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

Muscle Tissue and Function1. 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 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]

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(each skeletal muscle is an organ)

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 TissueCells

Single cells, uninucleateNo striations

Smooth Muscle-Involuntary2 layers-opposite orientation (peristalsis)

Surrounds hollow organs, blood vesselsConnective Tissue Component

Endomysium: surrounds cells

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

Cardiac MuscleCells 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.

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.