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Developmental Aspects of the Muscular System

This chapter explores the developmental stages of the muscular system, from the formation of muscles in the developing embryo to the effects of aging on muscle mass and strength. It also discusses muscular dystrophy and myasthenia gravis, two inherited muscle disorders.

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Developmental Aspects of the Muscular System

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  1. Developmental Aspects of the Muscular System Chapter 6

  2. Developing Embryo • Muscular system is laid down in segments • Each segment is then invaded by nerves • Muscles and their control by nervous system develop rather early in pregnancy • First movements are called quickening (16th week of pregnancy)

  3. After Birth • Baby’s movements are all reflex type • Nervous system must mature before baby can control muscles • Development of muscular system proceeds in caudal/cephalic direction then proximal/distal direction • Gross movements precede fine ones

  4. During Childhood • The nervous system’s control of skeletal muscles becomes more and more precise

  5. MidAdolescence • The natural control of muscular system is at peak of development • Bring to fine edge by athletic training

  6. AGing • Amount of connective tissue in muscles increases and amount of muscle tissue decreases • Muscles become stringier • Older person loses muscle mass which results in loss of weight • When muscle mass is lost, so is muscle strength (50% by age 80) • Regular exercise can offset the effects of aging on the muscular system

  7. Muscular Dystrophy • Inherited muscle-destroying disease • Muscles enlarge due to fat and connective tissue deposit, but muscle fibers degenerate and atrophy Duchenne's Muscular Dystrophy -Most common and serious form -Occurs mostly in boys from age 2 to 7 years old -Signs: clumsy and fall frequently as muscles weaken -Diseases progresses from extremities upward, finally affecting the head and chest muscles -Most rarely live beyond 20 years of age and die from respiratory failure -Cause: diseased muscle fibers lack protein (dystrophin) that helps maintain the sarcolemma -No cure

  8. Myasthenia Gravis • Affect muscles during adulthood • Signs include drooping of the upper eyelids, difficulty in swallowing and talking, and muscle weakness and fatigue • Involves a shortage of ACh receptors at neuromuscular junctions • Thought to be auto-immune disease because antibodies to ACh receptors found in patients • Loss of receptors means muscle cells are not stimulated properly and get progressively weaker • Death results from respiratory failure

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