Types of Muscle 1.Skeletal • Elongated Cells • Multi nucleated • Striated – striped appearance • Voluntary • Produces powerful contractions • Tires easily, needs rest (fatigue). • Covers bony skeleton (motility) Longitudinal View Notice striations and nuclei around outside of cell. Cross Section Notice nuclei around outside of cell.
2. Smooth • Spindle-shaped Cell • Single nucleus in each cell • No Striations • Involuntary • Slow, sustained contractions • In hollow visceral organs (stomach, bladder, respiratory passages) Cross Section Nucleus is in center of cell. Cells much smaller.
3. Cardiac (Heart) • Branched cell • Contain intercalated discs • Single nucleus in each cell • Striations • Involuntary • Steady, constant contractions • Never tires
Muscle Functions • Produce movement • locomotion & manipulation • Help blood move through veins & food thru small intestines • Maintain posture • Stabilize joints • Body temp homeostasis • Shivering: movement produces heat energy
Muscle Requirements Axon of neuron Motor end plate (terminus) • Demands continuous oxygen/nutrient supply. • Lots of arteries/capillaries to muscle. • Each muscle cell w/ its own nerve ending controlling its activity. • Produce much metabolic waste due to constant activity.
Muscle Attachments • Most muscles span joints • Attaches to bone in two places: (video) 1.Insertion: the moveable bone • Bicep insertion is the radius 2.Origin: the stationary bone • bicep originates in two different places in scapula • Attachment types • Direct: attaches right onto bone - ex. intercostal muscles of ribs • Indirect: via tendon or aponeurosis (sheet-like tendon) to connect to bone - leaves bone markings such as tubercle
Muscle Organization Muscles are complex bundled structures: fibers within fibers
Muscle organization Muscle (organ) Fascicle Muscle fiber (cell) Myofibril Sarcomere Myofilaments: Actin & Myosin
Muscle Fibers • A Muscle Fiber = Muscle Cell • HUGE cell: • 10 - 100m in diameter • can be hundreds of centimeters long (created by cytoplasmic fusion of multiple embryonic cells) • extends the length of the muscle • Main content: bundles of proteins (actin and myosin) • Multinucleated • to maintain high rate of protein synthesis. • Muscle fiber nucleus = myonucleus
Insulation of Muscles • Muscle cells must be insulated from one another by specialized membranes • Muscle cells work electrically • if not insulated, nerves cannot control individual muscles.
Epimysium surrounds entire muscle • Dense CT that merges with tendon • Epi = outer • Mys = muscle • Perimysium surrounds muscle fascicles • Peri = around • Within a muscle fascicle are many muscle fibers • Endomysium surrounds muscle fiber • Endo = within
Structural Terminology Associated with Muscle Fibers Prefixes: myo, mys, and sarco all refer to muscle • Sacroplasmic Reticulum = Smooth ER of muscle (regulates calcium levels for muscle contraction) • Sarcoplasm = Cytoplasm • To maintain ATP production during cellular respiration, contains high amounts of: • mitochondria • glycosomes that store sugar • oxygen binding protein called myoglobin • Sarcolemma = Plasma Membrane • T tubules - The sarcolemma of muscle cells are not just on the outside, rather forms tubes that dive into the muscle cells • Myosin and Actin= muscle proteins that create muscle cytoskeletal filaments for contraction
myofibril Sarcoplasmic Reticulum Myosin (red) and Actin (blue) T-tubule sarcolemma
Microstructures • Each muscle fiber (muscle cell), is composed of many myofibrils. • Organized system of cytoskeleton filaments of actin and myosin proteins that do the actual contracting • Myofibrils are NOT CELLS • A sarcomere is one segment of a myofibril (muscle segments). • The series of sarcomeres produce the striated appearance of muscles
Muscle Fiber Sarcomere
Sarcomere organization • Myofibril composed of repeating series of sarcomeres with dark A and light I bands. • I bands intersected by Z discs mark the outer edges of each sarcomere. • Contraction happens within one sarcomere.
How do muscle contract? Let’s sketch the sarcomere together and discuss the sliding filament model of muscle contraction