Ageing systems and commands part 1 Flashcards
old ages
> 65 yo
Muscle Mass
Decrease in muscle mass/ cross sectional area (CSA): ◦ ↓ Muscle fibre size (atrophy) and
number (hypoplasia)
Loss of lean body mass greatest in lower limbs
◦ De-training effect?
◦ Greater loss of motor units in legs versus arms?
muscle fibres
Loss of both fibre types occurs, but with different time course:
• Greater loss of Type II fibres up to the late 70s
• >80yrs, Type I fibres also lost: new ‘balance’ between two fibre types reached
•Aged muscles have fewer myofibrils so are smaller & weaker
• Sarcomeres become increasingly disorganised
• Muscle mitochondria are smaller and have reduced quantities of oxidative enzymes
Sarcomere
energy production
• Ageing muscles have reduced energy sources for muscle contraction:
intramuscular fat
Muscles exhibit more fat & fibrosis • ↓ Movement • ↓ Blood circulation • Fat infiltration can ↑ mass to be carried & sustain sarcopenia Adipose Tissue
neural control - motor neurons
Fewer α-motor neurons in the spinal cord
Some muscle shrinkage may represent denervation atrophy
Remaining neurons:
◦ i) produce less acetylcholine
◦ ii) show less efficient synaptic transmission
NMJ
- impaired calcium release and Ca2+ receptor channels
- Impaired dihydropyridine (DHPR) receptor expression
Motor Unit Remodelling
Motor neurons die with increasing age
Selective denervation of fibres within the motor unit
(particularly Type II, fast twitch fibres)
Motor Neuron
Reinervation by axonal sprouting (usually Type I, slow twitch neurons)
Net loss of functional motor units and fibres, but increase in:
motor unit size (fibres dispersed throughout a larger territory) amplitude motor unit action potential
duration of motor unit action potentialMotor Unit Remodel
slow twitch characteristics
Reinervated fibres: • Slower firing rates • Slower to contract • Produce less muscle force • Smaller in size
implications of slow twitch remodelling
Less efficient motor units
• Less precise control of movements
• Less force production
• Slowing of muscle
functional impairements
Loss of Strength
◦ Inability to carry out ADLs (e.g. carry a load) ◦ Major contributor to falls, ↑ dependency
◦ ↓myofibrils, mitochondria, oxidative enzymes
Loss of Power
◦ Inability to generate muscle force at speed
◦ Impaired ability to respond to a threat to balance ◦ Increased risk of falls and fracture
◦ ↓Type II fast twitch fibres
‘Sarcopenia’:
characterised by low muscle mass, low muscle strength, low physical performance
Joint degeneration
Degradation of articular cartilage & subchondral bone Narrowing of joint space Loss of fluid/mineral content (vertebrae) Formation of bony spurs/osteophytes ↓ Bone mass or density (OP)
Sensory Aging
vestibular
vision
hearing
Impaired Vestibular Function
◦ ↓ Ability to enhance/suppress VOR
◦ ↓ Reactivity to rotational stimulation
◦ Balance impairments: Risk factor for falls
Loss of Hearing & Sound Location ◦ Impacts balance/function? Risk of falling?
Restriction of social interaction: ↑ disablement
Shared pathology: vestibular & auditory systems Perceptual effects: ↑ Likelihood of being startled
