Aging, disease, and disuse Flashcards
what are the muscle changes with disuse
all of the below are reduced
size (CSA and volume)
max voluntary contraction (MVC)
muscle thickness
pennation angle (greatest changes seen in antigravity muscles - plantar flexors)
fascicle length
why is it tough to study what happens to muscles during aging
lots of variability in studies
hard to control for changes in lifestyle that occur with aging that also contribute to disuse
does the proportion of fast and slow fibres change with aging
no
- however, there are losses in the number of both
- CSA of fibres decreases
does the volume of the muscle change
not necessarily
- but intramuscular fat increases
- gaps between fibres filled with fat (keeps volume the same)
what happens to the amount of ECM during aging
intramuscular connective tissue increases
- can cause older muscle to be stuck in gear
- more ECM = stiffer
what is the difference in gear ratio between healthy and aging muscle
healthy = gear ratio decreases with increase in froce
old = gear ratio stays realtviely constant with changes in force
- ECM prevents shape change and rotation within muscle
what is CP (cerebral palsy)
often caused by white matter lesions in the brain around the time of birth
- often leads to muscle contractures (high passive force), spasticity (high involuntary active force), and muscle weakness
what is spasticity
high resting activation levels
what is the difference in the passive force of single myofibrils in kids with CP
reduced by 50% compared to controls
associated with decreased titin
what is the difference in the passive force of fibre bundles in kids with CP
increased
high stiffness due to high ECM (fibrosis)
what is the result of the overstretched sarcomeres present in kids with CP
contributes to reduced active force
- not enough overlap of actin and myosin for there to be active force production
what occurs in the perimysium that contributes to increased passive force
increased thickness of the perimysium
increased stiffness due to higher ECM content
what occurs after a stroke
often leads to hemiparesis
- weakness and loss of the control of one side of the body
- occurs contralateral to brain lesion
what occurs in paretic muscle compared to the non paretic side
decreased CSA and volume
increased stiffness
increased intramuscular fat/ECM
decreased sarcomeres in series
less increase in pennation angle as the muscle contracts
why do altered regional activation patterns occur after a stroke
loss of descending control to the muscle
causes remodelling at the NM junction
