AP-Ch09

Copyright © 2010 Pearson Education, Inc.

C h a p t e r

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


Skeletal Muscle Structures

  Muscle tissue (muscle cells or fibers)

  Connective tissues

  Nerves

  Blood vessels



  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


Figure 9–1 The Organization of Skeletal Muscles.




  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)



  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


Skeletal Muscle Fibers

  Are very long

  Develop through fusion of mesodermal

cells (myoblasts)

  Become very large

  Contain hundreds of nuclei



Figure 9–2 The Formation of a Multinucleate Skeletal Muscle Fiber.



Figure 9–2a The Formation of a Multinucleate Skeletal Muscle Fiber.



Figure 9–2b The Formation of a Multinucleate Skeletal Muscle Fiber.



  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




  Transverse tubules (T tubules)

 Transmit action potential through cell

 Allow entire muscle fiber to contract

simultaneously

 Have same properties as sarcolemma



  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



  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




  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



Figure 9–3 The Structure of a Skeletal Muscle Fiber.




  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)



  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



  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




  Sarcomeres

 Titin: – are strands of protein

– reach from tips of thick filaments to the Z line

– stabilize the filaments



Figure 9–4a Sarcomere Structure.



Figure 9–4b Sarcomere Structure.



Figure 9–5 Sarcomere Structure.



  Sarcomere Function

  Transverse tubules encircle the sarcomere

near zones of overlap

 Ca2+ released by SR causes thin and thick

filaments to interact



  Muscle Contraction

  Is caused by interactions of thick and thin

filaments

  Structures of protein molecules determine

interactions



  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

  Troponin   A globular protein   Binds tropomyosin to G-actin   Controlled by Ca2+



Figure 9–6a, b Thick and Thin Filaments.



  Initiating Contraction

 Ca2+ binds to receptor on troponin molecule

  Troponin–tropomyosin complex changes

  Exposes active site of F-actin



  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



Figure 9–6c, d Thick and Thin Filaments.



  Myosin Action

 During contraction, myosin heads

  Interact with actin filaments, forming cross-bridges

 Pivot, producing motion



  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



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



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



  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



Figure 9–8 An Overview of Skeletal Muscle Contraction.


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)



Figure 9–9a, b Skeletal Muscle Innervation.



Figure 9–9b, c Skeletal Muscle Innervation.



Figure 9–9c Skeletal Muscle Innervation.



  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)



Figure 9–9c Skeletal Muscle Innervation.



  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


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



Figure 9–10 The Contraction Cycle.



[INSERT FIG. 10.12, step 1]
















  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



  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



  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




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

Figure 9–11 The Effect of Sarcomere Length on Active Tension.


Tension Production


  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

  Relaxation phase   Ca2+ levels fall   Active sites are covered   Tension falls to resting levels


Tension Production

Figure 9–12a The Development of Tension in a Twitch.


Tension Production

Figure 9–12b The Development of Tension in a Twitch.


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


  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

 Complete Tetanus   If stimulation frequency is high enough, muscle

never begins to relax, and is in continuous contraction


Tension Production

Figure 9–13a, b Effects of Repeated Stimulations.


Tension Production

Figure 9–13c, d Effects of Repeated Stimulations.


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

Figure 9–14a The Arrangement and Activity of Motor Units in a Skeletal

Muscle.


Tension Production

Figure 9–14b The Arrangement and Activity of Motor Units in a Skeletal

Muscle.


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

Figure 9–15a, b Isotonic and Isometric Contractions.


Tension Production

Figure 9–15c, d Isotonic and Isometric Contractions.


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

  Muscle Relaxation   After contraction, a muscle fiber returns to resting

length by   Elastic forces   Opposing muscle contractions   Gravity


Tension Production

Figure 9–16 Load and Speed of Contraction.


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 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



  ATP Generation

 Cells produce ATP in two ways

 Aerobic metabolism of fatty acids in the

mitochondria

 Anaerobic glycolysis in the cytoplasm



  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





  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



Figure 9–17 Muscle Metabolism.



Figure 9–17a Muscle Metabolism.



Figure 9–17b Muscle Metabolism.



Figure 9–17c Muscle Metabolism.



  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



  The Recovery Period

  The time required after exertion for muscles to

return to normal

 Oxygen becomes available

 Mitochondrial activity resumes



  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 metabolic activities

  Resulting in heavy breathing



  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



  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



  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


Muscle Fiber Types

  Three Types of Skeletal Muscle Fibers

  Fast fibers

  Slow fibers

  Intermediate fibers


Muscle Fiber Types


  Fast fibers

 Contract very quickly

 Have large diameter, large glycogen reserves, few

mitochondria

 Have strong contractions, fatigue quickly


Muscle Fiber Types


  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


  Intermediate fibers

 Are mid-sized

 Have low myoglobin

 Have more capillaries than fast fibers, slower to

fatigue


Muscle Fiber Types

Figure 9–18 Fast versus Slow Fibers.


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)

 Most human muscles  Mixed fibers  Pink


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


Cardiac Muscle Tissue

  Structure of Cardiac Tissue

 Cardiac muscle is striated, found only in

the heart



  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



  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



Figure 9–19 Cardiac Muscle Tissue.



Figure 9–19a-b Cardiac Muscle Tissue.



Figure 9–19c 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



  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 contractions by cell membranes   Long refractory period


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

  In integumentary system   Arrector pili muscles cause “goose bumps”



  Structure of Smooth Muscle

 Nonstriated tissue

 Different internal organization of actin and

myosin

 Different functional characteristics



Figure 9–20a Smooth Muscle Tissue.



Figure 9–20b 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



  Functional Characteristics of Smooth Muscle

  Excitation–contraction coupling

  Length–tension relationships

  Control of contractions

  Smooth muscle tone




  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



  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)




  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



  Functional Characteristics of Smooth

Muscle

  Smooth muscle tone

 Maintains normal levels of activity

 Modified by neural, hormonal, or chemical factors


Comparing Muscle Tissues


Comparing Muscle Tissues

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