Edexcel Biology Gcse - Coordination And Control - The Nervous System Part 2

All reflex actions follow an overall sequence through the nervous system which is called the reflex arc. Crucially this does not involve the conscious part of the brain, which makes it much quicker. This in turn reduces damage to the body.

stimulus → receptor → sensory neurone → relay neurone → motor neurone → effector → response

1) A receptor in the skin detects a stimulus (the change in temperature).
2) Sensory neurones send electrical impulses to relay neurones, which are located in the spinal cord. They connect sensory neurones to motor neurones.
3) Motor neurones send electrical impulses to an effector.
4) The effector produces a response (muscle contracts to move hand away).

The brain controls complex behaviour. It is made of billions of interconnected neurones and has different regions that carry out different functions.

• Cerebral hemispheres

• Cerebellum

• Medulla oblongata

• Hypothalamus

The cerebrum's outer layer, it is split into two hemispheres and is highly folded. These two hemispheres make up the cerebral cortex. This controls most of our senses, intelligence, personality, conscious thought and high-level functions, such as language and verbal memory.

The nervous system enables humans to react to their surroundings and to coordinate their behaviour. It comprises millions of neurones, and it uses electrical impulses to communicate very quickly.

Modern science has allowed scientists to discover how different parts of the brain function. Neuroscientists have been able to map various regions of the brain to particular functions by studying patients with brain damage, electrically stimulating different parts of the brain and using MRI scanning techniques.

Scientists have stimulated different parts of the brain with a weak electrical current and asked patients to describe what they experienced. If the motor area is stimulated, the patient makes an involuntary movement. If the visual area is stimulated, they may see a flash of colour. EEGs (Electroencephalograms) can be created and studied, to observe the electrical activity in the brain.

• MRI (magnetic resonance imaging)

• CT (computed tomography)

• PET (positron emission tomography)

MRI scanners use strong magnetic fields and radio waves to show details of brain structure and function. Patients are asked to perform various tasks and, by looking at the scan, scientists can see which parts of the brain are active when the task is carried out. The patient lies on a bed which moves into the machine. Some people can feel claustrophobic inside an MRI scanner.

CT scanners are similar to MRIs. The patient lies on a bed which passes through a ring of equipment (not into the machine like in MRI). The ring takes a series of x-rays from different angles. These are processed by a computer to allow the doctors to see inside brains and other parts of the body.

PET scanners detect gamma rays that radiate from a chemical compound called a tracer. PET scans are used to detect high levels of metabolic reactions inside a person. Before going into the scanner the patient consumes the tracer. This travels to any area of the body which has unusually high levels of metabolic reactions. This is often a tumour and so PET scans are used to detect cancers.

• the force of impact

• the size or shape of the object hitting the skull

• the position the object hits the skull

• the time it takes for treatment

Many brain injuries are fatal. Longer-term symptoms of brain damage include speech or movement problems, reduced coordination, memory loss and personality changes.

Often impacts to the skull result in the brain swelling as it produces excessive fluid. Brain surgery may be needed to remove a tumour or excess fluid, such as blood. All surgery carries a level of risk, but due to the complexity and delicacy of the brain, investigating and treating brain disorders can be very difficult. If surgery is undergone more damage or side-effects may be created, which could affect the patients' quality of life. Serious considerations about the risks involved against the benefits need to be undertaken first. Physiotherapists play a very important role helping with the rehabilitation of patients with brain damage.

• Cornea

• Iris

• Retina

• optic nerve

• Sclera

• lens

• Suspensory ligament

• Pupil

• ciliary muscle

• Fovea