anatomy and physiology of muscle
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| Diseases related to muscle physiology | Sarcopenia- age related loss of muscle
Diabetes (1 and 2)- skeletal muscle removes glucose from blood
Cardiovascular disease- heart; Cardiac hypertrophy deals with cardiac muscle; Coronary artery disease deals with smooth muscle
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| Basic muscle function | turns chemical energy into mechanical force
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| Functional characteristics of muscle | 1.Excitability or irritability
2. Contractibility
3.Extensibility
4.Elasticity
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| Excitability or irritability | the ability to receive and respond to stimuli (depolarization)
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| Contractibility | the ability to shorten forcibly
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| Extensibility | the ability to be stretched or extended
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| Elasticity | The ability to recoil and resume the original resting length
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| 3 types of muscle | 1.Skeletal-striated and multi-nucleated; voluntary
2.Cardiac- striated and multi-nucleated; involuntary
3.Smooth- not striated and single nuclei for each cell; involuntary
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| Skeletal muscle | multiple nuclei; regular banding patterns that are organized by contractile proteins
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| Skeletal muscle development | muscle arises from the mesoderm; myoblast; multi-nucleated myotube; myofiber
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| Myoblast | muscle cell, fused together
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| multi-nucleated myotube | myoblasts fused together no longer have mitotic abilities; instead we alter size (weight lifting) by adding or subtracting nuclei by adding satellite cells (cells floating outside myotube)
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| Myofiber | smalles complete contractile system; activated when nerve hits myotube but if nerve fails to make contact the myotube will wither and die
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| Structure of skeletal muscle | 1.Epimysium
2.Fascicle
3.Fibers
4.Myofibril
5.Sarcomere
6.Perimysium
7.Endomysium
8.Sarcolemma
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| Epimysium | Layer of connective tissue outside muscle that covers the entire thing; dense irregular connective tissue
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| Fascicle | a bundle of muscle fibers wrapped in perimysium; contains smaller bundles of muscle fibers
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| Perimysium | A layer of connective tissue that wraps muscle fibers into bundles or fascicles; dense irregular tissue
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| Fibers | Formed by the fusion of myoblasts; a long, cylinder, multi-nucleated cell; nuclei is under sarcolemma and has other cell organelles like mitochondria; each fiber is wrapped in endomyseum
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| Endomysium | Areolar connective tissue; layer of connective tissue that surrounds muscle fibers
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| Sarcolemma | The plasma membrane of a muscle cell (muscle fiber)
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| Myofibril | The basic unit of a muscle; Where contraction takes place; a long strand of sarcomeres; found in the skeletal muscle fibers; held together in a long chain by proteins and organized into myofiliments
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| Sarcomere | Smallest functional unit of skeletal muscle; Shortens for muscle contraction; runs Z-disc to Z-disc; composed to thick filaments-Myosin and thin filaments- Actin (slide past each other to contract)
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| Overview of skeletal muscle contraction | Myosin binds to actin to shorten; myosin heads work with receptor proteins of actin
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| Muscle striations | made by sarcomeres; striations consist of A-bands, I-bands, M-lines, and H-zones
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| A-band | Anisotropic- light does not pass through due to high concentration of protein; Dark area
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| I-band | Isotropic- light can pass through due to less protein; light area
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| M-line | Dark band in the center of the sarcomere; consists of proteins that anchor thick filaments to the center of the sarcomere
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| H-zones | Light bands that are located on either side of the M-line
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| I-band (blue circles) | 6 actin form a circle; thin filaments (actin) molecules only
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| H-zone (red circles) | Thick filaments (myosin) molecules only
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| M-line (red circles connected) | proteins connect thick filaments (myosin) only; do not connect think filaments at all
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| A-band (blue and red circles) | thick and then filaments (actin and myosin); 6 thin filaments for every thick filament
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| Thick filaments (myosin) structure | Globular myosin head- binds to actin; tails- are intertwined that interact with other myosin subunits and regulate motor activity; neck- acts as a lever (hinges to change shape)
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| Thin filaments (actin) structure | long chains made of actin molecules (twisted); each actin has a myosin binding site; protein strands run through actin filament called tropomyosin; yellow proteins called troponin
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| Tropomyosin | Protein strands; blocks myosin binding site on actin and prevents contraction
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| Troponin complex | Yellow proteins complexes that contain 3 proteins; inhibit tropomyosin to allow binding and contraction when and action potential is created
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| T-Tubules | Part of the plasma membrane of the sarcolemma; studded with calcium channels for depolarization; run transversely through muscle fibers
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| Sarcoplasmic Reticulum | Located on either side of the T-tubules; Stores (muscle relaxation), releases (muscle contraction), and sequesters calcium
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| Terminal cisterna | Site where T-tubule tells sarcoplasmic reticulum to release calcium for contraction; large sac-like structure
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| Triad | T-tubules, Terminal cisterna, and sarcoplasmic reticulum
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| Voluntary control | A neuron must tell the muscle what to do
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| Cardiac muscle | specialized striated muscle; involuntary
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| Development of cardiac muscle | Cardiomyocyte- located in walls of heart; generate electrical impulses of the heart; single or multi-nucleated
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| Contraction of cardiac muscle | Automaticity- spontaneous contraction
Syncytium- single cell function and 1 (gap junction) because cells meet end to end; allows contractions to work together
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| Neural control of cardiac muscle | Autonomic nervous system- parasympathetic (relax) and sympathetic (stimulate)
no neural muscular junction
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| Cardiac muscle functional structures | Sarcomere- T-tubules, SR, Mitochondria
Intercolated disks with gap junctions
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| Sliding filament theory | during contraction the thin filaments slide past the thick filaments to they overlap; When sarcomere is contracted I-bands are gone and Z-discs are pulled to the center of the sarcomere
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| Cross-bridge cycling | 4 steps; when actin bind to myosin we have a cross-bridge; Cycling- going back and forth between strong and weak bonds
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| Step 1 Cross-bridge cycling | Myosin binds to actin forming a cross-bridge
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| Step 2 Cross-bridge cycling | Phosphate falls off and myosin bends forward which draws thin filaments towards center of the sarcomere and ADP falls off
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| Step 3 Cross-bridge cycling | ATP binds to myosin and disassociates or weakens bond between actin and myosin
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| Step 4 Cross bridge cycling | Myosin will change ATP to ADP and phosphate and re-cocks the myosin head
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| Role of calcium in contraction | Calcium binds to troponin C; Troponin then triggers tropomyosin to move
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| Neuron muscular junction | Site where the neuron makes contact with the muscle
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| Buton (neurotransmitter) | Releases vessicles containing ACH (acetylcholine) into the synaptic cleft; ACH binds to receptors on Na and K channels; ACH opens channels in the cleft which causes membrane potential which initiates and raises membrane potential
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| After acetylcholine is used... | It is broken down and leaves the cleft
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| Action potential | When a membrane depolarizes and repolarizes; membrane can depolarize and recover in 4ms
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| Threshold | a point you must reach or exceed for something to occur; all or none; when threshold is met or exceeded sodium channels will open
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| Depolarization | Na channels will be signaled to open and sodium will rush in the cell; the membrane potential will become positive; this action moves down the sarcolema
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| Repolarization | When a section of the membrane has a positive potential the potassium channels will open allowing the membrane to be polarized again; this also moves down the sarcolema right behind the depolarization
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| After Depolarization/repolarization | The channels close and Na (out) and K (in) are pumped back to the appropriate sides of the membrane through sodium potassium pumps
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| Resting membrane potential | -90
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| depolarization and the triad | signal to depolarize can travel down T-tubules by the Na channels; this process signals sarcoplasmic reticulum through receptors; the SR then releases Ca to bind to troponin ect.
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| End plate potential | The rise in membrane potential of the cleft; gets to about -40 or -50 which meets threshold requirements and causes depolarization
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| When acetylcholine stops and membrane potential is positive... | channels open and membrane repolarizes
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| Twitch | muscle contraction stimulated by a single stimulus
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| 3 periods of a twitch | 1.Latent period
2.Contraction period
3. Relaxation period
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| Latent period | Beginning; everything up to myosin binding to actin
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| Contraction period | Middle; Myosin binds to actin; takes about 30ms to peak
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| Relaxation period | End; decreasing amount of tension
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| Slow vs fast twitch | twitch characteristics come from the metabolic properties of myofibrils; no difference in latent period
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| Fast twitch | Very quick to peak in the contraction period and very quick to fatigue
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| Slow twitch | Slower to peak in contraction period and slower to fatigue
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| Gastrocnemius | (fast twitch); quick to peak and quick to relax
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| Soleus | (slow twitch); longer to peak and longer to relax
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| Graded muscle responses (i.e. tension production) | 1.Frequency stimulation
2.Amount of motor neurons activated
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| Frequency stimulation | crude; before the first contraction can relax we have a second contraction on top of the first; causes more force with the same muscle- energy is reserved and more Ca is being released to cause more reactions; can continue till max cross-bridges formed
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| motor neuron control | each fiber is controlled by a specific motor neuron but one motor neuron can be responsible for controlling 40-200 fibers
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| Amount of motor neurons activated | (size principle); as stimulus voltage increases the amount of fibers activated increases and higher the tension; high contraction force by increasing # of motor units contracting; smallest to largest
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| Smallest to largest | small units used for small tasks and vice versa; we can regulate force by regulating the motor neurons activated
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| Length tension relationship | optimal sarcomere length; too much contraction; too much stretching
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| Optimal sarcomere length | max number of cross bridges are formed
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| Over contracted | If we contract the sarcomere by too much the thin filaments will over lap and it will block binding sites so tension and # of cross-bridges will decrease; can continue to shorten until no more cross-bridges can be formed
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| Over stretched | If we extend the sarcomere by to much then tension and number of cross bridges will decrease as actin and myosin separate; will continue until no cross-bridges can be formed
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| Smooth muscle | Involuntary; not striated; single nucleated cells; found in the lining of most organs
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| Development in smooth muscle | Layers of cells can have different shapes- no cell phenotype; single, central nuclei;synchronous contractions due to cellular junctions; lacks organization; No sarcomere
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| Neural control in smooth muscle | Autonomic nervous system- parasympathetic, and sympathetic; no defined nerve ending plates
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| Contraction types of smooth muscle | 1.Phasic contraction- single unit (gastrointestinal)
2.Tonic contraction- multiunit (blood vessels)
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| Layers of cells | longitudinal and circular layers of cells; they contract at different times; cells have gap junctions that tell the cells around them to contract
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| Autonomic nervous system | Norepineprine is released by a varicosity of an autonomic nerve fiber and can cause numerous muscles to contract (involuntary)
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| Varicosity | bulbous swelling of innervating nerves; release neurotransmitters into wide synaptic clefts called diffuse junctions
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| Intermediate filaments | cytoskeletal structure, helps give the cell characteristics like twisting while shortening
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| Caveolae | (poorly developed SR); receptor mediated, concentrates calcium, helps to take calcium from outside the cell to make up for poor SR
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| Thin to thick filament ratio (smooth muscle) | 1 thick filament to every 13 thin filaments
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| Filaments in Smooth muscle | actin and myosin are not organized in sarcomeres; no troponin or tropomyosin
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| E-C coupling | Calcium is released into cell and binds to calmodulin; kinase phosphorilates myosin; the more phosphate groups the more contractions
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| Calmodulin | enzyme that phosphorilates kinase
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| Single unit contraction | single-unit muscle (visceral muscle); contracts rhythmically as a unit via gap junctions; may have spontaneous action potentials; arranged in opposing sheets to exhibit stress-relaxation response; (ex. gut contractions)
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| peristalsis | alternating contractions and relaxations of smooth muscle that mix and squeeze substances through the lumen (ex. stomach)
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| Mulit-unit | Rare gap junctions; infrequent spontaneous depolarizations; structurally independent muscle fibers; a rich nerve supply, may form motor units; graded contractions (ex. airways, blood vessels, arrector pili, internal eye)
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| Stress relaxation response | smooth muscle can expand due to a stimulus and if the expansion is held for long enough the muscle will then relax and allow more room for more tension all while keeping its ability to contract
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| hyperplasia | increase in the number of cells which may result in an increase of that organ; smooth muscles used this to undergo mitosis and increase number (only muscle that can divide)
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| Atherosclerosis | heart disease
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| Hyperplasia (estrogen and the uterus) | at puberty estrogen stimulates the synthesis of more smooth muscle which allows uterus to grow to adult size; also happens during pregnancy to accommodate the increasing size of the baby
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