SAYED

Chapter 10:Muscle Tissue

A&P Biology 141R.L. Brashear-Kaulfers

Muscle Tissue• One of 4 primary tissue types,

divided into:– skeletal muscle– cardiac muscle– smooth muscleWithout these muscles, nothing in the

body would move and no body movement would occur

Skeletal Muscles- Organs of skeletal muscle tissue

- are attached to the skeletal system and allow us to move

• Muscular System- Includes only skeletal muscles

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

6 Functions of Skeletal Muscles

1. Produce skeletal movement2. Maintain body position and posture3. Support soft tissues4. Guard body openings

(entrance/exit)5. Maintain body temperature6. Store Nutrient reserves

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:

1. Epimysium-Exterior collagen layer• Connected to deep fascia• Separates muscle from surrounding

tissue2. perimysium- Surrounds muscle fiber

bundles (fascicles)• Contains blood vessel and nerve supply

to fascicles3. endomysium

3. 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)

NervesSkeletal 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? • Skeletal muscle cells are called

fibers

Figure 10–2

Skeletal Muscle Fibers• Are very long • Develop through fusion of mesodermal

cells (myoblasts- embryonic cells))• Become very large • Contain hundreds of nuclei –

multinucleate• Unfused cells are satellite cells- assist

in repair after injury

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• All regions of the cell must contract

simultaneously

Transverse Tubules (T tubules)

• Transmit action potential – impulses through cell

• Allow entire muscle fiber to contract simultaneously

• Have same properties as sarcolemma

• Filled with extracellular fluid

Myofibrils- 1-2um in diameter • Lengthwise subdivisions within muscle

fiber• Made up of bundles of protein filaments

(myofilaments)• Myofilaments - are responsible for

muscle contraction 2 Types of Myofilaments

• Thin filaments: – made of the protein actin

• Thick filaments: – made of the protein myosin

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

A Triad• Is formed by 1 T tubule and 2

terminal cisterna Cisternae

• Concentrate Ca2+ (via ion pumps) • Release Ca2+ into sarcomeres to

begin muscle contraction

Structural components of the Sarcomeres

Figure 10–4

-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:

– 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

Figure 10–6 (1 of 5)

Level 1: Skeletal Muscle

Level 2: Muscle Fascicle

Level 3: Muscle Fiber

Figure 10–6 (3 of 5)

Level 4: Myofibril

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 Proteins1. F actin:

– is 2 twisted rows of globular G actin– the active sites on G actin strands bind to myosin

2. Nebulin:– holds F actin strands together

3. Tropomyosin:– is a double strand– prevents actin–myosin interaction

4. Troponin: - a globular protein

– binds tropomyosin to G actin– controlled by Ca2+

Troponin and Tropomyosin

Figure 10–7b

Ca2+ binds to receptor on troponin moleculeTroponin–tropomyosin complex changesExposes active site of F actin

Initiating Contraction

A Thick Filament

Contain twisted myosin subunits Contain titin strands that recoil after stretching

The Mysosin Molecule

• Tail:– binds to other myosin molecules

• Head:– 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

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

Sliding Filaments

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

key steps involved in 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

1. Exposure of active sites2. Formation of cross-bridges3. Pivoting of myosin heads4. Detachment of cross-bridges5. 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• 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

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

• 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

Figure 10–15a (Navigator)

Tension in a Twitch• Length of twitch depends on type

of muscle

Myogram• A graph of twitch tension

development

Figure 10–15b (Navigator)

3 Phases of Twitch1. Latent period before contraction:

– the action potential moves through sarcolemma

– causing Ca2+ release 2. Contraction phase:

– calcium ions bind– tension builds to peak

3. 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

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

Twitches reach maximum tension

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?

InterActive Physiology: Contraction of Whole MusclePLAY

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

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 UnitsPLAY

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 MetabolismPLAY

Figure 10–20a

Muscle Metabolism

Figure 10–20c

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 Fatigue1. Depletion of metabolic reserves2. Damage to sarcolemma and

sarcoplasmic reticulum3. Low pH (lactic acid)4. 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:

– 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 Fibers1. Fast fibers- Contract very quickly

• Have large diameter, large glycogen reserves, few mitochondria

• Have strong contractions, fatigue quickly2. Slow fibers-Are slow to contract, slow to fatigue• Have small diameter, more mitochondria• Have high oxygen supply• Contain myoglobin (red pigment, binds oxygen)3. 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 • 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• 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 Tissue1. Automaticity:

– contraction without neural stimulation– controlled by pacemaker cells

2. Variable contraction tension:– controlled by nervous system

3. Extended contraction time4. Prevention of wave summation and

tetanic contractions by cell membranes

Role of 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

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

1. Long, slender, and spindle shaped

2. Have a single, central nucleus3. Have no T tubules, myofibrils, or

sarcomeres4. Have no tendons or aponeuroses

8 Characteristics of Smooth Muscle Cells

5. Have scattered myosin fibers6. Myosin fibers have more heads

per thick filament7. Have thin filaments attached to

dense bodies8. Dense bodies transmit

contractions from cell to cell

Functional Characteristics of Smooth Muscle

1. Excitation–contraction coupling2. Length–tension relationships3. Control of contractions4. 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 3)• 3 types of muscle tissue:

– skeletal– cardiac– smooth

• Functions of skeletal muscles• Structure of skeletal muscle cells:

– endomysium– perimysium– epimysium

• Functional anatomy of skeletal muscle fiber:– actin and myosin

SUMMARY (2 of 3)• Nervous control of skeletal muscle fibers:

– neuromuscular junctions – action potentials

• Tension production in skeletal muscle fibers:– twitch, treppe, tetanus

• Tension production by skeletal muscles:– motor units and contractions

• Skeletal muscle activity and energy:– ATP and CP– aerobic and anaerobic energy

SUMMARY (3 of 3)• Skeletal muscle fatigue and recovery• 3 types of skeletal muscle fibers:

– fast, slow, and intermediate• Skeletal muscle performance:

– white and red muscles– physical conditioning

• Structures and functions of:– cardiac muscle tissue– smooth muscle tissue