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Chapter 3 The Biological Bases of Behavior AP EXAM Biological Bases of Behavior (8–10%) •An effective introduction to the relationship between physiological processes and •behavior — including the influence of neural function, the nervous system and the •brain, and genetic contributions to behavior — is an important element in the AP •course. •AP students in psychology should be able to do the following: •• Identify basic processes and systems in the biological bases of behavior, •including parts of the neuron and the process of transmission of a signal •between neurons. •• Discuss the influence of drugs on neurotransmitters (e.g., reuptake •mechanisms, agonists, antagonists). •• Discuss the effect of the endocrine system on behavior. •• Describe the nervous system and its subdivisions and functions: •— central and peripheral nervous systems; •— major brain regions, lobes, and cortical areas; •— brain lateralization and hemispheric specialization. •• Discuss the role of neuroplasticity in traumatic brain injury. •• Recount historic and contemporary research strategies and technologies that •support research (e.g., case studies, split-brain research, imaging techniques). •• Discuss psychology’s abiding interest in how heredity, environment, and •evolution work together to shape behavior. •• Predict how traits and behavior can be selected for their adaptive value. •• Identify key contributors (e.g., Paul Broca, Charles Darwin, Michael Gazzaniga, •Roger Sperry, Carl Wernicke). Our Neurons All thoughts, feelings, and actions are traced to the electrical impulses in neurons. Your brain contains 100 billion neurons and each neuron is linked to about 15,000 other neurons. Nerves • Nerves: Large bundles of axons and dendrites • Myelin sheath: Fatty layer that coats some axons – Multiple Sclerosis (MS) may occur when myelin layer is destroyed; numbness, weakness, and paralysis occur Communication in the Nervous System • Hardware: – – – – – Glia – structural support and insulation Neurons – communication Soma – cell body Dendrites – receive Axon – transmit away Neural Communication: Insulation and Information Transfer • Myelin sheath – speeds up transmission • Terminal Button – end of axon; secretes neurotransmitters • Neurotransmitters – chemical messengers • Synapse – point at which neurons interconnect Neuron and Its Parts • Neuron: Individual nerve cells that receive, integrate, and transmit information. – Soma: Egg shaped cell/body of the neuron. Receives messages and sends messages down axon. Provides fuel – Axon: Carries information away from the cell body at speeds up to 200 mph. – Axon Terminals: Branches that link the dendrites and somas of other neurons – Synapse: the meeting point between neurons; where neurons “talk” – Neurotransmitters: the chemical signal that transmits across the synapse – Dendrites: receive messages from other neurons – Glial Cells: Supports neuron structure; cleans up unused neurotransmitters ! ! An example of a neuron, or nerve cell, showing several of its important features. The right foreground shows a nerve cell fiber in cross section, and the upper left inset gives a more realistic picture of the shape of neurons. The nerve impulse usually travels from the dendrites and soma to the branching ends of the axon. The neuron shown here is a motor neuron. Motor neurons originate in the brain or spinal cord and send their axons to the muscles or glands of the body. See Fig 3.1 The Nerve Impulse • Resting Potential: Electrical charge of an inactive neuron • Threshold: Trigger point for a neuron’s firing • Action Potential: Nerve impulse/the firing • Ion Channels: Axon membrane has these tiny holes or tunnels • Absolute refractory period: When a neuron is cannot fire A highly magnified view of the synapse shown above. Neurotransmitters are stored in tiny sacs called synaptic vesicles. When a nerve impulse arrives at an axon terminal, the vesicles move to the surface and release neurotransmitters. These transmitter molecules cross the synaptic gap to affect the next neuron. The size of the gap is exaggerated here; it is actually only about one millionth of an inch. Transmitter molecules vary in their effects: Some excite the next neuron and some inhibit its activity. Receptor sites only accept neurotransmitters which “fit” the site. Neurotransmitters • Chemicals that alter activity in neurons; brain chemicals – Acetylcholine: Activates muscles (walking, breathing, etc.) – Dopamine: Large Muscle movement and control. In Parkinson’s Disease, the dopamine receptors die. – Serotonin: Mood and appetite control. A lack of serotonin may lead to depression. Drugs such as Paxil either encourage the production of serotonin or slow the reuptake of serotonin. – Endorphins: similar in structure and effects of opiates, pain suppression and pleasure. • Receptor Site: Areas on the surface of neurons and other cells that are receive neurotransmitters. It is a “lock and key” mechanism. Lock & Key Mechanism Neurotransmitters bind to the receptors of the receiving neuron in a key-lock mechanism. The neurotransmitters that do not bind are reabsorbed by the original Neuron. This process is know as “reuptake”. 13 Neurotransmitters and You ! • One of the 100 neurotransmitters in your brain is “GABA” (Gama-aminobutyric acid). – It is a common behavior inhibitor – GABA and alcohol have very similar shapes – As alcohol binds to the receptors in the brain, the brain reduces production of GABA in chronic stages of alcoholism. When we stop drinking, GABA receptors react to “no” neurotransmitters and we feel discomfort and withdrawal. Alcohol’s Immediate Effects • Alcohol displaces the GABA and as a result we feel more “friendly”; and certainly less inhibited. • This explains why drinking encourages different behaviors – our loss of inhibitions • And as you may guess, other drugs (such as opiates, morphine, cocaine, etc.) act similar to alcohol in blocking receptor sites by blocking neural impulses and creating altered behaviors Organization of the Nervous System • Central nervous system (CNS) – brain and spinal cord – Afferent = toward the CNS – Efferent = away from the CNS – Interneuron = connects afferent neurons and efferent neurons in neural pathways. Found within the central nervous system • Peripheral nervous system – nerves that lie outside the central nervous system – Somatic nervous system– voluntary muscles and sensory receptors – Autonomic nervous system (ANS) – controls automatic, involuntary functions • Sympathetic – Go (fight-or-flight) • Parasympathetic – Stop Subparts of the nervous system. Two Divisions of the Autonomic System • Runs internal organs and glands; controls involuntary activities such as heart, digestion, breathing, etc. – Sympathetic: Arouses body; emergency system – Parasympathetic: Quiets body; most active after an emotional event Autonomic Nervous System (ANS) Sympathetic NS “Arouses” (fight-or-flight) ! ! Parasympathetic NS “Calms” (rest and digest) 19 Central Nervous System The Spinal Cord and Reflexes Simple Reflex 20 Figure 3.6 Organization of the human nervous system Characteristics of the Brain • Do we only use 10% of our brain? • The brain is like 3 pounds (the size of a grapefruit) of firm tofu, like crumpled, compacted paper. The brain is divided into two hemispheres. • Does damage to the brain necessarily cause death? – Phineas Gage Experience: He was a railroad construction foreman now remembered for his incredible survival of an accident in which a large 3 ½ foot iron rod was driven completely through his head, destroying one or both of his brain's frontal lobes, and for that injury's reported effects on his personality and behavior—effects said to be so profound that friends saw him as "no longer Gage.“ – http://en.wikipedia.org/wiki/Phineas_Gage – Frontal Lobotomies in the 40s and 50s • Over 18,000 performed Tools for Researching the Brain • Ablation: Surgical removal of parts of the brain – The brain has no pain receptors (only on scalp and skull) – Patients can be awake during surgery on brain • Deep Lesioning: A thin wire electrode is lowered into a specific area inside the brain; Electrical current is then used to destroy a small amount of brain tissue • Electrical Stimulation of the Brain (ESB): When an electrode is used to activate target areas in the brain • Electroencephalograph (EEG): Detects, amplifies, and records electrical activity in the brain Researching the Brain (cont.) • Computed Tomographic Scanning (CT): Computerenhanced X-ray of the brain or body • Magnetic Resonance Imaging (MRI): Uses a strong magnetic field, not an X-ray, to produce an image of the body’s interior • Functional MRI: MRI that makes brain activity visible • Positron Emission Tomography (PET): Computergenerated color image of brain activity, based on glucose consumption in the brain Neural Transmissions • Tap your right finger when you see a command on a screen. It's a simple maneuver, yet carrying it out requires a vastly complicated series of actions. First, the image of the words on the screen (telling you to tap your finger) enters your eyes and strikes the retinas. The retinas then convert the image into electrical impulses. These impulses are sent to your brain. Your brain "sees" the words and gives meaning to them. Your brain then decides whether or not to carry out what it has read. If it decides yes, your brain's motor cortex, a small area that exists on the outer part of your brain, calls for messages to be sent through your spinal cord and down your arm to the muscles that control the finger. Only then does the finger move. This simplified drawing shows the main structures of the human brain and describes some of their most important features. (You can use the color code in the foreground to identify which areas are part of the forebrain, midbrain, and hindbrain.) Parts of the Brain Older Brain Structures Brainstem the oldest part of the brain, beginning where the spinal cord swells and enters the skull. Responsible for automatic survival functions. 27 Brain Stem Medulla [muh-DUL-uh] base of the brainstem, controls heartbeat and breathing. ! Reticular Formation a nerve network in the brainstem that plays an important role in controlling arousal. 28 Brain Stem Thalamus [THAL-uhmuss] the brain’s sensory switchboard, located on top of the brainstem. It directs messages to the sensory areas in the cortex and transmits replies to the cerebellum and medulla. 29 Cerebellum The “little brain” attached to the rear of the brainstem. It helps coordinate voluntary movements and balance. 30 The Limbic System Limbic System a doughnutshaped system of neural structures at the border of the brainstem and cerebrum, associated with emotions such as fear, aggression and drives for food and sex. It includes the hippocampus, amygdala, and hypothalamus. 31 Amygdala Amygdala [ah-MIG-dahla] two almond-shaped neural clusters linked to emotion of fear and anger. 32 Hypothalamus Hypothalamus lies below (hypo) the thalamus; directs several maintenance activities like eating, drinking body temperature, and emotions. Helps govern the endocrine system via the pituitary gland. This may be part of the “pleasure center” of the brain. 33 The Cerebral Cortex The intricate fabric of interconnected neural cells that covers the cerebral hemispheres. The body’s ultimate control and information processing center. 34 Structure of the Cerebral Cortex Each brain hemisphere is divided into four lobes, separated by prominent fissures. They are frontal lobes (forehead), parietal lobes (top to rear head), occipital lobes (back head) and temporal lobes (side of head). 35 4 Lobes of the Cerebral Cortex • Occipital Lobe: (Primary Visual Cortex) Back of brain; visual association area; not a “TV” screen as we will later learn. • Temporal Lobe: (Primary Auditory Cortex) Each side of the brain above the ears; auditory and language centers; recognizes and organizes sounds Central Cortex Lobes (contd) • Parietal Lobe: contains the sensory cortex and the motor cortex. This area is at the top, read of our brain and runs from ear to ear. Contains perception, senses and motor skills; bodily sensations such as touch, pain, and temperature – Mapped while stimulating areas in wide-awake patients • Frontal Lobe: Higher mental functions (Our Intelligence), movement, sense of smell – Contains Primary motor cortex; controls motor movement – Personality, emotions – Prefrontal Cortex may serve as an “executive function” of the brain Visual Function Functional MRI scan shows the visual cortex activates as the subject looks at faces. 38 Auditory Function Functional MRI scan shows the auditory cortex is active in patients who hallucinate. They are “hearing” voices. 39 Figure 3.19 – The cerebral cortex in humans Functions of the Cortex Motor Cortex area at the rear of the frontal lobes controls voluntary movements. Sensory Cortex (parietal cortex) receives information from skin surface and sense organs. 41 Figure 3.20 – Primary motor cortex with homunculus Specialization & Integration Brain activity when hearing, seeing, and speaking words 43 Association Areas More intelligent animals have increased “uncommitted” or association areas of the cortex. 44 When the Brain Fails to Function Properly • Association Cortex: Combine and process information from the five senses • Aphasia: Language disturbance resulting from brain damage (like from a stroke) • Broca’s Area: Related to language and speech production – If damaged, person knows what s/he wants to say but can’t say the words • Wernicke’s Area: Related to language comprehension; in left temporal lobe – If damaged, person has problems with meanings of words, NOT pronunciation Three Regions of the Brain Hindbrain, Midbrain, Forebrain Your Textbook Organization • The hindbrain includes the – Cerebellum (little brain) • Critical to coordination and movement – Medulla • Controls heartbeat and circulation, breathing, reflexes – Pons • Connects brainstem with the cerebellum • Involved with sleep and arousal • Coordinates movement Midbrain Reticular Formation (RF) • Midbrain coordinates sensory processes. Deterioration of this area has implications for Parkinson’s disease. • Reticular Formation: Inside hindbrain and midbrain – Associated with alertness, attention, and some reflexes (breathing, coughing, sneezing, vomiting) – Reticular Activating System (RAS): Part of RF that keeps it active and alert • RAS acts like the brain’s alarm clock • Activates and arouses cerebral cortex Forebrain • Largest, most complex region of the brain • Structures are part of Limbic System: System within forebrain closely linked to emotional response and motivating behavior – Thalamus: Relays sensory information on the way to the cortex; switchboard – Hypothalamus: Regulates emotional behaviors and motives (e.g., sex, hunger, rage, hormone release) – Amygdala: Associated with fear responses and aggression – Hippocampus: Associated with storing permanent memories; helps us navigate through space Forebrain (contd.) Cerebral Cortex • Definition: Outer layer of the cerebrum; contains 70% of neurons in CNS • Contains the association areas where we do our reasoning/thinking • Cerebrum: Two large hemispheres that cover upper part of the brain • Corticalization: Increase in size and wrinkling of the cortex • Cerebral Hemispheres: Right and left halves of the cerebrum • Corpus Callosum: Bundle of fibers connecting cerebral hemispheres Teenage Brain Pt III • Teenage Brain Part III (part 4 in video) • Teens often perceive their environment differently and thus react differently than older individuals. Speech Production Understanding speech Right Brain/Left Brain • About 95 percent of our left brain is used for language • Left hemisphere better at math, judging time and rhythm, and coordinating order of complex movements – Processes information sequentially and is involved with analysis (speech, writing, math, sequencing, analyzing) – Controls the right side of the body • Right hemisphere good at perceptual skills, and at expressing and detecting other’s emotions – Processes information simultaneously and holistically (music, puzzles, spatial tasks) – Controls the left side of the body Split Brains • Corpus Callosum is thicker in females; classical musicians • Corpus Callosum can be severed; done to control severe epilepsy (seizure disorder) • Result: The person now has two brains in one body • This operation is rare and is often used as a last resort. • The Divided Brain (6 min) Splitting the Brain A procedure in which the two hemispheres of the brain are isolated by cutting the connecting fibers (mainly those of the corpus callosum) between them. Martin M. Rother Courtesy of Terence Williams, University of Iowa Corpus Callosum 54 Specialized Abilities of the Two Hemispheres • Left Hemisphere – – – – Words, letters Language sounds Verbal Memory Speech, grammar, reading, writing – Logic, explaining events • Right Hemisphere – – – – – – – Faces Emotional expression Geometric patterns Music Nonverbal memory Emotion of tone/speech Judgment of distance The Brain’s Plasticity • Plasticity refers to the brain’s ability to modify itself after damage, especially in young children. Also this is the process of rehabilitation in stroke victims. – If the motor cortex area that controls the forefinger, the surrounding motor cortex areas may take over that function – If the language processing area in the left hemisphere is damaged, the right hemisphere may take over part of that task Can Life Experience Affect your Brain • Two groups of rats were studied. Group A lived in an impoverished environment (alone in a small cage); Group B lived in an enriched environment with other rats with new “toys” daily. • At the end of the study, the Group B rats had a heavier, thicker cortex. Even rats that only lived in that environment for a few days experienced gains. The Endocrine System Endocrine System is the body’s “slow” chemical communication system. Communication is carried out by hormones synthesized by a set of glands. 58 Endocrine System • The Body’s slower communication system. The bloodstream carries these “messengers” whereas the neurons are carried electrically. • Glands that pour chemical messengers (hormones) directly into the bloodstream or lymph system • Pituitary Gland: Regulates growth via growth hormone. Pituitary also governs functioning of other glands, especially thyroid, adrenals, and gonads • Pancreas: produces insulin to control metabolism of sugar • Gonads: ovaries and testes produce the hormones that control secondary sex characteristics and reproduction Endocrine System (cont.) • Pineal Gland: Regulates body rhythms and sleep cycles. – Releases hormone melatonin, which responds to daily variations in light • Thyroid: In neck; regulates metabolism – Hyperthyroidism: Overactive thyroid; person tends to be thin, tense, excitable, nervous – Hypothyroidism: Underactive thyroid; person tends to be inactive, sleepy, slow, obese Endocrine System (cont.) • Adrenal glands: Arouse body, regulate salt balance, adjust body to stress, regulate sexual functioning; located on top of kidneys – Releases epinephrine and norepinephrine (also known as adrenaline and noradrenaline) • Epinephrine arouses body; is associated with fear • Norepinephrine arouses body; is linked with anger Hormones Hormones are chemicals synthesized by the endocrine glands and secreted in the bloodstream. Hormones affect the brain many other tissues of the body. For example, epinephrine (adrenaline) increases heart rate, blood pressure, blood sugar and feelings of excitement during emergency situations. 62 Heredity and Genetics Nurture v. Nature • Twin Studies help separate heredity and the environmental effects. – Identical (or monozygotic) twins develop from the same fertilized egg – Fraternal (or dizygotic) twins develop from two different eggs. • Adoption Studies assess genetic influence by comparing traits to biological and adoptive parents Evolutionary Bases of Behavior • Natural Selection suggests that characteristics that provide a survival or reproductive advantage are more likely to be passed on to offspring. • The concept of natural selection applies to physical and behavioral characteristics. • Examine behaviors conserved across a related species to understand how that behavior maximizes success Evolutionary Psychology: Behavior in Terms of Adaptive Significance • Based on Darwin’s ideas of natural selection – Reproductive success key • Adaptations – behavioral as well as physical – Fight-or-flight response – Taste preferences – Parental investment and mating