Muscle Tissue PDF

MUSCLE TISSUE Chapter 10  Muscle Muscle – a Latin word for “little mouse” Muscle is the primary tissue in the: Heart (cardiac) Walls of hollow organs (smooth) Attached to the skeleton (skeletal) Muscle tissue Makes up nearly half the body’s mass ...

MUSCLE TISSUE Chapter 10  Muscle Muscle – a Latin word for “little mouse” Muscle is the primary tissue in the: Heart (cardiac) Walls of hollow organs (smooth) Attached to the skeleton (skeletal) Muscle tissue Makes up nearly half the body’s mass  Functions of Muscle Tissue Producing body movements Stabilizing body positions / posture / joints Movement of substances within the body Opening and closing passageways Producing heat  Muscle Tone Involuntary contraction of a small number of muscle fibres keeps muscles firm even though relaxed does not produce movement Essential for maintaining posture Stabilize and strengthen synovial joints Important in maintaining blood pressure  Properties of Muscle Tissue and thickening Contractility shortening of muscle to generate tension Excitability responsiveness of muscle to stimuli Extensibility allowingmuscle to be stretched without injury Elasticity allows mask to return to original shape Characterized by two main features: Presence or absence of striations Control is voluntary or involuntary  Skeletal Muscle Long, multinucleated cells Attaches to bone, skin or fascia Striated Voluntary control of contraction & relaxation  Cardiac Muscle Principle tissue of heart wall Shorter in length than skeletal and shows branching Striated Involuntary control Intercalated discs  Smooth Muscle In walls of hollow organs - blood vessels, urinary system, respiratory tubes, digestive tract Attached to hair follicles in skin Nonstriated Involuntary  Similarities of Muscle Tissue Muscle cells are known as fibres (skeletal and smooth) Muscle contraction (all 3) Depends on two types of myofilaments (contractile proteins) actin myosin Plasma membrane is called a sarcolemma Cytoplasm is called sarcoplasm Endoplasmic reticulum is called sarcoplasmic reticulum  Skeletal Muscle Each muscle is an organ Consists mostly of muscle tissue Skeletal muscle also contains: Connective tissue Blood vessels (muscle and epithelium) Nerves (nervous) Sarcolemma Mitochondrion Single muscle cell / fibre Myofibril Dark A band Light I band Nucleus  Connective Tissue Sheaths Endomysium Each muscle cell (fibre) is surrounded by a fine sheet of areolar connective tissue Perimysium Muscle cells are bundled together into fascicles which are each surrounded by a layer of dense irregular connective tissue Epimysium Layer of dense irregular connective tissue surrounding the whole muscle  Epimysium Bone Epimysium Perimysium Tendon Endomysium Muscle fibre in middle of a fascicle Blood vessel Fascicle (wrapped by perimysium) Endomysium (between individual muscle fibres) Epimysium Perimysium Fascicle Endomysium Muscle fibre  Myofibrils and Sarcomeres Striations result from internal structure of myofibrils Myofibrils Long rods within sarcoplasm Make up 80% of the sarcoplasm Are a specialized contractile organelle found in muscle tissue A long row of repeating segments called sarcomeres  The Sarcomere Basic functional unit of contraction of skeletal muscle Z disc (Z line) – boundary of each sarcomere Thin (actin) filaments – extend from Z disc toward the centre of the sarcomere Thick (myosin) filaments – located in the centre of the sarcomere Overlap inner ends of the thin filaments Thin (actin) filament Z disc H zone Z disc Thick (myosin) I band A band I band M line filament Sarcomere  A bands – full length of the thick filament H zone – centre part of A band where no thin filaments occur M line – in centre of H zone Contains tiny rods that hold thick filaments together I band – region with only thin filaments Lies within two adjacent sarcomeres A band Z disc M line Z disc Thin (actin) filament Elastic (titin) filaments Thick (myosin) filament Myosin heads H zone  Sarcoplasmic Reticulum A specialized smooth ER that acts as a calcium storage site Interconnecting tubules surround each myofibril Conduct the impulse to the deepest regions of the muscle fibre to trigger SR to release Ca2+ This initiates muscle contraction  I band A band I band Z disc H zone Z disc M line Myofibril Sarcolemma Sarcolemma Tubules of the sarcoplasmic reticulum Myofibrils Mitochondria  Mechanism of Contraction Thick (myosin) Thin (actin) filament filament Sliding filament theory  Myosin heads attach to actin in the thin filaments Thin (actin) filament Movement  Then pivot to pull thin filaments inward toward the centre of Myosin head the sarcomere Thick (myosin) filament  Changes in Striation During Contraction 1 Fully relaxed sarcomere of a muscle fibre 2 Fully contracted sarcomere of a muscle fibre Z H Z Z Z I A I I A I  The Role of Titin Titin – a spring-like molecule in sarcomeres Resists overstretching of sarcomeres Holds thick filaments in place Unfolds when muscle is stretched; helps sarcomeres return to their resting length Accounts for the elasticity & extensibility of myofibrils Thin (actin) filament Elastic (titin) filaments Thick (myosin) filament  Rigor Mortis deceased body stiffen Happens 3 - 4 hours after death at death, cell membranes become leaky Ca2+ leaks out to SR causing myosin to bind to actin contraction cannot detach because ATP synthesis stops goes away after 24 hours because lysosomes digest myosin & actin  Types of Skeletal Muscle Fibres Skeletal muscle fibres are categorized according to: How they manufacture energy (ATP) How quickly they contract breaking down of ATP to gain energy Are divided into 3 classes: Slow oxidative fibres (SO) – type 1 Fast oxidative fibres (FO) – type 2a Fast glycolytic fibres (FG) – type 2b  Slow oxidative fibres Red colour due to abundant myoglobin Contain a large number of mitochondria Richly supplied with capillaries Are O2 -dependent Contract slowly and resistant to fatigue as long as O2 is present Use ATP at a slow rate Adapted for: posture walking cycling to won in a period of time twino 1 48  Fast oxidative fibres Contract quickly Use ATP at a fast rate Are O2 -dependent Have high myoglobin content and rich supply of capillaries Somewhat fatigue-resistant Adapted for: can generate for quickly but tan also resist fatigue modernintensitysustainedactivities u  Fast glycolytic fibres Contain little myoglobin and few mitochondria Contain more myofilaments and generate a high amount of force in a short period Depend on anaerobic pathways to make ATP Are O2 -independent Contract rapidly and tire quickly Use ATP at a fast rate Adapted for: Iangenerate quick powerful contraction but fatigue rapidly FO SO FG  Fibre Types within a Whole Muscle Most muscles contain an equal mixture of all three fibre types Proportions vary with the usual action of the muscle: neck, back and leg muscles have a higher proportion of postural, slow oxidative fibres shoulder and arm muscles have a higher proportion of fast glycolytic fibres Elite sprinters can have up to 80% FG fibres in their quadriceps muscles!  Clinical Significance DELAYED-ONSET MUSCLE SORENESS / POST-EXERCISE MUSCLE SORENESS Begins 8-24 hours after activity Caused by microscopic tears in the muscle fibres Inflammatory response results in swelling in the connective tissues surrounding the muscle fibres (endomysium) Swelling compresses the sensory nerve endings in the muscle, causing soreness HOWEVER, these tears stimulate increased production of myofibrils and myofilaments, resulting in increased muscle strength and size  Roots to Remember… sarco – flesh - lemma – sheath; sarcolemma = plasma membrane of muscle cell fasci – bundle myo, mys – muscle