Edexcel A Level (IAL) Biology -8.16 Brain Disease- Study Notes- New Syllabus

Brain Chemicals, Ill Health and Drug Development

🌱 Introduction

The brain uses chemical messengers called neurotransmitters to pass signals between neurones. When their levels become too low or too high, brain function becomes disrupted and diseases can develop. Two key examples are dopamine and serotonin.

📍 Dopamine and Parkinson’s Disease

What Dopamine Normally Does

• Controls smooth, coordinated movement.
• Released by neurones in the basal ganglia, especially the substantia nigra.

What Goes Wrong in Parkinson’s

• Dopamine-producing neurones degenerate and die.
• Leads to very low dopamine levels.
• Motor pathways cannot operate smoothly.

Symptoms

• Tremors in hands
• Muscle stiffness
• Slow movement
• Difficulty starting or stopping movement
• Poor balance

How This Led to New Drugs

• Lack of dopamine inspired drugs that increase dopamine levels.
• Main treatment: L-DOPA, converted into dopamine by the brain.
• Often combined with drugs that slow L-DOPA breakdown.
• Some drugs mimic dopamine’s action (dopamine agonists).

💊 Serotonin and Depression

What Serotonin Normally Does

• Regulates mood, sleep, appetite and emotions.
• Low levels linked to low mood.

What Goes Wrong in Depression

• Serotonin levels in synapses drop too low.
• Weakens signalling in brain regions linked to mood, memory and reward.

Symptoms

• Persistent sadness
• Loss of motivation
• Sleep disturbances
• Low energy
• Anxiety

How This Led to New Drugs

• Goal is to increase serotonin levels in synapses.
• Most common treatment: SSRIs (Selective Serotonin Reuptake Inhibitors).
• SSRIs block reuptake pumps so serotonin stays longer in the synapse.
• Strengthens signalling and improves mood.

⭐ Why Understanding Brain Chemicals Helps Drug Development

• Reveals which neurotransmitters are too low or too high.
• Helps design targeted drugs that:
  • Replace the missing chemical
  • Prevent its breakdown
  • Increase its release
  • Or mimic its action
• Leads to more effective treatments with fewer side effects.