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120 terms

Ch. 10 Muscle Tissue

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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
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 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)
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
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
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
Sarcoplasmic reticulum (SR)
A membranous structure surrounding each myofibril,Helps transmit action potential to myofibril, 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
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 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
Titin:
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
Tropomyosin
Is a double strand
Prevents actin-myosin interaction
Troponin
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
Treppe
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..
ATP
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..
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
Active muscles produce heat
Up to 70% of muscle energy can be lost as heat, raising body temperature
Power
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
cardiocytes
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:
aponeurosis
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:
sarcomeres
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?
smooth
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:
epinephrine
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..
voluntary
__ plays a big role in muscle contraction
calcium