Psychology: Biopsychology and Human Genetics

Overview of Biopsychology

• Biopsychology is a field of study that explores the biological mechanisms underlying human behavior. Its primary areas of focus include:

  • Genetics: Investigating how inherited genes influence both physiological and psychological traits.

  • Nervous System Structure and Function: Analyzing the physical components and operations of the brain and nerves.

  • Endocrine System Interactions: Studying how the nervous system communicates and interacts with the body's hormonal system.

• Various brain imaging techniques allow scientists to see different aspects of brain function, including PET scans (positron emission tomography), CT scans (computed tomography), and fMRI (functional magnetic resonance imaging).

Human Genetics and Evolutionary Theory

• Inheritance and Evolution:

  • Charles Darwin's Theory of Evolution by Natural Selection (proposed in On the Origin of Species, 1859) states that organisms better suited for their environment are more likely to survive and reproduce.

  • Adaptive characteristics include those that protect against predators, increase access to food, and keep offspring alive.

  • Genetic Variation: The genetic difference between individuals that contributes to a species' adaptation. This variation begins when an egg containing $23$ chromosomes is fertilized by a sperm containing $23$ chromosomes.

• Cellular Components:

  • Chromosome: A long strand of genetic information known as DNA.

  • Deoxyribonucleic acid (DNA): A helix-shaped molecule composed of nucleotide base pairs.

  • Gene: A specific sequence of DNA that controls or partially controls physical characteristics (traits).

  • Allele: A specific version or variation of a gene.

• Example of Adaptation: Sickle Cell Anemia:

  • This genetic condition causes red blood cells to take a crescent shape, which can lead to early death.

  • However, carriers of just one copy of the gene are immune to malaria, making the gene beneficial in environments where malaria is common (e.g., Africa).

Genetic Expression and Inheritance Patterns

• Genotype vs. Phenotype:

  • Genotype: The actual genetic makeup of an individual based on DNA inherited from parents.

  • Phenotype: The observable physical characteristics (e.g., hair color, skin color, height, build).

• Allele Interaction:

  • Dominant Allele: Possession of this allele (inherited from one or both parents) always results in the expression of that phenotype.

  • Recessive Allele: This phenotype is only expressed if the individual is homozygous for that allele (inheriting it from both parents).

  • Homozygous: Two identical alleles ($AA$ or $aa$).

  • Heterozygous: Two different alleles ($Aa$).

  • Polygenic Traits: Traits controlled by more than one gene.

• Punnett Squares:

  • A tool used to predict how genes interact in offspring.

  • Example: Cleft chin is a dominant trait ($B$). A smooth chin ($bb$) only occurs with two recessive alleles.

  • Example: Phenylketonuria (PKU) is a recessive condition. If two heterozygous parents ($Np$) mate, there is a $25\%$ chance the offspring will express the PKU phenotype.

• Mutations: Sudden, permanent changes in a gene which can be harmful or occasionally beneficial.

Gene-Environment Interactions

• Range of Reaction: Asserts that our genes set boundary limits for our potential, while the environment determines where within that range we fall.

• Genetic Environmental Correlation: Suggests our genes influence our environment, and our environment influences the expression of our genes.

• Epigenetics: The study of how the same genotype can lead to different phenotypes based on environmental interaction.

Neuron Structure and Function

• Neuronal Components:

  • Semi-permeable membrane: Allows small or uncharged molecules to pass while blocking large or highly charged ones.

  • Dendrites: Receive incoming electrical signals from other neurons.

  • Axon: The long fiber down which signals travel.

  • Myelin Sheath: A fatty substance that insulates the axon to increase signal speed.

  • Terminal Buttons: Contain synaptic vesicles which store chemical messengers called neurotransmitters.

  • Synapse: The microscopic space between the terminal button of one neuron and the dendrite of another.

• Action Potential:

  • Resting Potential: The state of readiness where $Na^{+}$ is more concentrated outside and $K^{+}$ is more concentrated inside ($-70\,mV$).

  • Threshold of Excitation: The level of charge (typically $-55\,mV$) required to trigger an action potential.

  • Depolarization: The membrane potential becomes less negative ($Na^{+}$ rushes in), making the neuron more likely to fire ($Peak \approx +30\,mV$).

  • Hyperpolarization: The membrane potential becomes more negative, making the neuron less likely to fire.

  • All-or-none Principle: The signal is either sufficient to reach the threshold or it is not; there is no partial firing.

  • Reuptake: The process of moving a neurotransmitter from the synapse back into the axon terminal.

Neurotransmitters and Psychopharmacology

• Major Neurotransmitters:

  • Acetylcholine: Muscle action and memory.

  • Beta-endorphin: Pain and pleasure.

  • Dopamine: Mood, sleep, and learning.

  • Norepinephrine: Heart function, intestines, and alertness.

  • Serotonin: Mood and sleep.

  • GABA (Gamma-aminobutyric acid): Brain function and sleep (inhibitory).

  • Glutamate: Memory and learning (excitatory).

• Drugs and Medication:

  • Psychotropic medications: Drugs that restore neurotransmitter balance.

  • Agonist: Mimics or strengthens the effects of a neurotransmitter.

  • Antagonist: Blocks or impedes the normal activity of a neurotransmitter.

  • Clinical Correlation: Parkinson's disease is linked to low dopamine (treated with agonists); Schizophrenia is linked to high dopamine (treated with antagonists).

The Nervous System Structure

• Central Nervous System (CNS): Includes the Brain and Spinal Cord.

• Peripheral Nervous System (PNS): Connects the CNS to the rest of the body.

  • Somatic Nervous System: Relays sensory and motor information to and from the CNS.

  • Autonomic Nervous System: Controls internal organs and glands.

    • Sympathetic Nervous System: Prepares the body for "fight or flight" energy expenditure.

    • Parasympathetic Nervous System: Associated with "rest and restore" or "rest and digest" functions.

• Homeostasis: A state of equilibrium maintained by the balance of sympathetic and parasympathetic activities.

Brain Anatomy and Substructures

• The Brain Structure:

  • Bilateral: Divided into two hemispheres (left and right).

  • Lateralization: The concept that each hemisphere has specialized functions (e.g., left controls the right side of the body).

  • Corpus Callosum: A thick band of neural fibers connecting the two hemispheres.

• The Forebrain (Largest Part):

  • Cerebral Cortex: Surface of the brain associated with high-level processes (thought, emotion, memory).

  • Thalamus: Sensory relay center (except for smell).

  • Hypothalamus: Regulates homeostasis (temperature, appetite, blood pressure).

  • Pituitary Gland: The "master gland" of the endocrine system.

  • Limbic System: Includes the Amygdala (emotion/fear) and Hippocampus (learning/memory).

• Cerebral Lobes:

  • Frontal Lobe: Executive function, motor control, emotion, and language. Contains the Motor cortex, Prefrontal cortex, and Broca's area (language production).

  • Parietal Lobe: Processes sensory information. Contains the Somatosensory cortex.

  • Temporal Lobe: Hearing, memory, and emotion. Contains the Auditory cortex and Wernicke's area (speech comprehension).

  • Occipital Lobe: Visual processing. Contains the primary visual cortex.

• Midbrain and Hindbrain:

  • Midbrain: Contains the Reticular formation (sleep/wake cycle), Substantia Nigra, and Ventral Tegmental Area (VTA) (dopamine production).

  • Hindbrain: Contains the Medulla (heart rate/breathing), Pons (sleep regulation), and Cerebellum (balance/coordination).

• Historical Case: Phineas Gage sustained damage to his frontal lobe (prefrontal cortex), resulting in a loss of impulse control and a complete change in personality.

Brain Imaging and the Endocrine System

• Imaging Techniques:

  • Radiation-based: CT Scan (X-rays of varied density) and PET Scan (radioactive tracer monitoring blood flow).

  • Magnetic-based: MRI (tissue snapshots) and fMRI (metabolic activity over time).

  • Electrical-based: EEG (Electroencephalography) tracking brainwaves with scalp electrodes.

• The Endocrine System (Glands and Hormones):

  • Pituitary: Controls other glands.

  • Thyroid: Secretes thyroxine for growth and metabolism.

  • Adrenal: Secretes hormones for stress response (epinephrine/norepinephrine).

  • Pancreas: Regulates blood sugar.

  • Gonads: Secretes sex hormones (ovaries/testes).