Human Anatomy, Larry M. Frolich, Ph.D. Muscle Tissue and Function 1. Muscle Cell Architecture and Function 2. Mechanics of muscle contraction—the “sliding filament” model and role of actin and myosin proteins 3. Types of muscle cells 4. Motor Units 5. Energy Use in Muscles— fast and slow fibers

Human Anatomy, Larry M. Frolich, Ph.D. Muscle Cells and Neurons are unique to animals have “excitable” membranes that transmit action potentials allow for rapid large- scale movements Motor Unit is one motor neuron plus the muscle cells that it stimulates (or synapses with)

Human Anatomy, Larry M. Frolich, Ph.D.

Muscle cell or muscle “fiber” is composed of myofibrils which contain sarcomeres or contractile “units”

Human Anatomy, Larry M. Frolich, Ph.D. Muscle fibers are cells—visible to naked eye as fibers in meat, chicken, fish Sarcolemma is muscle cell membrane—”excitable” so has action potentials just like neurons Because cell is large, T-tubules carry action potential—ionic depolarization—into internal parts of cell Sarcoplasmic reticulum releases calcium which triggers actin-myosin protein filaments to contract Muscle cells Sequence of events Motor Neuron to Muscle contraction at cellular level (from the Brain Top to Bottom) [link]link

Human Anatomy, Larry M. Frolich, Ph.D. Molecular Basis of Muscle Function Actin-Myosin “sliding filament” model EXPLAINS: MUSCLE SHORTENING MUSCLE FORCE GENERATION OR “CONTRACTION”

Human Anatomy, Larry M. Frolich, Ph.D. Mechanics of Contraction (the sliding filament model) Action potential or depolarization of membrane triggers Ca release which causes actin and myosin to “slide” causing whole cell to“contract” Fig. 10.4

Human Anatomy, Larry M. Frolich, Ph.D. How actin-myosin complex (sarcomere) shorten muscle Ca triggers cross- bridges to form from myosin “thick” filament to actin “thin” filament Cross-bridges “row” or “reach” for next binding site on actin “thin” filaments

Human Anatomy, Larry M. Frolich, Ph.D. From Actin-Myosin to Whole Muscle

Human Anatomy, Larry M. Frolich, Ph.D. Skeletal Muscle Tissue Cells Long and cylindrical, in bundles Multinucleate Obvious Striations Skeletal Muscles-Voluntary Connective Tissue Components: Endomysium-between fibers Perimysium-surrounds bundles Epimysium-surround whole muscle Attached to bones, fascia, skin Origin & Insertion

Human Anatomy, Larry M. Frolich, Ph.D. Smooth Muscle Tissue Cells Single cells, uninucleate No striations Smooth Muscle-Involuntary 2 layers-opposite orientation (peristalsis) Surrounds hollow organs, blood vessels Connective Tissue Component Endomysium: surrounds cells

Human Anatomy, Larry M. Frolich, Ph.D. Cardiac Muscle Cells Branching, chains of cells Single or Binucleated Striations Connected by Intercalated discs Cardiac Muscle-Involuntary Myocardium-heart muscle Pumps blood through vessels Connective Tissue Component Endomysium: surrounding cells

Human Anatomy, Larry M. Frolich, Ph.D.

Carciac Muscle Smooth Muscle

Human Anatomy, Larry M. Frolich, Ph.D.

Muscles use lots of energy Muscle cells have complex pathways that provide the energy from high-energy phosphate bonds to power filament sliding

Human Anatomy, Larry M. Frolich, Ph.D. As muscles fatigue, they switch energy sources

Human Anatomy, Larry M. Frolich, Ph.D. Fast and Slow Muscle Fibers/Cells FAST-TWITCH Contract in.01 sec Large in diameter Myofibrils densely packed Fatigue rapidly since use lots of ATP Quickly switch to anaerobic metabolism “white” meat (chickens use their wings for short bursts) SLOW-TWITCH Take three times longer to contract About half the diameter of FAST Can continue contracting for long time Surrounded by more capillaries to provide O2 Capture O2 in myoglobin within cell “red” meat (chicken stands all day) in diameter