Ch10- Muscle Physio

8/2/2019 Ch10- Muscle Physio

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An Introduction to Muscle Tissue

Copyright 2009 Pearson Education,Inc., publishing as Pearson Benjamin

Muscle Tissue A primary tissue type, divided into

Skeletal muscle

Cardiac muscle Smooth muscle


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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


Produce skeletal movement Maintain body position

Support soft tissues Guard openings Maintain body temperature

Store nutrient reserves


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Skeletal Muscle Structures


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


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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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Figure 101 The Organization of Skeletal Muscles.


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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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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


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


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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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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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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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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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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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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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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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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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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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Titin:are strands of proteinreach from tips of thick filaments to the Z linestabilize the filaments


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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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Muscle Contraction Is caused by interactions of thick and thin filaments

Structures of protein molecules determine interactions


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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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Initiating Contraction Ca2+ binds to receptor on troponin molecule

Troponintropomyosin complex changes

Exposes active site ofF-actin


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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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Myosin Action During contraction, myosin heads

Interact with actin filaments, forming cross-bridges Pivot, producing motion


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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 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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Figure 109 An Overview of Skeletal Muscle Contraction.


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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)


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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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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


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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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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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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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


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


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


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


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


Treppe A stair-step increase in twitch tension Repeated stimulations immediately afterrelaxation phase

Stimulus frequency


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Tension Production


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


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


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


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


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


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


Two Types of Skeletal Muscle Tension Isotonic contraction Isometric contraction


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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)


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Tension Production


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


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


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


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


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 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 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 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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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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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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The Recovery Period The time required after exertion for muscles to return to

normal

Oxygen becomes available Mitochondrial activity resumes


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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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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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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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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


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


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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


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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)


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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


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Muscle Fiber Types


Figure 1021 Fast versus Slow Fibers.


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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


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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


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Muscle Fiber Types


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


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


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


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

heart


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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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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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Figure 1022a 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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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


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


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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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Functional Characteristics of Smooth Muscle Excitationcontraction coupling Lengthtension relationships Control of contractions Smooth muscle tone


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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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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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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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Functional Characteristics of Smooth Muscle Smooth muscle tone

Maintains normal levels of activity Modified by neural, hormonal, or chemical factors

Ch10- Muscle Physio

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