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Anatomy & Physiology - Muscle

by: Courtney Luber

Anatomy & Physiology - Muscle 80197 - BIOL 2220 - 001

Courtney Luber

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About this Document

These notes cover the lectures on 10/6 and 10/11 about muscle.
Human Anatomy and Physiology I
John R Cummings
Class Notes
anatomy, Physiology
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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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