Chapter 10 - Muscular Fibers: Microanatomy

Skeletal Muscle

Structure

• Highly Vascular - many blood vessels present

• Well innervated- many nerves present

• Fascia (hypodermis) - connective tissue beneath skin

  • Epimysium - around individual muscle

    • Holds blood vessels and nerves

Composed of muscle cells (fibers) connective tissue, Blood Vessels, Nerve fibers, Nervous Tissue, Skeletal Muscle Tissue

Fibers are long, cylindrical, multinucleated

Striated appearance

Parts of a Muscle

Several nuclei inside Sarcolemma

Sarcolemma - Plasma membrane of muscle fibers

Sarcoplasmic Reticulum - Calcium metabolization

Sarcoplasm - Cytoplasm filled with myofibrils: made of myofilaments

• myofilaments - thin (actin) and thick (myosin)

Sarcomeres - highly ordered repeating units of Myofilaments

Sarcomeres

Sarcomere - basic unit of muscle fiber

Z Disk - filamentous network of protein. Serves as attachment for actin

I Bands - from 2 disks to start of thick filaments

A Bands - length of thick filaments

H Zone - Region in A band where action and myosin do not overlap

M Line - Middle of H zone; delicate filaments holding myosin in place

Nerves and Blood

Motor Neurons

• stimulate muscle fibers to contract

• Axons branch so that each muscle fiber is innervated

• contact is neuromuscular Junction

• Motor End Plate - specialized area, part of neuromuscular Junction

• Transverse (T) Tubules - tube-like invaginations of plasma membrane that penetrate to deep part of fiber: conduct impulse rapidly through cell

• Neuromuscular Junction - Axon terminal resting n an investigation of sarcolemma

Smooth Muscle

fibers smaller than those in skeletal muscle

Spindle-Shaped: Single, central nucleus

More actin than myosin

Dense bodies instead of 2 disks as in skeletal muscle; have noncontractile intermediate filaments

Calcium is required to initiate contractions

Types of Smooth Muscle

Visceral/Unitary - cells in sheets; function as a unit

• numerous gap junctions; waves of contraction

• often autorhythmic

Multiunit - cells or groups of cells as independent units

• Sheets (blood vessels); bundles Corrector pili and Iris); single cells (capsule of Speen)

Cardiac Muscle

found only in heart

Striated

Each cell usually has one nucleus

Has intercalated disks and gap junctions

Autorhythmic Cells

Actin potentials of longer deration and longer refectory period

Calcium regulates contraction

Elongated, branching cells containing 1-2 centrally located nuclei

contains actin and myosin myofilaments

Intercalated disks - specialized cell-cell contacts

• cell membranes interdigitate

• Desmosomes hold cells together

• Gap junctions allow action potentials to move from one cell to the next

Electrically, Cardiac muscle of the atria and of the ventricles behaves as single unit