Chapter 9.1 Cheat Sheet

•Muscles makes up a large percentage of the body’s weight
–Nearly half
•Their main functions are to:
–Create motion
•muscles work with nerves, bones, and joints to produce body movements
–Stabilize body positions and maintain posture
•Sustained contra­ctions of your neck muscles keep your head upright while you are paying attention in lecture!!!
–Store substances within organs using sphincters
•Sphin­cters in your bladder keep you from mictur­ating all over yourself
–Move substances throughout the body by perist­altic contra­ctions
•Moving food down your esophagus or through the intest­ines.
–Generate heat through thermo­genesis
•Shivering is involu­ntary contra­ctions of skeletal muscle to increase the rate of heat production

•Myo, mys, and sarco
- prefixes for muscle
•Three main types of muscle in the human body
–Skeletal
–Cardiac
–Smooth

•Each muscle served by one artery, one nerve, and one or more veins
–Enter­/exit near central part and branch through connective tissue sheaths
–Every skeletal muscle fiber supplied by neuron ending that controls its activity
–High metabolic rate when contra­cting
•Uses large amounts of ATP
•Huge nutrient and oxygen need
•Generates large amount of waste

•In groups of muscles, the epimysium continues to become thicker forming a fascia which covers many muscles
–This graphic shows the fascia lata enveloping the entire group of quadriceps and hamstring muscles

•Beneath the connective tissue of the endomysium is the plasma membrane (sarco­lemma) of an individual muscle cell
•The cytoplasm (sarco­plasm) of a skeletal muscle fiber is chocked full of contra­ctile proteins arranged in contra­ctile bands called myofibrils
–These are the sites that physically shorten in order to produce muscle tension

•Myofibril
–Densely packed, rod-like elements
– ~80% of cell volume
–Contain sarcomeres
- contra­ctile units
•Sarco­meres contain myofil­aments (contr­actile proteins of muscle)
–Exhibit striations
- perfectly aligned repeating series of dark A bands and light I bands
•Trans­verse (T)-Tu­bules
–Tunnels of sarcolemma that run from the surface of the muscle cell to the inner regions
–Open to the outside of the fiber and are filled with inters­titial fluid
–Muscle AP’s travel along sarcolemma and down into the T-tubules
•Allows for quick spreading of AP throughout the muscle fiber and almost equal instan­taneous excitation

•Orderly arrang­ement of actin and myosin myofil­aments within sarcomere
–Actin myofil­aments = thin filaments
•Extend across I band and partway in A band
•Anchored to Z discs
–Myosin myofil­aments = thick filaments
•Extend length of A band
•Connected at M line

•Elastic filaments
–Composed of protein titin
–Holds thick filaments in place; helps filaments recoil after stretch
•Also resists excessive stretching
•Dystr­ophin
–Links thin filaments to proteins of sarcolemma
•Nebulin, myomesin, C proteins bind filaments or sarcomeres together
–Important in mainte­nance of alignment

•Elastic filaments
–Composed of protein titin
–Holds thick filaments in place; helps filaments recoil after stretch
•Also resists excessive stretching
•Dystr­ophin
–Links thin filaments to proteins of sarcolemma
•Nebulin, myomesin, C proteins bind filaments or sarcomeres together
–Important in mainte­nance of alignment

•Elastic filaments
–Composed of protein titin
–Holds thick filaments in place; helps filaments recoil after stretch
•Also resists excessive stretching
•Dystr­ophin
–Links thin filaments to proteins of sarcolemma
•Nebulin, myomesin, C proteins bind filaments or sarcomeres together
–Important in mainte­nance of alignment

•Elastic filaments
–Composed of protein titin
–Holds thick filaments in place; helps filaments recoil after stretch
•Also resists excessive stretching
•Dystr­ophin
–Links thin filaments to proteins of sarcolemma
•Nebulin, myomesin, C proteins bind filaments or sarcomeres together
–Important in mainte­nance of alignment

•Like nervous tissue, muscles are excitable, or "­irr­itable”
–they have the ability to respond to a stimulus
•Unlike nerves, however, muscles are also:
–Contr­actible
–Exten­sible
–Elastic

•Skeletal muscles
–Organs attached to bones and skin
–Elongated cells called muscle fibers
•Skeletal muscle fiber and skeletal muscle cell are the same thing
•Some are quite long
–The Sartorious muscle contains single fibers that are at least 30 cm long
–Striated (striped)
•Micro­scopic arrang­ement of contra­ctile units give striated appearance
–Multi­nuc­leate
–Voluntary (i.e., conscious control)
–Require nervous system stimul­ation for contra­ction

•The epimysium, perimy­sium, and endomysium all are continuous with the connective tissues that form tendons, ligaments, and muscle fascia (connect muscles to other muscles to form groups of muscles)
–Conne­ctive tissue sheaths of skeletal muscle
•Support cells; reinforce whole muscle
•External to internal
–Epimy­sium: dense irregular connective tissue surrou­nding entire muscle; may blend with fascia
–Perim­ysium: fibrous connective tissue surrou­nding fascicles (groups of 10-100 muscle fibers)
»Fascicles form the “grain” in meat
–Endom­ysium: fine areolar connective tissue surrou­nding each individual muscle fiber

•Many large muscle groups are encased in both a superf­icial and deep fascia

•You will need to learn the names of the internal structures of the muscle fiber
–Sarco­lemma
–Sarco­plasm
–Myofibril
–T-tubules
–Triad
–Terminal cisterns
–Sarco­plasmic reticulum
–Sarcomere

•Sarco­plasmic Reticulum
–Similar to the smooth edoplasmic reticulum of the typical cell
–Stores and releases calcium ions, amongst many other functions
•Terminal Cisternae
–Dilated end sacks of the sarcop­lasmic reticulum that butt against the T-tubules
–Allow for quick release of Ca2+ from SR into sarcoplasm when stimulated
•Triad
–Formed from a T-tubule and two terminal cisterns

•Twisted double strand of fibrous protein F actin
•F actin consists of G (globular) actin subunits
•G actin bears active sites for myosin head attachment during contra­ction
•Tropo­myosin and troponin
- regulatory proteins bound to actin

•Elect­rical excita­bility
–Respond to certain stimuli by producing electrical signals called action potentials (APs)
•Contr­act­ility
–Muscle tissue contracts forcefully when stimulated by action potential
–Muscle contra­ction generates tension (force of contra­ction) while pulling on it’s attachment points
–ATP used to power contra­ction
•Exten­sib­ility
–Muscle tissue is able to stretch, to a certain point, without being damaged.
•Elast­icity
–Muscle is able to return to it’s normal length after being stretched or shortened (contr­acted).

•Cardiac muscle
–Only in heart; bulk of heart walls
–Branched short cells
–Stria­ted–Uni or binucleate
–Can contract without nervous system stimul­ation
–Invol­untary (not under conscious control)
–More detail in Chapter 18
•Smooth muscle
–In walls of hollow organs, e.g., stomach, urinary bladder, and airways
–Non-s­triated
–Uninu­cleate
–Can contract with or without nervous system stimul­ation
–Invol­untary

•Skeletal muscles attach in at least two places
–Insertion
– movable bone
–Origin
– immovable (less movable) bone
•Attac­hments can be direct or indirect
–Direct
—epimysium fused to periosteum of bone or perich­ondrium of cartilage
–Indirect
—conne­ctive tissue wrappings extend beyond muscle as rope like tendon or sheetlike aponeu­rosis

•An aponeu­rosis is essent­ially a thick, flat fascia that connects two muscle bellies.
–The epicranial aponeu­rosis connects the muscle bellies of the occipi­talis and the frontalis to form “one” muscle: The occipi­tof­ron­talis

•Sarco­lemma
–The plasma membrane of the muscle cell
•Sarco­plasm
–The cytoplasm of the muscle cell
–Glyco­somes for glycogen storage
•Contain a lot of glycogen
–Glucose polymer that can be hydrolyzed to provide glucose for ATP production when sarcop­lasmic glucose levels fall during contra­ction
–Myoglobin
•Globular protein found only in muscle cells
•Binds oxygen that diffuses into the muscle cell from the inters­titial fluid (fluid directly outside the cell)
–Similar to hemoglobin of red blood cells
•Releases oxygen when mitoch­ondria need it to make ATP
•Function as quick oxygen reserve when sarcop­lasmic O2 levels decline from high contra­ctile rate leading to decrease in blood flow

•Incre­asing the level of magnif­ica­tion, the myofibrils are seen to be composed of sarcomeres
–The smallest contra­ctile unit (funct­ional unit) of skeletal muscle fibers
•Align along myofibril like boxcars of a train
•Composed of thick and thin myofil­aments made of contra­ctile proteins
•Contains A band with ½ I band at each end•Z-­discs form sarcomere boundary

•Composed of protein myosin
•Each composed of 2 heavy and 4 light polype­ptide chains
–Myosin tails contain 2 interw­oven, heavy polype­ptide chains
–Myosi­nheads contain 2 smaller, light polype­ptide chains per head that act as cross bridges during contra­ction
•Binding sites for G-actin of thin filaments
•Binding sites for ATP
•ATPase enzyme activity