lecture 6

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Questions and Answers

Which process is associated with sarcopenia?

Improved muscle contractile speed

Increased muscle mass

Loss of skeletal muscle mass (correct)

Enhanced muscle strength

What leads to larger motor units in older individuals?

Motor unit jitter

Increased physical activity

Collateral reinnervation (correct)

Motor unit death

Which factor can attenuate ageing-related motor unit remodeling?

Sarcopenia

Decreased physical activity

Increased muscle contractile speed

Physical activity (correct)

In ageing-related motor unit decline, what is a potential limit on physical activity's capacity?

Slower motor units Signup and view all the answers

What is a characteristic of motor unit jitter in some diseases?

Significantly increased timing variability Signup and view all the answers

Which age group is likely to have a higher number of motor units in the tibialis anterior muscle?

Young controls (~25y) Signup and view all the answers

What is one of the functional consequences of aging in relation to muscle fibers?

Slowed muscle contractile speed Signup and view all the answers

Which type of fiber area increases as a result of decades of aging?

Type I (ST) fibers Signup and view all the answers

What is a contributing factor to sarcopenia and whole muscle strength loss in aging individuals?

Fewer motor units & larger % of Type I fiber area Signup and view all the answers

Which type of muscle fibers are typically associated with slowed contractile response in older adults?

FT/Type II fibers Signup and view all the answers

In terms of fatiguability, which age group generally experiences less fatigue in isometric tasks according to the text?

Older adults Signup and view all the answers

What is one of the factors influencing fatiguability according to the text?

Sex Signup and view all the answers

What is a possible factor contributing to sarcopenia?

Reduced ability to activate knee extensors Signup and view all the answers

What is a characteristic of muscle weakness in old age?

Decreased ability to activate muscle with increasing force requirements Signup and view all the answers

How do old adults differ from young controls in terms of muscle activation?

'Not weak' old adults show no difference in muscle activation compared to young controls Signup and view all the answers

Which neurotransmitter level is NOT decreased in individuals experiencing sarcopenia?

testosterone Signup and view all the answers

What is a consequence of cortical hypo-excitability in the context of muscle function?

'Not weak' old adults exhibit significant reduction in muscle activation Signup and view all the answers

What factors does not cause sarcopenia?

increased testosterone Signup and view all the answers

Study Notes

Aging and Motor Unit Remodeling

A motor unit (MU) consists of a motoneuron and the muscle fibers it innervates
Aging leads to a decline in the number of MUs and an increase in the percentage of Type I (slow-twitch) fibers
Collateral reinnervation: an intact MU can reinnervate fibers orphaned by the death of another MU

Functional Consequences of Aging

Sarcopenia: age-related loss of skeletal muscle mass, strength, and power
Slowed contractile response in older adults
Decreased muscle strength and speed with aging

Number of MUs declines with advancing age, with an accelerated decline after 60 years
Case study: a 92-year-old with a single MU, demonstrating denervation 5 weeks later

Motor Unit Discharge Rate

Motor unit discharge rate (Hz) decreases with age
Average motor unit discharge rates for different muscles (e.g., First Dorsal Interosseous, Biceps Brachii, Triceps Brachii, etc.)

Motor Unit Jitter

Motor unit jitter is increased in some diseases and with aging compared to healthy young adults
Assessing motor unit jitter by overlaying many action potentials and aligning based on the 1st muscle fiber

Estimates of Motor Unit Numbers

Estimates of motor unit numbers in male tibialis anterior of young, older, and masters runners
Number of motor units decreases with age, with some attenuation in masters athletes

Take-Home Points

Sarcopenia is an age-related loss of skeletal muscle mass, strength, and power with central and peripheral components
Motor unit death and collateral reinnervation lead to larger and perhaps slower motor units
Physical activity can attenuate age-related motor unit remodeling, but may have limitations in very old age

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Description

Test your knowledge on identifying motor unit jitter in muscle fibers based on various research studies. Questions cover topics such as diseases affecting motor unit jitter, aging effects, and alignment techniques for muscle fiber action potentials.