Biology 2230 Muscular System Lecture Notes PDF

Structures that Move the Body - The Muscular System Biology 2230 Lecture 8.1 C. Kunkel Muscle Tissue Produces voluntary or involuntary movements. Closely packed cells with little extracellular fluid. Highly vascular, or a good...

Structures that Move the Body - The Muscular System Biology 2230 Lecture 8.1 C. Kunkel Muscle Tissue Produces voluntary or involuntary movements. Closely packed cells with little extracellular fluid. Highly vascular, or a good blood supply. All muscle cells possess myofilaments composed of actin and myosin proteins. Shared terminology for muscles Myo- and mys- = “muscle” Sarco- =“flesh” Additional Characteristics of ALL Muscle Tissues Contractility is the ability to become shorter in length if stimulated. Extensibility is the ability to extend or stretch beyond its normal length. Elasticity is the ability to recoil to its normal resting length. Conductivity is the ability to hold an electrical charge at rest. Excitability is the ability to change electrical charge if stimulated.  Type CARDIAC SMOOTH SKELETAL Cell Shape Cell structu res Functio n Locatio n Develo p From Other Cardiac Muscle Tissue Makes up the walls of the heart and causes involuntary movement of blood through the heart. Derived from splanchnic mesoderm. Medium-size, branched cells with: one nucleus myofilaments arranged as myofibrils and appear as striations intercalated discs between cells and other special organelles Smooth Muscle Make up the walls of hollow organs, causing involuntary movement of substances through hollow organs. Derived from splanchnic mesoderm. Small-size spindle cells with: one nucleus myofilaments not arranged as myofibrils, no striations Skeletal Muscle Attach to skin and bones, causing voluntary movement of skin and bones. Derived from somite and somatic mesoderm. Long, cylindrical cells are known as fibers with: many nuclei myofilaments arranged as myofibrils and appear as striations other special organelles Function of Skeletal Muscles Producing voluntary movement (mostly). Maintains posture and body position Guards entrances and exits Supporting soft tissues and organs Maintaining body temperature Storing nutrients Organization of Skeletal Muscles A skeletal muscle organ is made of many parallel fascicles. – The epimysium is connective tissue wrapping all the fascicles a vein, artery, and nerve to create a single skeletal muscle organ. It is attached to the bone as a tendon. Clinical Implications Tendons are the connective tissue that attach muscles to bones. – Tendonitis is inflammation of the tendon sheath due to overuse. – Tendinosis is the breakdown (degeneration) of the collagen fibers in the tendon due to overuse. – How would this affect the muscle? https://my.clevelandclinic.org/health/diseases/22289- tendinopathy Skeletal Muscle Attachments and Actions When the muscle contracts, the insertion moves toward the origin. Origins (O) of biceps brachii A simple way to remember this is “I move Short head: coracoid process of scapula toward O. ” Long head: supraglenoid tubercle Origin (O) The origin is the more Action fixed ? attachment Biceps brachii, short head of Biceps brachii, long head the muscle. The insertion Insertion (I) is the more Radial tuberosity mobile of radius Biceps brachii, common tendon Insertion (I) attachment of insertion of the muscle. (a) Biceps brachii before contraction (b) Biceps brachii after contraction Skeletal Muscle Relationships and Actions Synergist: Muscles that work together to produce a given action. Prime mover: Muscle that causes the desired action. Antagonist: muscles whose action opposes that of the prime What if the mover. action is to extend the elbow? What is the Organization of Skeletal Muscles A fascicle is a bundle of parallel muscle fibers or cells. – Perimysium is connective tissue wrapping around all the muscle fibers (cells) that create a fascicle. Skeletal Muscle Organization The fascicle pattern and the epimysium Fascicle s Epimysiu can be used to differentiate between muscles. m Fascicles vary in size and shape, resulting in muscles with different shapes and capabilities. Fascicles parallel the body’s long axis, creating a strap-like or fusiform muscle. Fascicles with a broad origin with fascicles converge toward single tendon insertion. Short fascicles attach at an angle to a central tendon, running the length of the muscle. Fascicles are arranged in a circle around an opening. Skeletal Muscle Organization The muscle fiber is a long, cylindrical cell that spans muscle attachment points. – Endomysium is the connective tissue that fills the space between each muscle fiber (cell). Blood vessel Fascicle wrapped with perimysium Endomysium (between individual muscle fibers) Muscle fiber Myofibrils Fascicle Perimysium Comparison of Different Cells Muscle fibers (cells) are long and cylindrical cells with many nuclei and specialized organelles. – The sarcolemma is the outer boundary and contains the sarcoplasm, which holds the mitochondria, nuclei, and myofibrils surrounded by the sarcoplasmic reticulum. Skeletal Muscle cell Generalized cell Cell Sarcolemma membrane Cytoplasm Sarcoplasm Smooth Sarcoplasmic endoplasmic reticulum reticulum Myofibril Mitochondrion Nucleus Nucleus Mitochondrion Anatomy of the Skeletal Muscle Fiber Sarcolemma is the charged cell membrane that contains protein channels for muscle stimulation. – The sarcolemma dips into the cell as transverse tubules (T-tubules) and connects to the sarcoplasmic reticulum. Muscle fiber Transverse (T-) tubule Sarcolemma Endomysium Myofilaments Openings of T-tubules Myofibrils Sarcoplasmic reticulum Anatomy of the Skeletal Muscle Fiber The sarcoplasmic reticulum is a modified smooth endoplasmic reticulum that stores calcium (Ca2+). – It surrounds each myofibril and connects to the transverse tubules. Muscle fiber Transverse (T-) tubule Sarcolemma Endomysium Myofilaments Openings of T-tubules Myofibrils Sarcoplasmic reticulum Anatomy of the Skeletal Muscle Fiber The myofibrils are long cylindrical organelles composed of myofilaments. – Contain sarcomeres which are the contractile units of the muscle fiber. Muscle fiber Transverse (T-) tubule Sarcolemma Endomysium Myofilaments Openings of T-tubules Myofibrils Sarcoplasmic reticulum Anatomy of the Myofibril Sarcomeres are individual units of the myofibril. – They are organized with thick and thin myofilaments spanning from Z disc to Z disc. elastic Anatomy of the Myofilaments The thin filaments are composed of long strands of actin proteins, each containing a myosin-binding site – Two strands twisted around each other. The tropomyosin protein covers myosin binding sites on actin when muscles are relaxed. The troponin is the protein that holds tropomyosin in place. Anatomy of the Myofilaments The thick filaments are bundles of myosin proteins with many heads at the end. – They are secured to the sarcomere by M-line proteins at the midline and elastin at the Z-discs. – The myosin heads will move, pulling the thin filament during muscle contraction. elasti c M- line Regions of the Sarcomere The center of the sarcomere, where only the myosin and M line proteins overlap, is the H zone. The area where the actin and myosin filaments overlap creates a dark area known as the A band. The area where only actin filaments and z-disc proteins overlap creates a lighter area known as the I band. Regions of the Sarcomere Striations of the muscle fiber result from the A and I bands aligning for all the myofibrils. Types of Skeletal Muscle Fibers Slow Oxidative Fast Oxidative Fast Glycolytic Fibers Fibers Fibers Small diameter Intermediate Large diameter w/ fewer diameter w/ lots of myofibrils myofibrils Contain Contain myoglobin No myoglobin myoglobin Many Many Few mitochondria mitochondria mitochondria Contract Contract slowly Contract fast quickly Resistant to Powerful but Not resistant to fatigue only somewhat fatigue, tires Types of Skeletal Muscle Fibers Each muscle organ varies in the number of FG, SO, and FO fibers it is composed of. Depends on muscle location and movements the muscle performs. Exercise and Muscle Growth Exercise can increase muscle size, strength, and endurance. Aerobic exercise (running or biking) creates stronger, more flexible muscles with greater fatigue resistance. What should increase because of resistance exercise (weightlifting)? Check your understanding Compare and contrast cardiac, smooth, and skeletal muscle tissue characteristics. What do they have in common, and how do they differ? Place the following terminology in order from microscopic to macroscopic: Epimysium, endomysium, permysium Myofibrils, muscle organ fascicle, myofilament, muscle fiber, sarcomere Describe the anatomy of the myofibril and sarcomere. Compare the roles of the three concentric layers of connective tissue wrappings in the organization of skeletal muscle. Check your understanding Describe the anatomy of the myofilaments. How does their anatomy relate to their function during muscle contraction? What are the two types of attachment points for skeletal muscles? What is the general rule for the movement of skeletal muscles? Describe the structural relationships among the following in a resting skeletal muscle fiber: A band, H, and I band. Check your understanding Compare the three types of skeletal muscle fibers. How will each create ATP? Which type(s) will a sprinter have versus a bodybuilder? Which type will be red, pink, and white? Why will they be different colors? Which is larger and why? Which will resist fatigue and why? How should the muscle organ or fiber change if you want to build larger muscles like a bodybuilder or fiber change? Check your understanding…Label the images Check your understanding…Label the images TEM (38,000) Check your understanding…Label the images Myofibril Heads (a) Thick filament (b) Thin filament (c) Elastic filament