Muscles - Anatomy & Physiology

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Introduction

Muscle mass accounts for a large majority of the carcass weight of domestic animals. Muscular contraction is necessary for voluntary and involuntary movement of limbs, stabilization of joints, maintaining luminal diameter (in the case of arteries, bowel, etc), and to produce heat. The number of muscle fibers an individual possesses is determined by genetics and is set at birth. Further muscle development therefore occurs by hypertrophy, rather than hyperplasia of muscle fibers. Three types of muscle can be described:

• Skeletal (aka Striated, Somatic, Voluntary)
• Smooth (aka Visceral)
• Cardiac

Skeletal Muscle

• Each muscle is composed of multiple fascicles, each of which consists of a bundle of muscle fibers
• Muscle "fiber" means a single cell, which are multi-nucleate, and known as syncitia
• Within each fiber are groups of parallel, longitudinal myofibrils
  • Myofibrils are arranged as sarcomeres, bound by Z-discs
  • Each sarcomere contains 2 separate groups of myofilaments:
    • Thin filament, containing Actin, located centrally
    • Thick filament, containing Myosin, originating from either side of each Z-disc

• Skeletal muscle includes muscles of:
  • Posture
  • Movement
  • Respiration

• Two basic types of skeletal myofibre:
  • Type I
    • Grossly red
    • High myoglobin level
    • Slow rate of contraction
    • High oxidative activity
    • Function - postural
  • Type II
    • Grossly white
    • Low myoglobin level
    • Fast rate of contraction
    • High glycolytic activity
    • Function - exercise

Tendon

Histology of tendon (Courtesy of RVC Histology images)

• Consists of dense collagen type 1 fibres and fibroblasts (tenocytes)

Links

• Muscle Pathology
• Bursae and Tendons Pathology

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