ch10- muscle physio
TRANSCRIPT
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An Introduction to Muscle Tissue
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Muscle Tissue A primary tissue type, divided into
Skeletal muscle
Cardiac muscle Smooth muscle
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Copyright 2009 Pearson Education,Inc., publishing as Pearson Benjamin
Skeletal Muscles Are attached to the skeletal system Allow us to move The muscular system
Includes only skeletal muscles
An introduction to Skeletal Muscles
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Functions of Skeletal Muscles
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Produce skeletal movement Maintain body position
Support soft tissues Guard openings Maintain body temperature
Store nutrient reserves
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Skeletal Muscle Structures
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Muscle tissue (muscle cells or fibers) Connective tissues Nerves Blood vessels
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Skeletal Muscle Structures
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Organization of Connective Tissues Muscles have three layers of connective tissues
Epimysium - Separates muscle from surrounding tissues
Perimysium : surrounds muscle fiber bundles (fascicles) contains blood vessel and nerve supply to fascicles
Endomysium : surrounds individual muscle cells (muscle fibers) contains capillaries and nerve fibers contacting muscle cells contains myosatellite cells (stem cells) that repair damage
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Skeletal Muscle Structures
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Figure 101 The Organization of Skeletal Muscles.
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Skeletal Muscle Structures
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Organization of Connective Tissues Muscle attachments
Endomysium, perimysium, and epimysium come together: at ends of muscles to form connective tissue attachment to bone matrix i.e.,tendon (bundle) or aponeurosis (sheet)
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Skeletal Muscle Structures
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Nerves Skeletal muscles are voluntary muscles, controlled by nerves
of the central nervous system (brain and spinal cord)
Blood Vessels Muscles have extensive vascular systems that
Supply large amounts of oxygen Supply nutrients Carry away wastes
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Skeletal Muscle Fibers
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Are very long Develop through fusion of mesodermal cells (myoblasts) Become very large Contain hundreds of nuclei
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Skeletal Muscle Fibers
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Internal Organization of Muscle Fibers The sarcolemma
The cell membrane of a muscle fiber (cell) Surrounds the sarcoplasm (cytoplasm of muscle fiber) A change in transmembrane potential begins contractions
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Skeletal Muscle Fibers
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Internal Organization of Muscle Fibers Transverse tubules (T tubules)
Transmit action potential through cell
Allow entire muscle fiber to contract simultaneously Have same properties as sarcolemma
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Skeletal Muscle Fibers
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Internal Organization of Muscle Fibers Myofibrils
Lengthwise subdivisions within muscle fiber Made up of bundles of protein filaments (myofilaments) Myofilaments are responsible for muscle contraction Types of myofilaments: thin filaments:
made of the protein actin thick filaments:
made of the protein myosin
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Skeletal Muscle Fibers
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Internal Organization of Muscle Fibers Sarcoplasmic reticulum (SR)
A membranous structure surrounding each myofibril Helps transmit action potential to myofibril Similar in structure to smooth endoplasmic reticulum Forms chambers (terminal cisternae) attached to T tubules
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Skeletal Muscle Fibers
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Internal Organization of Muscle Fibers Triad
Is formed by one T tubule and two terminal cisternae
Cisternae:concentrate Ca2+ (via ion pumps)release Ca2+ into sarcomeres to begin muscle
contraction
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Skeletal Muscle Fibers
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Internal Organization of Muscle Fibers Sarcomeres
The contractile units of muscle Structural units ofmyofibrils Form visible patterns within myofibrils
Muscle striations A striped or striated pattern within myofibrils: alternating dark, thick filaments (A bands) and light, thin filaments (I
bands)
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Skeletal Muscle Fibers
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Internal Organization of Muscle Fibers Sarcomeres Muscle striations
alternating dark, thick filaments (A bands) and light, thin filaments(I bands)
The THIN (acTIN) filaments look lIght and form the I band,the A bands are dArk
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Skeletal Muscle Fibers
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Internal Organization of Muscle Fibers Sarcomeres
M Lines and Z Lines:M line:the center of the A bandat midline of sarcomere
Z lines:the centers of the I bandsat two ends of sarcomere
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Skeletal Muscle Fibers
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Internal Organization of Muscle Fibers Sarcomeres
Zone of overlap: the densest, darkest area on a light micrograph where thick and thin filaments overlap
The H Band: the area around the M line has thick filaments but
no thin filaments
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Skeletal Muscle Fibers
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Internal Organization of Muscle Fibers Sarcomeres
Titin:are strands of proteinreach from tips of thick filaments to the Z linestabilize the filaments
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Skeletal Muscle Fibers
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Sarcomere Function Transverse tubules encircle the sarcomere near zones of
overlap
Ca2+ released by SR causes thin and thick filaments to interact
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Skeletal Muscle Fibers
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Muscle Contraction Is caused by interactions of thick and thin filaments
Structures of protein molecules determine interactions
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Skeletal Muscle Fibers
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Four Thin Filament Proteins F-actin (Filamentous actin)
Is two twisted rows of globular G-actin The active sites on G-actin strands bind to myosin Nebulin
Holds F-actin strands together Tropomyosin
Is a double strand Prevents actinmyosin interaction
Troponin A globular protein Binds tropomyosin to G-actin Controlled by Ca2+
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Skeletal Muscle Fibers
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Initiating Contraction Ca2+ binds to receptor on troponin molecule
Troponintropomyosin complex changes
Exposes active site ofF-actin
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Skeletal Muscle Fibers
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Thick Filaments Contain twisted myosin subunits Contain titin strands that recoil after stretching
The mysosin molecule Tail: binds to other myosin molecules
Head: made of two globular protein subunits
reaches the nearest thin filament
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Skeletal Muscle Fibers
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Myosin Action During contraction, myosin heads
Interact with actin filaments, forming cross-bridges Pivot, producing motion
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Skeletal Muscle Fibers
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Skeletal Muscle Contraction Sliding filament theory
Thin filaments of sarcomere slide toward M line, alongside thickfilaments
The width of A zone stays the same Z lines move closer together
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Skeletal Muscle Fibers
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Skeletal Muscle Contraction The process of contraction
Neural stimulation of sarcolemma: causes excitationcontraction coupling
Cisternae of SR release Ca2+: which triggers interaction of thick and thin filaments consuming ATP and producing tension
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Skeletal Muscle Fibers
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Figure 109 An Overview of Skeletal Muscle Contraction.
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The Neuromuscular Junction
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Is the location of neural stimulation Action potential (electrical signal)
Travels along nerve axon Ends at synaptic terminal
Synaptic terminal:releases neurotransmitter (acetylcholine or ACh)into the synaptic cleft (gap between synaptic terminal
and motor end plate)
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The Neuromuscular Junction
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The Neurotransmitter Acetylcholine or ACh
Travels across the synaptic cleft Binds to membrane receptors on sarcolemma (motor end plate) Causes sodiumion rush into sarcoplasm Is quickly broken down by enzyme (acetylcholinesterase or
AChE)
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The Neuromuscular Junction
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Action Potential Generated by increase in sodium ions in sarcolemma Travels along the T tubules Leads to excitationcontractioncoupling
Excitationcontraction coupling: action potential reaches a triad:
releasing Ca2+ triggering contraction
requires myosin heads to be in cocked position:
loaded by ATP energy
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The Contraction Cycle
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Five Steps of the Contraction Cycle Exposure of active sites Formation of cross-bridges Pivoting of myosin heads Detachment of cross-bridges Reactivation of myosin
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The Contraction Cycle
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Fiber Shortening As sarcomeres shorten, muscle pulls together, producing
tension
Contraction Duration Depends on
Duration of neural stimulus
Number of free calcium ions in sarcoplasm Availability of ATP
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The Contraction Cycle
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Relaxation Ca2+ concentrations fall Ca2+ detaches from troponin Active sites are re-covered by tropomyosin Sarcomeres remain contracted
Rigor Mortis A fixed muscular contraction after death Caused when
Ion pumps cease to function; ran out of ATP Calcium builds up in the sarcoplasm
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The Contraction Cycle
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Skeletal muscle fibers shorten as thin filaments slidebetween thick filaments
Free Ca2+ in the sarcoplasm triggers contraction SR releases Ca2+ when a motor neuron stimulates the
muscle fiber Contraction is an active process Relaxation and return to resting length are passive
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Tension Production
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The allornone principle As a whole, a muscle fiber is either contracted or relaxed
Tension of a Single Muscle Fiber Depends on
The number of pivoting cross-bridges The fibers resting length at the time of stimulation The frequency of stimulation
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Tension Production
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Tension of a Single Muscle Fiber Lengthtension relationship
Number of pivoting cross-bridges depends on: amount of overlap between thick and thin fibers
Optimum overlap produces greatest amount of tension: too much or too little reduces efficiency
Normal resting sarcomere length: is 75% to 130% of optimal length
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Tension Production
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Tension of a Single Muscle Fiber Frequency of stimulation
A single neural stimulation produces: a single contraction or twitch which lasts about 7100 msec.
Sustained muscular contractions: require many repeated stimuli
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Tension Production
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Three Phases of Twitch Latent period before contraction
The action potential moves through sarcolemma Causing Ca2+ release
Contraction phase Calcium ions bind Tension builds to peak
Relaxation phase Ca2+ levels fall Active sites are covered Tension falls to resting levels
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Tension Production
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Treppe A stair-step increase in twitch tension Repeated stimulations immediately afterrelaxation phase
Stimulus frequency
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Tension Production
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Tension of a Single Muscle Fiber Wave summation
Increasing tension or summation of twitches Repeated stimulations before the endof relaxation phase: stimulus frequency >50/second
Causes increasing tension or summation of twitches
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Tension Production
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Tension of a Single Muscle Fiber Incomplete tetanus
Twitches reach maximum tension If rapid stimulation continues and muscle is not allowed to relax,
twitches reach maximum level of tension
Complete Tetanus If stimulation frequency is high enough, muscle never begins to relax,
and is in continuous contraction
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Tension Production
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Tension Produced by Whole Skeletal Muscles Depends on
Internal tension produced by muscle fibers External tension exerted by muscle fibers on elastic extracellular
fibers
Total number of muscle fibers stimulated
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Tension Production
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Tension Produced by Whole Skeletal Muscles Motor units in a skeletal muscle
Contain hundreds of muscle fibers That contract at the same time Controlled by a single motor neuron
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Tension Production
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Tension Produced by Whole Skeletal Muscles Recruitment (multiple motor unit summation)
In a whole muscle or group of muscles, smooth motion and increasingtension are produced by slowly increasing the size or number of motor
units stimulated
Maximum tension Achieved when all motor units reach tetanus Can be sustained only a very short time
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Tension Production
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Tension Produced by Whole Skeletal Muscles Sustained tension
Less than maximum tension Allows motor units rest in rotation
Muscle tone The normal tension and firmness of a muscle at rest Muscle units actively maintain body position, without motion Increasing muscle tone increases metabolic energy used, even at rest
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Tension Production
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Two Types of Skeletal Muscle Tension Isotonic contraction Isometric contraction
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Tension Production
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Two Types of Skeletal Muscle Tension Isotonic Contraction
Skeletal muscle changes length: resulting in motion
If muscle tension > load (resistance): muscle shortens (concentric contraction)
If muscle tension < load (resistance): muscle lengthens (eccentric contraction)
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Tension Production
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Two Types of Skeletal Muscle Tension Isometric contraction
Skeletal muscle develops tension, but is prevented from changinglength
Note: iso- = same, metric= measure
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Tension Production
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Resistance and Speed of Contraction Are inversely related The heavier the load (resistance) on a muscle
The longer it takes for shortening to begin
And the less the muscle will shorten Muscle Relaxation
After contraction, a muscle fiber returns to resting length by Elastic forces Opposing muscle contractions Gravity
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Tension Production
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Elastic Forces The pull of elastic elements (tendons and ligaments)
Expands the sarcomeres to resting length Opposing Muscle Contractions
Reverse the direction of the original motion Are the work of opposing skeletal muscle pairs
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Tension Production
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Gravity Can take the place of opposing muscle contraction to return a
muscle to its resting state
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ATP and Muscle Contraction
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Sustained muscle contraction uses a lot of ATP energy Muscles store enough energy to start contraction Muscle fibers must manufacture more ATP as needed
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ATP and Muscle Contraction
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ATP and CP Reserves Adenosine triphosphate (ATP)
The active energy molecule Creatine phosphate (CP)
The storage molecule for excess ATP energy in resting muscle Energy recharges ADP to ATP
Using the enzyme creatine phosphokinase (CPK or CK) When CP is used up, other mechanisms generate ATP
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ATP and Muscle Contraction
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ATP Generation Cells produce ATP in two ways
Aerobic metabolism of fatty acids in the mitochondria Anaerobic glycolysis in the cytoplasm
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ATP and Muscle Contraction
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ATP Generation Aerobic metabolism
Is the primary energy source of resting muscles Breaks down fatty acids Produces 34 ATP molecules per glucose molecule
Anaerobic glycolysis Is the primary energy source for peak muscular activity Produces two ATP molecules per molecule of glucose Breaks down glucose from glycogen stored in skeletal muscles
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ATP and Muscle Contraction
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Energy Use and Muscle Activity At peak exertion
Muscles lack oxygen to support mitochondria Muscles rely on glycolysis for ATP Pyruvic acid builds up, is converted to lactic acid
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ATP and Muscle Contraction
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Muscle Fatigue When muscles can no longer perform a required activity,
they are fatigued
Results of Muscle Fatigue Depletion of metabolic reserves Damage to sarcolemma and sarcoplasmic reticulum Low pH (lactic acid) Muscle exhaustion and pain
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ATP and Muscle Contraction
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The Recovery Period The time required after exertion for muscles to return to
normal
Oxygen becomes available Mitochondrial activity resumes
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ATP and Muscle Contraction
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The Cori Cycle The removal and recycling of lactic acid by the liver Liver converts lactic acid to pyruvic acid Glucose is released to recharge muscle glycogen reserves
Oxygen Debt After exercise or other exertion
The body needs more oxygen than usual to normalize metabolicactivities
Resulting in heavy breathing
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ATP and Muscle Contraction
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Skeletal muscles at rest metabolize fatty acids andstore glycogen (use beta-oxidation when possible)
During light activity, muscles generate ATP throughanaerobic breakdown of carbohydrates, lipids, or
amino acids
At peak activity, energy is provided by anaerobicreactions that generate lactic acid as a byproduct
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ATP and Muscle Contraction
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Heat Production and Loss Active muscles produce heat Up to 70% of muscle energy can be lost as heat, raising body
temperature
Hormones and Muscle Metabolism Growth hormone Testosterone Thyroid hormones Epinephrine
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ATP and Muscle Contraction
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Muscle Performance Power
The maximum amount of tension produced Endurance
The amount of time an activity can be sustained Power and endurance depend on
The types of muscle fibers Physical conditioning
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Muscle Fiber Types
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Three Types of Skeletal Muscle Fibers Fast fibers Slow fibers Intermediate fibers
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Muscle Fiber Types
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Three Types of Skeletal Muscle Fibers Fast fibers
Contract very quickly Have large diameter, large glycogen reserves, few mitochondria Have strong contractions, fatigue quickly
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Muscle Fiber Types
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Three Types of Skeletal Muscle Fibers Slow fibers
Are slow to contract, slow to fatigue Have small diameter, more mitochondria Have high oxygen supply Contain myoglobin (red pigment, binds oxygen)
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Muscle Fiber Types
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Three Types of Skeletal Muscle Fibers Intermediate fibers
Are mid-sized Have low myoglobin Have more capillaries than fast fibers, slower to fatigue
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Muscle Fiber Types
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Figure 1021 Fast versus Slow Fibers.
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Muscle Fiber Types
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Muscles and Fiber Types White muscle
Mostly fast fibers Pale (e.g., chicken breast)
Red muscle Mostly slow fibers Dark (e.g., chicken legs)
Most human muscles Mixed fibers Pink
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Muscle Fiber Types
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Muscle Hypertrophy Muscle growth from heavy training
Increases diameter of muscle fibers Increases number of myofibrils Increases mitochondria, glycogen reserves
Muscle Atrophy Lack of muscle activity
Reduces muscle size, tone, and power
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Muscle Fiber Types
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Physical Conditioning Improves both power and endurance
Anaerobic activities (e.g., 50-meter dash, weightlifting):
use fast fibersfatigue quickly with strenuous activity
Improved by:frequent, brief, intensive workoutshypertrophy
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Muscle Fiber Types
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Physical Conditioning Improves both power and endurance
Aerobic activities (prolonged activity): supported by mitochondria require oxygen and nutrients
Improved by: repetitive training (neural responses) cardiovascular training
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Muscle Fiber Types
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What you dont use, you lose Muscle tone indicates base activity in motor units of
skeletal muscles
Muscles become flaccid when inactive for days orweeks
Muscle fibers break down proteins, become smallerand weaker
With prolonged inactivity, fibrous tissue may replacemuscle fibers
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End of Skeletal System Info
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Cardiac Muscle Tissue
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Structure of Cardiac Tissue Cardiac muscle is striated, found only in the
heart
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Cardiac Muscle Tissue
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Seven Characteristics of Cardiocytes Unlike skeletal muscle, cardiac muscle cells (cardiocytes)
Are small Have a single nucleus Have short, wide T tubules Have no triads Have SR with no terminal cisternae Are aerobic (high in myoglobin, mitochondria) Have intercalated discs
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Cardiac Muscle Tissue
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Intercalated Discs Are specialized contact points between cardiocytes Join cell membranes of adjacent cardiocytes (gap junctions,
desmosomes)
Functions of intercalated discs Maintain structure Enhance molecular and electrical connections Conduct action potentials
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Cardiac Muscle Tissue
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Figure 1022a Cardiac Muscle Tissue.
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Cardiac Muscle Tissue
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Intercalated Discs Coordination of cardiocytes
Because intercalated discs link heart cells mechanically, chemically, andelectrically, the heart functions like a single, fused mass of cells
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Cardiac Muscle Tissue
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Four Functions of Cardiac Tissue Automaticity
Contraction without neural stimulation Controlled by pacemaker cells
Variable contraction tension Controlled by nervous system
Extended contraction time Ten times as long as skeletal muscle
Prevention of wave summation and tetanic contractionsby cell membranes
Long refractory period
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Smooth Muscle Tissue
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Smooth Muscle in Body Systems Forms around other tissues In blood vessels
Regulates blood pressure and flow In reproductive and glandular systems
Produces movements In digestive and urinary systems
Forms sphincters Produces contractions
In integumentary systemArrector pilimuscles cause goose bumps
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Smooth Muscle Tissue
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Structure of Smooth Muscle Nonstriated tissue Different internal organization of actin and myosin Different functional characteristics
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Smooth Muscle Tissue
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Eight Characteristics of Smooth Muscle Cells Long, slender, and spindle shaped Have a single, central nucleus Have no T tubules, myofibrils, or sarcomeres Have no tendons or aponeuroses Have scattered myosin fibers Myosin fibers have more heads per thick filament Have thin filaments attached to dense bodies Dense bodies transmit contractions from cell to cell
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Smooth Muscle Tissue
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Functional Characteristics of Smooth Muscle Excitationcontraction coupling Lengthtension relationships Control of contractions Smooth muscle tone
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Smooth Muscle Tissue
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Functional Characteristics of Smooth Muscle Excitationcontraction coupling
Free Ca2+ in cytoplasm triggers contraction Ca2+ binds with calmodulin: in the sarcoplasm activates myosin lightchain kinase
Enzyme breaks down ATP, initiates contraction
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Smooth Muscle Tissue
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Functional Characteristics of Smooth Muscle LengthTension Relationships
Thick and thin filaments are scattered Resting length not related to tension development Functions over a wide range of lengths (plasticity)
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Smooth Muscle Tissue
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Functional Characteristics of Smooth Muscle Control of contractions
Multiunit smooth muscle cells: connected to motor neurons
Visceral smooth muscle cells: not connected to motor neurons
rhythmic cycles of activity controlled by pacesetter cells
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Smooth Muscle Tissue
Functional Characteristics of Smooth Muscle Smooth muscle tone
Maintains normal levels of activity Modified by neural, hormonal, or chemical factors