AP-Ch09 by EVE ROAKE

Chapter

9 Muscle Tissue

PowerPoint® Lecture Slides prepared by Jason LaPres Lone Star College - North Harris

An Introduction to Muscle Tissue   Muscle Tissue   A primary tissue type, divided into   Skeletal muscle   Cardiac muscle   Smooth muscle

An Introduction to Muscle Tissue   Skeletal Muscles   Are attached to the skeletal system   Allow us to move   The muscular system   Includes only skeletal muscles

Functions of Skeletal Muscles   Produce skeletal movement   Maintain body position   Support soft tissues   Guard openings   Maintain body temperature   Store nutrient reserves Copyright © 2010 Pearson Education, Inc.

Skeletal Muscle Structures   Muscle tissue (muscle cells or fibers)   Connective tissues   Nerves   Blood vessels

Skeletal Muscle Structures   Organization of Connective Tissues   Muscles have three layers of connective tissues   Epimysium: –  exterior collagen layer –  connected to deep fascia –  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 Copyright © 2010 Pearson Education, Inc.

Skeletal Muscle Structures

Skeletal Muscle Structures   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)

Skeletal Muscle Structures   Nerves   Skeletal muscles are voluntary muscles, controlled by nerves of the central nervous system (brain and spinal cord)

Skeletal Muscle Fibers   Are very long   Develop through fusion of mesodermal cells (myoblasts)   Become very large   Contain hundreds of nuclei

Skeletal Muscle Fibers

Skeletal Muscle Fibers   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

Skeletal Muscle Fibers   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

Skeletal Muscle Fibers   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 Copyright © 2010 Pearson Education, Inc.

Skeletal Muscle Fibers   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

Skeletal Muscle Fibers   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

Skeletal Muscle Fibers

Skeletal Muscle Fibers   Internal Organization of Muscle Fibers   Sarcomeres   The contractile units of muscle   Structural units of myofibrils   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)

Skeletal Muscle Fibers   Internal Organization of Muscle Fibers   Sarcomeres  M Lines and Z Lines: – M line: » the center of the A band » at midline of sarcomere – Z lines: » the centers of the I bands » at two ends of sarcomere Copyright © 2010 Pearson Education, Inc.

Skeletal Muscle Fibers   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

Skeletal Muscle Fibers   Internal Organization of Muscle Fibers   Sarcomeres  Titin: – are strands of protein – reach from tips of thick filaments to the Z line – stabilize the filaments

Skeletal Muscle Fibers

Figure 9–4a Sarcomere Structure.

Skeletal Muscle Fibers

Figure 9–4b Sarcomere Structure.

Skeletal Muscle Fibers

Skeletal Muscle Fibers   Sarcomere Function   Transverse tubules encircle the sarcomere near zones of overlap   Ca2+ released by SR causes thin and thick filaments to interact

Skeletal Muscle Fibers   Muscle Contraction   Is caused by interactions of thick and thin filaments   Structures of protein molecules determine interactions

Skeletal Muscle Fibers   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 actin–myosin interaction

Skeletal Muscle Fibers

Skeletal Muscle Fibers   Initiating Contraction   Ca2+ binds to receptor on troponin molecule   Troponin–tropomyosin complex changes   Exposes active site of F-actin

Skeletal Muscle Fibers   Thick Filaments   Contain twisted myosin subunits   Contain titin strands that recoil after stretching   The mysosin molecule   Tail: –  binds to other myosin molecules

Skeletal Muscle Fibers

Skeletal Muscle Fibers   Myosin Action   During contraction, myosin heads   Interact with actin filaments, forming cross-bridges   Pivot, producing motion

Skeletal Muscle Fibers   Skeletal Muscle Contraction   Sliding filament theory   Thin filaments of sarcomere slide toward M line, alongside thick filaments   The width of A zone stays the same   Z lines move closer together

Skeletal Muscle Fibers

Figure 9–7a Changes in the Appearance of a Sarcomere during the Contraction of a Skeletal Muscle Fiber.

Skeletal Muscle Fibers

Skeletal Muscle Fibers   Skeletal Muscle Contraction   The process of contraction   Neural stimulation of sarcolemma: –  causes excitation–contraction coupling

  Cisternae of SR release Ca2+: –  which triggers interaction of thick and thin filaments –  consuming ATP and producing tension

Skeletal Muscle Fibers

The Neuromuscular Junction   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) Copyright © 2010 Pearson Education, Inc.

The Neuromuscular Junction

The Neuromuscular Junction   The Neurotransmitter   Acetylcholine or ACh   Travels across the synaptic cleft   Binds to membrane receptors on sarcolemma (motor end plate)   Causes sodium–ion rush into sarcoplasm   Is quickly broken down by enzyme (acetylcholinesterase or AChE)

The Neuromuscular Junction

The Neuromuscular Junction   Action Potential   Generated by increase in sodium ions in sarcolemma   Travels along the T tubules   Leads to excitation–contraction coupling   Excitation–contraction coupling: –  action potential reaches a triad: »  releasing Ca2+ »  triggering contraction –  requires myosin heads to be in cocked position: »  loaded by ATP energy Copyright © 2010 Pearson Education, Inc.

The Contraction Cycle   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

The Contraction Cycle

[INSERT FIG. 10.12, step 1]

The Contraction Cycle

The Contraction Cycle   Fiber Shortening   As sarcomeres shorten, muscle pulls together, producing tension

The Contraction Cycle   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 Copyright © 2010 Pearson Education, Inc.

The Contraction Cycle   Skeletal muscle fibers shorten as thin filaments slide between 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 Copyright © 2010 Pearson Education, Inc.

The Contraction Cycle

Tension Production   The all–or–none 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 fiber s resting length at the time of stimulation   The frequency of stimulation

Tension Production   Tension of a Single Muscle Fiber   Length–tension 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

Tension Production

Tension Production   Tension of a Single Muscle Fiber   Frequency of stimulation   A single neural stimulation produces: –  a single contraction or twitch –  which lasts about 7–100 msec.

  Sustained muscular contractions: –  require many repeated stimuli

Tension Production   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

Tension Production

Tension Production   Treppe   A stair-step increase in twitch tension   Repeated stimulations immediately after relaxation phase   Stimulus frequency <50/second

  Causes a series of contractions with increasing tension

Tension Production   Tension of a Single Muscle Fiber   Wave summation   Increasing tension or summation of twitches   Repeated stimulations before the end of relaxation phase: –  stimulus frequency >50/second

  Causes increasing tension or summation of twitches

Tension Production   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

Tension Production

Tension Production   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

Tension Production   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

Tension Production   Tension Produced by Whole Skeletal Muscles   Recruitment (multiple motor unit summation)   In a whole muscle or group of muscles, smooth motion and increasing tension 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

Tension Production

Tension Production   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

Tension Production   Two Types of Skeletal Muscle Tension   Isotonic contraction   Isometric contraction

Tension Production   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)

Tension Production   Two Types of Skeletal Muscle Tension   Isometric contraction   Skeletal muscle develops tension, but is prevented from changing length

Note: iso- = same, metric = measure

Tension Production

Tension Production   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

Tension Production

Tension Production   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

Tension Production   Gravity   Can take the place of opposing muscle contraction to return a muscle to its resting state

ATP and Muscle Contraction   Sustained muscle contraction uses a lot of ATP energy   Muscles store enough energy to start contraction   Muscle fibers must manufacture more ATP as needed

ATP and Muscle Contraction   ATP and CP Reserves   Adenosine triphosphate (ATP)   The active energy molecule

  Creatine phosphate (CP)   The storage molecule for excess ATP energy in resting muscle

ATP and Muscle Contraction   ATP Generation   Cells produce ATP in two ways   Aerobic metabolism of fatty acids in the mitochondria   Anaerobic glycolysis in the cytoplasm

ATP and Muscle Contraction   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

ATP and Muscle Contraction

ATP and Muscle Contraction   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

ATP and Muscle Contraction

ATP and Muscle Contraction   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 Copyright © 2010 Pearson Education, Inc.

ATP and Muscle Contraction   The Recovery Period   The time required after exertion for muscles to return to normal   Oxygen becomes available   Mitochondrial activity resumes

ATP and Muscle Contraction   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

ATP and Muscle Contraction   Skeletal muscles at rest metabolize fatty acids and store glycogen   During light activity, muscles generate ATP through anaerobic breakdown of carbohydrates, lipids, or amino acids   At peak activity, energy is provided by anaerobic reactions that generate lactic acid as a byproduct Copyright © 2010 Pearson Education, Inc.

ATP and Muscle Contraction   Heat Production and Loss   Active muscles produce heat   Up to 70% of muscle energy can be lost as heat, raising body temperature

ATP and Muscle Contraction   Muscle Performance   Power   The maximum amount of tension produced

  Endurance   The amount of time an activity can be sustained

Muscle Fiber Types   Three Types of Skeletal Muscle Fibers   Fast fibers   Slow fibers   Intermediate fibers

Muscle Fiber Types   Three Types of Skeletal Muscle Fibers   Fast fibers   Contract very quickly   Have large diameter, large glycogen reserves, few mitochondria   Have strong contractions, fatigue quickly

Muscle Fiber Types   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)

Muscle Fiber Types   Three Types of Skeletal Muscle Fibers   Intermediate fibers   Are mid-sized   Have low myoglobin   Have more capillaries than fast fibers, slower to fatigue

Muscle Fiber Types

Muscle Fiber Types   Muscles and Fiber Types   White muscle   Mostly fast fibers   Pale (e.g., chicken breast)

  Red muscle   Mostly slow fibers   Dark (e.g., chicken legs)

Muscle Fiber Types   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

Muscle Fiber Types   Physical Conditioning   Improves both power and endurance   Anaerobic activities (e.g., 50-meter dash, weightlifting): –  use fast fibers –  fatigue quickly with strenuous activity   Improved by: –  frequent, brief, intensive workouts –  hypertrophy

Muscle Fiber Types   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

Muscle Fiber Types   What you don t use, you lose   Muscle tone indicates base activity in motor units of skeletal muscles   Muscles become flaccid when inactive for days or weeks   Muscle fibers break down proteins, become smaller and weaker   With prolonged inactivity, fibrous tissue may replace muscle fibers Copyright © 2010 Pearson Education, Inc.

Cardiac Muscle Tissue   Structure of Cardiac Tissue   Cardiac muscle is striated, found only in the heart

Cardiac Muscle Tissue   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 Copyright © 2010 Pearson Education, Inc.

Cardiac Muscle Tissue   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 Copyright © 2010 Pearson Education, Inc.

Cardiac Muscle Tissue

Cardiac Muscle Tissue   Intercalated Discs   Coordination of cardiocytes   Because intercalated discs link heart cells mechanically, chemically, and electrically, the heart functions like a single, fused mass of cells

Cardiac Muscle Tissue   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

Smooth Muscle Tissue   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

Smooth Muscle Tissue   Structure of Smooth Muscle   Nonstriated tissue   Different internal organization of actin and myosin   Different functional characteristics

Smooth Muscle Tissue

Smooth Muscle Tissue   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 Copyright © 2010 Pearson Education, Inc.

Smooth Muscle Tissue   Functional Characteristics of Smooth Muscle   Excitation–contraction coupling   Length–tension relationships   Control of contractions   Smooth muscle tone

Smooth Muscle Tissue   Functional Characteristics of Smooth Muscle   Excitation–contraction coupling   Free Ca2+ in cytoplasm triggers contraction   Ca2+ binds with calmodulin: –  in the sarcoplasm –  activates myosin light–chain kinase

  Enzyme breaks down ATP, initiates contraction

Smooth Muscle Tissue   Functional Characteristics of Smooth Muscle   Length–Tension Relationships   Thick and thin filaments are scattered   Resting length not related to tension development   Functions over a wide range of lengths (plasticity)

Smooth Muscle Tissue   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

Smooth Muscle Tissue   Functional Characteristics of Smooth Muscle   Smooth muscle tone   Maintains normal levels of activity   Modified by neural, hormonal, or chemical factors

Comparing Muscle Tissues