1. Developmental Aspects of the Muscular System
Chapter 6

2. Muscular system is laid down in segments
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. The natural control of muscular system is at peak of development
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