Cells and control revision notes

Cerebral Hemispheres

The cerebral hemispheres form the largest part of the brain. They are responsible for intelligence, memory, language, and conscious thought. They also control sensations and voluntary actions across the body. The cerebrum is divided into two hemispheres, left and right, which are connected by a band of nerve fibres.

Cerebellum

Positioned at the back of the brain, below the cerebrum, the cerebellum plays a vital role in motor control. Its functions include coordinating muscle movements, maintaining balance, and regulating posture. Damage to the cerebellum can lead to problems with coordination and movement.

Medulla Oblongata

The medulla oblongata is located at the base of the brain, connecting to the spinal cord. It regulates involuntary life-sustaining functions. These include the control of breathing, heartbeat, blood pressure, and reflexes such as vomiting, coughing, and sneezing. It forms part of the brainstem.

Integrated Brain Function

While each part has specialised roles, the brain's regions work together. For instance, the cerebral hemispheres initiate a voluntary movement, the cerebellum refines its coordination, and the medulla oblongata ensures vital functions like breathing continue unimpeded during the action. This interconnectedness allows for complex physiological and cognitive processes.

What is Cancer?

Cancer is a disease characterised by the uncontrolled division of abnormal cells. Rather than following the body's normal regulatory processes for cell growth and division, cancerous cells multiply continuously.

Cell Division Normal vs. Abnormal

Normally, cell division is a highly regulated process where cells divide only when needed for growth or repair. In cancer, genetic changes disrupt these controls, causing cells to divide excessively and without proper regulation.

Formation of Tumours

Uncontrolled cell division leads to the formation of a mass of cells called a tumour. Tumours can be either benign (non-spreading) or malignant (cancerous, with the ability to invade and spread).

Causes of Cell Changes

Changes in cells that lead to cancer are often due to mutations in specific genes that control cell growth and division. These mutations can be caused by various factors, including exposure to carcinogens (e.g., UV radiation, tobacco smoke) or inherited genetic predispositions.

The Cell Cycle: Interphase

The cell cycle involves a period of growth and DNA replication (interphase) followed by cell division (mitotic phase). Interphase is crucial for preparing the cell for division. During the S phase of interphase, the cell's DNA is duplicated, leading to chromosomes that consist of two identical sister chromatids joined at a centromere. The cell also grows and synthesises proteins during the G1 and G2 phases.

Stages of Mitosis and Cytokinesis

Mitosis is the division of the nucleus, ensuring each new cell receives an identical set of chromosomes. It comprises several distinct stages:

1. Prophase: Chromosomes condense and become visible, the nuclear envelope starts to break down, and the spindle fibres begin to form.
2. Metaphase: Chromosomes line up individually along the cell's equator (metaphase plate).
3. Anaphase: Sister chromatids separate and are pulled to opposite poles of the cell by the shortening spindle fibres.
4. Telophase: Chromosomes decondense at opposite poles, new nuclear envelopes form around each set of chromosomes, and the spindle fibres disappear.

Following nuclear division, Cytokinesis occurs, which is the division of the cytoplasm, resulting in two separate, genetically identical daughter cells.

What are Percentile Charts?

Percentile charts are graphical tools used in healthcare to track physical growth (e.g., height, weight, head circumference) in children and adolescents. They compare a child's measurements to those of a large, healthy reference population of the same age and gender. Each line on the chart represents a percentile, indicating the proportion of the reference population that falls below that measurement.

Interpreting Percentiles

The 50th percentile line represents the average measurement. A child on the 75th percentile for weight means 75% of children of the same age and gender weigh less. Consistent growth along a percentile line is generally healthy. Significant deviations (e.g., crossing multiple percentile lines rapidly) can indicate potential health issues like undernutrition, overnutrition, or underlying medical conditions, requiring medical review.

Purpose of Growth Monitoring

Using percentile charts allows healthcare professionals to: 1. Identify normal growth patterns. 2. Detect deviations from expected growth early. 3. Monitor the effectiveness of nutritional or medical interventions. 4. Reassure parents about their child's development. Regular plotting helps to build a growth curve for individual children.