Chapter 2: Brain and Behavior

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 Axon: Carries information away from the cell body Axon Terminals: Branches that link the dendrites and soma of other neurons

Figure 2. 1 A neuron, or nerve cell Figure 2.1 A neuron, or nerve cell. In the right foreground you can see a nerve cell fiber in cross section. The upper left photo gives a more realistic picture of the shape of neurons. Nerve impulses usually travel from the dendrites and soma to the branching ends of the axon. The nerve cell shown here is a motor neuron. The axons of motor neurons stretch from the brain and spinal cord to muscles or glands of the body. Figure 2.1

Main Parts of the Neuron

Figure 2.2 Electrical probes placed inside and outside an axon measure its activity. (The scale is exaggerated here. Such measurements require ultra-small electrodes, as described later in this chapter.) The inside of an axon at rest is about 60 to 70 millivolts, compared with the outside. Electrochemical changes in a neuron generate an action potential. When sodium ions (Na) that have a positive charge rush into the cell, its interior briefly becomes positive. This is the action potential. After the action potential, positive potassium ions (K) flow out of the axon and restore its negative charge. (See Fig. 2.3 for further explanation.) Figure 2.2

The Nerve Impulse Resting Potential: Electrical charge of an inactive neuron Threshold: Trigger point for a neuron’s firing Action Potential: Nerve impulse

More on Nerves Ion Channels: Tiny holes through the axon membrane Negative After-Potential: When a neuron is less willing to fire Synapse: Microscopic space between two neurons over which messages pass

Figure 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. Figure 2.3

Figure 2. 4 The interior of an axon Figure 2.4 The interior of an axon. The right end of the top axon is at rest. Thus, it has a negative charge inside. An action potential begins when ion channels open and sodium ions (Na) rush into the axon. In this drawing, the action potential would travel from left to right along the axon. 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 that it can fire again. Sodium ions that enter the axon during an action potential are pumped out more slowly. Removing them restores the original resting potential. Figure 2.4

Neuron and Neural Impulse Windows Mac OS 8-9 Mac OS X

Neurotransmitters Chemicals that alter activity in neurons; brain chemicals Acetylcholine: Activates muscles Dopamine: Muscle control Serotonin: Mood and appetite control Receptor Site: Areas on the surface of neurons and other cells that are sensitive to neurotransmitters or hormones

Normal Synaptic Transmission of Dopamine

Synaptic Transmission Windows Mac OS 8-9 Mac OS X

Figure 2. 6 A highly magnified view of a synapse Figure 2.6 A highly magnified view of a synapse. Neurotransmitters are stored in tiny sacs called synaptic vesicles (VES-ih-kels). When a nerve impulse reaches the end of an axon, the vesicles move to the surface and release neurotransmitters. These 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. Some transmitter molecules excite the next neuron and some inhibit its activity. Figure 2.6

Neural Regulators Neuropeptides: Brain chemicals that 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

Interaction of Endorphins & Opiates

Nerves and Neurons Nerves: Large bundles of axons and dendrites Myelin: Fatty layer of tissue that coats axons Multiple Sclerosis (MS) occurs when myelin layer is destroyed; numbness, weakness, and paralysis occur

Nerves and Neurons (cont.) Neurilemma: Thin layer of cells wrapped around axons outside brain and spinal cord; forms a tunnel that damaged fibers can follow as they repair themselves Neurogenesis: Production of new brain cells; brain loses thousands of cells each day and grows new neurons at same time to replace them

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

Two Divisions of the Peripheral Nervous System 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

Two Divisions of the Autonomic Nervous System Sympathetic: Arouses body; emergency system Parasympathetic: Quiets body; most active after an emotional event

Figure 2. 7 (a) Central and peripheral nervous systems Figure 2.7 (a) Central and peripheral nervous systems. (b) Spinal nerves, cranial nerves, and the autonomic nervous system. Figure 2.7

Figure 2.8 Subparts of the nervous system.

Figure 2.9 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 its messages through clusters of nerve cells outside the spinal cord. Figure 2.9

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 without passing through the spinal cord; also work to communicate messages

The Spinal Cord and Behavior Reflex Arc: Simplest behavior in which a stimulus provokes an automatic response Sensory Neuron: Nerve cell that carries messages from the senses toward the CNS Motor Neuron: Cell that carries commands from the CNS to the muscles and glands Effector Cells: Cells capable of producing a response

Researching the Brain Ablation: Surgical removal of tissue 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): A device that detects, amplifies, and records electrical activity in the brain

Figure 2.10 A sensory-motor arc, or 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. Such reflexes provide an “automatic” protective device for the body. Figure 2.10

Brain Imaging Techniques 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 brain and body

More Brain Imaging Techniques Functional MRI (fMRI): MRI that makes brain activity visible Positron Emission Tomography (PET): Computer-generated color image of brain activity, based on glucose consumption in the brain

Figure 2.11 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. Figure 2.11

Figure 2.16 Figure 2.16

Cerebral Cortex Outer layer of the cerebrum 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 Spatial Neglect: Right hemisphere stroke victims pay no attention to the left side of visual space

Split Brains Corpus Callosum: Bundle of fibers connecting cerebral hemispheres In 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 2.21 A circle is flashed to the left brain of a split-brain patient and he is asked what he saw. He easily replies, “a circle.” He can also pick out the circle by merely touching shapes with his right hand, out of sight behind a screen. However, his left hand can’t identify the circle. If a triangle is flashed to the patient’s right brain, he can’t say what he saw (speech is controlled by the left hemisphere). He also can’t identify the triangle by touch with the right hand. Now, however, the left hand has no difficulty picking out the triangle. In other tests, the hemispheres reveal distinct skills, as listed above the drawing. Figure 2.21

The Corpus Callosum

Figure 2.18 Figure 2.18

Right Brain/Left Brain Humans use 95 percent of our left brain for language

The Left Hemisphere Left hemisphere is better at math, judging time and rhythm, and coordinating order of complex movements Processes information sequentially

The Right Hemisphere Right hemisphere is good at perceptual skills, and at expressing and detecting other’s emotions Processes information simultaneously

Figure 2. 20 Basic nerve pathways of vision Figure 2.20 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 sent to just one hemisphere by flashing it in the right or left visual field as the person stares straight ahead. Figure 2.20

Figure 2.30 Language is controlled by the left side of the brain in the majority of right- and left-handers. Figure 2.30

Central Cortex Lobes Areas bordered by major grooves or fissures or defined by their functions Occipital Lobe: Back of brain; vision center Parietal Lobe: Just above occipital; bodily sensations such as touch, pain, and temperature (somatosensory area)

The Occipital Lobe

The Parietal Lobe

The Last Two Lobes Temporal Lobe: Each side of the brain; auditory and language centers Frontal Lobe: Movement, sense of smell, higher mental functions Contains motor cortex; controls motor movement

Figure 2.23 Figure 2.23

The Temporal Lobe

The Frontal Lobe

Figure 2.24 The lobes of the cerebral cortex and the primary sensory, motor, and association areas on each. The top diagrams show (in cross section) the relative amounts of cortex “assigned” to the sensory and motor control of various parts of the body. (Each cross section, or “slice,” of the cortex has been turned 90 degrees so that you see it as it would appear from the back of the brain.) Figure 2.24

When the Brain Fails to Function Properly Association Cortex: All areas of the cerebral cortex that are not primarily sensory or motor in function Aphasia: Speech disturbance resulting from brain damage

Broca’s Area Language area related to grammar and pronunciation If damaged, person knows what s/he wants to say but can’t say the words

Wernicke’s Area Wernicke’s Area: Related to language comprehension; in left temporal lobe If damaged, person has problems with meanings of words, NOT pronunciation

Figure 2.28 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.” Figure 2.28

Subcortex All brain structures below cerebral cortex; immediately below cerebral hemispheres Hindbrain (Brainstem) Medulla: Connects brain with the spinal cord and controls vital life functions such as heart rate and breathing

More Subcortex Structures 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

The Brainstem

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 activates cerebral cortex Its alarm clock

Forebrain Structures are part of Limbic System: System within forebrain closely linked to emotional response and motivating behavior Thalamus: Relays sensory information on to the cortex; switchboard Hypothalamus: Regulates emotional behaviors and motives (e.g., sex, hunger, rage, hormone release)

More Forebrain Structures Amygdala: Associated with fear responses Hippocampus: Associated with storing permanent memories; helps us navigate through space

The Limbic System

Figure 2. 27 Parts of the limbic system Figure 2.27 Parts of the limbic system. Although only one side is shown here, 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. Figure 2.27

Figure 2.26 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.) Figure 2.26

Endocrine System Glands that pour chemicals (hormones) directly into the bloodstream or lymph system Pituitary Gland: Regulates growth via growth hormone

Pituitary Problems Too little means person will be smaller than average Hypopituitary Dwarfs: As adults, perfectly proportioned but tiny Treatable by using growth hormone; will add a few inches Treatment is long and expensive

Endocrine System (cont.) Too much growth hormone leads to giantism (excessive body growth) Acromegaly: Enlargement of arms, hands, feet, and facial bones; due to too much growth hormone released late in growth period Andre the Giant Pituitary also governs functioning of thyroid, adrenals, and gonads

Figure 2.29 Figure 2.29

The Pineal Gland Regulates body rhythms and sleep cycles Releases hormone melatonin, which responds to daily variations in light

The Thyroid Gland 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 noradrenalin)

The Adrenal Glands (cont.) Adrenal Medulla: Source of epinephrine and norepinephrine Adrenal Cortex: Produces hormones known as corticoids Regulate salt balance Deficiency in some types will cause powerful salt cravings in humans

Adrenal Hormones Epinephrine arouses body; is associated with fear Norepinephrine arouses body; is linked with anger

Adrenal Problems Oversecretion of adrenal sex hormones can cause virilism: exaggerated male characteristics (Bearded woman) May also cause premature puberty if occurs early in life

Figure 2.31 Research suggests that the hand position used in writing may indicate which brain hemisphere is used for language. (Redrawn from an illustration by M. E. Challinor.) Figure 2.31

Handedness Preference for right or left hand in most activities Dominant Hemisphere: Term usually applied to the side of the human brain that produces language Lateralization: Specialization in abilities of brain hemispheres