Biology and Behavior Study Notes

Introduction to the Nervous System

  • Definition: The nervous system is a complex network of cells and structures that controls and coordinates body functions, allowing organisms to interact with their environment.

  • Relevance to Psychology: It serves as the biological foundation for understanding behavior, emotions, cognitive processes, and psychopathology.

The Neuron and Supporting Cells

  • The Neuron: The fundamental unit of the nervous system.

    • Dendrites: Branch-like extensions that receive chemical signals from other neurons.

    • Soma (Cell Body): Contains the nucleus and maintains the health of the neuron.

    • Axon: A long fiber that carries electrical impulses (action potentials) away from the cell body.

    • Myelin Sheath: A fatty insulation layer that speeds up signal transmission. Gaps in the sheath are called Nodes of Ranvier.

    • Terminal Buttons: Found at the end of axons; they release neurotransmitters into the synapse.

    • Synapse: The microscopic gap where chemical communication occurs.

  • Glial Cells: Crucial supporting cells that often outnumber neurons. They provide physical support, deliver nutrients, and produce myelin. Astrocytes help form the blood-brain barrier, while microglia act as the brain's immune system.

Neural Communication: The Action Potential

  • Resting Potential: The state of a neuron when not firing, typically around -70 mV (millivolts). The inside is more negative than the outside.

  • Action Potential: A rapid change in electrical charge.

    • Threshold: The level of stimulation required to trigger a neural impulse, usually around -55 mV.

    • All-or-None Law: A neuron either fires at full strength or not at all; there is no "weak" or "strong" action potential.

    • Depolarization: Sodium (Na^+) ions rush in, making the inside more positive.

    • Repolarization: Potassium (K^+) ions rush out to restore the negative charge.

  • Refractory Period: A brief period after firing during which a neuron cannot fire again while it resets its electrical balance.

Chemical Communication: Neurotransmitters

  • Neurotransmitters: Chemical messengers released into the synapse to bind with receptor sites on the receiving neuron.

    • Acetylcholine (ACh): Involved in muscle action, learning, and memory. (Deficit linked to Alzheimer’s).

    • Dopamine: Influences movement, learning, attention, and emotion. (Excess linked to Schizophrenia; deficit linked to Parkinson’s).

    • Serotonin: Affects mood, hunger, sleep, and arousal. (Deficit linked to Depression).

    • Norepinephrine: Helps control alertness and arousal (the "stress" hormone).

    • GABA (Gamma-aminobutyric acid): A major inhibitory neurotransmitter; it "quiets" the brain.

    • Glutamate: A major excitatory neurotransmitter involved in memory.

    • Endorphins: Natural, opiate-like neurotransmitters linked to pain control and pleasure.

  • Agonists and Antagonists:

    • Agonists: Mimic or enhance the effect of a neurotransmitter (e.g., morphine mimics endorphins).

    • Antagonists: Block or inhibit the effect of a neurotransmitter (e.g., Curare blocks ACh receptors, causing paralysis).

Systems of the Nervous System

  1. Central Nervous System (CNS)

    • Consists of the brain and the spinal cord.

    • Spinal Reflexes: Simple, automatic responses to stimuli that are processed in the spinal cord before reaching the brain (e.g., pulling a hand away from a hot stove).

  2. Peripheral Nervous System (PNS)

    • Somatic Nervous System: Controls voluntary skeletal muscle movements.

    • Autonomic Nervous System: Manages involuntary functions.

      • Sympathetic Division: "Fight or Flight"; dilates pupils, inhibits digestion, and increases heart rate.

      • Parasympathetic Division: "Rest and Digest"; constricts pupils, stimulates digestion, and slows heart rate.

Major Brain Structures and Their Functions

  1. The Brainstem (Survival Center)

    • Medulla Oblongata: Controls heartbeat, breathing, and swallowing.

    • Pons: Coordinates movements and influences sleep/dreaming.

    • Reticular Formation: Controls arousal, alertness, and consciousness.

  2. The Cerebellum (The "Little Brain")

    • Coordinates voluntary movement, balance, and motor learning.

  3. The Limbic System (Emotion/Memory)

    • Thalamus: The "Relay Station" for all senses except smell.

    • Hypothalamus: Regulates hunger, thirst, temperature, and the Endocrine System via the Pituitary Gland.

    • Hippocampus: Formation of new long-term memories.

    • Amygdala: Emotional processing, especially fear and aggression.

    • Basal Ganglia: Movement control and reward processing.

  4. Cerebral Cortex and Lobes

    • Corpus Callosum: Connects the hemispheres. Damage results in "Split-Brain" patients.

    • Frontal Lobe: Prefrontal Cortex (Judgment), Motor Cortex (Motion), and Broca’s Area (Speech Production).

    • Parietal Lobe: Somatosensory Cortex (Touch/Feel).

    • Temporal Lobe: Auditory Cortex (Hearing) and Wernicke’s Area (Language Comprehension).

    • Occipital Lobe: Visual Cortex (Sight).

Brain Plasticity and Growth

  • Neuroplasticity: The brain's ability to reorganize itself by forming new neural connections throughout life, especially after injury.

  • Neurogenesis: The formation of new neurons, primarily in the hippocampus.

Real-Life Examples and Applications

  • The Case of Phineas Gage (Frontal Lobe): Illustrated that personality is rooted in the physical brain.

  • Patient H.M. (Hippocampus): Removal of the hippocampus led to the inability to form new semantic/episodic memories.

  • Selective Serotonin Reuptake Inhibitors (SSRIs): Antidepressant medications that work by preventing the reabsorption (reuptake) of serotonin, keeping it in the synapse longer to improve mood.

  • Phantom Limb Pain (Parietal Lobe): When a limb is lost, the somatosensory cortex reorganizes; neighboring areas (like the face) may "take over" the space, causing the sensation of a limb being touched when the face is touched.

  • Split-Brain Research (Corpus Callosum): Conducted by Roger Sperry; patients with a severed corpus callosum could draw what they saw in their left visual field (right hemisphere) but couldn't name it verbally (left hemisphere).