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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
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)
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 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)
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
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
A striped or striated pattern within myofibrils: alternating dark, thick filaments (A bands) and light, thin filaments (I bands)
Zone of overlap:
the densest, darkest area on a light micrograph
where thick and thin filaments overlap
are strands of protein
reach from tips of thick filaments to the Z line
stabilize the filaments
Is caused by interactions of thick and thin filaments
Structures of protein molecules determine interactions
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
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
A fixed muscular contraction after death, Ion pumps cease to function; ran out of ATP, Calcium builds up in the sarcoplasm
If stimulation frequency is high enough, muscle never begins to relax, and is in continuous contraction
The normal tension and firmness of a muscle at rest, Increasing muscle tone increases metabolic energy used, even at rest
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
After contraction, a muscle fiber returns to resting length by
Elastic forces, Opposing muscle contractions, Gravity
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
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
After exercise or other exertion, The body needs more oxygen than usual to normalize metabolic activities resulting in heavy breathing
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
Coordination of cardiocytes
Because intercalated discs link heart cells mechanically, chemically, and electrically, the heart functions like a single, fused mass of cells
A blending of epimysium, perimysium, and endomysium that forms a broad sheet at the end of a muscle is known as:
Skeletal muscles are often called voluntary muscles because:
they contract when stimulated by motor neurons of the central nervous system
Nerves and blood vessels are contained within the connective tissues of the:
epimysium and perimysium
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?
Peak tension production occurs when all motor units in the muscle contract in a state of:
In an isotonic contraction, the:
crossbridges must produce enough tension to overcome the resistance
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
Which type of muscle fiber would be dominant in a muscle like the gastrocnemius, a calf muscle that contracts during standing and walking?
Extensive blood vessels, mitochondria, and myoglobin are found in the greatest concentration in:
The length of time a muscle can continue to contract while supported by mitochondrial activities is referred to as:
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.
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:
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
The hormone responsible for stimulating muscle metabolism and increasing the force of contraction during a sudden crisis is:
The major support that the muscular system gets from the cardiovascular system is:
nutrient and oxygen delivery and carbon dioxide removal
Action potentials must travel along which structure internal to the sarcolemma to cause the release of calcium ions from the sarcoplasmic reticulum?
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
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