Unit 2: Biological Bases of Behavior

Techniques to Learn About Structure and Function

• Paul Broca (1861) performed an autopsy on the brain of a patient, nicknamed Tan, who had lost the capacity to speak, although his mouth and his vocal cords weren’t damaged and he could still understand language.
• Tan’s brain showed deterioration of part of the frontal lobe of the left cerebral hemisphere, as did the brains of several similar cases.
• This connected destruction of the part of the left frontal lobe known as Broca’s area to loss of the ability to speak, known as expressive aphasia.
• Carl Wernicke similarly found another brain area involved in understanding language in the left temporal lobe.
• Destruction of Wernicke’s area results in loss of the ability to comprehend written and spoken language, known as receptive aphasia.
• Lesions, precise destruction of brain tissue, enabled more systematic study of the loss of function resulting from surgical removal (also called ablation), cutting of neural connections, or destruction by chemical applications.
• Studies by Roger Sperry and Michael Gazzaniga of patients with these “split brains” have revealed that the left and right hemispheres do not perform exactly the same functions (brain lateralization) that the hemispheres specialize in.
• Computerized axial tomography (CAT or CT) creates a computerized image using X-rays passed through various angles of the brain showing two-dimensional “slices” that can be arranged to show the extent of a lesion.
• In magnetic resonance imaging (MRI), a magnetic field and pulses of radio waves cause the emission of faint radio frequency signals that depend upon the density of the tissue.

Measuring Brain Function

• An EEG (electroencephalogram) is an amplified tracing of brain activity produced when electrodes positioned over the scalp transmit signals about the brain’s electrical activity (“brain waves”) to an electroencephalograph machine.
• The amplified tracings are called evoked potentials when the recorded change in voltage results from a response to a specific stimulus presented to the subject.
• Positron emission tomography (PET) produces color computer graphics that depend on the amount of metabolic activity in the imaged brain region.
• Functional MRI (fMRI) shows the brain at work at higher resolution than the PET scanner.
  • Changes in oxygen in the blood of an active brain area alters its magnetic qualities, which is recorded by the fMRI scanner.
• A magnetic source image (MSI), which is produced by magnetoencephalography (MEG scan), is similar to an EEG, but the MEG scans are able to detect the slight magnetic field caused by the electric potentials in the brain.

Organization of Your Nervous System

• Central nervous system: consists of your brain and your spinal cord.
• Peripheral nervous system : includes two major subdivisions: your somatic nervous system and your autonomic nervous system.
• Your peripheral nervous system lies outside the midline portion of your nervous system carrying sensory information to and motor information away from your central nervous system via spinal and cranial nerves.
• Somatic nervous system: has motor neurons that stimulate skeletal (voluntary) muscle.
• Autonomic nervous system: has motor neurons that stimulate smooth (involuntary) and heart muscle.
  • Your autonomic nervous system is subdivided into the antagonistic sympathetic nervous system and parasympathetic nervous system.
• Sympathetic stimulation results in responses that help your body deal with stressful events including dilation of your pupils, release of glucose from your liver, dilation of bronchi, inhibition of digestive functions, acceleration of heart rate, secretion of adrenaline from your adrenal glands, acceleration of breathing rate, and inhibition of secretion of your tear glands.
• Parasympathetic stimulation calms your body following sympathetic stimulation by restoring digestive processes (salivation, peristalsis, enzyme secretion), returning pupils to normal pupil size, stimulating tear glands, and restoring normal bladder contractions.
• Spinal cord, protected by membranes called meninges and your spinal column of bony vertebrae, starts at the base of your back and extends upward to the base of your skull where it joins your brain.

The Brain

• According to one evolutionary model (triune brain), the human brain has three major divisions, overlapping layers with the most recent neural systems nearest the front and top.
• The reptilian brain, which maintains homeostasis and instinctive behaviors, roughly corresponds to the brainstem, which includes the medulla, pons, and cerebellum.
• The old mammalian brain roughly corresponds to the limbic system that includes the septum, hippocampus, amygdala, cingulate cortex, hypothalamus, and the thalamus, which are all important in controlling emotional behavior, some aspects of memory, and vision.
• The new mammalian brain or neocortex, synonymous with the cerebral cortex, accounts for about 80 percent of brain volume and is associated with the higher functions of judgment, decision making, abstract thought, foresight, hindsight and insight, language, and computing, as well as sensation and perception.
• The surface of your cortex has peaks called gyri and valleys called sulci, which form convolutions that increase the surface area of your cortex.
• Deeper valleys are called fissures.
• The last evolutionary development of the brain is the localization of functions on different sides of your brain.

Localization and Lateralization of the Brain’s Function

• Association areas are regions of the cerebral cortex that do not have specific sensory or  motor functions but are involved in higher mental functions, such as thinking, planning, remembering, and communicating.

  

• Medulla oblongata—regulates heart rhythm, blood flow, breathing rate, digestion, vomiting.

• Pons—includes portion of reticular activating system or reticular formation critical for arousal and wakefulness; sends information to and from medulla, cerebellum, and cerebral cortex.

• Cerebellum—controls posture, equilibrium, and movement.

• Basal ganglia—regulates initiation of movements, balance, eye movements, and posture, and functions in processing of implicit memories.

• Thalamus—relays visual, auditory, taste, and somatosensory information to/from appropriate areas of cerebral cortex.

• Hypothalamus—controls feeding behavior, drinking behavior, body temperature, sexual behavior, threshold for rage behavior, activation of the sympathetic and parasympathetic systems, and secretion of hormones of the pituitary.

• Hippocampus—enables formation of new long-term memories.

• Cerebral cortex—center for higher-order processes such as thinking, planning, judgment; receives and processes sensory information and directs movement.

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• Plasticity: Although specific regions of the brain are associated with specific functions, if one region is damaged, the brain can reorganize to take over its function.

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Structure and Function of the Neuron

• Glial cells guide the growth of developing neurons, help provide nutrition for and get rid of wastes of neurons, and form an insulating sheath around neurons that speeds conduction.
• The neuron is the basic unit of structure and function of your nervous system.
• The cell body (a.k.a. cyton or soma) contains cytoplasm and the nucleus, which directs synthesis of such substances as neurotransmitters.
• The dendrites are branching tubular processes capable of receiving information.
• The axon emerges from the cyton as a single conducting fiber (longer than a dendrite) that branches and ends in tips called terminal buttons, axon terminals, or synaptic knobs.
• The axon is usually covered by an insulating myelin sheath (formed by glial cells).
• Neurogenesis, the growth of new neurons, takes place throughout life.
• Neurotransmitters are chemicals stored in structures of the terminal buttons called synaptic vesicles.
• Dopamine stimulates the hypothalamus to synthesize hormones and affects alertness and movement.
• Glutamate is a major excitatory neurotransmitter involved in information processing throughout the cortex and especially memory formation in the hippocampus.
• Serotonin is associated with sexual activity, concentration and attention, moods, and emotions.
• Opioid peptides such as endorphins are often considered the brain’s own painkillers. Gamma-aminobutyric acid (GABA) inhibits firing of neurons.
• Norepinephrine, also known as noradrenaline, is associated with attentiveness, sleeping, dreaming, and learning.
• Agonists may mimic a neurotransmitter and bind to its receptor site to produce the effect of the neurotransmitter.
• Antagonists block a receptor site, inhibiting the effect of the neurotransmitter or agonist.

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Neuron Functions

• The neuron at rest is more negative inside the cell membrane relative to outside of the membrane.
• The neuron’s resting potential results from the selective permeability of its membrane and the presence of electrically charged particles called ions near the inside and outside surfaces of the membrane in different concentrations.
• When sufficiently stimulated (to threshold), a net flow of sodium ions into the cell causes a rapid change in potential across the membrane, known as the action potential.
• If stimulation is not strong enough, your neuron doesn’t fire. The strength of the action potential is constant whenever it occurs.
  • This is the all-or-none principle.
• The wave of depolarization and repolarization is passed along the axon to the terminal buttons, which release neurotransmitters.
• Spaces between segments of myelin are called nodes of Ranvier.
• When the axon is myelinated, conduction speed is increased since depolarizations jump from node to node.
  • This is called saltatory conduction.
• Excitatory, the neurotransmitters cause the neuron on the other side of the synapse to generate an action potential (to fire); other synapses are inhibitory, reducing or preventing neural impulses.

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Reflex Action

• Reflex involves impulse conduction over a few (perhaps three) neurons. The path is called a reflex arc.
• Sensory or afferent neurons transmit impulses from your sensory receptors to the spinal cord or brain.
• Interneurons, located entirely within your brain and spinal cord, intervene between sensory and motor neurons.
• Motor or efferent neurons transmit impulses from your sensory or interneurons to muscle cells that contract or gland cells that secrete.
• Muscle and gland cells are called effectors.

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The Endocrine System

• Your endocrine system consists of glands that secrete chemical messengers called hormones into your blood.
• The hormones travel to target organs where they bind to specific receptors.
• Endocrine glands include the pineal gland, hypothalamus, and pituitary gland in your brain; the thyroid and parathyroids in your neck; the adrenal glands atop your kidneys; pancreas near your stomach; and either testes or ovaries.
• Pineal Gland: endocrine gland in brain that produces melatonin that helps regulate circadian rhythms and is associated with seasonal affective disorder.
• Hypothalamus: portion of brain part that acts as endocrine gland and produces hormones that stimulate (releasing factors) or inhibit secretion of hormones by the pituitary.
• Pituitary Gland: endocrine gland in brain that produces stimulating hormones, which promote secretion by other glands including TSH (thyroid-stimulating hormone); ACTH (adrenocorticotropic hormone), which stimulates the adrenal glands; FSH (follicle stimulating hormone), which stimulates egg or sperm production; ADH (antidiuretic hormone) to help retain water in your body; and HGH (human growth hormone).
• Thyroid Gland: endocrine gland in neck that produces thyroxine, which stimulates and maintains metabolic activities.
• Parathyroids: endocrine glands in neck that produce parathyroid hormone, which helps maintain calcium ion level in blood necessary for normal functioning of neurons.
• Adrenal Glands: endocrine glands atop kidneys
• Pancreas: gland near stomach that secretes the hormones insulin and glucagon, which regulate blood sugar that fuels all behavioral processes.
• Ovaries and Testes: gonads in females and males, respectively, that produce hormones necessary for reproduction and development of secondary sex characteristics.

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Genetics and Evolutionary Psychology

• The nature-nurture controversy deals with the extent to which heredity and the environment each influence behavior.
• Evolutionary psychologists study how natural selection favored behaviors that contributed to survival and the spread of our ancestors’ genes and may currently contribute to our survival into the next generations.
• Evolutionary psychologists look at universal behaviors shared by all people.

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Genetics and Behavior

• Behavioral geneticists study the role played by our genes and our environment in mental ability, emotional stability, temperament, personality, interests, and so forth; they look at the causes of our individual differences.
• Identical twins are two individuals who share all of the same genes/heredity because they develop from the same fertilized egg or zygote; they are monozygotic twins.
• Fraternal twins are siblings that share about half of the same genes because they develop from two different fertilized eggs or zygotes; they are dizygotic twins.
• Heritability is the proportion of variation among individuals in a population that is due to genetic causes.

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Transmission of Hereditary Characteristics

• Each DNA segment of a chromosome that determines a trait is a gene.
• Chromosomes carry information stored in genes to new cells during reproduction.
• Normal human body cells have 46 chromosomes, except for eggs and sperms that have 23 chromosomes.
• Turner syndrome have only one X sex chromosome (XO).
• Klinefelter’s syndrome arise from an XXY zygote.
• Males with Klinefelter’s tend to be passive. The presence of three copies of chromosome 21 results in the expression of Down syndrome.
• The genetic makeup for a trait of an individual is called its genotype.
• The expression of the genes is called its phenotype.
• If the genes are different, the expressed gene is called the dominant gene; the hidden gene is the recessive gene.
• Tay-Sachs syndrome produces progressive loss of nervous function and death in a baby.
• Albinism arises from a failure to synthesize or store pigment and also involves abnormal nerve pathways to the brain, resulting in quivering eyes and the inability to perceive depth or three-dimensionality with both eyes.
• Phenylketonuria (PKU) results in severe, irreversible brain damage unless the baby is fed a special diet low in phenylalanine within 30 days of birth; the infant lacks an enzyme to process this amino acid, which can build up and poison cells of the nervous system.
• Huntington’s disease is an example of a dominant gene defect that involves degeneration of the nervous system.
• A form of familial Alzheimer’s disease has been attributed to a gene on chromosome 21, but not all cases of Alzheimer’s disease are associated with that gene.

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Levels of Consciousness

• Preconscious is the level of consciousness that is outside of awareness but contains feelings and memories that you can easily bring into conscious awareness.
• Nonconscious is the level of consciousness devoted to processes completely inaccessible to conscious awareness, such as blood flow, filtering of blood by kidneys, secretion of hormones, and lower-level processing of sensations, such as detecting edges, estimating size and distance of objects, recognizing patterns, and so forth.
• Unconscious, sometimes called the subconscious, is the level of consciousness that includes often unacceptable feelings, wishes, and thoughts not directly available to conscious awareness.
• Dual processing refers to processing information on conscious and unconscious levels at the same time.
• Unconsciousness is characterized by loss of responsiveness to the environment, resulting from disease, trauma, or anesthesia.

Sleep and Dreams

• Hypothalamus: systematically regulates changes in your body temperature, blood pressure, pulse, blood sugar levels, hormonal levels, and activity levels over the course of about a day.

• Circadian rhythm is a natural, internal process that regulates the sleep-wake cycle and repeats roughly every 24 hours.

  • It's also known as your body’s clock — it influences when you fall asleep and wake up.
  • Your circadian rhythm mainly responds to light and darkness in your environment.

• Sleep is a complex combination of states of consciousness, each with its own level of consciousness, awareness, responsiveness, and physiological arousal.

• Electroencephalograms (EEGs) can be recorded with electrodes on the surface of the skull.

• Hypnagogic state; you feel relaxed, fail to respond to outside stimuli, and begin the first stage of sleep, Non-REM-1.

• EEGs of NREM-1 sleep show theta waves, which are higher in amplitude and lower in frequency than alpha waves.

• As you pass into NREM-2, your EEG shows high-frequency bursts of brain activity (called sleep spindles) and K complexes.

• NREM-3 sleep EEG shows very high amplitude and very low-frequency delta waves.

• REM sleep (Rapid Eye Movement sleep) about 90 minutes after falling asleep.

• Nightmares are frightening dreams that occur during REM sleep.

• Lucid dreaming, the ability to be aware of and direct one’s dreams, has been used to help people make recurrent nightmares less frightening.

  

  

Interpretation of Dreams

• Freud tried to analyze dreams to uncover the unconscious desires (many of them sexual) and fears disguised in dreams.
  • He considered the remembered story line of a dream its manifest content, and the underlying meaning its latent content.
• Psychiatrists Robert McCarley and J. Alan Hobson proposed another theory of dreams called the activation-synthesis theory.
• Pons generates bursts of action potentials to the forebrain, which is activation.

Sleep Disorders

• Insomnia is the inability to fall asleep and/or stay asleep.
• Narcolepsy is a condition in which an awake person suddenly and uncontrollably falls asleep, often directly into REM sleep.
• Sleep apnea is a sleep disorder characterized by temporary cessations of breathing that awaken the sufferer repeatedly during the night.
• Night terrors are most frequently childhood sleep disruptions from the deepest part of NREM-3 (formerly referred to as stage 4) sleep characterized by a bloodcurdling scream and intense fear.
• Sleepwalking, also called somnambulism, is also most frequently a childhood sleep disruption that occurs during deep NREM-3 sleep characterized by trips out of bed or carrying on complex activities.

Hypnosis

• Hypnosis is an altered state of consciousness characterized by deep relaxation and heightened suggestibility.
• Under hypnosis, subjects can change aspects of reality and let those changes influence their behavior.
• Hypnotized individuals may feel as if their bodies are floating or sinking; see, feel, hear, smell, or taste things that are not there; lose sense of touch or pain; be made to feel like they are passing back in time; act as if they are out of their own control; and respond to suggestions by others.
• According to the dissociation theory, hypnotized individuals experience two or more streams of consciousness cut off from each other.

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Meditation

• Meditation is a set of techniques used to focus concentration away from thoughts and feelings in order to create calmness, tranquility, and inner peace.
• Meditation is popular in Asia, where Zen Buddhists meditate.
• EEGs of meditators show alpha waves characteristic of relaxed wakefulness.

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Drugs

• Psychoactive drugs are chemicals that can pass through the blood-brain barrier into the brain to alter perception, thinking, behavior, and mood, producing a wide range of effects from mild relaxation or increased alertness to vivid hallucinations.
• Psychological dependence develops when the person has an intense desire to achieve the drugged state in spite of adverse effects.
• Tolerance: decreasing responsivity to a drug
• Physiological dependence or addiction develops when changes in brain chemistry from taking the drug necessitate taking the drug again to prevent withdrawal symptoms.
• Withdrawal symptoms include intense craving for the drug and effects opposite to those the drug usually induces.
• Depressants are psychoactive drugs that reduce the activity of the central nervous system and induce relaxation.
  • Depressants include sedatives, such as barbiturates, tranquilizers, and alcohol.
• Narcotics are analgesics (pain reducers) that work by depressing the central nervous system.
  • They can also depress the respiratory system.
• Stimulants are psychoactive drugs that activate motivational centers and reduce activity in inhibitory centers of the central nervous system by increasing activity of serotonin, dopamine, and norepinephrine neurotransmitter systems.
• Hallucinogens, also called psychedelics, are a diverse group of psychoactive drugs that alter moods, distort perceptions, and evoke sensory images in the absence of sensory input.

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