The Biology of Behavior

Heredity and Genes

  • Chromosome: a coiled-up thread of DNA.

  • Heredity shapes our behavior and experience

  • DNA (deoxyribonucleic acid): a large molecule that contains genes.

  • Genes: small segments of DNA that contain information for producing proteins.

  • Genes and Behavior: genes contribute to traits and behaviors, but are part of a complex system influenced by environment.

Genome, Genotype, and Phenotype

  • Genome: all the genetic information in DNA.

  • Genotype: the entire genetic makeup of an organism.

  • Phenotype: an organism’s observed characteristics.

The Principles of Behavioral Genetics

  • Behavioral genetics: the scientific study of the role of heredity in behavior.

  • Principle 1: The relationship between genes and behavior is complex; many genes are involved in each trait. Specific genes can cause a specific physical trait or disease, but single genes play only a small part in creating a given behavior.

  • Principle 2: Studying twins and adoptees helps disentangle heredity and environment. Key terms:

    • Heritability: the extent to which a characteristic is influenced by genetics.

    • Gene-by-environment studies: examine whether genes are correlated with a particular trait.

  • Principle 3: The environment affects how and when genes affect behavior.

    • Epigenetics: changes in how genes are turned on or off without changing the DNA sequence.

    • Genes are the starting point for biological structures—they are not destiny.

Polygenic vs. Monogenic Traits

  • Polygenic: many genes interact to create a single characteristic.

  • Monogenic: traits determined by a single gene.

  • Example: lactose tolerance/intolerance is one of the few traits passed on by a single gene.

Heredity, Environment, and Research Approaches

  • Twin and adoptee studies help separate genetic and environmental influences.

  • Behavioral Genetics: scientific study of the role of heredity of behavior

  • Heritability: extent to which a characteristic is influenced by genetics

  • Gene-by-environment studies: explore how genes relate to traits in different environments.

Epigenetics and Destiny

  • The environment can influence when and how genes affect behavior.

  • Epigenetics: modifications that affect gene expression without changing the DNA sequence.

  • Important takeaway: genes predispose, but environment shapes outcomes.

The Nervous System: Overview

  • Central nervous system (CNS): brain and spinal cord(command center)

  • Peripheral nervous system (PNS): all nerve cells outside the CNS(sends info to CNS)

The Peripheral Nervous System Components

  • Somatic nervous system: nerve cells of PNS serving skeletal muscles and conveying sensory information to the CNS.

  • Autonomic nervous system (ANS): nerve cells of PNS serving involuntary systems (organs and glands)(ex:digesting food, blinking)

The Autonomic Nervous System: Sympathetic and Parasympathetic

  • Sympathetic nervous system:

    • Activates bodily systems in times of emergency (fight-or-flight).

    • Effects (examples): dilates pupil; dilates bronchi; accelerates/strengthens heartbeat; inhibits digestive activity; contracts blood vessels; inhibits bladder contraction; redirects blood flow toward sex organs

  • Parasympathetic nervous system:

    • Relaxes or returns the body to a restful state.

    • Effects (examples): constricts pupil; constricts bronchi; slows heartbeat; stimulates digestive activity; dilates blood vessels; contracts bladder; stimulates ejaculation in males.

The Cells of the Nervous System

  • Glial cells:

    • Hold the CNS together.

    • Provide structural support.

    • Promote efficient communication between neurons.

    • Act as scavengers, removing cellular debris.

  • Neurons: the cells that process and transmit information in the nervous system.

The Neuron: Key Structures

  • Soma: cell body (contains nucleus).

  • Axon: projection that transmits signals.

  • Dendrites: receive signals.

  • Impulse: electrical signal traveling along the neuron.

  • Myelin sheath: insulation around the axon.

  • Synapse: the junction where axon meets dendrite.

The Neuron: Extended Structures

  • Terminal button (end of a neuron).

  • Synaptic vesicles: contain neurotransmitters.

  • Synaptic cleft: the small gap between neurons.

  • Receptor site: location on the receiving neuron for neurotransmitters.

Neural Communication: Two Stages

  • Stage 1: Action potential.

  • Stage 2: Neurotransmission (neurotransmitters cross the synapse to convey signals).

Neural Communication: Action Potential Details

  • Action potential: a positively charged impulse that moves one way down an axon (in response to stimulation of neuron)

  • Resting potential: electrical charge difference inside vs outside the axon when at rest.

  • Occurs in response to stimulation of the neuron.

  • Refractory period: time between an action potential and the neuron’s resting state.

  • All-or-none principle: once threshold is crossed, an action potential fires fully or not at all.

  • Nodes of Ranvier: gaps in the myelin sheath where the action potential jumps across.

  • The neuron:

Neural Communication: Neurotransmission Details

  • Arrival of an action potential at the end of the axon triggers neurotransmission.

  • Electrical impulse is converted into a chemical signal.

  • Neurotransmitters: chemicals that transmit information between neurons.

  • Neurotransmitters can be excitatory (increase likelihood of an action potential) or inhibitory (decrease likelihood).

Quick Reference: The Neuron Diagram Elements

  • Soma, Axon, Dendrites, Impulse, Myelin sheath, Synapse, Terminal Button, Synaptic vesicles, Synaptic cleft, Receptor site

Brain Regions: Hindbrain and Midbrain

  • Hindbrain:

    • Medulla: regulates breathing, heart rate, and blood pressure.

    • Pons: similar functions as the medulla, plus involvement in body movement.

    • Cerebellum: the “little brain”; involved in body movement, balance, coordination, fine-tuning motor skills, and learning.

  • Midbrain: regulates eye muscles, processes auditory and visual information, and initiates voluntary movement.

Forebrain and Limbic System

  • Forebrain: the largest brain part; contains structures for cognitive functioning, motor movement, temperature regulation, eating, sleeping, and more.

  • Limbic System: structures crucial for emotion, memory, and motivation, including hypothalamus, amygdala, hippocampus, and cingulate cortex.

Thalamus, Hypothalamus, and Memory/Emotion Centers

  • Thalamus: sensory relay station; receives sensory information (except smell) and relays to the corresponding cortical areas.

  • Hypothalamus: regulates drives and motivations (hunger, thirst, temperature, sexual behavior).

  • Hippocampus: essential for learning and memory.

  • Amygdala: processes emotional significance of stimuli, especially fear.

  • Cingulate gyrus: involved in attention and cognitive control.

  • Basal ganglia: involved in voluntary motor control.

The Cerebrum, Cortex, and Lobes

  • Cerebrum: upper brain region with two hemispheres; contains four lobes and a thin outer layer called the cerebral cortex.

  • Cerebral Cortex: outer layer of the cerebrum.

  • Lobes of the brain (and their general roles):

    • Frontal lobes: planning, impulse control, attention, abstract thinking, personality; contain primary motor cortex.

    • Parietal lobes: sensation and perception of touch; contain somatosensory cortex.

    • Temporal lobes: hearing; contain auditory cortex; Broca’s area (producing speech); Wernicke’s area (language comprehension and meaningful speech).

    • Occipital lobes: vision; contain primary visual cortex.

  • Corpus callosum: connects the two hemispheres and enables communication for both logical and creative tasks.

Broca’s and Wernicke’s Areas

  • Broca’s area: producing speech.

  • Wernicke’s area: understanding and meaningful speech.

The Four Lobes: Summary of Roles

  • Frontal lobe: planning, impulse control, attention, abstract thinking, personality; primary motor cortex.

  • Parietal lobe: somatosensation and perception; somatosensory cortex.

  • Temporal lobe: hearing; auditory cortex; language processing (Broca’s and Wernicke’s areas).

  • Occipital lobe: vision; primary visual cortex.

Brain Plasticity and Neurogenesis

  • Neuroplasticity: the brain’s ability to adopt new functions, reorganize itself, or form new neural connections.

  • Plasticity varies across brain regions and ages.

  • Neurogenesis: development of new neurons.

Measuring the Brain

  • Electroencephalography (EEG): records electrical activity using electrodes on the scalp.

  • Magnetic Resonance Imaging (MRI): uses magnetic fields to produce detailed images of brain structure and soft tissues.

  • Functional Magnetic Resonance Imaging (fMRI): measures brain activity indirectly by detecting changes in oxygen use.

  • Positron Emission Tomography (PET): measures blood flow to active areas of the brain.

End of Chapter 3

  • This set summarizes the core concepts covered in the chapter, linking genetic influences with brain structure and function and outlining methods for studying the brain and behavior.

Heredity and Genes

  • Chromosomes, DNA, Genes: DNA forms coiled chromosomes; genes are DNA segments producing proteins, influencing traits and behaviors complexly.

  • Genome, Genotype, Phenotype: The genome is all DNA; genotype is an organism's genetic makeup; phenotype is its observed characteristics.

Behavioral Genetics

  • Complex Gene-Behavior Link: Many genes interact for a single trait (polygenic); environment affects gene expression (epigenetics) without DNA changes. Genes predispose, environment shapes.

  • Research Methods: Twin and adoptee studies, along with gene-by-environment studies, help determine heritability (genetic influence on a trait's variance).

The Nervous System

  • Divisions: Central Nervous System (CNS - brain and spinal cord) and Peripheral Nervous System (PNS - all other nerves).

  • PNS Components: Somatic (skeletal muscles, sensory info) and Autonomic (ANS - involuntary processes).

  • ANS Subdivisions: Sympathetic (fight-or-flight, activates systems) and Parasympathetic (rest and digest, relaxes systems).

Neural Communication

  • Cells: Glial cells (support) and Neurons (process/transmit information).

  • Neuron Structures: Soma (cell body), Axon (transmits signals), Dendrites (receive signals), Myelin sheath (insulation).

  • Process: Action potential (electrical impulse) moves down the axon, triggering neurotransmission where neurotransmitters (chemical signals) cross the synapse between neurons.

Brain Regions

  • Hindbrain: Medulla, Pons (vital functions, movement), Cerebellum (balance, coordination, motor skills, learning).

  • Midbrain: Eye muscles, auditory/visual processing, involuntary movement initiation.

  • Forebrain: Largest part, responsible for cognitive functions, motor control, and regulation of drives.

    • Limbic System: Hypothalamus (drives), Hippocampus (memory), Amygdala (emotion, fear), Cingulate gyrus (attention/control), Basal ganglia (motor control) for emotion, memory, motivation.

    • Thalamus: Sensory relay station.

Cerebrum and Lobes

  • Cerebrum & Cerebral Cortex: Upper brain with two hemispheres connected by the Corpus Callosum; cortex is the outer layer.

  • Four Lobes:

    • Frontal: Planning, impulse control, personality, motor cortex.

    • Parietal: Sensation/perception of touch, somatosensory cortex.

    • Temporal: Hearing, auditory cortex, language (Broca's for speech production, Wernicke's for comprehension).

    • Occipital: Vision, primary visual cortex.

Brain Dynamics and Measurement

  • Plasticity: Neuroplasticity (brain's ability to reorganize) and Neurogenesis (new neuron development).

  • Measuring Techniques: EEG (electrical activity), MRI (brain structure), fMRI (brain activity via oxygen use), PET (blood flow to active areas).