The Biology of Mind

Chapter 2: The Biology of Mind

Chapter Overview

  • The Cerebral Cortex

  • Structure of the Cortex

  • Functions of the Cortex

  • Responses to Damage

  • The Divided Brain

Biology, Behavior, and Mind (part 1)

  • Everything psychological is biological.

  • Psychologists studying from a biological perspective examine the connections between biology and behavior.

  • Humans are biopsychosocial systems characterized by the interaction of biological, psychological, and social-cultural factors influencing behavior.

Biology, Behavior, and Mind (part 2)

  • Our understanding of the brain-mind relationship has changed over time:

    • Aristotle: Proposed that the mind is located in the heart.

    • Franz Gall: Suggested phrenology, which claimed that by examining skull bumps, one could identify mental abilities and character traits.

    • Critique: This theory is false, as bumps on the skull do not correlate with brain functions. Despite this, some of Gall's ideas had a lasting impact.

A Wrongheaded Theory

  • Initial acceptance of Gall's theories was widespread; however, examination of skull bumps (phrenology) provides no insight into brain functions.

The Adaptive Brain

  • The brain adapts and forms pathways based on experiences:

    • Brain changes and shifts in response to our experiences are indicated by neuroplasticity.

Neuron Structure

  • Dendrites: Receive messages from other cells.

  • Cell Body: The cell's life-support center.

  • Axon: Carries messages away from the cell body to other neurons, muscles, or glands.

  • Myelin Sheath: Covers the axon of some neurons and speeds up neural impulses.

  • Action Potential: An electrical signal that travels down the axon after neuron stimulation.

Action Potential

  1. Neuron stimulation causes a brief change in electrical charge, leading to depolarization termed action potential if the threshold of -55 mV is exceeded.

  2. This depolarization influences neighboring areas of the axon, allowing positively charged sodium ions ($Na^+$) to flow in, while potassium ions ($K^+$) flow out to repolarize the previous section.

  3. The action potential travels down the axon, while sodium/potassium pumps restore the resting potential.

How Neurons Communicate

  1. Electrical impulses travel down a neuron to the synapse.

  2. Upon arriving at the axon terminal, neurotransmitters are released, cross the synaptic gap, and bind to receptor sites on the receiving neuron, allowing charged atoms to enter and generate a new action potential.

  3. Excess neurotransmitters undergo reuptake, diffuse away, or are broken down by enzymes.

How Drugs and Other Chemicals Alter Neurotransmission

  • Agonist: A molecule that increases a neurotransmitter's action.

  • Antagonist: A molecule that inhibits or blocks a neurotransmitter's action.

Functional Divisions of the Human Nervous System

  • Peripheral Nervous System:

    • Autonomic Nervous System: Controls self-regulated action of internal organs and glands.

    • Sympathetic (arousing).

    • Parasympathetic (calming).

    • Somatic Nervous System: Controls skeletal muscles and sensory input.

  • Central Nervous System: Comprises the brain and spinal cord.

The Peripheral Nervous System

  • Comprised of two parts with subdivisions:

    • Somatic Nervous System.

    • Autonomic Nervous System with:

    • Sympathetic: Mobilizes body resources in stressful situations.

    • Parasympathetic: Calms the body after stress.

The Central Nervous System

  • The adult brain has approximately 86 billion neurons.

  • The brain accounts for 2% of body weight and consumes 20% of the body's energy.

  • Neural networks and pathways govern reflex actions through efficient electrochemical systems.

A Simple Reflex

  1. Information from skin receptors travels along a sensory neuron to the spinal cord.

  2. It is processed through interneurons to motor neurons, enabling a response such as withdrawing a hand from a hot surface.

  3. The reflex action occurs before the brain processes the information regarding pain.

The Endocrine System

  • Feedback System:

    • Brain signals the pituitary gland, which influences other glands, releasing hormones that affect the body and brain.

  • Hypothalamus: Controls the pituitary gland, influencing various endocrine functions.

  • Various glands regulate functions such as metabolism, blood sugar levels, and sexual hormones.

Methods for Assessing Brain Function

  • Electroencephalogram (EEG): Measures brain's electrical activity.

  • Magnetoencephalography (MEG): Maps brain activity by recording magnetic fields produced by neural activity.

  • Positron Emission Tomography (PET): Uses radioactive tracers to measure blood flow and brain activity.

  • Magnetic Resonance Imaging (MRI): Provides detailed images of brain structure.

  • Functional MRI (fMRI): Measures brain activity by detecting changes in blood flow.

Beautiful Brain Connections

  • Human Connectome Project: Research initiative mapping neural connections in the brain.

  • Diffusion Spectrum Imaging: Advanced imaging techniques to explore intricate neural pathways.

Older Brain Structures

  • The less complex brains of primitive vertebrates manage basic survival functions.

  • More complex brains in mammals contain added structures built on the foundational parts.

The Brainstem: Oldest and Innermost Region

  • Medulla: Located at the brainstem base, regulates heartbeat and breathing.

  • Pons: Above the medulla; helps coordinate movement.

The Cerebellum

  • Aids in the judgment of time, sound, and texture discrimination.

  • Coordinates voluntary movement and sustains life functions.

  • Processes and stores information outside of conscious awareness.

The Limbic System

  • Positioned between older brain structures and cerebral hemispheres.

  • Composed of neural centers including:

    • Hippocampus: Involved in memory processing and storage; decreases with age.

    • Amygdala: Linked to emotion.

  • Controls the nearby pituitary gland, which regulates various bodily functions.

Brain Structures and Their Functions

  • Amygdala: Linked to emotion.

  • Hippocampus: Linked to conscious memory.

  • Cerebral Cortex: The brain's ultimate control and information-processing center.

  • Thalamus: Relays messages between lower brain centers and the cerebral cortex.

  • Hypothalamus: Governs maintenance functions; linked to emotion and reward.

  • Pituitary Gland: Master gland controlling the endocrine system.

  • Medulla & Pons: Control basic functions like breathing and movement coordination.

The Cerebral Cortex

  • Comprised of two hemispheres, each with four lobes:

    • Frontal Lobe: Associated with decision-making and planning.

    • Parietal Lobe: Processes sensory information and spatial orientation.

    • Temporal Lobe: Involved in auditory processing and memory.

    • Occipital Lobe: Processes visual information.

Motor Cortex and Somatosensory Cortex

  • Motor Cortex: Controls voluntary movements by sending signals to muscles.

    • Each body part is represented, with specific areas devoted to limbs, facial features, etc.

  • Somatosensory Cortex: Receives input from the body's sensory receptors and processes tactile information.

Functions of the Cortex (part 1)

  • Sensory functions include processing information from skin senses and body movement via the somatosensory cortex.

Functions of the Cortex (part 2)

  • Visual Cortex: Located in the occipital lobes; receives visual input.

  • Auditory Cortex: Located in the temporal lobes; processes auditory information.

Functions of the Cortex (part 3)

  • Association Areas: Areas within all four lobes facilitating complex functions:

    • In frontal lobes: Enable judgment, planning, and processing of new memories.

    • Damage to these areas results in deficits in specific functions, underscoring their specialization.

Responses to Damage (part 1)

  • Severed neurons in the brain and spinal cord typically do not regenerate.

  • Certain functions are localized to specific brain areas.

  • Neural tissues can reorganize due to neuroplasticity, especially post-damage.

Responses to Damage (part 2)

  • Constraint-Induced Therapy: Aims to rewire the brain to regain functionality in individuals with brain injuries.

  • Conditions like blindness or deafness allow unused brain areas for repurposing, highlighting the brain’s adaptability.

The Corpus Callosum

  • Composed of axon fibers connecting the two hemispheres of the brain, allowing communication and integration of cognitive functions.

The Information Highway from Eye to Brain

  • Visual inputs are processed through the optic nerves and routed to appropriate visual areas in each hemisphere of the brain.

One Skull, Two Minds

  • The hemispheres of the brain perform specialized functions, allowing for unified yet distinct processing in humans.

  • Left Hemisphere: Strong in rapid, precise language interpretation.

  • Right Hemisphere: Excels at making inferences and enhancing self-awareness.