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Muscle Tissue

A primary tissue type, divided into: Skeletal muscle, Cardiac muscle, Smooth muscle

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

Muscles have three layers of connective tissues:

Epimysium, Perimysium, Endomysium


exterior collagen layer, connected to deep fascia, Separates muscle from surrounding tissues


surrounds muscle fiber bundles (fascicles), contains blood vessel and nerve supply to fascicles


surrounds individual muscle cells (muscle fibers), contains myosatellite cells (stem cells) that repair damage

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 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

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


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

Sarcoplasmic reticulum (SR)

A membranous structure surrounding each myofibril,Helps transmit action potential to myofibril, Forms chambers (terminal cisternae) attached to T tubules


Is formed by one T tubule and two terminal cisternae


concentrate Ca2+ (via ion pumps)
release Ca2+ into sarcomeres to begin muscle contraction


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 line

the center of the A band, at midline of sarcomere

Z lines:

the centers of the I bands, at two ends of sarcomere

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


are strands of protein
reach from tips of thick filaments to the Z line
stabilize the filaments

Ca2+ released by SR cause

thin and thick filaments to interact

Muscle Contraction

Is caused by interactions of thick and thin filaments
Structures of protein molecules determine interactions


Is a double strand
Prevents actin-myosin interaction


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

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

The Neuromuscular Junction

Is the location of neural stimulation

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

Rigor Mortis

A fixed muscular contraction after death, Ion pumps cease to function; ran out of ATP, Calcium builds up in the sarcoplasm


A stair-step increase in twitch tension

Wave summation

Increasing tension or summation of twitches

Complete Tetanus

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

Incomplete tetanus

Twitches reach maximum tension

Muscle tone

The normal tension and firmness of a muscle at rest, Increasing muscle tone increases metabolic energy used, even at rest

Two Types of Skeletal Muscle Tension

Isotonic contraction
Isometric contraction

Isotonic Contraction

Skeletal muscle changes length: resulting in motion

Isometric contraction

Skeletal muscle develops tension, but is prevented from changing length

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

Adenosine triphosphate (ATP)

The active energy molecule

Creatine phosphate (CP)

The storage molecule for excess ATP energy in resting muscle

Energy recharges ADP to..


Cells produce ATP in two ways

Aerobic metabolism of fatty acids in the mitochondria,Is the primary energy source of resting muscles;
Anaerobic glycolysis in the cytoplasm, Is the primary energy source for peak muscular activity

Muscle Fatigue

When muscles can no longer perform a required activity, they are fatigued

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..


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

Active muscles produce heat

Up to 70% of muscle energy can be lost as heat, raising body temperature


The maximum amount of tension produced

Power and endurance depend on

The types of muscle fibers, Physical conditioning

Three Types of Skeletal Muscle Fibers

Fast fibers, Slow fibers, Intermediate fibers

Fast fibers

Contract very quickly, few mitochondria, Have strong contractions, fatigue quickly

Slow fibers

Are slow to contract, slow to fatigue

Intermediate fibers

Are mid-sized, Have more capillaries than fast fibers, slower to fatigue

Muscle Atrophy

Lack of muscle activity, Reduces muscle size, tone, and power

Muscle Hypertrophy

Muscle growth from heavy training

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 is

striated, found only in the heart


cardiac muscle cells

Intercalated Discs

Are specialized contact points between cardiocytes

Coordination of cardiocytes

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

Structure of Smooth Muscle

Nonstriated tissue

A blending of epimysium, perimysium, and endomysium that forms a broad sheet at the end of a muscle is known as:


The three types of muscle tissue are

skeletal, cardiac, smooth

Skeletal muscles are often called voluntary muscles because:

they contract when stimulated by motor neurons of the central nervous system

Repeating contractile units that make up a myofibril are called:


Nerves and blood vessels are contained within the connective tissues of the:

epimysium and perimysium

The thin filaments consist of:

a pair of protein strands together to form chains of actin molecules

The thick filaments consist of:

a helical array of myosin molecules

All of the muscle fibers controlled by a single motor neuron constitute a

motor unit

The reason that control over leg muscles is less precise than control over the muscles of the eye is:

many muscle fibers are controlled by a single motor neuron

The sliding filament theory:

the thin filaments are sliding toward the center of the sarcomere alongside the thick filaments

Troponin and tropomyosin are two proteins that can prevent the contractile process by

covering the active site and blocking the actin-myosin interaction

The amount of tension produced by an individual muscle fiber ultimately depends on the:

number of pivoting crossbridges

The transmission of an action potential along the T tubules stimulates the release of calcium from which structure in the sarcomere?

terminal cisternae

Peak tension production occurs when all motor units in the muscle contract in a state of:

complete tetanus

In an isotonic contraction, the:

crossbridges must produce enough tension to overcome the resistance

example of an isometric contraction:

holding a heavy stack of books above the ground

A high blood concentration of the enzyme creatine phosphokinase (CPK) usually indicates:

serious muscle damage

Mitochondrial activities are relatively efficient, but their rate of ATP generation is limited by the:

availability of oxygen

Which of the following has been correlated with muscle fatigue?

a decline in pH within the muscle altering enzyme activities

During the recovery period, the body's oxygen demand is:

elevated above normal resting levels

Which type of muscle fiber would be dominant in a muscle like the gastrocnemius, a calf muscle that contracts during standing and walking?

slow fibers

Extensive blood vessels, mitochondria, and myoglobin are found in the greatest concentration in:

slow fibers

The length of time a muscle can continue to contract while supported by mitochondrial activities is referred to as:

aerobic endurance

What type of muscle tissue does not contain sarcomeres?


Structurally, smooth muscle cells differ from skeletal muscle cells because smooth muscle cells

lack myofibrils and sarcomeres

necessary for smooth muscle contraction..

Calcium ions must interact with calmodulin to trigger muscle contraction.

Smooth muscle contractions in the respiratory passageways cause:

increased resistance to air flow

The cardiovascular system uses which types of muscle?

cardiac and smooth

The area of the A band in the sarcomere consists of:

M line, H band, zone of overlap

The order of the sequential-cyclic reactions that occur at an active site during cross-bridging is:

attach, pivot, detach, return

Excitation-contraction coupling forms the link between:

electrical activity in the sarcolemma and the initiation of a contraction

The phases of a single twitch, in sequential order, are

latent period, contraction phase, relaxation phase

After contraction, a muscle fiber returns to its original length through:

elastic forces and the movement of opposing muscles

A muscle producing peak tension during rapid cycles of contraction and relaxation is said to be in:

incomplete tetanus

The process of reaching complete tetanus is obtained by:

increasing the rate of stimulation until the relaxation phase is completely eliminated

The two mechanisms used to generate ATP from glucose are:

aerobic respiration and anaerobic glycolysis

In anaerobic glycolysis, glucose is broken down to pyruvic acid, which is converted to:

lactic acid

The hormone responsible for stimulating muscle metabolism and increasing the force of contraction during a sudden crisis is:


The type of skeletal muscle fibers that have low fatigue resistance are:

fast fibers

An example of an activity that requires anaerobic endurance is:

a 50-yard dash

Athletes training to develop anaerobic endurance perform:

frequent, brief, intensive workouts

The major support that the muscular system gets from the cardiovascular system is:

nutrient and oxygen delivery and carbon dioxide removal

Skeletal muscle functions in

maintaining body temperature.

Action potentials must travel along which structure internal to the sarcolemma to cause the release of calcium ions from the sarcoplasmic reticulum?

T tubules

In which part of the sarcomere are myosin heads able to form crossbridges with actin?

zone of overlap

When Jennifer looks through the microscope at skeletal and cardiac muscles, she sees striations. What are these striations?

A bands and I bands

skeletal muscles are..


__ plays a big role in muscle contraction


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