Chapter 3 The Brain, Biology, and Behavior

n Neuron: Individual nerve cell  Dendrites: Receive messages from other neurons  Soma: Cell body; body of the neuron  Axon: Carries information away from the cell body  Axon Terminals: Branches that link the dendrites and soma of other neurons n Myelin sheath – speeds up transmission n Terminal Buttons – end of axon; secrete neurotransmitters  Neurotransmitters – chemical messengers n Synapse – point at which neurons interconnect Neuron and its parts

Figure 3.1 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.

Figure 3.3 The inside of an axon normally has a negative electrical charge. The fluid surrounding an axon is normally positive. As an action potential passes along the axon, these charges reverse, so that the interior of the axon briefly becomes positive.

Figure 3.5 A highly magnified view of the synapse. 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.

n Chemicals that alter activity in neurons; brain chemicals. Some examples:  Acetylcholine: Activates muscles  Dopamine: Muscle control  Serotonin: Mood and appetite control n Messages from one neuron to another pass over a microscopic gap called a synapse n Receptor Site: Areas on the surface of neurons and other cells that are sensitive to neurotransmitters or hormones Neurotransmitters

n Neural Peptides: Regulate activity of other neurons  Enkephalins: Relieve pain and stress Neural Regulators

n Central Nervous System (CNS): Brain and spinal cord. n Peripheral Nervous System: All parts of the nervous system outside of the brain and spinal cord.  Somatic System: Links spinal cord with body and sense organs. Controls voluntary behavior  Autonomic System: Serves internal organs and glands. Controls automatic functions such as heart rate and blood pressure Sympathetic: Arouses body- Go (fight-or-flight) Parasympathetic: Quiets body- Stop n Afferent = toward the CNS n Efferent = away from the CNS Neural Networks

Figure 3.6 (a) Central and peripheral nervous systems. (b) Spinal nerves, cranial nerves, and the autonomic nervous system.

Figure 3.7 Subparts of the nervous system.

Figure 3.8 Sympathetic and parasympathetic branches of the autonomic nervous system. Both branches control involuntary actions. The sympathetic system generally activates the body. The parasympathetic system generally quiets it. The sympathetic branch relays through a chain of ganglia (clusters of cell bodies) outside the spinal cord.

Figure 3.9 A simple sensory-motor (reflex) arc. A simple reflex is set in motion by a stimulus to the skin (or other part of the body). The nerve impulse travels to the spinal cord and then back out to a muscle, which contracts. Reflexes provide an “automatic” protective device for the body.

n Electroencephalograph (EEG): Detects, amplifies and records electrical activity in the brain n Computed Tomographic Scanning (CT): Computer-enhanced X-Ray of the brain or body n Magnetic Resonance Imaging (MRI): Uses a strong magnetic field, not an X-Ray, to produce an image n Functional MRI: MRI that also records brain activity n Positron Emission Tomography (PET): Computer- generated color image of brain activity, based on glucose consumption in the brain. Researching the Brain

n Hindbrain – vital functions – medulla, pons, and cerebellum n Midbrain – sensory functions – dopaminergic projections, reticular activating system n Forebrain – emotion, complex thought – thalamus, hypothalamus, limbic system, cerebrum, cerebral cortex Brain Regions and Functions

n Outer layer of the cerebrum n Cerebrum: Two large hemispheres that cover upper part of the brain n Cerebral Hemispheres: Right and left halves of the cerebrum  Left hemisphere – verbal processing: language, speech, reading, writing  Right hemisphere – nonverbal processing: spatial, musical, visual recognition n Corpus Callosum: Bundle of fibers connecting cerebral hemispheres Cerebral Cortex

Figure 3.15 An illustration showing the increased relative size of the human cerebrum and cerebral cortex, a significant factor in human adaptability and intelligence.

Figure 3.17 The corpus callosum is the major “cable system” through which the right and left cerebral hemispheres communicate. A recent study found that the corpus callosum is larger in classically trained musicians than it is in nonmusicians. When a person plays a violin or piano, the two hemispheres must communicate rapidly as they coordinate the movements of both hands. Presumably, the size of the corpus callosum can be altered by early experience, such as musical training.

n Occipital: Back of brain; vision center n Parietal: Just above occipital; bodily sensations such as touch, pain, and temperature n Temporal: Each side of the brain; auditory and language centers n Frontal: Movement, sense of smell, higher mental functions  Contains motor cortex; controls motor movement Central Cortex Lobes

Basic nerve pathways of vision. Notice that the left portion of each eye connects only to the left half of the brain; likewise, the right portion of each eye connects to the right brain. When the corpus callosum is cut, a “split brain” results. Then visual information can be directed to one hemisphere or the other by flashing it in the right or left visual field as the person stares straight ahead.

Many of the lobes of the cerebral cortex are defined by larger fissures on the surface of the cerebrum. Others are regarded as separate areas because their functions are quite different.

n Aphasia: Speech disturbance resulting from brain damage n 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 n Wernicke’s Area: Related to language comprehension.  If damaged, person has problems with meanings of words, NOT pronunciation n Agnosia: Inability to identify seen objects n Facial agnosia: Inability to perceive familiar faces When the brain fails to function properly

Figure 3.21 Language processing in the brain. This view of the left hemisphere highlights the location of two centers for language processing in the brain: Broca’s area, which is involved in speech production, and Wernicke’s area, which is involved in language comprehension.

Language is controlled by the left side of the brain in the majority of right- and left-handers.

A direct brain-computer link may provide a way of communicating for people who are paralyzed and unable to speak. Activity in the patient’s motor cortex is detected by an implanted electrode. The signal is then amplified and transmitted to a nearby computer. By thinking in certain ways, patients can move an on-screen cursor. This allows them to spell out words or select from a list of messages, such as “I am thirsty.”

n Hindbrain (brainstem)  Medulla: Connects brain with the spinal cord and controls vital life functions such as heart rate and breathing  Pons (Bridge): Acts as a bridge between brainstem and other structures. Influences sleep and arousal  Cerebellum: Located at base of brain. Regulates posture, muscle tone and muscular coordination Subcortex

n Reticular Formation (RF): Inside medulla.  Associated with alertness, attention and some reflexes n Reticular Activating System (RAS): Part of RF that keeps it active and alert.  Its alarm clock  Activates and arouses cerebral cortex Subcortex: Reticular Formation (RF)

n Structures are part of Limbic System:  System within forebrain closely linked to emotional response 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 Hippocampus: Associated with storing memories Forebrain

Parts of the limbic system are shown in this highly simplified drawing. Although only one side is shown, the hippocampus and the amygdala extend out into the temporal lobes at each side of the brain. The limbic system is a sort of “primitive core” of the brain strongly associated with emotion.

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.)

n Glands that pour chemicals (hormones) directly into the bloodstream or lymph system  Pituitary Gland: Regulates growth via growth hormone Too little means person will be smaller than average Too much leads to giantism:  Excessive body growth Acromegaly: Enlargement of arms, hands, feet and facial bones.  Too much growth hormone released late in growth period  Andre the Giant Endocrine System

< Low Pituitary Acromegaly > < Giantism

n Pineal Gland: Regulates body rhythms and sleep cycles.  Releases hormone melatonin, which responds to variations in light n 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 n Adrenals: Arouse body, regulate salt balance, adjust body to stress, regulate sexual functioning Endocrine System Continued

Figure 3.27 Locations of the endocrine glands in the male and female.

n Behavioral genetics = the study of the influence of genetic factors on behavioral traits  Basic terminology: Chromosomes – strands of DNA carrying genetic information  Human cells each contain 46 chromosomes in pairs (sex-cells – 23 single)  Each chromosome – thousands of genes, also in pairs  Dominant, recessive Genes and Behavior: The Interdisciplinary Field of Behavioral Genetics Genotype/Phenotype and Polygenic inheritance Homozygous, heterozygous

n Plasticity: Brain’s capacity to change its structure and functions n Neurogenesis: Production of new brain cells Neurogenesis and Plasticity

Neuroscientists are searching for ways to repair damage caused by strokes and other brain injuries. One promising technique involves growing neurons in the laboratory and injecting them into the brain. These immature cells are placed near damaged areas, where they can link up with healthy neurons. The technique has proved successful in animals and is now under study in humans.

n Molecular Genetics = the study of the biochemical bases of genetic inheritance  Genetic mapping – locating specific genes n Behavioral Genetics  The interactionist model Richard Rose (1995) – “We inherit dispositions, not destinies.” Modern Approaches to the Nature vs. Nurture Debate

n Based on Darwin’s ideas of natural selection  Reproductive success key n Adaptations – behavioral as well as physical  Fight-or-flight response  Taste preferences Evolutionary Psychology: Behavior in Terms of Adaptive Significance