The effect of ageing on the nervous system

Welcome to Your Guide on Ageing and the Nervous System!

As we get older, our bodies go through many changes. One of the most important areas where these changes happen is the nervous system. In this chapter, we will explore how ageing affects our senses, our memory, and how certain diseases like Alzheimer's can change the very structure of our brains. Don't worry if some of the biological terms seem a bit heavy at first—we'll break them down step-by-step with simple analogies!

1. General Effects of Ageing on the Nervous System

Just like a computer might get a bit slower as it gets older, the human nervous system undergoes "wear and tear." This affects how we perceive the world around us and how quickly we can react to it.

Sensory Impairment: Vision and Hearing

Ageing often leads to a decline in our sensory receptors. The syllabus focuses on four specific conditions you need to know:

A. Visual Impairment

1. Cataracts: This is when the lens of the eye becomes cloudy. Imagine trying to look through a window that has become "foggy." This happens because proteins in the lens start to clump together.
2. Glaucoma: This is caused by a build-up of pressure inside the eye. If the fluid in the eye doesn't drain properly, the pressure can damage the optic nerve. Think of it like a tire being over-inflated until the delicate rubber starts to weaken.
3. Macular Degeneration: This affects the macula, the part of the retina responsible for sharp, central vision. People with this condition lose the "middle" of their vision but can often still see things at the edges (peripheral vision).

B. Hearing Impairment

As we age, the tiny hair cells in the cochlea (inner ear) can become damaged or die. These cells do not regrow, leading to a permanent loss of hearing, especially for high-pitched sounds. This is often why elderly people might find it hard to hear a phone ringing or a bird chirping.

Memory Loss and Reaction Times

It is normal for reaction times to slow down as we age. This is often because the myelin sheath (the fatty insulation around our neurones) starts to thin, meaning nerve impulses don't travel as fast. Memory loss also occurs because the number of synaptic connections in the brain can decrease over time.

Quick Review Box:
• Cataracts = Cloudy lens.
• Glaucoma = High pressure damaging the optic nerve.
• Macular Degeneration = Loss of central (middle) vision.
• Slower reactions = Thinner myelin or fewer synapses.

Key Takeaway: Ageing reduces the efficiency of our sensory organs and the speed of our nerve impulses, making it harder to process information quickly.

2. Alzheimer’s Disease: A Closer Look

While some memory loss is normal, Alzheimer’s disease is a specific, progressive condition that is much more severe. It is the most common cause of dementia.

Symptoms and Behavioural Changes

Alzheimer's isn't just about forgetting where you put your keys. It involves:
• Cognitive impairment: Severe memory loss, confusion, and difficulty with speech.
• Behavioural changes: Anxiety, irritability, and changes in personality.
• Example: A person might forget the names of close family members or get lost in a place they have lived for forty years.

Histological Changes (What's happening in the brain tissue?)

If we looked at the brain of someone with Alzheimer’s under a microscope, we would see two major changes:

1. Amyloid Plaques: These are clumps of a protein called beta-amyloid that build up outside the neurones. They act like "roadblocks," preventing neurones from communicating with each other.
2. Neurofibrillary Tangles: These are made of a protein called tau that builds up inside the neurones. Imagine the internal "skeleton" of the cell becoming twisted and tangled, eventually causing the cell to die.

Did you know? Because so many neurones die, the brain of an Alzheimer’s patient actually shrinks in size. This is called atrophy.

Causes of Alzheimer's

Scientists believe it is a mix of two factors:
• Genetic causes: Certain genes (like the APOE gene) can increase the risk of developing the disease.
• Environmental causes: Factors like smoking, high blood pressure, and even repeated head injuries (like those in contact sports) may contribute to the risk.

Memory Aid: The "A-B-T" of Alzheimer's
A = Atrophy (brain shrinkage)
B = Beta-amyloid (plaques outside)
T = Tau (tangles inside)

Key Takeaway: Alzheimer's is characterized by physical changes in the brain (plaques and tangles) that lead to the death of neurones and severe loss of function.

3. Practical Investigations: Testing the Ageing Brain

In your Biology B course, you may be asked to interpret data from investigations into how age affects the nervous system.

Investigating Reaction Times

A common way to test this is the ruler drop test. When comparing a 17-year-old to a 70-year-old, you would typically find that the older person has a larger "drop distance" because their reflex arc takes longer to process the stimulus and trigger the muscle contraction.

Investigating Memory

Psychologists and biologists often use "digit span" tests (how many numbers you can remember in a row). As people age, their short-term memory capacity often decreases. When analyzing this data, look for correlations—as age increases, memory performance usually decreases.

Analyzing Secondary Data

You might be given audiograms (hearing tests) or Snellen charts (sight tests) to interpret.
• An audiogram for an older person usually shows a "dip" at higher frequencies (measured in Hertz, \(Hz\)).
• A sight test might show a decrease in visual acuity (the ability to see fine detail).

Common Mistake to Avoid: Don't assume everyone follows the exact same pattern. While the average reaction time slows down, some older individuals may remain very sharp due to "cognitive reserve" (staying mentally active)!

Key Takeaway: Practical tests like the ruler drop or memory span provide measurable evidence of how the nervous system changes over time.

Final Summary: Genetics, Control and Homeostasis

Ageing is a process where our control systems (the nervous system) lose their ability to maintain homeostasis and respond to the environment. Whether it's the physical "roadblocks" of plaques in Alzheimer's or the simple "clouding" of a cataract, these changes explain why our sensory and cognitive abilities decline as we get older.

Keep practicing those data interpretation questions—they are key to mastering this section! You've got this!