Introduction to Biological Psychology and Neural Communication

Localization of Function and the Biopsychosocial Perspective

• Localization of Function: While the historical science of phrenology is primarily used today as a reminder of the necessity for critical thinking, it succeeded in focusing attention on the concept of localization. This is the idea that various brain regions possess particular functions.

• Biological Perspective: Biological psychologists utilize advanced technologies to examine the links between biological systems—such as genetic, neurohormonal, and physiological processes—and our behavior and mind.

• The Biopsychosocial System: Humans are complex systems composed of smaller subsystems.

  • Tiny cells organize to form body organs.

  • Organs form larger systems for digestion, circulation, and information processing.

  • These systems comprise the person, who is a part of a larger family, community, and culture.

  • Understanding behavior requires studying how these biological, psychological, and social-cultural systems work and interact over time. We are formed by evolution, enduring cultures, daily experiences, functioning hormones, and immediate neuroactivity.

Neuroplasticity: The Adaptive Brain

• Definition of Neuroplasticity: The brain's ability to change—especially during childhood—by building new pathways based on experience or by reorganizing after damage. The brain you are born with is not the brain you will die with; it is a work in progress constantly being sculpted by genes and life.

• Developmental Timeline: Neuroplasticity is greatest early in life but continues across the entire lifespan.

• Case Studies and Examples of Neuroplasticity:

  • London Taxi Driver Trainees: These individuals spend years memorizing the locations and connections of $26,000$ streets. Those who pass the final test exhibit an enlarged hippocampus, one of the brain's memory centers responsible for processing spatial memory. In contrast, bus drivers who navigate a more limited, fixed set of routes receive no similar neural reward.

  • Musicians and Dancers: Experienced musicians tend to have a larger-than-usual auditory cortex, the region for sound processing. Specific physical practices likewise sculpt the brains of ballet dancers, jugglers, and unicyclists.

  • Timed Practice Effects: Even limited practice times can produce neural benefits. Spending $45\,minutes$ learning the piano can grow motor-learning-related brain areas. Mere minutes of word learning can produce subtle brain changes.     

• Socioeconomic Impacts on Brain Development: Neuroplasticity underlies interventions aimed at reducing child poverty. In an experiment, families with newborns were randomly assigned either large ($333\,dollars$) or small ($20\,dollars$) unconditional monthly cash transfers. One year later, children in the high-cash group showed significantly more brain activity in areas associated with language, thinking, and social understanding.

• Cultural Influences: Experience with specific cultural traditions, beliefs, and rituals can create distinct behavior and brain activation patterns. For instance, people in the United States and Mexico tend to value expressing positive emotions, while people in China may perceive emotional expression more negatively. This results in higher brain activation in emotional expression areas for Americans and Mexicans when viewing emotion-arousing photos compared to Chinese individuals.

Building Blocks of the Nervous System: Neurons

• Neurons (Nerve Cells): These are the basic building blocks of the nervous system. Throughout life, new neurons are born while unused neurons wither away.

• Anatomy of a Neuron:

  • Cell Body: The part of the neuron containing the nucleus; it acts as the cell's life-support center.

  • Dendrites: Often bushy, branching extensions that receive and integrate messages, conducting impulses toward the cell body. Dendrites "listen."

  • Axon: A segmented neuron extension that passes messages through its branches to other neurons, muscles, or glands. Axons "speak."

  • Scale of a Neuron: Axons can be very long. A human neuron carrying orders from the brain to a leg muscle has a cell body and axon on a scale comparable to a basketball attached to a rope that is $4\,miles$ long.

• Myelin Sheath: A layer of fatty tissue that segmentally encases the axons of some neurons. It insulates the axon and increases the speed of neural impulses.

  • Myelin is laid down up to approximately age $25$, supporting the growth of efficiency, judgment, and self-control.

  • If the myelin sheath degenerates, as in multiple sclerosis, communication to muscles and brain regions slows, resulting in diminished muscle control and sometimes impaired cognition.

• Glial Cells (Glia): These are cells in the nervous system that support, nourish, and protect neurons.

  • If neurons are like "queen bees," glial cells are the "worker bees" that provide nutrients, insulate with myelin, guide connections, and clean up after messages.

  • Glia also participate in information transmission, learning, thinking, and memory.

  • In complex animal brains, the ratio of glia to neurons increases. A postmortem analysis of Albert Einstein’s brain found a much greater concentration of glial cells than the average person, though his neurons were not larger or more numerous.

The Neural Impulse and Action Potential

• Action Potential: A brief electrical charge that travels down an axon. It is triggered by chemical events—the exchange of ions (electrically charged atoms).

• Transmission Speed: Neural impulses travel at speeds ranging from $2\,mph$ to over $200\,mph$. While fast, this is $3,000,000$ times slower than electricity through a wire. Humans respond much more slowly than computers; brain activity is measured in milliseconds ($1/1000\,of\,a\,second$) while computers operate in nanoseconds ($1/1,000,000,000\,of\,a\,second$).

• Ion Exchange Process:

  • Resting Potential: The positive-outside/negative-inside state of a resting axon. The fluid outside the membrane has mostly positively charged sodium ions; the interior contains large negatively charged protein ions and smaller positively charged potassium ions.

  • Selective Permeability: The axon surface is selective about which ions pass through its gates.

  • Depolarization: When a neuron fires, the first section of the axon opens its gates, allowing positively charged sodium ions to flood the interior. This causes the next set of channels to open in a chain reaction.

• The Firing Process:

  • Excitatory vs. Inhibitory Signals: Excitatory signals act like an accelerator, while inhibitory signals act like a brake.

  • Threshold: The level of stimulation required to trigger a neural impulse. If excitatory signals exceed inhibitory signals by a minimum intensity, they trigger an action potential.

  • Refractory Period: A brief resting pause after a neuron fires. Subsequent action potentials cannot occur until the axon returns to its resting state.

  • All-or-None Response: A neuron’s reaction is binary; it either fires with full strength or it does not fire at all. Stronger stimuli (like a big hug versus a gentle touch) trigger more neurons to fire and to fire more frequently, but the strength or speed of individual action potentials remains constant.

Neural Communication via Neurotransmitters

• Synapse: The meeting point between neurons. The axon terminal of the sending neuron is separated from the receiving neuron by a tiny space called the synaptic gap or synaptic cleft.

• Neurotransmitters: Chemical messengers that cross the synaptic gap. When an action potential reaches the axon terminals, it triggers the release of these molecules.

  • They cross the gap within $1/10,000\,of\,a\,second$ and bind to receptor sites on the receiving neuron like a key in a lock.

  • Reuptake: The process by which excess neurotransmitters are reabsorbed by the sending neuron. They can also be broken down by enzymes or simply drift away.

• Specific Neurotransmitters and Chemicals:

  • Acetylcholine ($ACh$): Plays a role in learning and memory. It is the messenger at every junction between motor neurons and skeletal muscles. When $ACh$ is released to muscle receptors, the muscle contracts. Blockage of $ACh$ leads to paralysis.

  • Endorphins: Natural, opiate-like neurotransmitters (endogenous morphine) linked to pain control and pleasure, explaining phenomena like "runner's high."

  • Agonists: Molecules that increase a neurotransmitter's action by increasing production, blocking reuptake, or mimicking the neurotransmitter's effect (e.g., some opioid drugs).

  • Antagonists: Molecules that inhibit or block a neurotransmitter's action. They are similar enough to occupy a receptor site but not enough to stimulate it (e.g., Botulinum/Botox blocks $ACh$ release; Curare blocks $ACh$ receptor sites to cause paralysis).

The Nervous System Structure

• Central Nervous System ($CNS$): Composed of the brain and spinal cord; it acts as the body’s decision-maker.

• Peripheral Nervous System ($PNS$): Responsible for gathering information and transmitting $CNS$ decisions to body parts.

  • Nerves: Electrical cables formed from bundles of axons. For example, the optic nerve bundles $1,000,000$ axons into a single cable.

• Three Types of Neurons:

  • Sensory (Afferent) Neurons: Carry messages from the body’s tissues and receptors inward to the $CNS$. There are a few million in the human body.

  • Motor (Efferent) Neurons: Carry instructions from the $CNS$ outward to muscles and glands. There are a few million in the human body.

  • Interneurons: Neurons within the brain and spinal cord that communicate internally and process information between sensory input and motor output. Humans have billions and billions of interneurons.

• Subdivisions of the Peripheral Nervous System:

  • Somatic Nervous System (Skeletal Nervous System): Enables voluntary control of skeletal muscles (e.g., turning your head when someone taps your shoulder).

  • Autonomic Nervous System ($ANS$): Controls glands and internal organ muscles (e.g., heartbeat, digestion). It usually operates autonomously but can be consciously overridden.