Biology and Psychology – Key Notes

Nervous System Overview

  • Integrates thought, sensation, movement, and vital functions via brain, spinal cord, peripheral nerves. It serves as the body's primary communication system.
  • Two main parts: Central Nervous System (CNS) + Peripheral Nervous System (PNS).

Neuron Structure & Function

  • Key parts: dendrites (receive input signals, often from other neurons), cell body (soma; contains nucleus and performs metabolic functions for the neuron), axon (transmits output signals away from the cell body), axon terminals (release neurotransmitters to communicate with other cells).
  • Myelin sheath (glial-produced, e.g., Schwann cells in PNS, oligodendrocytes in CNS) insulates the axon, dramatically speeding up nerve impulse conduction; myelination supports early motor milestones and efficient neural processing.
  • One-way flow: dendrite
    →
    cell body
    →
    axon
    →
    terminals. Neurons are specialized for communication: sensory neurons (afferent) carry information to the CNS, motor neurons (efferent) carry commands from the CNS, and interneurons (associative) connect other neurons.

Neural Impulses

  • Resting potential is maintained by the sodium-potassium (Na+/K+\text{Na}^+/\text{K}^+) pump, which actively transports 3 Na+3\text{ Na}^+ ions out for every 2 K+2\text{ K}^+ ions in, resulting in a negative charge inside relative to outside (approx. −70 mV-70\ \text{mV}).
  • Adequate stimulation (reaching threshold) opens voltage-gated Na+\text{Na}^+ channels
    →
    rapid influx of Na+\text{Na}^+ ions
    →
    depolarization (inside becomes positive); action potential peak approx. +40+40 to +50 mV+50\ \text{mV} (about 110 mV110\ \text{mV} swing). This is followed by repolarization (K+\text{K}^+ efflux) and a brief refractory period (neuron cannot fire again immediately) which prevents re-firing and ensures one-way signal propagation.
  • All-or-none law: if the threshold is reached, an impulse fires at its full, constant strength, regardless of stimulation intensity. If the threshold is not reached, no impulse fires.
  • Conduction speed varies: 22–225 mph225\ \text{mph} (slower in unmyelinated axons due to continuous conduction, much faster in myelinated axons due to saltatory conduction).

Synapse & Neurotransmitters

  • Synapse = axon terminal (presynaptic neuron) + synaptic cleft (gap) + receptor site (postsynaptic neuron).
  • Neurotransmitters are chemical messengers released from synaptic vesicles into the cleft; they bind to specific receptors on the postsynaptic membrane. Excess neurotransmitters are removed from the cleft by reuptake (reabsorbed by the presynaptic neuron) or enzymatic breakdown (degraded by enzymes).
  • Key transmitters:
    • Acetylcholine (ACh): involved in muscle contraction (neuromuscular junction), learning, and memory. Imbalances linked to Alzheimer's disease.
    • Dopamine (DA): associated with pleasure, reward, voluntary movement, and attention. Imbalances linked to Parkinson's disease (low DA) and schizophrenia (high DA).
    • Norepinephrine (NE): impacts arousal, vigilance, mood, and stress response; also acts as a hormone (noradrenaline) in the endocrine system.
    • Serotonin (5-HT): regulates mood, sleep, appetite, and emotional states. Imbalances linked to depression and anxiety.
    • GABA (Gamma-aminobutyric acid): the primary inhibitory neurotransmitter in the brain, reducing neuronal excitability. Imbalances linked to anxiety disorders and epilepsy.
    • Endorphins: natural pain relievers and mood elevators, involved in feelings of well-being.
  • Imbalances in these neurotransmitters are linked to various neurological and psychological disorders (e.g., depression, anxiety disorders, schizophrenia, Parkinson's disease).

Divisions of Nervous System

  • PNS: Somatic Nervous System (voluntary control of body movements via skeletal muscles) & Autonomic Nervous System (regulates involuntary functions of internal organs and glands).
    • Somatic System: includes afferent nerves (sensory input from skin, muscles, joints to CNS) and efferent nerves (motor output from CNS to skeletal muscles).
      • Autonomic splits into Sympathetic (activates fight-or-flight response, expending energy: increases heart rate, dilates pupils, inhibits digestion) and Parasympathetic (promotes rest-and-digest, conserving energy: slows heart rate, constricts pupils, stimulates digestion). These two divisions often have opposing effects to maintain homeostasis.
  • CNS: spinal cord (mediates reflexes independently of the brain via sensory neuron → interneuron → motor neuron pathways) + brain (processing and integration center).

Brain Imaging Techniques

  • CAT/CT (Computed Axial Tomography): Uses a series of X-ray images taken from different angles to create cross-sectional slices for detailed structural analysis of the brain (e.g., identifying tumors, hemorrhages).
  • PET (Positron Emission Tomography): Involves injecting a radioactive tracer (e.g., glucose) into the bloodstream; active brain areas consume more glucose, emitting positrons that are detected to produce a colored metabolic activity map, showing real-time brain function.
  • MRI (Magnetic Resonance Imaging): Uses strong magnetic fields and radio waves to generate highly detailed images of brain structures by detecting the alignment of hydrogen atoms in water molecules. Provides superior anatomical resolution compared to CT.
  • fMRI (functional Magnetic Resonance Imaging): Rapid MRI sequences detect changes in blood flow and oxygenation (BOLD signal) in the brain, indicating neural activity. Allows for real-time observation of brain function during specific tasks.

Brain Structures & Functions

  • Hindbrain:
    • Medulla Oblongata: Controls vital involuntary functions like heart rate, breathing, blood pressure, and reflexes (e.g., vomiting, sneezing).
    • Pons: Acts as a bridge connecting the cerebellum to the cerebral cortex; involved in sleep, respiration, swallowing, bladder control, and facial sensations/movements.
    • Cerebellum ("little brain"): Crucial for balance, posture, coordination of voluntary movements, motor learning, and possibly some cognitive functions.
  • Reticular Formation (extends from hindbrain into midbrain): A network of neurons involved in arousal, attention, sleep-wake cycles; damage can lead to a coma.
  • Forebrain:
    • Thalamus: ~200200 million fibers). Serves as the brain's sensory relay station, directing all sensory information (except smell) to appropriate areas of the cerebral cortex.
    • Hypothalamus: Regulates essential homeostatic functions (e.g., body temperature, hunger, thirst, sexual behavior); acts as the primary link between the nervous system and the endocrine system by controlling the pituitary gland.
    • Limbic System: A group of structures involved in emotion, motivation, and memory. Includes:
    • Amygdala: Processes emotions, particularly fear and aggression.
    • Hippocampus: Critical for the formation of new long-term memories and spatial navigation.
    • Cerebrum: The largest part of the brain, responsible for higher-level functions such as thinking, language, voluntary action, perception, and reasoning.

Cerebral Cortex & Lobes

  • Highly folded outer cerebrum; two hemispheres (left and right) linked by the corpus callosum (a thick band of neural fibers connecting the two hemispheres, allowing them to communicate).
  • Lobes:
    • Frontal Lobe: Involved in executive functions (planning, decision-making, problem-solving), voluntary motor control (contains the primary motor cortex), personality, and impulse control.
    • Parietal Lobe: Processes somatosensory information (touch, temperature, pain, pressure); involved in spatial awareness and navigation. The somatosensory cortex is located here.
  • Temporal Lobe: Primarily processes auditory information (hearing) and is crucial for language comprehension (contains Wernicke's area) and memory formation.
  • Occipital Lobe: Processes visual information; contains the primary visual cortex.
  • Somatosensory cortex (located in the parietal lobe) receives and processes sensory input from the entire body, with different areas mapping to specific body parts.
  • Association areas: Integrate information from various sensory and motor areas, enabling complex cognitive functions (e.g., the prefrontal cortex in the frontal lobe is vital for working memory, planning, and judgment).

Language Areas

  • Broca’s area (typically in the left frontal lobe): Crucial for speech production; damage leads to Broca’s aphasia, characterized by slow, labored, and non-fluent speech, though comprehension remains relatively intact.
  • Wernicke’s area (typically in the left temporal lobe): Essential for language comprehension; damage leads to Wernicke’s aphasia, where speech is fluent but often meaningless or nonsensical ("word salad"), and comprehension is severely impaired.

Endocrine System Overview

  • Ductless glands (endocrine glands) secrete hormones directly into the bloodstream; hormones act as chemical messengers, regulating various body functions. This system is closely coordinated by the hypothalamus (part of the CNS) and the pituitary gland (often called the "master gland" due to its control over other glands), forming a complex feedback loop.

Major Glands & Hormones

  • Pituitary Gland: Located at the base of the brain, controlled by the hypothalamus.
    • Growth Hormone (GH): Regulates growth and metabolism.
    • Prolactin: Stimulates milk production.
    • Vasopressin (Antidiuretic Hormone, ADH): Regulates water balance.
    • Oxytocin: Involved in social bonding, uterine contractions during childbirth, and milk let-down.
  • Pineal Gland: Secretes Melatonin, which regulates sleep-wake cycles (circadian rhythms).
  • Thyroid Gland: Produces Thyroxin, which regulates metabolism; excess leads to hyperthyroidism (increased metabolism, weight loss, anxiety); deficiency leads to hypothyroidism.
  • Adrenal Glands (Adrenal Cortex): Outer part of the adrenal glands, located atop the kidneys. Secretes Corticosteroids (e.g., cortisol) important for stress response, metabolism, and immune function, under the control of ACTH (Adrenocorticotropic Hormone) from the pituitary.
  • Gonads (Sex Glands):
    • Testes (in males): Produce Testosterone, responsible for the development of male primary (reproductive organs) and secondary sex traits (e.g., deeper voice, body hair, muscle mass) and sperm production.
    • Ovaries (in females): Produce Estrogen and Progesterone, which regulate the menstrual cycle, development of female primary and secondary sex traits (e.g., breast development, fat distribution), and pregnancy.

Evolution & Behavior

  • Darwin's Theory of Evolution by Natural Selection: posits that species gradually evolve over generations through the process where individuals with traits best suited for their environment are more likely to survive, reproduce, and pass those adaptive traits (both physical and behavioral) to their offspring.
  • Evolutionary psychology: studies how natural selection has shaped universal human behavior patterns and cognitive processes over time, often focusing on instincts and predispositions.

Genetics Basics

  • Genes: Fundamental units of heredity, segments of DNA that contain instructions for building proteins, which in turn determine traits; genes reside on chromosomes.
  • Humans: Typically have 4646 chromosomes arranged in 2323 pairs; the last pair consists of sex chromosomes (XX for females, XY for males) which determine biological sex.
  • Genotype: The complete genetic makeup of an individual (all the genes inherited).
  • Phenotype: The observable, expressed traits of an individual; these are a result of the interaction between the genotype and environmental factors (Phenotype=Genotype×EnvironmentPhenotype = Genotype \times Environment).
  • Many psychological traits (e.g., intelligence, personality, susceptibility to certain disorders) are polygenic, meaning they are influenced by multiple genes acting together, rather than a single gene.

Studying Heredity

  • Kinship comparisons: Research methods (e.g., family studies, twin studies, adoption studies) that assess the relative influence of genetic and environmental factors on traits by comparing individuals with varying degrees of genetic relatedness.
  • Twin studies: Crucial for disentangling genetic vs. environmental influences.
    • Monozygotic (MZ) twins (identical): Develop from a single fertilized egg, sharing nearly 100%100\% of their genes.
    • Dizygotic (DZ) twins (fraternal): Develop from two separate fertilized eggs, sharing approximately 50%50\% of their genes, similar to regular siblings.
    • By comparing the concordance (similarity) rates of MZ and DZ twins for a particular trait, researchers can estimate the heritability (proportion of variation in a trait attributable to genetic factors) of that trait.