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Chapter 2. Brain and Behavior. Table of Contents. Exit. Neuron and Its Parts. Neuron: Individual nerve cell; 100 billion in brain Dendrites: Receive messages from other neurons Soma: Cell body; body of the neuron. Receives messages and sends messages down axon

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Chapter 2

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Chapter 2

Chapter 2

Brain and Behavior

Table of Contents

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Neuron and its parts

Neuron and Its Parts

  • Neuron: Individual nerve cell; 100 billion in brain

    • Dendrites: Receive messages from other neurons

    • Soma: Cell body; body of the neuron. Receives messages and sends messages down axon

    • Axon: Carries information away from the cell body

    • Axon Terminals: Branches that link the dendrites and somas of other neurons

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Brain and behavior

Fig. 2.1 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.

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Brain and behavior

Fig. 2.2 Activity in an axon can be measured by placing electrical probes inside and outside the axon. (The scale is exaggerated here. Such measurements require ultra-small electrodes, as described later in this chapter.) At rest, the inside of an axon is about –60 to –70 millivolts, compared with the outside. Electrochemical changes in a nerve cell generate an action potential. When positively charged sodium ions (Na+) rush into the cell, its interior briefly becomes positive. This is the action potential. After the action potential, an outward flow of positive potassium ions (K+) restores the negative charge inside the axon. (See Figure 2.3 for further explanation.)

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Brain and behavior

Fig. 2.5 A highly magnified view of the synapse shown in Fig. 2.1. 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.

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The nerve impulse

The Nerve Impulse

  • Resting Potential: Electrical charge of an inactive neuron

  • Threshold: Trigger point for a neuron’s firing

  • Action Potential: Nerve impulse

  • Ion Channels: Axon membrane has these tiny holes or tunnels

  • Negative After-Potential: When a neuron is less willing to fire

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Brain and behavior

Fig. 2.3 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.

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Brain and behavior

Fig. 2.4 Cross-sectional views of an axon. The right end of the top axon is at rest, with a negatively charged interior. An action potential begins when the ion channels open and sodium ions (Na+) enter the axon. In this drawing the action potential would travel rapidly along the axon, from left to right. In the lower axon the action potential has moved to the right. After it passes, potassium ions (K+) flow out of the axon. This quickly renews the negative charge inside the axon, so it can fire again. Sodium ions that enter the axon during an action potential are pumped back out more slowly. Their removal restores the original resting potential.

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Animation neuron neural impulse

Animation: Neuron & Neural Impulse

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Neurotransmitters

Neurotransmitters

  • Chemicals that alter activity in neurons; brain chemicals

    • Acetylcholine: Activates muscles

    • Dopamine: Muscle control

    • Serotonin: Mood and appetite control

  • Messages from one neuron to another pass over a microscopic gap called a synapse

  • Receptor Site: Areas on the surface of neurons and other cells that are sensitive to neurotransmitters

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Animation synaptic transmission

Animation: Synaptic Transmission

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Neural regulators

Neural Regulators

  • Neuropeptides: Regulate activity of other neurons

    • Enkephalins: Relieve pain and stress; similar to endorphins

    • Endorphins: Released by pituitary gland; also help to relieve pain

      • Placebos raise endorphin levels

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Nerves and neurons

Nerves and Neurons

  • Nerves: Large bundles of axons and dendrites

  • Myelin: Fatty layer that coats some axons

    • Multiple Sclerosis (MS) occurs when myelin layer is destroyed; numbness, weakness, and paralysis occur

  • Neurilemma: Thin layer of cells wrapped around axons outside brain and spinal cord; forms a tunnel that damaged fibers follow as they repair themselves

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Neural networks

Neural Networks

  • Central Nervous System (CNS): Brain and spinal cord

  • Peripheral Nervous System: All parts of the nervous system outside of the brain and spinal cord

    • Somatic System: Carries messages to and from skeletal muscles and sense organs; controls voluntary behavior

    • Autonomic System: Serves internal organs and glands; controls automatic functions such as heart rate and blood pressure

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Two divisions of the autonomic system

Two Divisions of the Autonomic System

  • Sympathetic: Arouses body; emergency system

  • Parasympathetic: Quiets body; most active after an emotional event

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Brain and behavior

Fig. 2.6 (a) Central and peripheral nervous systems. (b) Spinal nerves, cranial nerves, and the autonomic nervous system.

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Fig 2 7 subparts of the nervous system

Fig. 2.7 Subparts of the nervous system.

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Fig 2 8 sympathetic and parasympathetic branches of the autonomic nervous system

Fig. 2.8 Sympathetic and parasympathetic branches of the autonomic nervous system.

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Brain and behavior

Fig. 2.9 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.

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The spinal cord

The Spinal Cord

  • Spinal Nerves: 31 of them; carry sensory and motor messages to and from the spinal cord

  • Cranial Nerves: 12 pairs that leave the brain directly; also work to communicate messages

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How is the spinal cord related to behavior

How is the Spinal Cord Related to Behavior?

  • Reflex Arc: Simplest behavioral pattern; occurs when a stimulus provokes an automatic response

  • Sensory Neuron: Nerve cell that carries messages from the senses toward the CNS

  • Connector Neuron: Nerve cell that links two others

  • Motor Neuron: Cell that carries commands from the CNS to muscles and glands

  • Effector Cells: Cells capable of producing a response

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Researching the brain

Researching the Brain

  • Ablation: Surgical removal of parts of the 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

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Brain and behavior

Fig. 2.10 The functions of brain structures are explored by selectively activating or removing them. Brain research is often based on electrical stimulation, but chemical stimulation is also used at times.

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Fig 2 11 an eeg recording

Fig. 2.11 An EEG recording.

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Researching the brain cont

Researching the Brain (cont.)

  • Computed Tomographic Scanning (CT): Computer-enhanced 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): Computer-generated color image of brain activity, based on glucose consumption in the brain

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Fig 2 12 an mri scan of the brain

Fig. 2.12 An MRI scan of the brain.

© Huntington Magnetic Resonance Center, Pasadena, California

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Fig 2 13 pet scans

Fig. 2.13 PET scans.

Washington University School of Medicine, St. Louis

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Brain and behavior

Fig. 2.14 The bright spots you see here were created by a PET scan. They are similar to the spots in Figure 2.13. However, here they have been placed over an MRI scan so that the brain’s anatomy is visible. The three bright spots are areas in the left brain related to language. The spot on the right is active during reading. The top-middle area is connected with speech. The area to the left, in the frontal lobe is linked with thinking about a word’s meaning (Montgomery, 1989).

Washington University School of Medicine, St. Louis

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Brain and behavior

Fig. 2.16 In the images you see here, red, orange, and yellow indicate high consumption of glucose; green, blue, and pink show areas of low glucose use. The PET scan of the brain on the left shows that a man who solved 11 out of 36 reasoning problems burned more glucose than the man on the right, who solved 33.

Courtesy of Richard Haier, University of California, Irvine

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Cnn brain mapping

CNN – Brain Mapping

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Cerebral cortex

Cerebral Cortex

  • Definition: Outer layer of the cerebrum; contains 70% of neurons in CNS

  • 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

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Split brains

Split Brains

  • Corpus Callosum is cut; 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

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Figure 2 17 corpus callosum

Figure 2.17 Corpus Callosum

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Brain and behavior

Fig. 2.19 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.

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Right brain left brain

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

  • Right hemisphere good at perceptual skills, and at expressing and detecting other’s emotions

    • Processes information simultaneously and holistically

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Brain and behavior

Fig. 2.20 If a circle is flashed to the left brain and a split-brain patient is asked to say what she or he saw, the circle is easily named. The person can also pick out the circle by touching shapes with the right hand, out of sight under a tabletop (shown semi-transparent in the drawing). However, the left hand will be unable to identify the shape. If a triangle is flashed to the right brain, the person cannot say what was seen (speech is controlled by the left hemisphere). The person will also be unable to identify the correct shape by touch with the right hand. Now, however, the left hand will have no difficulty picking out the hidden triangle. Separate testing of each hemisphere reveals distinct specializations, as listed above.

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Central cortex lobes

Central Cortex Lobes

  • Occipital: Back of brain; vision center

  • Parietal: Just above occipital; bodily sensations such as touch, pain, and temperature (somatosensory area)

  • Temporal: Each side of the brain; auditory and language centers

  • Frontal: Movement, sense of smell, higher mental functions

    • Contains motor cortex; controls motor movement

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Brain and behavior

Fig. 2.21 The left and right brain have different information processing styles. The right brain gets the big pattern; the left focuses on small details.

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When the brain fails to function properly

When the Brain Fails to Function Properly

  • Association Cortex: Combine and process information from the five senses

  • Aphasia: Language disturbance resulting from brain damage

  • 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

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When the brain fails to function properly cont

When the Brain Fails to Function Properly (cont.)

  • Agnosia: Inability to identify seen objects

  • Facial Agnosia: Inability to perceive familiar faces

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Cnn stroke brain repair

CNN – Stroke Brain repair

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Subcortex

Subcortex

  • Immediately below cerebral hemispheres

    • Hindbrain (Brainstem): Consists mainly of medulla and cerebellum

    • Medulla: Controls vital life functions such as heart rate, swallowing, and breathing

    • Pons (Bridge): Acts as a bridge between medulla and other structures

      • Influences sleep and arousal

    • Cerebellum: Located at base of brain

    • Regulates posture, muscle tone, and muscular coordination

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Brain and behavior

Fig. 2.25 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.)

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Subcortex reticular formation rf

Subcortex: Reticular Formation (RF)

  • Reticular Formation: Inside medulla and brainstem

    • 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

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Forebrain

Forebrain

  • 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

    • Hippocampus: Associated with storing permanent memories; helps us navigate through space

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Endocrine system

Endocrine System

  • 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

    • Hypopituitary Dwarfs: As adults, perfectly proportioned but tiny

      • Treatable by using human or synthetic growth hormone; will add a few inches

      • Treatment is long and expensive

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Cnn thought control

CNN – Thought Control

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Brain and behavior

Fig. 2.26 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.

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Endocrine system cont

Endocrine System (cont.)

  • Too much growth hormone leads to giantism

    • Excessive body growth

  • Acromegaly: Enlargement of arms, hands, feet, and facial bones

    • Caused by too much growth hormone secreted late in growth period

      • Andre the Giant

  • Pituitary also governs functioning of other glands, especially thyroid, adrenals, and gonads

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Endocrine system cont1

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

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The adrenal glands

The Adrenal Glands

  • Adrenals: 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

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The adrenal glands cont

The Adrenal Glands (cont.)

  • Adrenal Medulla: Inner core of adrenals; source of epinephrine and norepinephrine

  • Adrenal Cortex: Produces hormones known as corticoids

    • Regulate salt balance

    • Deficiency in some types will cause powerful salt cravings

    • Also help body to adjust to stress

    • Secondary source of sex hormones

  • Oversecretion of adrenal sex hormones can cause virilism: exaggerated male characteristics (Bearded woman)

    • May also cause premature puberty if oversecretion occurs early in life

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Neurogenesis and plasticity

Neurogenesis and Plasticity

  • Neurogenesis: Production of new brain cells

  • Plasticity: Brain’s ability to change its structure and functions

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Brain and behavior

Fig. 2.31 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.

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Brain and behavior

Fig. 2.27 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.”

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