Rucete ✏ Campbell Biology In a Nutshell
Unit 7 ANIMAL FORM AND FUNCTION — Concept 49.5 Many Nervous System Disorders Can Now Be Explained in Molecular Terms
Nervous system disorders such as schizophrenia, depression, Alzheimer’s, and Parkinson’s disease are major global health issues. Though once poorly understood, advances in neuroscience have revealed underlying molecular and genetic mechanisms, guiding the development of new treatments and ongoing research efforts.
1. Nervous System Disorders and Research
- Nervous system disorders result in more hospitalizations than heart disease or cancer
- Many were once untreatable, but now some (e.g., depression) can be managed with medication
- Research focuses on identifying genetic and environmental factors
- Family and twin studies help distinguish genetic vs. environmental roles
2. Schizophrenia
- Affects ~1% of the global population
- Characterized by psychotic episodes, hallucinations, and disorganized thought
- Strong genetic basis (48% risk in identical twins), but not solely genetic
- Dopamine hypothesis: excess dopamine activity contributes to symptoms
- Dopamine blockers relieve symptoms; amphetamines mimic them
- Recent studies implicate the complement protein C4 in susceptibility
3. Depression
- Includes major depressive disorder and bipolar disorder
- Major depression: persistent sadness, loss of interest; affects 1 in 7 adults
- Bipolar disorder: mood alternates between manic and depressive phases
- Manic states are sometimes associated with creative bursts
- Treated with medications that enhance biogenic amines like serotonin (e.g., Prozac)
4. Drug Addiction and the Brain’s Reward System
- Reward pathway involves dopamine release from VTA to nucleus accumbens and prefrontal cortex
- This circuit motivates vital behaviors like eating and reproduction
- Drugs such as cocaine, alcohol, and opioids hijack this pathway
- Chronic use alters brain circuits, leading to compulsive craving
- 130 Americans died per day from opioid overdoses in 2018
- Animals will self-administer drugs over food, indicating addictive potential
5. Alzheimer’s Disease
- Most common cause of dementia; affects 10% of people at 65, 35% at 85
- Progressive decline in memory and cognitive ability
- Key brain pathologies:
- Amyloid plaques: toxic aggregates of β-amyloid
- Neurofibrillary tangles: tau protein clumps disrupting neuron structure
- Causes shrinkage in cortex and hippocampus
- Early-onset cases often involve tau gene mutations
- CTE: similar tau-linked condition seen in athletes and soldiers with head injuries
6. Parkinson’s Disease
- Progressive motor disorder: tremors, rigidity, balance issues
- Can also lead to dementia in advanced stages
- Caused by death of dopamine-producing neurons in midbrain
- Some cases linked to genetic defects affecting mitochondria
- Treatment options include L-dopa, which converts to dopamine in the brain
- Also managed with deep-brain stimulation and experimental therapies
7. The BRAIN Initiative
- U.S. launched the BRAIN Initiative in 2014 as a 12-year neuroscience project
- Goals: map brain circuits, track brain activity, understand cognition and behavior
- Inspired by the Human Genome Project and space exploration programs
In a Nutshell
Many nervous system disorders once considered untreatable are now understood at the molecular and genetic levels. From schizophrenia and depression to neurodegenerative diseases like Alzheimer’s and Parkinson’s, breakthroughs in neuroscience have revealed key mechanisms and opened pathways for treatment, while large-scale initiatives like the BRAIN project aim to decode the brain’s deepest mysteries.