Muscle Tissue and Function 1 Muscle Cell Architecture

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 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 largescale 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 cells 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 Sequence of events Motor Neuron to Muscle contraction at cellular level (from the Brain Top to Bottom) [link] Human Anatomy, Larry M. Frolich, Ph. D.

Molecular Basis of Muscle Function Actin-Myosin “sliding filament” model EXPLAINS: n n 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 (each skeletal muscle is an organ) Cells n n n Long and cylindrical, in bundles Multinucleate Obvious Striations Skeletal Muscles-Voluntary Connective Tissue Components: n n n 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 n n Branching, chains of cells Single or Binucleated Striations Connected by Intercalated discs Cardiac Muscle-Involuntary Myocardium-heart muscle n Pumps blood through vessels Connective Tissue Component n Endomysium: surrounding cells Human Anatomy, Larry M. Frolich, Ph. D.

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

Carciac Muscle Smooth Muscle Human Anatomy, Larry M. Frolich, Ph. D.

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

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