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The Elusive Search for an AIDS Vaccine




View the step-by-step solution to;1. A 2 full-pages reflection paper with mixing cha...;View AnswerStatus: Answered Category: Biology Date Answered: Apr 25, 2014 Tutor: khushiosheen;BenShi posted a question Apr 21, 2014 at 8:55pm;1. A 2 full-pages reflection paper with mixing chapter 24 and 27 only, no need other sources with a paper tittle please;2. Homework assignment;All due 25th before 8p.m.;Attachments Preview;BSC1020_Chapter24_PPT.pdf Download Attachment;Biology and Society;The Elusive Search for an AIDS Vaccine;Chapter... Show more;BSC1020_Chapter27_PPT.pdf Download Attachment;Chapter 27;Nervous, Sensory;and Motor Systems;es;Many species of fish use electroreception to;generate weak electric fields that reveal objects in;low-visibility environments;Biology and Society;The Seismic Sense of Elephants;Many animals perceive the world in ways we;cannot.;Bats and porpoises generate ultrasonic sounds in;echolocation to detect echoes;Determine the size;shape, location, speed;and direction of objects;in the environment;Figure;27.0;Migratory birds, fish, turtles, and bees use;magnetoreception, the ability to detect Earths;magnetic fields;Elephants can communicate using low-rumbling;infrasounds too low to be heard by human ears;Recent research suggests that elephants can;detect seismic waves using specialized pressuresensing nerve endings in their feet and trunk;AN OVERVIEW OF ANIMAL NERVOUS;SYSTEMS;The nervous system forms a communication and;coordination network throughout an animals;body;Neurons are nerve cells that carry electrical;signals from one part of the body to another;Your brain contains about 100 billion neurons;Migrating elephants may use long-distance;seismic waves to communicate;Organization of Nervous Systems;The nervous system of most animals has two;main divisions.;1. The central nervous system (CNS) is made;up of the brain and spinal cord (in;vertebrates).;2. The peripheral nervous system (PNS) is;made up of mostly nerves that carry signals;into and out of the CNS.;1;A nerve is a communication line made from cablelike bundles of neuron fibers tightly wrapped in;connective tissue;SENSORY INPUT;Sensory receptor;The three interconnected functions of the nervous;system are carried out by three types of neurons;Motor;neuron;Interneurons integrate information;Effector cells;Effector cells perform the bodys responses to;motor output.;Neurons;INTEGRATION;MOTOR OUTPUT;Sensory neurons function in sensory input;Motor neurons function in motor output;Sensory;neuron;Interneuron;Brain and spinal cord;Peripheral nervous;system (PNS);Central nervous;system (CNS);Organization of a nervous system;Signal direction;Figure 27.2;Dendrites;Neurons;Are the functional units of the nervous system;Figure 27.1;Cell;body;Vary widely in shape;Share some common features;Supporting;cell;Structure of a motor neuron;This diagram shows a motor;neuron. The flow of the;electrical signal through a;neuron follows this path;dendrite cell body axon.;Signal;pathway;Synaptic;terminals;Nucleus;Myelin sheath;Axon;The cell body houses the nucleus and other;organelles;Supporting cells;Outnumber neurons by as many as 50 to 1;Two types of extensions project from the cell body;Dendrites, which;Receive incoming messages from other;cells;Convey the information toward the cell;body;Axons, which transmit signals toward another;neuron or toward an effector;Protect, insulate, and reinforce the neurons;The myelin sheath;Forms an insulating material around an axon;Helps increase the speed of the electrical signal;along an axon;Note: Multiple sclerosis leads to a gradual;destruction of these myelin sheaths;2;Neurons;Sending a Signal through a Neuron;An axon ends in a cluster of branches, each with;a bulb-like synaptic terminal;A resting neuron has potential energy that can be;put to work to send nerve signals from one part;of the body to another;This relays signals to;This difference in charge (voltage) across the;plasma membrane of a resting neuron is the;resting potential;another neuron;or;an effector cell (such as a muscle cell);Caused by the presence of differently charged;ions on either side of the membrane;Figure 27.3;The Action Potential;A stimulus is any factor that causes a nerve;signal to be generated.;A stimulus of sufficient strength can trigger an;action potential, a nerve signal that carries;information along a neuron.;If the stimulus is strong enough, a sufficient;number of channels open to reach the;threshold, the minimum change in a;membranes voltage that must occur to trigger;the action potential.;Neuron interior;Resting potential;1;First set of;channels closes;and inactivates;second set of;channels opens;and positive ions;rush out;membrane goes;back to;resting potential;4;2;3;A stimulus;opens;first set of;ion channels;If threshold is;reached;action potential;is triggered;Additional;channels open;in that region;of the neuron;interior of cell;becomes;more positive;than outside;Neuron interior;1 Resting potential;2 A stimulus opens the;first set of ion channels;if threshold is reached;an action potential is;triggered.;3 Additional channels;open, in that region of;the neuron, the interior;of the cell becomes;more positive than the;outside.;4 The first set of channels;closes and inactivates;a second set of;channels opens and;positive ions rush out;the membrane returns;to resting potential.;3;The Action Potential;Propagation of the Signal;Within a living neuron, this whole process takes;just a few milliseconds, meaning a neuron can;produce hundreds of nerve signals in a second;An action potential is a localized electrical event;BioFlix Animation: How Neurons Work;Figure 27.4;Propagation of an;action potential;along an axon;1 Action potential;2;Action potential;3;To function as a long-distance signal, this local;event must be passed along the neuron;Action potential propagation is like a domino;effect along a neuron;Blast Animation: Action Potential;Axon;A rapid change from the resting potential at a;specific place along the neuron;Action potential;Lets focus on the axon region at the far left in;each panel of Figure 27.4;1) When this region of the axon (blue) has its first;set of channels open, positive ions diffuse;inward (blue arrows), and an action potential is;generated.;2) That same region then opens the second set of;channels, allowing other positive ions to diffuse out;of the axon (green), while closing the first set of;channels that allow ions in;3) A short time later, we would see no action potential;at this (far left) spot because the membrane here has;restored itself and returned to its resting potential;Propagation of the Signal;Action potentials are all-or-none events;The same no matter how strong or weak the;stimulus that triggers them (as long as the;threshold is reached);So, how can they relay different intensities of;information?;Well, such information can be achieved by;sending more action potentials in a given;amount of time;Passing a Signal from a Neuron to a Receiving;Cell;A synapse is a relay point;between two neurons or;between a neuron and an effector cell.;Synapses come in two varieties;1. Electrical;2. Chemical;4;Chemical synapses;Electrical synapses;Electric current passes directly from one;neuron to the next;Found in the heart and digestive tract;Have a narrow gap, the synaptic cleft;separating a synaptic terminal of the sending;neuron from the receiving cell;Rely on neurotransmitters, chemicals that;carry information from one nerve cell to;another kind of cell;Where steady, rhythmic muscle;contractions are maintained;Chemical synapses are prevalent in most other;organs, including skeletal muscles, and the;central nervous system;Blast Animation: Signal Amplification in Neurons;Blast Animation: Signal Transmission at Synapses;SYNAPSE;Neurotransmitter;Sending neuron;Receptor;Action;potential;arrives.;Vesicles;Synaptic;terminal;Vesicle fuses;with plasma;membrane.;Ions;Neurotransmitter;is released into;synaptic cleft.;Synaptic;cleft;Receiving;neuron;Ion channels;Neurotransmitter;molecules;Neurotransmitter;binds to receptor.;Ion channel opens and;triggers or inhibits a;new action potential.;Ion channel closes.;Neurotransmitter is;broken down and;released.;Figure 27.5;Figure 27.5;Dendrites;Chemical synapses can process extremely;complex information.;A neuron may receive input from hundreds of;other neurons via thousands of synaptic;terminals.;Myelin;sheath;Receiving;cell body;Axon;Synaptic;terminals;SEM;BioFlix Animation: How Synapses Work;Figure 27.6;5;Neurotransmitters;Drugs and the Brain;A variety of small molecules can act as;neurotransmitters;Many drugs, such as caffeine, nicotine, and;alcohol, act at synapses by increasing or;decreasing the normal effect of neurotransmitters;Amines;Derived from amino acids;Prescription drugs used to treat psychological;disorders alter the effects of neurotransmitters.;Affect sleep, mood, attention, and learning;Peptides;Short chains of amino acids;Include endorphins, which decrease pain;perception;THE HUMAN NERVOUS SYSTEM;A CLOSER LOOK;For example, tranquilizers such as Valium and Xanax;activate receptors for an inhibitory neurotransmitter;In other cases, a drug may physically block a;receptor, preventing the neurotransmitter from;binding, thereby reducing its effect;Central nervous;system (CNS);Brain;Spinal cord;Peripheral nervous;system (PNS);Although there is remarkable uniformity in the;way nerve cells function, there is great variety in;how nervous systems as a whole are organized.;Vertebrate nervous systems are diverse in;structure and level of sophistication;A vertebrate;nervous system;(back view);However, all are concentrated at the head;end, and have distinct central and peripheral;nervous systems (CNS and PNS);Figure 27.7;The Central Nervous System;The brain and spinal cord;Vertebrate central nervous systems (CNS);Contain spaces;Integrate information coming from the senses;Transmit signals that produce responses;Consist of the;Brain, the master control center of the;nervous system;Spinal cord, a jellylike bundle of nerve;fibers inside the spinal column;Are filled with cerebrospinal fluid, a liquid;that;Cushions the CNS;Helps supply the CNS with nutrients;hormones, and white blood cells;Also protecting the brain and spinal cord are;layers of connective tissues called meninges.;6;The Peripheral Nervous System;Brain;The vertebrate peripheral nervous system (PNS);is divided into two functional components;Cerebrospinal fluid;Meninges;The voluntary nervous system;Also called the motor system;The autonomic nervous system;Spinal cord;(cross section);Is involuntary;Spinal cord;Figure 27.8;The voluntary nervous system;The autonomic nervous system contains two sets;of neurons with opposing effects on most organs;Carries signals to and from skeletal muscles;The parasympathetic division primes the;body for digesting food and resting.;Mainly responds to external stimuli;The autonomic nervous system;Effects include decreasing heart rate and;narrowing bronchi;Regulates the internal environment;The sympathetic division prepares the body;for intense, energy-consuming activities.;Controls smooth and cardiac muscles;And organs and glands of the digestive;cardiovascular, excretory, and endocrine;systems;Effects include dilating of the bronchi and;adrenal gland secretion of the hormones;adrenaline and noradrenaline;Chapter Review Figure;PERIPHERAL NERVOUS SYSTEM;Voluntary nervous system;Autonomic nervous system;(involuntary);Parasympathetic division;(rest and digest);Sympathetic division;Central Nervous System;(CNS);Brain;LM;(fight or flight);Voluntary leg muscles;NERVOUS SYSTEM;Involuntary heart muscle;Spinal cord;nerve bundle;that;communicates;with body;Peripheral Nervous System;(PNS);Voluntary nervous;system;voluntary control;over muscles;Autonomic nervous;system;involuntary control;over organs;Parasympathetic;division;rest and digest;Sympathetic division;fight or flight;Figure 27.9;7;The Human Brain;The Human Brain;The human brain is more powerful than the most;sophisticated computer, and consists of;The brain is divided structurally into three;regions, the;Up to 100 billion intricately organized;neurons;1. Hindbrain;2. Midbrain;Many more supporting cells;Cerebrum;Forebrain;3. Forebrain;Cerebral;cortex;Thalamus;Hypothalamus;Pituitary;gland;Midbrain;Pons;Hindbrain;Medulla;oblongata;Spinal cord;Cerebellum;Figure 27.10;The brainstem;Consists of the hindbrain (medulla oblongata;and pons) and the midbrain;Serves as a sensory filter, selecting which;information reaches higher brain centers;The cerebellum, another part of the hindbrain, is;a planning center for body movements and;balance;8;The Cerebral Cortex;The forebrain contains the most sophisticated;integrating centers in the brain;The thalamus, which relays information to;the cerebral cortex;The cerebrum consists of right and left cerebral;hemispheres interconnected by the corpus;callosum.;The cerebral cortex;The hypothalamus, with many regulatory;functions, including body temperature, sex;drive, and the fight-or-flight response;Is a highly folded layer of tissue that forms the;surface of the cerebrum;The cerebrum, the largest and most;sophisticated part of the brain;Helps produce our most distinctive human traits;A rear view;of the brain;Left cerebral;hemisphere;Accounts for over 80% of the total brain mass;Language, mathematical skills, artistic;talents, personality traits, etc.;Right cerebral;hemisphere;The right and left cerebral hemispheres;Have four lobes, each names for a nearby;skull bone;Corpus;callosum;Thalamus;Are specialized for different mental tasks in a;phenomenon known as lateralization;Higher mental activities occur in association;areas of the brain.;Medulla oblongata;Figure 27.11;Figure 27.12;Frontal lobe;Parietal lobe;Somatosensory;Speech association;area;Taste;Reading;Frontal;association;area;Speech;Smell;Temporal lobe;Cerebellum;Hearing;Auditory;association;area;Visual;association;area;Chapter Review Figure;BRAIN;Forebrain;(sophisticated;integration);Thalamus;Hypothalamus;Cerebrum;Midbrain;Hindbrain;Pons;Medulla oblongata;Cerebellum;(coordinates;movement);Brainstem;(filters motor and;sensory input);Vision;Functional areas of the;Occipital lobe;cerebrums left hemisphere;9;Brain Trauma;Evidence from brain surgery patients indicates;that patterns of lateralization are not fixed.;In hemispherectomy, one half of the brain is;Figure 27.13;surgically removed;Patients have partial;paralysis in side of body;opposite surgery;However, they have;undiminished;intellectual capacities;In 1848, a railroad accident to a man named;Phineas Gage propelled a three-foot-long spike;through his head;He survived but had;significant changes;in his personality;Might have damaged;both frontal lobes of;his brain;A 1994 computer simulation;of the injury;Figure 27.14;Neurological Disorders;Neurological disorders can also affect brain;function;Major depression is extreme and persistent;sadness and loss of interest in pleasurable;activities;Depressed person;Area;of decreased;brain activity;Bipolar disorder, or manic-depressive;disorder, involves extreme mood swings;Alzheimers disease causes mental;deterioration or dementia;Healthy person;Figure 27.15;THE SENSES;Sensory Input;Sensory structures;Sensory input is the process of using receptors to;Gather information;Sense the environment;Pass it on to the CNS;Send information about it to the CNS to be;integrated and acted upon;Sensory transduction is the conversion of a;stimulus signal to an electrical signal by a;sensory receptor cell;10;Figure 27.16;Sensory Transduction;Receptor;Sugar;molecule;(stimulus);Receptor potentials;Are changes in membrane potentials caused;by sensory stimuli;Vary in intensity, depending on the strength;of the stimulus;Sugar;molecule;Taste;bud;Signal transduction;pathway;Ion;channels;Sensory;receptor;cell;Ion;Receptor;potential;Sensory;receptor;cells;Sensory neuron;Figure 27.16 shows sensory transduction in a;human taste bud;Membrane;of sensory;receptor cell;Neurotransmitter;Sensory neuron;Action potential;(to brain);Types of Sensory Receptors;Sensory adaptation;Causes some sensory receptors to be less;sensitive when they are stimulated repeatedly;Keeps the body from continuously reacting to;normal background stimuli;Without it, our nervous system would become;overloaded with useless information;Sensory receptors can be grouped into five;categories, which work in various combinations;to produce the five human senses;A section of human skin reveals why the surface;of our body is sensitive to such a variety of;stimuli;Chapter Review Figure;Stimulus;Heat;Sensory;Receptor;receptor;potential;cell;Light;touch;Pain;Sensory;Action;neuron potential;Cold;CNS;Pain receptors respond to stimuli causing injury;or disease;(Hair);Thermoreceptors detect heat or cold;Epidermis;Hair;movement;Mechanoreceptors are stimulated by various;forms of mechanical energy (e.g.: touch, sound);Chemoreceptors respond to chemicals in the;external environment or body fluids;Dermis;Strong;pressure;Nerve to CNS;Figure 27.17;Electromagnetic receptors are sensitive to;energy of various wavelengths;Example: Photoreceptors detect light;11;Vision;Structure of the Human Eye;Human eyes are able to;The human eye consists of;Detect a multitude of colors;A tough outer covering, the sclera;Form images of faraway objects;A transparent cornea in front of the lens;Respond to minute amounts of light energy;An iris with a center opening, the pupil;The retina, at the back of the eyeball, where;photoreceptors respond to light;The optic nerve connects the retina to the brain;Sclera;Two fluid-filled chambers make up the bulk of;the eye;Choroid;Muscle;Retina;Ligament;1. The large chamber behind the lens is filled;with jellylike vitreous humor;2. The much smaller chamber in front of the;lens contains a thinner fluid called the;aqueous humor;Cornea;Iris;Optic nerve;Pupil;Aqueous;humor;Lens;Vitreous humor;Blind spot;Figure 27.18;Function of the Human Eye;Near vision;Choroid;Muscle contracted;The cornea lets light into the eye and helps focus;light;The iris;Regulates the size of the pupil;Lets light shine onto the lens;The lens of the eye changes shape and refracts;light, which focuses light onto the retina;Ligaments;slacken;Light from a;near object;Distance vision;Muscle relaxed;Retina;Lens;How the lens;of the eye;focuses light;Ligaments;pull on lens;Light from a;distant object;Figure 27.19;12;Photoreceptors;Photoreceptors;The human retina contains two types of;photoreceptors;2. Cones;Are less sensitive to light;1. Rods;Can distinguish color;Are extremely sensitive to light;Are concentrated at the center of focus;on the retina;Perceive only shades of gray;Are distributed at the outer edges of the;retina, and absent from its center;Photoreceptor cells. Your eyes contains;many more rods than cones;Rods and cones are stimulus transducers that;Rod;Synaptic;terminals Cell body;Rods and cones detect light using an array of;membranous disks containing visual pigments;Absorb light;Convert it to an electrical signal;Membranous;disks;containing;visual pigments;Other retinal neurons;Cone;Integrate the resulting receptor potentials;Generate action potentials that travel along;the optic nerve to the brain;Figure 27.20;The vision pathway from light source to optic nerve;Retina;Neurons;Vision Problems and Corrections;The most common visual problems are;Photoreceptors;Cone Rod;Optic;nerve;fibers;Nearsightedness (myopia) the inability to;focus on distant objects;Farsightedness (hyperopia) the inability to;focus on near objects;Retina;Astigmatism blurred vision caused by a;misshapen lens or cornea;Optic;nerve;To brain;Figure 27.21;13;Figure 27.22;Lens;Shape of;normal;eyeball;Figure 27.22;Shape of;normal;eyeball;Retina;Point of;focus;Point of;focus;Corrective lenses;help;vision problems;by focusing;the image;exactly;on the retina;Corrective;lens;Point;of;focus;(a) A nearsighted eye (eyeball too long);Corrective lenses;help;vision problems;by focusing;the image;exactly;on the retina;Corrective;lens;Point of;focus;(b) A farsighted eye (eyeball too short);Fig. 27-23a;Hearing;The Structure of the Human Ear;Figure 27.23;Outer ear;Middle ear Inner ear;The human ear is less sensitive that that of many;other animals;The ear is composed of;The outer ear;The middle ear;The inner ear;Pinna;Auditory;canal;Eardrum;Eustachian tube;(a) Ear structure;The outer ear;Consists of the flap-like pinna and the;auditory canal;Collects sound waves;Passes sound waves to the eardrum, a sheet;of tissue that separates the outer ear from the;middle ear;In the middle ear, the vibrating eardrum passes;the sound waves to three small bones that relay;the sound to the inner ear;The Eustachian tube;Conducts air between the middle ear and back;of the throat;Allows air pressure to stay equal on either;side of the eardrum;14;Stirrup;Hammer;Skull;bones;Anvil;Auditory;nerve;to brain;The inner ear consists of fluid-filled channels in;the bones of the skull;One of the channels, the cochlea, is a long coiled;tube;The cochlea contains the organ of Corti, which;is the actual hearing organ;and;Eardrum;Eustachian tube;Cochlea;(b) The middle and inner ears;Cross section;through cochlea;includes hair cells, the ears receptor cells;Figure 27.23;Overlying membrane;Bone;Hair cells;Fluid;Supporting;cells;Sensory;neurons;Organ of Corti;Auditory;nerve;Basilar membrane;To auditory nerve and brain;Figure 27.24;Figure 27.24;The route of sound waves through the ear.;The figure traces the path of a sound;stimulus as it passes from the environment;to the brain;Function of the Human Ear;When we hear, sound waves are collected by the;outer ear;Outer ear;Are passed through the middle ear bones, and;transmitted to the cochlea, which causes;Pinna;Auditory;canal;Middle ear;Ear- Hammer;drum anvil, stirrup;Inner ear;Cochlea;Nerve cells to send signals to the brain;Pressure;Hair cells in the organ of Corti to bend;Louder sounds cause greater movement of the;hair cells;And therefore more action potentials;Amplitude;One;vibration;Concentration;in middle ear;Organ;Time;of Corti;stimulated;Figure 27.25;15;Hearing Problems;Chapter Review Figure;Deafness, the loss of hearing, can be caused by;Outer ear;Middle ear;Inner ear;Middle ear infections;Injury, such as a ruptured eardrum;Eardrum;Bones;Stiffening of the middle-ear bones (a common;age-related problem);Organ of Corti;(inside cochlea);Overexposure to loud noises;Ear plugs can provide protection;LOCOMOTOR SYSTEMS;The Skeletal System;Movement;The skeletal system provides;Is one of the most distinctive features of;animals;Relies upon an interplay of organ systems;The nervous system issues commands to the;muscular system;Anchoring;Support;Protection of internal organs;For example, your ribs form a cage;around your heart and lungs;The muscular system exerts the forces that make;animals move by acting on the skeletal system;Organization of the Human Skeleton;Skull;All vertebrates have an endoskeleton, situated;among soft tissues, and consisting of;Bones, hard supporting elements;Cartilage at points of flexibility;The human skeleton is organized into two basic;units: the axial skeleton and the appendicular;skeleton;Shoulder;girdle;Clavicle;Scapula;Sternum;Ribs;Humerus;Vertebra;Ulna;Radius;Pelvic girdle;Carpals;Metacarpals;Phalanges;(curled under);Figure 27.26;16;The axial skeleton;Supports the axis of the body;Includes the skull, vertebral column, and ribs;Femur;Patella;The appendicular skeleton is made up of the;bones of the;Tibia;Limbs;Fibula;Tarsals;Metatarsals;Phalanges;Shoulders;Figure 27.26;Pelvis;Much of the versatility of our skeleton comes;from three types of movable joints;JOINTS;Ball-and-socket joints in the shoulder and;hip;Hinge joints that permit movement in a;single plane;Pivot joints that allow rotation;Ball-and-socket;(example: shoulder);Head of;humerus;Hinge;(e.g.: elbow flexing);Pivot;(e.g.: elbow rotation);Humerus;Radius;Ulna;Scapula;Ulna;The bones of the skeleton are held together at;movable joints by strong fibrous ligaments;Figure 27.27;The Structure of Bones;Bones are covered with a connective tissue;membrane;Have cartilage at their ends that cushions the;joints;Are served by blood vessels and nerves;The central cavity of a long bone contains yellow;bone marrow, which is mostly stored fat;The;structure;of an arm;bone;Cartilage;Spongy bone;(contains red;bone marrow);Compact bone;Central cavity;Yellow bone marrow;Fibrous;connective tissue;Blood vessels;The end of a long bone contains red bone marrow;a specialized tissue that produces blood cells;Cartilage;Figure 27.28;17;Skeletal Diseases and Injuries;The human skeleton is quite strong and provides;reliable support;But, it is susceptible to disease and injury;Arthritis;Is an inflammation of the joints;Rheumatoid arthritis;Is an autoimmune disease;Usually begins between ages 40 and 50;Affects more women than men;Osteoporosis;Seems to occur as a result of aging;Makes bones thinner and more porous;Affects one out of every seven people in the;United States;Is most common in women after menopause;Figure 27.29;Bones are rigid but not inflexible;If a force applied to a bone exceeds its capacity;to bend, the result is a broken bone or fracture.;The treatment of a fracture involves;putting the bone back into its natural shape;and;immobilizing it until the bodys natural bonebuilding cells can repair the fracture.;The Muscular System;The muscular system is made of all the skeletal;muscles in the body;These X-rays;show the same;set of fractured;bones (tibia and;fibula) before;(left) and after;they have been;held together;with screws and;plates (right);Antagonistic action of muscles in the human arm.;Contraction of the biceps muscle raises the forearm;while contraction of the triceps muscle lowers it;Skeletal muscles;Biceps;relaxed;Biceps;contracted;Are attached to the skeleton;Pull on bones to produce movements;Tendons connect muscles to bones;Antagonistic pairs of muscles produce opposite;movements;Triceps;relaxed;Tendon;Triceps;contracted;Figure 27.30;18;Figure 27.31;The Cellular Basis of Muscle Contraction;Skeletal muscle is made up of a hierarchy of;smaller and smaller parallel strands;The contractile;apparatus of;skeletal muscle;Muscle;A muscle consists of bundles of parallel muscle;fibers;Each muscle fiber is a single cell with many;nuclei;Blast Animation: Anatomy of Muscle;Nuclei;Bundle of;muscle fibers;Single muscle fiber;(cell);Figure 27.31;Single muscle fiber;(cell);Figure 27.31;Light;Light;band Dark band band;Thick;filaments;(myosin);Sarcomere;Light;band;Dark band;Light;band;TEM;Myofibril;Thin;filaments;(actin);TEM;Sarcomere;Each skeletal muscle cell, or fiber;Contains bundles of myofibrils;Is called striated, because the myofibrils;exhibit alternating light and dark bands when;viewed with a light microscope;A sarcomere;Is the region between two dark, narrow lines;called Z lines;A myofibril is composed of two kinds of;filaments;Thin filaments, made mostly of the protein;actin;Thick filaments, made mostly of the protein;myosin;A sarcomere contracts (shortens) when its thin;filaments slide across its thick filaments.;Is the functional unit of muscle contraction;19;Sarcomere;The sliding-filament;model of muscle;contraction;Figure 27.32;Dark band;Relaxed;muscle;In the sliding-filament model, the key events are;the binding between;Parts (called heads) of the myosin molecules;in the thick filaments;Specific sites on actin molecules in the thin;filaments;Contracting;muscle;Contraction requires energy supplied by ATP.;Fully;contracted;muscle;Figure;27.33;BioFlix Animation: Muscle Contraction;Thick filament (myosin);Thin filament;(actin);ATP;Figure;27.33;Myosin head;(low-energy;configuration);3 The myosin head attaches to an actin binding site.;1 ATP binds to a myosin head, which is then released;from an actin filament.;ATP;ADP + P;Myosin head;(high-energy;configuration);2 The breakdown of ATP cocks the myosin head.;4 The power stroke slides the actin (thin) filament;toward the center of the sarcomere.;5 As long as ATP is available, the process can be;repeated until the muscle is fully contracted.;Motor Neurons: Control of Muscle Contraction;Motor neurons;Are part of the central nervous system;Release neurotransmitters that cause muscle;fibers to contract;Can branch to a number of muscle fibers;A neuromuscular junction is the connection;between a motor neuron and the muscle fibers;associated with that neuron;A motor unit consists of;a neuron and;all the muscle fibers it controls.;Motor units may consist of;just one muscle fiber or;up to hundreds of muscle fibers.;The strength of a muscle contraction depends on;the number of motor units activated.;20;Spinal cord;Motor;unit 1;Motor;unit 2;The Process of Science;How Do New Senses Arise?;Observation: Two species of electric fish use;special ion channel proteins in muscle cells to;generate electric fields.;Nerve;Motor;neuron;cell body;Motor;neuron axon;Nuclei;Neuromuscular;junctions;Muscle fibers (cells);Muscle;Tendon;Bone;The relationship;between motor;neurons and;muscle fibers;Question: Did different ion channel proteins;evolve in these two species?;Hypothesis: Ion channel genes of the two;electric species had mutated in unique ways.;Figure 27.34;Experiment: The DNA sequence of the genes in;the two electric fish was determined and;compared to a closely related but non-electric;South American fish.;Results: A single ion channel gene duplicated in;the common ancestor, into forms a and b.;The a form mutated differently in the two;electric fish species.;The b form retained its muscle functions in;electric and non-electric fishes.;Stimulus and Response: Putting It All Together;An animals nervous;system connects;sensations derived;from environmental;stimuli to responses;carried out by its;muscles.;Figure 27.36;Duplication of the gene for a muscle ion channel protein;led to an electric organ;African species;South American species;Electric fish;Electric fish Nonelectric fish;Location of;gene function;Muscle;Gene b;b;a and b;Electric organ;Gene a;(mutation 1);a;(mutation 2);none;Figure 27.35;Evolution Connection: Seeing Ultraviolet light;Many birds can see UV light, which seems to be;important in social communication and food gathering;Researchers have discovered that a single amino acid;change in the pigment protein rhodopsin converted it;to a UV-detecting form;This is another example of a;large scale change that can be;traced to a small change: a;single mutation;A European kestrel;a bird with UV vision;Figure;27.37;21


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