2 Support and Movement Fundamentals of Anatomy & Physiology Unit Frederic H. Martini PowerPoint® Lecture Slides prepared by Professor Albia Dugger, Miami–Dade College, Miami, FL Professor Robert R. Speed, Ph.D., Wallace Community College, Dothan, AL Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Chapter 10: Muscle Tissue

Muscle Tissue A primary tissue type, divided into: skeletal muscle cardiac muscle smooth muscle

What are the functions of skeletal muscle tissue?

Skeletal Muscles Are attached to the skeletal system Allow us to move

The Muscular System Includes only skeletal muscles

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

Functions of Skeletal Muscles Produce skeletal movement Maintain body position Support soft tissues Guard body openings Maintain body temperature

How is muscle tissue organized at the tissue level?

Organization of Connective Tissues Figure 10–1

Organization of Connective Tissues Muscles have 3 layers of connective tissues: epimysium perimysium endomysium

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 satellite cells (stem cells) that repair damage

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

Blood Vessels Muscles have extensive vascular systems that: supply large amounts of oxygen supply nutrients carry away wastes

What are the characteristics of skeletal muscle fibers?

Formation of Skeletal Muscle Fibers Skeletal muscle cells are called fibers Figure 10–2

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

Organization of Skeletal Muscle Fibers Figure 10–3

The Sarcolemma The cell membrane of a muscle 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 simulataneously Have same properties as sarcolemma

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: Thick filaments: made of the protein actin Thick filaments: made of the protein myosin

Sarcoplasmic Reticulum 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

A Triad Is formed by 1 T tubule and 2 terminal cisternae

Cisternae Concentrate Ca2+ (via ion pumps) Release Ca2+ into sarcomeres to begin muscle contraction

What are the structural components of a sarcomere?

Sarcomeres Figure 10–4

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)

M Lines and Z Lines M line: Z lines: the center of the A band at midline of sarcomere Z lines: the centers of the I bands at 2 ends of sarcomere

Zone of Overlap The densest, darkest area on a light micrograph Where thick and thin filaments overlap

The H Zone The area around the M line Has thick filaments but no thin filaments

Titin Are strands of protein Reach from tips of thick filaments to the Z line Stabilize the filaments

Sarcomere Structure Figure 10–5

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

Level 1: Skeletal Muscle Figure 10–6 (1 of 5)

Level 2: Muscle Fascicle Figure 10–6 (2 of 5)

Level 3: Muscle Fiber Figure 10–6 (3 of 5)

Level 4: Myofibril Figure 10–6 (4 of 5)

Level 5: Sarcomere Figure 10–6 (5 of 5)

Muscle Contraction Is caused by interactions of thick and thin filaments Structures of protein molecules detemine interactions

A Thin Filament Figure 10–7a

4 Thin Filament Proteins F actin: is 2 twisted rows of globular G actin the active sites on G actin strands bind to myosin

4 Thin Filament Proteins Nebulin: holds F actin strands together

4 Thin Filament Proteins Tropomyosin: is a double strand prevents actin–myosin interaction

4 Thin Filament Proteins Troponin: a globular protein binds tropomyosin to G actin controlled by Ca2+

Troponin and Tropomyosin Figure 10–7b

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

A Thick Filament Figure 10–7c

Thick Filaments Contain twisted myosin subunits Contain titin strands that recoil after stretching

The Mysosin Molecule Figure 10–7d

The Mysosin Molecule Tail: Head: binds to other myosin molecules made of 2 globular protein subunits reaches the nearest thin filament

Mysosin Action During contraction, myosin heads: interact with actin filaments, forming cross-bridges pivot, producing motion

Sliding Filaments Figure 10–8

Skeletal Muscle Contraction Sliding filament theory: thin filaments of sarcomere slide toward M line between thick filaments the width of A zone stays the same Z lines move closer together InterActive Physiology: Sliding Filament Theory PLAY

What are the components of the neuromuscular junction, and the events involved in the neural control of skeletal muscles?

Skeletal Muscle Contraction Figure 10–9 (Navigator)

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 Innervation Figure 10–10a, b (Navigator)

Skeletal Muscle Innervation Figure 10–10c

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)

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)

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

What are the key steps involved in the contraction of a skeletal muscle fiber?

Exposing the Active Site Figure 10–11

The Contraction Cycle Figure 10–12 (1 of 4)

The Contraction Cycle Figure 10–12 (2 of 4)

The Contraction Cycle Figure 10–12 (3 of 4)

The Contraction Cycle Figure 10–12 (Navigator) (4 of 4)

5 Steps of the Contraction Cycle Exposure of active sites Formation of cross-bridges Pivoting of myosin heads Detachment of cross-bridges Reactivation of myosin

Fiber Shortening As sarcomeres shorten, muscle pulls together, producing tension Figure 10–13

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 recovered by tropomyosin Sarcomeres remain contracted

Rigor Mortis A fixed muscular contraction after death Caused when: ion pumps cease to function calcium builds up in the sarcoplasm

A Review of Muscle Contraction Table 10–1 (1 of 2)

A Review of Muscle Contraction Table 10–1 (2 of 2)

KEY CONCEPT (Part 1) 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

KEY CONCEPT (Part 2) Contraction is an active process Relaxation and return to resting length is passive

What is the mechanism responsible for tension production in a muscle fiber, and what factors determine the peak tension developed during a contraction?

Tension Production The all–or–none principal: 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 and Sarcomere Length Figure 10–14

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

Length–Tension Relationship Normal resting sarcomere length: is 75% to 130% of optimal length

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 in a Twitch Length of twitch depends on type of muscle Figure 10–15a (Navigator)

Myogram A graph of twitch tension development Figure 10–15b (Navigator)

3 Phases of Twitch Latent period before contraction: the action potential moves through sarcolemma causing Ca2+ release

3 Phases of Twitch Contraction phase: calcium ions bind tension builds to peak

3 Phases of Twitch Relaxation phase: Ca2+ levels fall active sites are covered tension falls to resting levels

Treppe A stair-step increase in twitch tension Figure 10–16a

Treppe Repeated stimulations immediately after relaxation phase: stimulus frequency < 50/second Causes a series of contractions with increasing tension

Wave Summation Increasing tension or summation of twitches Figure 10–16b

Wave Summation Repeated stimulations before the end of relaxation phase: stimulus frequency > 50/second Causes increasing tension or summation of twitches

Incomplete Tetanus Twitches reach maximum tension Figure 10–16c

Incomplete Tetanus If rapid stimulation continues and muscle is not allowed to relax, twitches reach maximum level of tension

Complete Tetanus Figure 10–16d

Complete Tetanus If stimulation frequency is high enough, muscle never begins to relax, and is in continuous contraction

What factors affect peak tension production during the contraction of an entire skeletal muscle, and what is the significance of the motor unit in this process?

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 InterActive Physiology: Contraction of Whole Muscle PLAY

Motor Units in a Skeletal Muscle Figure 10–17

Motor Units in a Skeletal Muscle Contain hundreds of muscle fibers That contract at the same time Controlled by a single motor neuron InterActive Physiology: Contraction of Motor Units PLAY

Recruitment (Multiple Motor Unit Summation) In a whole muscle or group of muscles, smooth motion and increasing tension is produced by slowly increasing size or number of motor units stimulated

Maximum Tension Achieved when all motor units reach tetanus Can be sustained only a very short time

Sustained Tension Less than maximum tension Allows motor units to rest in rotation

KEY CONCEPT Voluntary muscle contractions involve sustained, tetanic contractions of skeletal muscle fibers Force is increased by increasing the number of stimulated motor units (recruitment)

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

What are the types of muscle contractions, and how do they differ?

2 Types of Skeletal Muscle Tension Isotonic contraction Isometric contraction

Isotonic Contraction Figure 10–18a, b

Isotonic Contraction Skeletal muscle changes length: resulting in motion If muscle tension > resistance: muscle shortens (concentric contraction) If muscle tension < resistance: muscle lengthens (eccentric contraction)

Isometric Contraction Figure 10–18c, d

Isometric Contraction Skeletal muscle develops tension, but is prevented from changing length Note: Iso = same, metric = measure

Resistance and Speed of Contraction Figure 10–19

Resistance and Speed of Contraction Are inversely related The heavier the 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

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

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

What are the mechanisms by which muscle fibers obtain energy to power contractions?

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

Recharging ATP Energy recharges ADP to ATP: using the enzyme creatine phosphokinase (CPK) When CP is used up, other mechanisms generate ATP

Energy Storage in Muscle Fiber Table 10–2

ATP Generation Cells produce ATP in 2 ways: aerobic metabolism of fatty acids in the mitochondria anaerobic glycolysis in the cytoplasm

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 2 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

Muscle Metabolism InterActive Physiology: Muscle Metabolism PLAY Figure 10–20a

Muscle Metabolism Figure 10–20b

Muscle Metabolism Figure 10–20c

Muscle Metabolism Figure 10–20 (Navigator)

What factors contribute to muscle fatigue, and what are the stages and mechanisms involved in muscle recovery?

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: the body needs more oxygen than usual to normalize metabolic activities resulting in heavy breathing

KEY CONCEPT 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

How do the types of muscle fibers relate to muscle performance?

Muscle Performance Power: Endurance: Power and endurance depend on: 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

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

Fast Fibers Contract very quickly Have large diameter, large glycogen reserves, few mitochondria Have strong contractions, fatigue quickly

Slow Fibers Are slow to contract, slow to fatigue Have small diameter, more mitochondria Have high oxygen supply Contain myoglobin (red pigment, binds oxygen)

Intermediate Fibers Are mid-sized Have low myoglobin Have more capillaries than fast fiber, slower to fatigue

Fast versus Slow Fibers Figure 10–21

Comparing Skeletal Muscle Fibers Table 10–3

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 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

What is the difference between aerobic and anaerobic endurance, and their effects on muscular performance?

Physical Conditioning Improves both power and endurance

Anaerobic Endurance Anaerobic activities (e.g., 50-meter dash, weightlifting): use fast fibers fatigue quickly with strenuous activity Improved by: frequent, brief, intensive workouts hypertrophy

Aerobic Endurance Aerobic activities (prolonged activity): supported by mitochondria require oxygen and nutrients Improved by: repetitive training (neural responses) cardiovascular training

KEY CONCEPT (1 of 2) What you don’t use, you loose Muscle tone indicates base activity in motor units of skeletal muscles Muscles become flaccid when inactive for days or weeks

KEY CONCEPT (2 of 2) Muscle fibers break down proteins, become smaller and weaker With prolonged inactivity, fibrous tissue may replace muscle fibers

What are the structural and functional differences between skeletal muscle fibers and cardiac muscle cells?

Structure of Cardiac Tissue Cardiac muscle is striated, found only in the heart Figure 10–22

7 Characteristics of Cardiocytes Unlike skeletal muscle, cardiac muscle cells (cardiocytes): are small have a single nucleus have short, wide T tubules

7 Characteristics of Cardiocytes 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

Coordination of Cardiocytes Because intercalated discs link heart cells mechanically, chemically, and electrically, the heart functions like a single, fused mass of cells

4 Functions of Cardiac Tissue Automaticity: contraction without neural stimulation controlled by pacemaker cells Variable contraction tension: controlled by nervous system

4 Functions of Cardiac Tissue Extended contraction time Prevention of wave summation and tetanic contractions by cell membranes

What role does smooth muscle play in systems throughout the body?

Smooth Muscle in Body Systems (Part 1) Forms around other tissues In blood vessels: regulates blood pressure and flow In reproductive and glandular systems: produces movements

Smooth Muscle in Body Systems (Part 2) In digestive and urinary systems: forms sphincters produces contractions In integumentary system: arrector pili muscles cause goose bumps

What are the structural and functional differences between skeletal muscle fibers and smooth muscle cells?

Structure of Smooth Muscle Nonstriated tissue Figure 10–23

Comparing Smooth and Striated Muscle Different internal organization of actin and myosin Different functional characteristics

8 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

8 Characteristics of Smooth Muscle Cells 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

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

Characteristics of Skeletal, Cardiac, and Smooth Muscle Table 10–4

SUMMARY (1 of 6) 3 types of muscle tissue: skeletal cardiac smooth Functions of skeletal muscles

SUMMARY (2 of 6) Structure of skeletal muscle cells: endomysium perimysium epimysium Functional anatomy of skeletal muscle fiber: actin and myosin

SUMMARY (3 of 6) Nervous control of skeletal muscle fibers: neuromuscular junctions action potentials Tension production in skeletal muscle fibers: twitch, treppe, tetanus

SUMMARY (4 of 6) Tension production by skeletal muscles: motor units and contractions Skeletal muscle activity and energy: ATP and CP aerobic and anaerobic energy

SUMMARY (5 of 6) Skeletal muscle fatigue and recovery 3 types of skeletal muscle fibers: fast, slow, and intermediate Skeletal muscle performance: white and red muscles physical conditioning

SUMMARY (6 of 6) Structures and functions of: cardiac muscle tissue smooth muscle tissue