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Muscular/Alexander Rodrigo/
Period: 1, (., ● Bicep brachii, ● Brachialis,…
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:white_small_square: Functions of general muscle: produce movement, produce heat as they, maintain posture, and stabilize joints
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- Skeletal: used to produce movement in bones, located on bones, single, very long, cylindrical, multinucleate cells with striations
- Cardiac: pumps blood and circulates oxygen, lines walls of heart, branching chains of cells; uni or uninucleate; striations
- Smooth: controls involuntary movements in internal organs, blood vessels, etc; lines walls of visceral organs, single, spindle shaped, uninucleate; no striations
- Excitability(responsiveness): ability to receive and respond to stimuli
- Extensibility: ability to be stretched
- Elasticity: ability to recoil to resting length
- contractility: ability to shorten forcibly when stimulated
:white_small_square: a skeletal muscle is an organ made of different tissues with three feautures: nerve and blood supply, connective tissue sheath, attachments
- each muscle receives a nerve, an artery, and veins; consciously controlled skeletal muscle has nerves supplying every fiber; contracting fibers need a lot of oxygen and nutrients and quick waste removal
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- Skeletal: used to produce movement in bones, located on bones, single, very long, cylindrical, multinucleate cells with striations
- Cardiac: pumps blood and circulates oxygen, lines walls of heart, branching chains of cells; uni or uninucleate; striations
- Smooth: controls involuntary movements in internal organs, blood vessels, etc; lines walls of visceral organs, single, spindle shaped, uninucleate; no striations
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- Each skeletal muscle and each muscle fiber is covered in connective tissue that supports cells and reinforces the whole muscle
- Epimysium: dense irregular connective tissue surrounding the entire muscle; may blend with fascia
- Perimysium: fibrous connective tissue surrounding fascicles (groups of muscle fibers)
- Endomysium: fine areolar connective tissue surounding each muscle fiber
-Muscle (organ): hundreds to thousands of muscle cells plus connective tissue wrappings, blood vessels, nerve fibers [WRAPPED BY EPIMYSIUM]
-Fascicle (portion of the muscle): discrete bundle of muscle cells, separated from the rest by a connective tissue sheath [WRAPPED BY PERIMYSIUM]
-Muscle Fiber (cell): elongated multinucleate cell with a banded (striated) appearance [WRAPPED BY ENDOMYSIUM]
- Skeletal muscle fibers are long, cylindrical cells that contain multiple nuclei
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-Sarcoplasm: muscle fiber cytoplasm; contains many glycosome (glycogen storage) and myoglobin (oxygen storage)
- modified organelles: myofibrils, sarcoplasmic, reticulum T tubules myofibrils
- features: striations, sarcomeres, myofilaments molecular composition of myofilaments
-striations: stripes formed, from repeating dark and light bands along each myofibril
:white_small_square:A bands: dark regions; H zone is the lighter region in the middle of the A band; the M line (protein myomesin) bisects the H zone
:white_small_square:I bands: lighter regions; the Z disc (line) is a coin shaped sheet of proteins on the middle of the I band
-Sarcomere: smallest contractile unit (functional unit) of a muscle fiber; contains an A band with half of an I band at each end; the area between Z discs; sarcomeres align and end to end like boxcars of a train
- contraction: the activation of cross bridges to generate force; shortening occurs when tension from cross bridges on thin filaments exceeds exposing forces; contraction ends when cross bridges become inactive
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- Relaxed: thin and thick filaments overlap only slighlty at the ends of the A band
- Sliding Filament Model of Contraction: during contraction, thin filaments slide past thick filaments, so actin and myosin overlap more; neither filament changes length they just overlap more
- when the nervous system stimulates the fiber, myosin heads bind actin, forming cross bridges that start the sliding; attachments form and break several times, pulling thin filaments towards the center of the sarcomere in a ratcheting action
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- sarcomeres align and end to end like boxcars of a train
- contains an A band with half of an I band at each end; the area between Z discs;
- Duchenne Muscular Dystrophy (DMD): most common and serious muscular dystrophy; muscle-destroying diseases that generally appear in childhood
-inherited as a sex-linked recessive disease, so almost only in males (1 in 3,600 births); appears at ages 2 to 7 when a boy becomes clumsy and falls often
-progresses from the extremities upward to the head, chest muscles, and cardiac muscle; with supportive care patients can live into their 30's and beyond
-caused by a defective gene for dystrophy, which links thin filaments to the extracelluar matric and stabilizes the sarcolemma; the sarcolemma tears easily, letting in excess calcium that damges contractile fibers; inflammation follows, regneration is lost, and muscle cells die (apoptosis) and muscle mass drops
- Many toxins, drugs, and diseases interfere with events at the nueromuscular junction
-Example: myasthenia gravis: disease characterized by drooping upper eyelids, differentl swallowing and talking, and generalized muscle weakness
-involves shortage of Acytlcholine receptors because person's Acytylcholine receptors are attacked by own antibodies, which suggest this is an autoimumne disease
- Rigor Mortis: 3-4 hours after death, muscles begin to stiffen
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- intracelluar calcium levels increase because ATP is no longer being synthesized, so calcium cannot be pumped back into SR
- the resting sarcolemma is polarized: a voltage exsists across the membrane, negative inside compared with outside
- An action potenetial is caused by changes in electrical charges, in three steps: 1.) Generation of end plate potential, 2.) Depolarization, 3.)Repolarization
- refractory period: muscle fiber cannot be stimulated for a specific amount of time, until repolarization is coplete
-Na+ that into cell is puped back out, and K+ hat flowed outside is pumped back into cell
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2.) voltage gated calcium channels open, calcium enters motor nueron
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5.) ACh binding to receptors, opens gates, allowing Na+ to enter resulting in end plate potential
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