178 Clinical Anatomy of the Visual System

Epimysium

Perimysium

Endomysium

FIGURĘ 10-1

Connective tissue network of striated muscle.

the overall effect of shortening the sarcomere and tł entire muscle.

STRUCTURE OF THE EXTRAOCULAR MUSCLES

The extraocular muscles have a denser blood suppl; and their connective tissue sheaths are morę delicat and richer in elastic fibers than is skeletal muscle Fewer muscle fibers are included in a motor unit ii extraocular muscle than are found in skeletal musd elsewhere. Striated muscle of the leg can contain severa hundred muscle fibers per motor unit;⁶ in the extra ocular muscles, each axon innervates 3 to 10 fibers. Precise fine motor control and ąuick accurate movemen of the extraocular muscles occur because of this denst innervation. Singly innervated fibers have the classic end piąte (en placjue) seen in skeletal muscle; multiph

FIGURĘ 10-2

Myosin and actin myofibrils. A, Myosin fibril is composed of two-headed filaments, with heads arranged in a spiral. B, Actin myofibril is composed of double-helix filament to which troponin-tropomyosin complex is attached.

A band    I band

llllł

lilii

MIII

HITIT

FIGURĘ 10-3

A, Arrangement of thick and thin filaments in sarcomere. B, Photomicrograph of striated muscle, with parts of sarcomere indicated.

(B from Krause W), Cutts JH: Concise text of histology, Baltimore, 1981, Williams & Wilkins.)

B

Actin

filaments

Myosin

filaments

Z linę

A band

M linę

H band

Z linę