Anatomy & Physiology - Muscle
Anatomy & Physiology - Muscle 80197 - BIOL 2220 - 001
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80197 - BIOL 2220 - 001
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This 5 page Class Notes was uploaded by Courtney Luber on Tuesday October 11, 2016. The Class Notes belongs to 80197 - BIOL 2220 - 001 at Clemson University taught by John R Cummings in Fall 2016. Since its upload, it has received 2 views. For similar materials see Human Anatomy and Physiology I in Biology at Clemson University.
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Date Created: 10/11/16
Muscle Classification criteria o Striations o Nervous control – voluntary or involuntary o Number of nuclei Muscle types o Skeletal Nuclei pushed toward the outer edge of the cell Multinucleated Striated Voluntary o Cardiac Striated Uninucleated Involuntary Intercalated discs o Smooth Uninucleated Involuntary Non-striated Spindle cells Properties of muscle o Excitability – ability to respond to a stimulus o Contractility – shortens & thickens No muscle will contract unless its stimulated to contract depends on NS o Extensibility – ability to be stretched While one muscle shortens and thickens, the other is stretched o Elasticity – muscle can return back to its resting state Functions of muscle o Motion Any muscle contraction results in this Skeletal muscle contraction results in locomotion Cardiac muscle contraction results in blood movement Smooth muscle contraction moves food through digestive system, moves urine through tract, etc. o Maintenance of posture Contraction of skeletal muscle opposes gravity o Stabilizing joints Muscles are partially contracted and hold joints Muscles pretty much surround every joint, even sutural joints in skull o Heat production All muscle produces heat when it contracts Skeletal muscle composition o Skeletal muscle fibers o Blood vessels o Nerve fibers (bring stimulation) o Connective tissue Gross anatomy o Muscle o Attachment Skeletal muscle attaches to bone Muscle fuses directly to periosteum (direct) OR tendon attaches to bone (indirect) Indirect muscle attachment Tendon – ropelike connective tissue Aponeurosis – flat sheet of connective tissue o Consist of 100 -1000s of individual cells o Epimysium – connective tissue that envelopes the whole muscle Dense irregular connective tissue o Fascicle – bundle of muscle cells Wrapped by a connective tissue covering Plural is fasciculi o Perimysium – covers each fascicle Made up of connective tissue o Muscle fiber – muscle cell “myofiber” o Endomysium – covers muscle fiber made up of reticular connective tissue Attachment to bone o Origin – attachment of muscle to the immovable bone Can have one or more Usually proximal to insertion o Insertion – attachment to moveable bone Can have one or more Microscopic anatomy o Myofibers – muscle fiber o Sarcolemma – plasma membrane of muscle cell o Sarcoplasm – cytoplasm of muscle cell Contain glycosomes – vesicle that stores glycogen (storage form of glucose) Muscle cells need energy in order to contract o easiest is they store their own energy Myoglobin – pigment that stores oxygen Need oxygen to contract o Nuclei o Myofibrils – contractile components Thousands of these per muscle fiber o Sarcoplasmic reticulum – modified smooth ER Surrounds the myofibrils Run longitudinally Terminal cisternae – perpendicular channels that runs between sarcoplasmic reticulum o T tubule – hollow internal projection of the sarcolemma T tubule & two terminal cisternae make up a triad Myofibrils o Sarcomeres – segments of myofibrils Brick wall each brick in a line of bricks is a sarcomere Functional unit for contraction Muscle contraction is interaction of proteins o Myofilaments – collected into units (sarcomeres) Thick myofilament – made up of myosin Thin myofilament – made up of actin Sarcomere o Z line – ends of sarcomere Thick filament does not extend to z line o A band – portion of sarcomere that represents entire length of thick filament o I band – portion that does not have thick myofilament; only thin o H zone – portion that only has thick myofilament o M line – dead center of sarcomere Contraction of muscle is shortening of sarcomere o Z lines pulled toward M line Thick myofilaments o Myosin – 2 heads (on ends) – each head has 2 binding sites Actin-binding site ATP-binding site When ATP is bound to myosin, it disables the actin binding site o Myosin cross bridge - when myosin attaches to actin Thin myofilaments o Actin Twisted helix of proteins Myosin-binding site Myosin attaches to actin; actin binding site binds to myosin binding site o Tropomyosin Wraps around to hold helix together o Troponin Troponin I – binds to actin; holds troponin/tropomyosin complex in place; covers myosin binding site; only uncovered when muscle is excited Troponin T – binds to tropomyosin Troponin C – binds to Calcium; Ca is only available when muscle is excited; disables troponin I; exposes myosin binding site *Calcium involved in muscle contraction* *Sarcoplasmic reticulum stores Calcium* Elastic myofilaments o Titin – connects thick myofilaments to z lines o Z discs are made out of protein nebulin Nebulizers relax muscle Sliding filament theory o ATP changes position of myosin head o Myosin heads bind to actin o Thin filaments move across thick filaments Excitation-Contraction Coupling o How we stimulate the muscle in order for it to contract o Voluntary in skeletal muscle o Somatic motor neuron – part of nervous system that is under voluntary control o Excitation from NS, contraction from muscle o Step 1: nervous impulse sent to muscle o Step 2: Muscle is stimulated to become active Neuromuscular junction o Area of “connection” between neuron and muscle No direct connection Synaptic cleft o Each muscle cell only has one connection to the NS Only one neuromuscular junction per fiber o Contraction of muscle is an all or none phenomenon If we stimulate the muscle to contract, it will contract to its greatest ability o Synaptic vesicles Contain neurotransmitters o Chemical contained in vesicle are released and change the membrane permeability change from rest to active o Motor end plate Somatic motor neuron always uses ACh ACh receptors Only found at motor end plate on junctional folds Acetylcholinesterase Enzyme that breaks down Ach so muscle can go back to relaxed state Excitation-Contraction Coupling o Ach triggers generation of action potential across sarcolemma and down T tubules (internal hollow projections of sarcolemma) o Action potential passes triads o Terminal cisternae release calcium into sarcoplasm Ca binds with troponin C o Some calcium binds to troponin (TnC) o Removes tropomyosin from active sites on actin o Myosin heads attach to actin and pull thin myofilaments toward center of sarcomere Sarcoplasmic reticulum o Triads Terminal cisternae T tubules Power stroke o Thick & thin myofilaments bound through cross bridge Head of myosin attaches to actin o Myosin head changes from high energy to low energy configuration Shortening sarcomere o Pulls thin myofilament toward H zone o ATP binds with myosin head o Myosin and actin separate o ATPase splits ATP and released energy returns myosin head to high energy position o Cycle repeats as long as calcium and ATP are present ATP jobs o Disconnects the thick & thin myofilaments o Right after death, there is no ATP being produced, so body becomes contracted Recovery o Calcium actively pumped back into sarcoplasmic reticulum Using energy o Reduced calcium frees tropomyosin to block actin active sites o Cross bridges disconnects o Muscle relaxes Motor unit o Combination of motor neuron and all the fibers it stimulates o Number of motor units determines the strength of contraction (more fibers stronger contraction) o Not all motor units in a muscle fire at the same time o Allows muscle to stay active longer – prevents muscle fatigue
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