Chapter 2 Brain and Behavior Table of Contents Exit.

Chapter 2

Brain and Behavior

Table of ContentsTable of Contents ExitExit

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


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. Table of ContentsTable of Contents ExitExit

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.)


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.


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


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.


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.


Animation: Neuron & Neural Impulse


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


Animation: Synaptic Transmission


Neural Regulators

Neuropeptides: Regulate activity of other neuronsEnkephalins: Relieve pain and stress;

similar to endorphinsEndorphins: Released by pituitary gland;

also help to relieve painPlacebos raise endorphin levels


Nerves and Neurons

Nerves: Large bundles of axons and dendritesMyelin: 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


Neural Networks

Central Nervous System (CNS): Brain and spinal cordPeripheral 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


Two Divisions of the Autonomic System

Sympathetic: Arouses body; emergency system

Parasympathetic: Quiets body; most active after an emotional event


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


Fig. 2.7 Subparts of the nervous system. Table of ContentsTable of Contents ExitExit

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


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.


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


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


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


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.


Fig. 2.11 An EEG recording.


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


Fig. 2.12 An MRI scan of the brain.

© Huntington Magnetic Resonance Center, Pasadena, California


Fig. 2.13 PET scans.

Washington University School of Medicine,

St. Louis Table of ContentsTable of Contents ExitExit

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


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


CNN – Brain Mapping


Cerebral Cortex

Definition: Outer layer of the cerebrum; contains 70% of neurons in CNSCerebrum: Two large hemispheres that cover upper part of the brainCorticalization: Increase in size and wrinkling of the cortexCerebral Hemispheres: Right and left halves of the cerebrumCorpus Callosum: Bundle of fibers connecting cerebral hemispheres


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


Figure 2.17 Corpus Callosum Table of ContentsTable of Contents ExitExit

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.


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


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.


Central Cortex Lobes

Occipital: Back of brain; vision centerParietal: Just above occipital; bodily sensations such as touch, pain, and temperature (somatosensory area)Temporal: Each side of the brain; auditory and language centersFrontal: Movement, sense of smell, higher mental functions Contains motor cortex; controls motor movement


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.


When the Brain Fails to Function Properly

Association Cortex: Combine and process information from the five senses Aphasia: Language disturbance resulting from brain damageBroca’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


When the Brain Fails to Function Properly (cont.)

Agnosia: Inability to identify seen objects

Facial Agnosia: Inability to perceive familiar faces


CNN – Stroke Brain repair


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


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.)


Subcortex: Reticular Formation (RF)

Reticular Formation: Inside medulla and brainstemAssociated 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 clockActivates and arouses cerebral cortex


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


Endocrine System

Glands that pour chemicals (hormones) directly into the bloodstream or lymph systemPituitary Gland: Regulates growth via growth hormoneToo 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


CNN – Thought Control


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.


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


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


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


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

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Neurogenesis and Plasticity

Neurogenesis: Production of new brain cells

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


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.


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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