Muscular Changes Flashcards
When do Myoblasts become post-miotic
after birth
Satellite Cells
provide nuclei to the muscle cells as they get larger - important for muscle growth and repair
When do most skeletal muscles present in mature form?
8 weeks gestation
Fiber type in prenatal
All are present, but the proportions change
Prenatal Type 1 muscle fibers develop from
- primarily myotubules –> do NOT require neural input to develop into fiber types
- seen in the fetus first
Prenatal Type 2 fibers develop from
Develop from secondary myotubules –> DO require neural input
-not seen until 31-37 weeks gestation
Progression of muscle fiber formation in prenatal stage
Myogenic precursor cells - embryonic myoblasts - primary myotubue - secondary myotube - muscle fibers
Characteristic of muscular system from infancy-childhood in first year
Increase in muscle fiber size and number of fibers
Increase in fiber number (in first year) due to
division of existing muscle cells
Fiber type differentiation continues into:
adolescense (or young adulthood)
Children up to 15 years have more ___ than ___
Type 1 than Type II muscles fibers
When do you achieve adult levels of Type IIb until
young adulthood
Strength gains follow a typical growth curve and are related to
- Height and weight
- Muscle mass
- Fiber type distribution
Muscles add the number of sarcomeres and fibrils to
add length
Does bone growth proceed during adolescence?
Yes & stimulates muscle length
Boys increase strength > girls and its related to hormones
testosterone, growth horomone, insulin, thyroid hormone
1% year decline in number and size of muscle fibers after
20 years of age
Characteristics of muscular system during older adulthood
- decreased number of motor units due to nervous system changes
- decreased number of contractile proteins due to decreased muscle protein synthesis
- hormonal changes: less growth horomone and testosterone
- increased basement membrane thickness - hypoxia - decreased mass
Older adulthood muscle fiber changes
- Increase in Type I
- Decrease in type II; primary decrease in type IIb = decreases in power
- hypothesized that Type IIb become Type IIa or Type I
In older adulthood, muscle fibers are replaced with:
fat & connective tissue (non-contractile) – increases stiffness
increased connective tissue in the endomesium =
thickened basement membrane
Motor end plate changes in oder adult
- enlarged synaptic cleft
- slower axoplasmic transport
- thickening of basement
- clumping of synaptic vesicles
Muscle strength peaks in
age 30
Muscle strength stays steady until
30-50s
30% decrease in muscle strength between:
50-70; accelerates after age 70
Is eccentric or concentric strength maintained better>
eccentric
Is LE loss or UE muscle loss greater?
LE
Does muscle endurance change much with age?
NO - not if you maintain exercise
Muscle power in older adults
-Loss of power is greater than strength due to loss of type IIB fibers
Best types of exercise for baby/young child
Short bouts of exercise with frequent rest breaks
As childhood progresses: increase the bout of activity time, introduce more power activities, but understand you won’t get greatest response of IIb fibers until adolesence
Endochondroal bone growth
- rapid bone growth through childhood
- completed at adolescence (closure of growth plates)
- increased risk for epiphyseal and apophyseal injuries
secondary ossificiation centers appear in
endochondral bone growth
endochondral bone growth is stimulated by stress/loading on bone
- weight bearing
- muscle activity
epiphysis
stimulated by weight bearing
Apophysis
- growth zone at site of muscle attachment
- results in change of bone shape
- stimulated by a muscle pull
Mechanostat theory
How mechanical input is used to develop effective load-bearing bone
- size
- shape
- density
As mechanical strain is placed upon bone by muscle or gravity, the bone adapts to effectively support the body
Nutritional, hormonal, and behavioral factors are also considered
Endochondral ossification happens first in the
diaphysis
Endochondral ossification happens second in the
epiphysis
Appositional bone growth
- occurs throughout life
- stimulated by weight bearing and muscle pull
- increases diameter of bone; reduction in cortical thickness, increase in marrow cavity diameter
50% of peak bone mass by
10 years of age
90% of peak bone mass by
20 years of age
architectural changes in bone with aging
- fibers are more longitudinal
- osteons shorter
- haversian canal wider
- increased mineral deposition; cancellous bone
- increased cross linkage and rearrangement of collagen
