The brain

Techniques used to picture the brain There are three different techniques used to create a picture of the brain: MRI (Magnetic resonance imaging) scan – Measures brain activity using magnets and radio waves. It detects the changes in blood oxygenation and flow that occur in response to neural activity. When the brain is more active it uses more oxygen. MRI’s can be used to produce activation maps that show which parts of the brain are involved in particular processes.

CT (Computed tomography) scan – Builds up a picture of the brain based on how much each part absorbs X-rays. During a CT scan the person lies on a table that moves in and out of an x-ray which rides on a ring around the inside of a tube. The x-ray is aimed at the patients head. After passing through the head, the X-rays are sampled by one of the many detectors that line the machine’s circumference. Images made using x-rays depend on the absorption of the beam by the tissue it passes through. CT scans reveal the features of the brain but do not resolve its structure well. PET (Positron Emission Tomography)scan uses the same techniques as a CT scan.

Advantages of an MRI scan An MRI scan can produce very detailed images of the brain and spinal cord. This makes MRI ideal for helping to diagnose conditions that affect the brain and nervous system. For example: Brain tumours. Dementia.  Alzheimer’s disease. Stroke. Parkinson’s disease. Multiple sclerosis.  Motor neurone disease. Brain infections, such as meningitis and encephalitis. Injuries to the brain or spinal cord. MRI systems do not use ionizing radiation so have a very low incidence of side effects.

Disadvantages of an MRI scan People with pacemakers cannot have MRIs. Some people who are morbidly obese cannot fit in into an MRI system. Claustrophobic patients cannot usually make it through a MRI. The machine makes a lot of noise during a scan.

Advantages of a CT scan CT scan is a painless non invasive procedure with good sensitivity to detect pathology of the head CT scan is far superior to an MRI when evaluating skull fractures CT scan can provide detailed images of the brain nervous tissue CT scan is much cheaper than an MRI an equally as fast

Disadvantages of a CT scan CT scan is associated with a radiation CT scan should never be done in a pregnant female because of the exposure of radiation risk to the foetus. CT is not very good at identifying pathology of the soft tissues. CT is not good at identifying areas of inflammation or infection of the brain compared to MRI

Why are neurons unable to regenerate? In the central nervous system there are two types of glial cells. These cells inhibit axon regeneration. These are; oligodendrocytes and astrocytes. Both play key roles in the central nervous system; support and metabolism. This growth-inhibiting action helps enormously in stabilizing the complex CNS. These cells stop neurones from regenerating so that neurones stay in their intended place, rather than spreading out. This is done as the CNS is very complex. The inhibitors lock the connections into place. Without these proteins, the CNS may not be able to organize itself and work properly. The disadvantage of this is that the CNS has no ability to regenerate itself in the event of injury.