Biological Psychology: Structure, Function, and Mechanisms of the Nervous System

1. Neurons — Structure & Function

Neurons are specialized nerve cells responsible for communication within the nervous system. Understanding their structure is fundamental to grasping how the brain processes information.

• Dendrites: Branch-like extensions that receive incoming signals from other neurons or sensory cells.

• Soma (Cell Body): Contains the nucleus; integrates signals and generates output.

• Axon: Transmits the action potential away from the soma to other neurons or muscles; often covered by a myelin sheath.

• Axon Terminal (Synaptic Terminal): Releases neurotransmitters into the synaptic cleft to communicate with the next neuron.

• Myelin Sheath: Fatty, insulating layer that speeds up signal transmission; formed by oligodendrocytes in the CNS.

• Nodes of Ranvier: Gaps between myelin segments where the action potential regenerates (saltatory conduction).

Glial Cells: Supportive cells that protect and nourish neurons; they do not transmit electrical signals.

Additional info: Glia outnumber neurons and are essential for maintaining the neural environment.

2. Neural Transmission & the Synapse

Neurons communicate via synapses, specialized junctions where chemical signals are transmitted.

• Synapse: The gap between the axon terminal of one neuron and the dendrite of another (synaptic cleft).

• Neurotransmitter Release: Neurotransmitters are released from synaptic vesicles in the presynaptic neuron.

• Binding: Neurotransmitters bind to receptors on the postsynaptic neuron, opening ion channels.

• Excitatory Postsynaptic Potential (EPSP): Increases likelihood of firing an action potential.

• Inhibitory Postsynaptic Potential (IPSP): Decreases likelihood of firing.

• Integration: Neuron firing depends on the balance of EPSPs and IPSPs.

Example: Glutamate typically produces EPSPs, while GABA produces IPSPs.

3. The Action Potential & Conduction

An action potential is a rapid electrical impulse that travels along the axon, enabling neural communication.

• Resting Potential: Approximately −70 mV; maintained by ion gradients.

• Threshold: Depolarization must reach a critical level to trigger an action potential.

• Depolarization: Sodium (Na+) channels open, Na+ enters the cell.

• Refractory Period: Na+ channels close; neuron cannot fire again immediately.

• Repolarization: Potassium (K+) leaves the cell, restoring negative potential.

• Restoration: Sodium-potassium pump restores ion balance (requires energy).

All-or-Nothing Principle: Action potentials fire at full strength or not at all; intensity is coded by firing rate, not amplitude.

Saltatory Conduction: In myelinated axons, action potentials jump between nodes of Ranvier, increasing speed.

Equation:

4. Neurotransmitters — Role & Drug Interactions

Neurotransmitters are chemical messengers that influence mood, arousal, and behavior. Many drugs act by modifying neurotransmitter activity.

Example: Exercise increases endorphin release, reducing pain perception.

5. The Nervous System — CNS, PNS, Somatic & Autonomic

The nervous system is divided into central and peripheral components, each with specialized functions.

• Central Nervous System (CNS): Brain and spinal cord; processes information and coordinates responses.

• Peripheral Nervous System (PNS): Connects CNS to the body; includes somatic and autonomic divisions.

• Somatic Nervous System: Controls voluntary movements; afferent (sensory) and efferent (motor) pathways.

• Autonomic Nervous System: Regulates involuntary functions; subdivided into:

  • Sympathetic: "Fight or flight" response (emergency/stress).

  • Parasympathetic: "Rest and digest" (routine maintenance).

Example: Increased heart rate during stress is mediated by the sympathetic system.

6. The Endocrine System & Hormones

The endocrine system uses hormones to regulate long-term bodily functions and behavior.

• Hormones: Chemical messengers secreted into the bloodstream by glands (e.g., insulin, cortisol).

• Speed: Hormonal effects are slower and longer-lasting than neurotransmitters.

• Key Hormones:

  • Cortisol: Stress response; prolonged elevation can impair immunity.

  • Oxytocin: Bonding and attachment.

  • Thyroid Hormones: Affect mood and energy; imbalances can cause psychological symptoms.

Example: Oxytocin release during social bonding enhances trust and attachment.

7. The Cerebral Cortex — Four Lobes

The cerebral cortex is divided into four lobes, each with distinct functions essential for cognition and behavior.

Example: Damage to Broca's area impairs speech production but not comprehension.

8. The Limbic System

The limbic system is a group of interconnected structures involved in emotion, motivation, and memory.

Example: Removal of the hippocampus (as in patient H.M.) leads to inability to form new long-term memories.

9. Brainstem & Other Major Structures

The brainstem and associated structures control basic life functions and coordinate communication between brain regions.

Example: Damage to the medulla can be fatal due to its role in vital functions.

10. Measuring Brain Function — Lesion Studies, Recording & Imaging

Various techniques are used to study brain structure and function, each with unique advantages and limitations.

Example: fMRI has been instrumental in identifying the brain's reward system.

11. Neural Plasticity — Development, Learning & Injury

Neural plasticity refers to the brain's capacity to change its structure and function in response to experience, learning, or injury.

• Learning/Experience: Strengthens neural connections (synaptic plasticity).

• Injury/Compensation: Surviving regions may take over lost functions, especially in younger brains.

• Development: Brain changes continue throughout life, not just in childhood.

Example: Rehabilitation after stroke can lead to functional recovery due to plasticity.

12. Genes, Heritability & Localisation of Function — Challenging Assumptions

Understanding the genetic and environmental influences on psychological traits is essential for interpreting research findings.

• Localisation of Function: Most traits involve multiple brain regions; no simple 1:1 mapping.

• Brain Usage: The "10% of the brain" myth is false; most regions are active daily.

• Heritability: Proportion of trait variation due to genetic differences; can change with environment.

• Nature and Nurture: Both genes and environment shape psychological traits.

• Brain Size vs Intelligence: Brain size alone does not predict intelligence; organization matters more.

Example: Imaging studies show religious experiences activate multiple brain areas, not a single "God spot."

Quick-Reference: Lecturer's Self-Evaluation Questions