Download ANPS 019 Beneyto-Santonja 10-08

ANPS 019 Beneyto-Santonja 10/08/12
Skeletal Muscle Histology
Learning Objectives
 Describe the organization of muscle and the unique characteristics of skeletal muscle
cells
 Identify the structural components of the sarcomere
 Explain the key concepts involved in skeletal muscle contraction and tension production
Skeletal muscle Functions
 Produce skeletal movement
 Maintain posture and body position
 Support soft tissues
 Guard entrances and exits
 Maintain body temperature
Skeletal muscle fibers
 Sarcolemma (cell membrane)
 Sarcoplasm (muscle cell cytoplasm)
 Sarcoplasmic reticulum (modified ER)
 T-tubules and myofibrils aid in contraction
 Sarcomeres  regular arrangment of myofilaments organized into myofibrils
 Sarcosome  mitochondria in the muscle
 Muscle fibers develop through the fusion of mesodermal cells called myoblasts
Organization of connective tissues
 Epimysium: surrounds whole muscle
 Perimysium: sheathes bundles of muscle fibers  surrounds fascicles
o Epimysium and perimysium contain blood vessels and nerves which branch into
the Endomysium
 Endomysium: covers individual muscle fibers
 Tendons or aponeuroses attach muscle to bone
Notes that nuclei of muscle fibers are peripheral nuclei, not inside the cells
Levels of Functional Organization in Skeletal Muscle Fiber
 Skeletal Muscle  Surrounded by Epimysium; contains muscle fascicles
 Muscle Fascicle  Surrounded by Perimysium; contains muscle fibers
 Muscle Fiber  Surrounded by Endomysium; contains myofibrils
 Myofibril  Surrounded by Sarcoplasmic reticulum; consists of sarcomeres (Z line to Z
line)
 Sarcomere  Contains thick filaments and thin filaments
Sarcomere Structure, Part I
 Thin Filament  Actin: 5-6 nm diameter, 1 um long, 300-400 G actin monomers for
each thin filament
 Titin prevents over stretching of the sarcomere
 Thick Filament  Myosin 10-12 nm in diameter; 1.6 um long; each thick filament
contains about 300 myosin molecules
 Defined as Z line to Z line  Consists of A band and half of an I band on each side
Sarcomere Structure, Part II
 Thick filaments  form triangles with each other; in the middle of each triangle is a thin
filament
 Thin filaments  6 surround each thick filament
 In the H-zone  only consists of myosin w/ titin in the middle of each
 M line  myosin molecules are supported by a matrix to stay organized
 I band  Thin filaments without the myosin; shows actin and titin only
 Z line  matrix supporting actin, keeping them organized
Thin Filaments
 F-actin (filamentous actin)  consists of 2 “chains” of polymerized G-actin protein
wrapped around each other
 Nebulin
 Tropomyosin  covers active site on G-actin; rod shaped protein
 Troponin  binds to G-actin holds tropomyosin in place; gobular protein
Thick Filaments
 Bundles of myosin fibers around titan core
o Myosin molecules have an elongated tail and a globular head
o Heads form cross-bridges during contraction
o Interactions between G-actin and myosin prevented by the location of
tropomyosin at rest