrane

MOTOR NEURONES take information from the CNS to the effectors
SENSORY NEURONES take information from the sense organs to the CNS
How the nervous system works

  • Stimulus is detected by the receptor
  • The information is sent along a sensory neurone
  • to the CNS (brain and spinal cord)
  • CNS coordinates the response (effectively decides what to do!) and 
  • sends information to the motor neurones which
  • cause the effectors to respond (eg, muscles contracting)
So, what's the difference between a neurone and a nerve? Well a neurone is a single nerve cell whereas a nerve is a bundle of hundreds or even thousands of neurones. You can see nerves with the naked eye, whereas neurones you need to use a microscope! It's a bit like a rope. A rope is made up of many individual fibres a bit like a nerve is made up of many individual neurones
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A nerve in the arm, clearly visible to the naked eye
Neurones are not joined up directly but instead have minute gaps between them. These junctions are called synapses. Here the electrical impulse is converted into a chemical called a neurotransmitter. The neurotransmitter is released from the presynaptic membrane and diffuses across the synaptic gap where it binds to receptors on the postsynaptic membrane. This triggers a new impulse in the postsynaptic neurone.
THE REFLEX ARC
Reflexes are automatic, involuntary and incredibly fast responses of the body which help you to avoid danger or harm. Classic examples are if you touch something very hot or you step on something painful. You have blinking and pupil reflexes which protect your eyes. There are also lots of reflexes that take care of your basic body functions so you don't have to think about them - things like breathing and peristalsis. Can you imagine what would happen if you had to remember to breath?!
The pathway that an impulse takes in order to cause a reflex response is called the reflex arc
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The interneurone is another name for the relay neurone
THE RELAY NEURONE IS FOUND EXCLUSIVELY IN THE CNS. IN THE REFLEX PATHWAY, THE RELAY NEURONE COORDINATES THE RESPONSE. THIS MAKES THE REFLEX VERY FAST - IT DOESN'T INVOLVE CONSCIOUS THOUGHT
  • When you touch an object the pain receptor in your skin is stimulated
  • The impulse passes along a sensory neurone to the CNS - in this case, the spinal cord rather than the brain
  • The information crosses a synapse to the relay neurone, and again at the junction between the relay neurone and the motor neurone
  • The motor neurone carries the impulse to the effector (in the case on the left this is the muscle in the arm), which is stimulated to respond (contract)
  • This action moves the hand away from the flame

The impulse is also sent to the brain so that you know what has happened. This is for info only!
The Brain
Along with the spinal cord, the brain makes up the Central Nervous System (CNS), the processing centre of the nervous system. It is divided up into a number of section, and each section has a different function.
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Cerebrum (also known as cerebral hemispheres or cerebral cortex): made up of 4 lobes (frontal, parietal, occipital and temporal) on each side of the brain (this part of the brain is divided into 2 halves). Function of cerebrum is to control intelligence, memory, emotions, personality, social inhibitions, language, consciousness and thought

Cerebellum (the 'little brain'): Controls balance, movement, coordination and learned motor skills (such as riding a bike, playing the piano, etc).
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Brain stem: connects the main part of the brain to the spinal cord, with which it is continuous. It controls all of the basic, involuntary functions including breathing, heart beat, peristalsis, and reflexes such as coughing and sneezing. Damage to this part of the brain is often lethal.

Hypothalamus: regulates many bodily functions, including thermoregulation. Connected to the pituitary gland and so is involved in the release of hormones

Pituitary gland (the 'master gland'): releases hormones that control growth, blood pressure, stress and the function of the sex hormones.

For more interesting information on the brain and it's functions, check out the history of lobotomies!
The brain can be imaged in a number of different ways. This gives us an idea about the function of the brain, and how various different regions might be involved in controlling the body.
Brain injuries
Doctors can study patients who have suffered brain damage to determine what effect the injury has on the function of the patient
Electrical stimulation
Brain surgery can be done on a conscious patient (as there are no pain receptors in the brain). This allows doctors to electrically stimulate parts of the brain and then see the effect it has on the patient
Magnetic resonance imaging (MRI)
A way of taking images of a brain in living patients. Allows doctors to link loss of function with damage to a particular part of the brain. Recent MRI scanners can take images of a patient while they are carrying out simple tasks, allowing doctors to monitor brain activity in real time
There's a nice section on the BBC Science website on the brain and mind, including articles on psychology, intelligence, personality and emotions. Check it out
Check out this excellent website for more information on the nervous system