the biological model

1. Overview of the Biological Model

• Basic Assumption:
  The nervous system controls all thought and behavior — normal and abnormal.

• Cause of Abnormal Behavior:
  Arises from changes in neural functioning triggered by:

  • Drugs

  • Hormone imbalances

  • Environmental toxins

  • Head trauma

  • Major infections

  • Genetic defects

  • Other biological factors

• Treatment Implication:
  Biological/medical interventions (e.g., medication, medical procedures) are used to alter physical conditions to improve mental functioning.

2. The Medical Model

• Perspective:
  Disturbed behavior is seen as symptoms of an underlying illness.

• Key Concepts:

  • Etiological factors: Specific, identifiable causes.

  • Syndrome: Pattern of symptoms that co-occur and follow a predictable course.

  • Prognosis: Expected course/outcome of illness.

• Approach:

  • Look for biochemical, genetic, or physical causes.

  • Patient’s role: treated as a “patient” with a diagnosable condition.

3. Nervous System Structures & Functions

Major Brain Regions:

1. Hindbrain:

   • Medulla: Breathing, heart rate, swallowing, BP.

   • Reticular formation: Arousal, attention, sleep–wake cycles.

   • Cerebellum: Balance, posture, locomotion, coordination.

   • Damage → coma risk.

2. Midbrain:

   • Coordinates head/eye movements.

   • Controls gross body/limb movement.

   • Responses to visual, auditory, tactile stimuli.

   • Regulates responses to rewarding stimuli.

3. Forebrain:

   • Thalamus: Relay station for sensory signals (except smell).

   • Hypothalamus: Regulates hunger, thirst, temperature, sex drive (“4 Fs”); links nervous & endocrine systems; involved in stress & emotion/memory regulation.

   • Connected to pituitary gland (master gland for hormones).

   • Cerebrum: Largest brain part; outer layer = cerebral cortex.

     • Functions: Abstract thought, complex language, planning, imagination.

     • Divided into lobes: frontal, parietal, occipital, temporal.

4. Neurotransmitters & Abnormality

• Neurotransmitters: Chemical messengers between neurons, affecting whether the next neuron fires.

• Key terms:

  • Synapse: Gap between neurons.

  • Dendrites: Receive incoming signals.

  • Axon: Sends signals to other neurons.

  • Reuptake: Reabsorption of neurotransmitters into original neuron.

• Important Neurotransmitters:

  • Acetylcholine (ACH): Movement, arousal, learning, memory, sleep.

  • Norepinephrine: Heart rate, sleep/arousal, attention, mood, eating.

  • Dopamine: Movement, reward; high levels linked to schizophrenia.

  • Serotonin: Emotion regulation, sleep, behavioral control; linked to depression.

  • GABA: Inhibits neuronal firing; linked to anxiety control.

• Drug Effects:

  • Many psychiatric medications alter neurotransmitter levels (e.g., Prozac ↑ serotonin, Thorazine ↓ dopamine).

5. Genetic Influences

• Genes: DNA sequences on chromosomes; blueprint for proteins that build/maintain all body systems.

• Genotype: Full genetic makeup.

• Phenotype: Observable traits from gene–environment interaction.

• Example: PKU disorder — single gene defect interacts with diet to produce/avoid severe problems.

• Nature & Nurture:
  Genes interact with prenatal, environmental, and social factors.

• Epigenetics:

  • Study of gene expression changes without DNA sequence changes.

  • Mechanisms can switch genes on/off, influenced by environment, stress, trauma, drugs.

  • Linked to disorders like autism spectrum, substance abuse, PTSD.

6. Behavioral Genetics Research

• Goal: Separate and measure genetic vs. environmental contributions to traits/disorders (heritability).

• Family studies: Closer relatives share more genes → higher shared disorder rates suggest genetic influence.

• Adoption studies: Compare adopted individuals to biological and adoptive parents.

• Twin studies:

  • Monozygotic (identical) share 100% of genes; dizygotic (fraternal) share ~50%.

  • Compare twins reared together vs. apart.

• Key finding: Higher genetic similarity often → higher concordance rates, but environment also plays a major role.

7. Research Domain Criteria (RDoC)

• Developed by NIMH to guide research beyond DSM categories.

• Purpose: Identify biological/psychological systems underlying symptoms; dimensional, not categorical.

• Six Major Constructs:

  1. Negative valence systems (response to threat/loss)

  2. Positive valence systems (response to reward/motivation)

  3. Cognitive systems (perception, memory, thought)

  4. Social processes (interactions, self-understanding)

  5. Arousal/regulatory systems (activation and regulation)

  6. Sensorimotor systems (movement control)

• Encourages study of overlapping biology across disorders (e.g., schizophrenia & bipolar).

Quick Study Summary

• Biological model: Abnormality = physical/nervous system malfunction.

• Medical model: Symptoms → underlying illness with identifiable cause & course.

• Brain structures:

  • Hindbrain (vital life functions),

  • Midbrain (movement, stimuli responses),

  • Forebrain (complex thought, emotion regulation).

• Neurotransmitters: Chemical messengers (dopamine, serotonin, norepinephrine, GABA, ACH) linked to various disorders.

• Genetics: DNA → proteins → brain/body structure/function; interacts constantly with environment.

• Epigenetics: Environment can switch gene activity on/off; relevant to many mental disorders.

• Behavioral genetics: Family, twin, adoption studies estimate heritability & environment effects.

• RDoC: Research approach examining underlying functional systems across disorders.