The Biology of Behavior - Chapter 2

Biology, Behavior, and Mind

  • Humans are biopsychosocial systems, intricate combinations of biological, psychological, and social-cultural influences that shape our thoughts, feelings, and behaviors.

  • Biology and experience interact dynamically, facilitating new neural pathways as the brain adapts to a changing world. This interaction underscores the brain's plasticity, allowing it to reorganize itself by forming new neural connections throughout life.

  • Biological psychologists employ advanced technologies to explore these intricate links and uncover new insights into brain functions and their effects on behavior. These technologies include neuroimaging techniques and genetic analyses.

Neural Communication

  • Neuron (nerve cell): The fundamental unit of the brain, designed to transmit information through electrical and chemical signals.

    • The adult human brain contains approximately 86 billion neurons.

    • Each neuron can form approximately 10,000 connections with other neurons, creating a vast and complex network.

Anatomy of a Neuron

  • Cell Body (Soma): The neuron's life-support center, housing the nucleus and other essential organelles. It integrates signals received from dendrites.

  • Dendrites: Branch-like extensions that receive information from other neurons and transmit it to the cell body.

  • Axon: A long, slender fiber that carries signals away from the soma to other neurons, muscles, or glands. Axons can vary in length, from fractions of an inch to several feet.

  • Myelin Sheath: A fatty tissue layer encasing the axons of some neurons, enabling faster transmission speed of neural impulses as they hop from one node to the next. Damage to the myelin sheath can lead to neurological disorders.

  • Terminal Buttons (Axon Terminal): Small knobs at the end of axons that secrete chemical messengers called neurotransmitters to transmit signals to other neurons.

Synapse

  • The junction between two neurons where communication occurs.

  • A small gap (synaptic cleft) separates the sending axon and receiving dendrite.

  • Neurotransmitters and synapse operate like a lock and key; specific neurotransmitters bind to specific receptor sites on the receiving neuron.

Action Potential

  • The way neurons communicate; communication is chemical between neurons and electrical within neurons.

  • Resting Potential: The state of a neuron when it is not firing a signal, maintained by ion concentrations.

  • Action Potential: An all-or-nothing electrical signal that travels down the axon when the threshold of excitation is reached.

  • Absolute Refractory Period: A brief period after an action potential, during which another action potential cannot occur.

  • Postsynaptic Potential: The change in the postsynaptic membrane potential caused by the influx of neurotransmitters.

Reuptake

  • The process where neurotransmitters that have not bound to receptors are reabsorbed back into the sending neuron, effectively clearing the synapse, and allowing the neuron to fire again.

Glial Cells (Glia)

  • Cells in the nervous system that support, nourish, and protect neurons; they play a crucial role in neural health and function.

  • There are 10-50x more glia than neurons, highlighting their importance in brain function.

  • Four main functions:

    • Surround neurons and hold them in place, providing structural support.

    • Supply nutrients and oxygen to neurons, ensuring they have the energy to function.

    • Insulate one neuron from another, preventing interference and maintaining signal integrity.

    • Destroy pathogens and remove dead neurons, protecting the nervous system from damage and infection.

Neurotransmitters (NTs)

  • Chemical messengers that transmit signals between neurons, influencing behavior and mental processes.

  • Neurotransmitters bind to receptor sites on receiving neurons, much like a lock and key.

  • Agonists: Drugs that mimic NTs, activating receptor sites and amplifying the effects of the neurotransmitter.

  • Antagonists: Chemicals that oppose the action of NTs by blocking receptor sites and preventing the neurotransmitter from binding.

Examples of NTs

  • Dopamine: Influences movement, learning, attention, and emotion. Imbalances in dopamine levels are associated with various disorders.

    • Excess dopamine is linked to Schizophrenia, while a lack of dopamine is associated with Parkinson’s disease.

  • Endorphins: Natural pain relievers that elevate mood. Released during exercise, stress, and pain.

    • Opiates (heroin, morphine, Oxycontin) mimic endorphins, providing powerful pain relief and euphoria.

  • Serotonin: Regulates mood, arousal, and various functions. It plays a crucial role in mental health.

    • Drugs like LSD and Ecstasy affect serotonin levels, leading to altered perceptions and emotional states.

  • Norepinephrine: Involved in alertness, arousal, and the fight-or-flight response. It increases heart rate, blood pressure, and energy levels.

The Nervous System

  • A complex communication network that takes information from the world and the body’s tissues, makes decisions, and sends back information and orders to the body’s tissues to facilitate responses.

Types of Neurons

  • Sensory: Receive information from the environment and transmit it to the central nervous system (CNS).

  • Interneurons: Connect sensory and motor neurons within the CNS, facilitating communication between them.

  • Motor: Transmit signals from the CNS to muscles, enabling movement.

Peripheral Nervous System (PNS)

  • Sensory and motor neurons that connect the CNS to the rest of the body, allowing for communication between the brain and the external world.

    • Somatic system: Enables voluntary control of skeletal muscles, allowing for conscious movement and interaction with the environment.

    • Autonomic (ANS) system: Controls glands and internal organs, regulating involuntary functions such as heart rate, digestion, and respiration.

      • Sympathetic nervous system: Arouses the body and expends energy during times of stress or excitement, initiating the fight-or-flight response.

      • Parasympathetic nervous system: Conserves energy as it calms the body, maintaining homeostasis (equilibrium) and promoting relaxation.

Central Nervous System (CNS)

  • Brain: The control center of the nervous system, responsible for processing information, making decisions, and coordinating bodily functions.

    • Neural networks: Interconnected clusters of neurons that work together to process information and perform specific tasks.

  • Spinal cord: A long, cylindrical structure that connects the brain to the rest of the body, serving as a two-way system of ascending and descending neural fibers.

    • Reflexes: Automatic responses to stimuli, mediated by the spinal cord without conscious input from the brain.

Endocrine System

  • A slow chemical communication system comprising a set of glands that secrete hormones into the bloodstream.

    • Hormones: Chemical messengers produced by endocrine glands that travel through the bloodstream to target tissues and organs, regulating various physiological processes.

    • Adrenal glands: Secrete hormones such as epinephrine (adrenaline) and norepinephrine (noradrenaline), which are involved in the stress response.

    • Pituitary gland: The master gland of the endocrine system, regulating the activity of other glands and releasing hormones that control growth, reproduction, and metabolism.

How Does It All Function?

  • The brain influences the pituitary gland, which in turn affects other glands. These glands release hormones that impact both the body and the brain, demonstrating a feedback loop.

  • The nervous system controls endocrine secretions, which subsequently affect the nervous system, illustrating the interconnectedness of these systems.

  • The brain serves as the conductor and coordinator of the entire system, ensuring that the body functions in a coordinated and harmonious manner.

Methods to Study the Brain

  • Transcranial Magnetic Stimulation (TMS).

  • Brain Imaging

    • Computerized Tomography (CT scan).

    • Electroencephalogram (EEG).

    • Magnetoencephalography (MEG).

    • Positron emission tomography (PET scan).

    • Magnetic resonance imaging (MRI).

    • Functional MRI (fMRI).

Important Terms

  • Synapse

  • Action potential

  • Reuptake

  • Neurotransmitters

  • Important neurotransmitters

  • Nervous system

  • Peripheral Nervous System

  • Central Nervous System

  • Endocrine System

Structure of the Brain

Three Main Divisions of the Brain

  • Hindbrain: The lower end of the brain, responsible for essential survival functions.

    • Medulla, pons, cerebellum

    • Directs essential survival functions, such as breathing, heart rate, and blood pressure.

  • Midbrain: Located at the top of the brainstem, connecting the hindbrain with the forebrain.

    • Controls some motor movement, coordinating muscle activity and movement patterns.

    • Transmits auditory and visual information, relaying sensory signals to higher brain regions for processing.

  • Forebrain: The largest and most complex division of the brain, consisting of the cerebral cortex, thalamus, and hypothalamus.

    • Manages complex cognitive activities, including learning, memory, and decision-making.

    • Governs sensory and voluntary motor activities, allowing for conscious perception and voluntary movement.

Brainstem

  • An extension of the spinal cord, connecting the brain to the rest of the body.

  • Consists of:

    • Medulla: Located at the base of the brainstem, responsible for regulating vital functions such as circulation, breathing, muscle tone, and reflexes.

    • Pons: Important in sleep and arousal, regulating sleep-wake cycles and influencing states of consciousness.

    • Reticular formation: A nerve network that travels through the brainstem into the thalamus, controlling arousal, sleep, breathing, and pain perception.

Brain Regions & Structures

  • Cerebellum: The "little brain" at the rear of the brainstem, critical in the coordination of movement and equilibrium.

    • Enables nonverbal learning and memory, allowing for the acquisition of skills and habits.

  • Thalamus: Located on top of the brainstem, serving as the brain’s sensory control center.

    • A way station for all incoming sensory information before it is passed on to appropriate higher brain regions, filtering and relaying sensory signals to the cortex.

Limbic System

  • Located mostly in the forebrain, associated with emotions and drives.

  • Consists of:

    • Amygdala: Linked to emotion, particularly fear and aggression, playing a role in emotional processing and memory.

    • Hypothalamus: Located below (hypo) the thalamus, regulating basic biological needs such as hunger, thirst, sex drive, and temperature regulation.

      • Linked to emotion, motivation, and memory, influencing various aspects of behavior.

    • Hippocampus: A neural center that helps process explicit (conscious) memories, playing a key role in the formation of new memories.

Cerebrum and Cerebral Cortex

  • The cerebrum, the largest part of the human brain, is the ultimate control and information-processing center of the body.

  • Cerebrum: The outer layer of the cerebrum is the cerebral cortex, responsible for complex mental activities such as learning, remembering, thinking, and consciousness.

    • Two hemispheres (left and right):

      • Left: Controls speech, logic, and analytical functions, processing information in a sequential and analytical manner.

      • Right: Specializes in spatial processing, rhythm, and abstract thought, processing information in a holistic and integrative manner.

Damage Responses to Brain

  • The brain exhibits remarkable plasticity, allowing it to reorganize itself in response to damage or experience.

  • Neural plasticity and reorganization: The brain's ability to change in response to experiences, forming new neural connections and pathways.

  • Neurogenesis: The production of new neurons, which can occur in certain brain regions such as the hippocampus.

Split-Brain Surgery

  • Corpus callosum severed, disconnecting the two hemispheres of the brain.

  • Seizures disappeared; personality and intellect remained largely intact, demonstrating the resilience of the brain.

  • Visual information-sharing ended, preventing each hemisphere from accessing information processed by the other.

  • Behavior and agency were affected, altering the individual's sense of self and control.

  • The left hemisphere gives rational goal-related orders, while the right hemisphere gives conflicting demands, leading to internal conflict and indecision.

The Lobes

  • Each hemisphere has 4 lobes, each responsible for different functions:

    • Frontal lobes

    • Parietal lobes

    • Occipital lobes

    • Temporal lobes

Association Areas

  • Found in all four lobes – cerebral cortex areas that are not involved in primary motor or sensory functions.

  • Involved in higher mental functions such as learning, remembering, thinking, and speaking.

Frontal Lobes

  • Located at the front of the brain, behind the forehead, the frontal lobes are involved in speaking, muscle movements, and making plans/judgments.

  • Primary motor cortex: Located at the rear of the frontal lobes, it controls voluntary movements, coordinating muscle activity and movement patterns.

  • Phineas Gage: Survived an accident where an iron rod went through his frontal lobe, resulting in alterations to his personality and behavior.

Motor and Speech Areas

  • Motor Area: Responsible for voluntary movements, coordinating muscle activity, and executing motor plans.

  • Speech Areas

    • Broca’s Area: Controls language expression, directing muscle movements involved in speech production.

    • Broca’s Aphasia: Results from damage to Broca’s Area, impairing the ability to speak fluently.

Parietal Lobes

  • Located at the top of the head towards the rear, the parietal lobes process sensory information.

  • Primary somatosensory cortex: Receives sensory input for touch and body position, allowing for perception of touch, pressure, temperature, and pain.

    • Somatosensory cortex: Receives incoming messages from skin senses and movement of body parts, mapping sensory information onto the cortex.

Occipital Lobes

  • Located at the back of the head, the occipital lobes are responsible for visual processing.

  • Primary visual cortex: Receives information from the visual fields, allowing for perception of shapes, colors, and movement.

    • Visual Cortex: Receives input from eyes and sends information to other task-specialized areas for face identification, emotion detection, and face recognition.

Temporal Lobes

  • Located roughly above the ears, the temporal lobes are involved in auditory processing and language comprehension.

  • Primary auditory cortex: Receives information primarily from the opposite ear, allowing for perception of sounds and tones.

    • Auditory Cortex: Receives information from ears, following a circuitous route from one ear to the auditory receiving area above the other ear.

    • Wernicke’s Area: Controls language reception, allowing for comprehension of spoken language.

    • Wernicke’s Aphasia: Results from damage to Wernicke’s Area, impairing the ability to understand language.

Prefrontal Cortex

  • Found in all four lobes, the prefrontal cortex enables judgment, planning, social interactions, and new memory processing.

  • Can alter personality and inhibitions when damaged, affecting behavior and decision-making.

  • Disconnects moral behavior from behavior, impairing ethical judgment and moral reasoning.

Genetics and Evolutionary Psychology

Basic Principles of Genetics

  • Chromosomes: Strands of DNA carrying genetic information, organizing genetic material within the cell.

    • Human cells contain 46 chromosomes in pairs (sex-cells – 23 single), with one set inherited from each parent.

  • Each chromosome contains thousands of genes, also in pairs, coding for specific traits and characteristics.

  • Polygenic traits: Traits influenced by multiple genes, with each gene contributing to the expression of the trait.

Research Methods in Behavioral Genetics

  • Family studies: Examine whether traits run in families, assessing the degree to which family members share certain characteristics.

  • Twin studies: Compare the resemblance of identical (monozygotic) and fraternal (dizygotic) twins on a trait, providing insights into the relative contributions of genes and environment.

  • Adoption studies: Examine the resemblance between adopted children and their biological and adoptive parents, helping to disentangle genetic and environmental influences.

  • Genetic relatedness: The degree to which individuals share genes, with closer relatives sharing more genes in common.

Gene-Environment Interaction

  • Genes and environment interact dynamically, shaping behavior and development.

  • Genes are self-regulating, with their expression influenced by environmental factors.

  • Environments trigger gene activity, activating or suppressing gene expression.

  • Genetically influenced traits evoke significant responses in others, shaping social interactions and relationships.

  • Experiences create epigenetic marks, altering gene expression without changing the underlying DNA sequence.

  • Environmental factors can affect epigenetic molecules that regulate gene expression, influencing cellular processes and development.

The Evolutionary Basis of Behavior

  • Based on Darwin’s ideas of natural selection, which posits that traits that enhance survival and reproduction are more likely to be passed on to future generations.

  • Reproductive success is key, driving the evolution of traits that increase the likelihood of passing on genes to offspring.

  • Adaptations: Behavioral as well as physical traits that enhance survival and reproduction in a particular environment.

    • Fight-or-flight response: A physiological reaction to perceived threats or stressors, preparing the body to either confront or evade danger.

    • Taste preferences: Innate preferences for certain tastes, such as sweet and salty, which were advantageous in ancestral environments.

    • Parental investment and mating: Behaviors and strategies related to parental care and mate selection, influencing reproductive success and offspring survival.