Cells and control revision notes

Cataract Correction

Cataracts cause the lens of the eye to become cloudy, scattering light and leading to blurred vision. The primary treatment is surgical removal of the clouded natural lens. An artificial intraocular lens (IOL) is then implanted to replace its focusing function, restoring clear vision.

Long-Sightedness (Hyperopia) Correction

In hyperopia, light from near objects focuses behind the retina, often due to an eyeball that is too short or a lens that is too weak. Convex (converging) lenses in glasses or contact lenses correct this by bringing light rays together sooner. Laser surgery can also reshape the cornea to increase its curvature, enhancing its focusing power.

Short-Sightedness (Myopia) Correction

Myopia occurs when light from distant objects focuses in front of the retina, typically because the eyeball is too long or the lens is too strong. Concave (diverging) lenses in glasses or contact lenses are used to spread out light rays slightly before they enter the eye, ensuring they focus on the retina. Laser eye surgery can correct myopia by flattening the cornea, reducing its ability to converge light.

Animal Growth: Cell Division and Differentiation

In animals, growth primarily occurs through cell division (mitosis), which increases the number of cells. This process is crucial for development from a zygote into a multicellular organism, and for repairing tissues and replacing dead cells throughout life. Cells then differentiate, meaning they become specialised to perform specific functions, such as nerve cells, muscle cells, or blood cells. Once an animal reaches its mature size, the rate of cell division for overall growth generally slows down significantly, although cell replacement for maintenance continues.

Plant Growth: Division, Elongation, and Differentiation

Plant growth is a continuous process occurring in specific regions known as meristems. These regions, such as the tips of roots and shoots, contain cells that undergo rapid cell division (mitosis), increasing the cell number. Following division, these new cells undergo cell elongation, where they absorb water and expand significantly, increasing the plant's size. Finally, these elongated cells differentiate into various specialised plant tissues, like xylem for water transport, phloem for nutrient transport, or epidermal cells for protection, contributing to the complete structure of the plant.

Challenges of Brain Access

Directly examining brain tissue inside the skull is highly invasive and carries significant risks due to the brain's delicate nature and its vital functions. Surgical access can lead to infection, haemorrhage, or damage to critical brain regions, hence non-invasive methods are preferred. The skull itself provides a strong protective barrier, making direct observation impossible without intervention.

CT Scans: Structural Insights

CT (Computed Tomography) scans use multiple X-ray beams from different angles to create detailed cross-sectional images of the brain. These images show the brain's structure, allowing identification of abnormalities like tumours, strokes, or trauma. They are primarily used for diagnosing structural problems rather than functional activity. CT scans are quicker and cheaper than MRI, but involve ionising radiation.

PET Scans: Functional Insights

PET (Positron Emission Tomography) scans detect brain activity and function. A radioactive tracer (often a glucose analogue) is injected; active brain cells uptake more glucose. The tracer emits positrons which release gamma rays detected by the scanner. This creates images showing metabolic activity, highlighting areas of the brain that are more active during specific tasks. PET scans are valuable for studying neurological disorders and cognitive processes.

Comparison and Complementary Use

CT scans provide structural 'snapshots' of the brain, while PET scans illustrate its functional activity. Neither method requires direct surgical access to brain tissue. Often, both techniques are used together to gain a comprehensive understanding of a neurological condition, combining anatomical detail with metabolic function. This non-invasive approach significantly reduces risk to patients while maximising diagnostic and research capabilities.

Cataracts

Cataracts are a condition where the lens of the eye becomes cloudy or opaque. This clouding prevents light from passing through clearly to the retina, leading to blurred vision, faded colours, and difficulty seeing at night. They commonly develop with age but can also be caused by injury, diabetes, or certain medications. Surgery to replace the cloudy lens with an artificial one is the primary treatment.

Refractive Errors: Myopia (Short-sightedness) and Hyperopia (Long-sightedness)

Myopia, or short-sightedness, occurs when the eye is too long or the cornea is too curved, causing light to focus in front of the retina. This results in distant objects appearing blurry, while near objects are clear. Hyperopia, or long-sightedness, occurs when the eye is too short or the cornea is not curved enough, causing light to focus behind the retina. This makes near objects appear blurry, while distant objects may be clear. Both conditions are corrected using corrective lenses (glasses or contact lenses) that adjust the focal point of light onto the retina, or through refractive surgery.

Colour Blindness

Colour blindness, also known as colour vision deficiency, is typically an inherited condition that affects an individual's ability to distinguish certain colours. It is most commonly caused by a mutation in the genes responsible for the light-sensitive cone cells in the retina, which are responsible for colour perception. The most common form is red-green colour blindness. There is currently no cure, but some people use special lenses or apps to help distinguish colours.