Cells and control study guide

Accessing brain tissue for direct study inside the skull presents significant challenges due to its delicate nature and vital protective structures. To overcome these difficulties, non-invasive imaging techniques like Computed Tomography (CT) scans and Positron Emission Tomography (PET) scans are employed to investigate brain structure and function. CT scans use X-rays to create detailed cross-sectional images of the brain. They are particularly effective for visualising bone, blood vessels, and soft tissues, allowing clinicians to detect structural abnormalities such as tumours, haemorrhages, or damage from injury. While CT scans provide anatomical information, they offer limited insight into brain activity.

PET scans, on the other hand, reveal brain function by detecting metabolic activity. A small amount of a radioactive tracer, typically a glucose analogue, is injected into the bloodstream. As the brain consumes glucose for energy, active areas absorb more of the tracer. The tracer emits positrons, which collide with electrons, producing gamma rays that are detected by the PET scanner. A computer then creates a colourful, three-dimensional image showing which parts of the brain are most active during specific tasks or at rest. For example, a PET scan can identify areas of the brain involved in language processing or memory formation, aiding in the diagnosis of conditions like Alzheimer's disease or epilepsy. Both CT and PET scans are crucial tools for neuroscientists and medical professionals, allowing them to study the brain without invasive surgery.

The human eye is a complex organ, but various conditions can affect its ability to focus and perceive light correctly. These conditions are known as eye defects. Common defects include cataracts, which involve clouding of the lens, and refractive errors like long-sightedness (hyperopia) and short-sightedness (myopia). Long-sightedness is when light focuses behind the retina, making distant objects clear but near objects blurry. Short-sightedness causes light to focus in front of the retina, resulting in clear near vision but blurry distant vision. Colour blindness is a different type of defect, usually inherited, where certain cone cells in the retina do not function correctly, leading to difficulty distinguishing between specific colours, most commonly red and green.