Effects of Aging on Muscle and Motor Functions

Decline in motor performance with age, characterized by reduced speed and efficiency of movement.

The number of motor neurons in both the spinal cord and muscles decreases significantly with age.

As motor neurons die off, remaining neurons take over the innervation of more muscle fibers, resulting in larger motor units.

Larger motor units translate to a larger amplitude in electromyography (EMG) signals, despite a reduction in motor neuron number.

The gradual loss of muscle mass due to age, primarily affecting the lower limbs more than the upper limbs.

Type I muscle fibers, which are slow-twitch and responsible for endurance, are less affected by age-related muscle loss compared to other fiber types.

Reduction in motor neuron number leads to muscle fiber atrophy (death) or being innervated by a different neuron.

Aging affects motor performance due to changes in muscle mass, motor neuron number, and motor unit size.

The process of aging causes a reduction in hair cell receptors and vestibular nerve fibers, leading to reduced sensitivity to head movements.

Older adults experience increased sensitivity to virtual rotations, especially at frequencies around 1 Hz, which is a crucial range for the vestibular system.

A common age-related eye condition where the central part of the retina deteriorates, leading to reduced visual acuity.

A tiny pit in the retina aligned with the central axis of the lens that provides the sharpest visual detail.

A larger area in the retina surrounding the fovea, vulnerable to age-related damage.

Small, yellow deposits on the retina, particularly in the macula, that can damage photoreceptors and contribute to macular degeneration.

The eye's ability to focus light on the retina can be affected by changes in the eyeball's length or the cornea's curvature, resulting in blurry vision.

The point where light entering the eye is focused, ideally on the retina. If the focus point falls in front or behind the retina, it causes blurriness.

A decrease in the number of hair cell receptors and vestibular nerve fibers in the inner ear with age.

The Vestibulo-ocular reflex (VOR) is a reflex that stabilizes gaze during head movements. It is slightly reduced with age, but the effect is minimized due to central gain enhancement.

A method of measuring eye torsion (twisting) during head movements. Small dots are placed on the white part of the eye (sclera), allowing precise tracking of eye rotation.

A laboratory technique that stimulates the vestibular system directly, bypassing mechanoreceptors, and measuring the VOR. This is used to assess central gain.

The process of the afferent pathway (carrying signals from the sensory organs to the brain) degenerating with age, but at a slower rate compared to the loss of hair cells.

A reflex that helps maintain balance during head movements by adjusting muscle activity. It is also enhanced with age through central gain mechanisms.

A technique for measuring balance responses using electrical stimulation of the vestibular system. Small electrical currents are applied, and muscle activity in the legs is measured.

The range of frequencies at which head movements occur naturally during daily activities.

A condition where distant objects appear clear, but near objects are blurry. This happens because the eyeball is too short or the lens is too flat, causing light to focus behind the retina.

The area of the visual scene from which an individual can process information. It's essential for safe driving, especially in older adults.

The ability to detect vibrations on the soles of the feet. This sensory input plays a crucial role in maintaining balance and preventing falls.

A measure of how stable someone is when standing still. It helps assess the risk of falling in older adults.

A reflex triggered by touch, helping control balance. It becomes weaker with age, contributing to an increased risk of falls.

The tendency to sway more while standing still, primarily in the direction of front to back.

The detection threshold for vibration on the feet, meaning the minimum intensity needed to feel the vibration.

A significant health concern in older adults, often leading to serious injuries, hospitalizations, and even death.

Type I muscle fibers, responsible for slow and sustained contractions, experience the smallest loss (around 20%) compared to other muscle fiber types with aging. This means they are somewhat resilient to age-related decline.

The rate at which motor units (groups of muscle fibers controlled by a single nerve) fire decreases with age. This leads to slower muscle contractions in older adults.

Older muscles have slower twitch contractions compared to younger counterparts. This results in a slower rate of torque (rotational force) development in older adults.

Older adults experience a significant drop (~50%) in maximal contraction rate compared to younger adults. This decline is linked to a lengthening (~30%) of intervals between the initial nerve impulses.

There is a significant loss of hair cell receptors (~40%) and nerve fibers (~40%) in the vestibular system with aging. This system is crucial for balance and spatial orientation.

Despite the significant loss of hair cells and nerve fibers, the vestibulo-ocular reflex (VOR) – which helps stabilize vision during head movements - is only slightly reduced with aging. This is due to central gain enhancement, where the brain compensates for the loss by amplifying the remaining signal.

Central gain enhancement is a mechanism where the central nervous system (CNS) increases the sensitivity of remaining sensory receptors to compensate for age-related losses. This helps maintain functionality despite reduced sensory input.

Central gain enhancement plays a crucial role in maintaining balance and coordination in older adults, despite the significant loss of vestibular hair cells and nerve fibers. This adaptive mechanism helps preserve functional abilities...

A decrease in the number of hair cell receptors and vestibular nerve fibers in the inner ear as we age. This loss is typically around 40%.

The ability to detect and perceive changes in head position and movement, such as rotations or translations, is reduced with age.

The minimum amount of head rotation needed to be detected by the individual. It is typically higher in older adults compared to younger adults, especially at frequencies outside the common range of daily life.

A specific example of central gain enhancement; the brain adapts by amplifying the signal from the vestibular system to make up for the loss of hair cells and nerve fibers. This is particularly noticeable at certain frequencies that are common in daily life.

This is a common frequency range we experience in daily life and the brain is especially good at compensating for losses at these frequencies. This is likely why the difference in perception between age groups is smaller at 1 Hz.

A type of vestibular stimulation that involves rotating the body around a vertical axis. It is used to study the vestibular system.

The direction of the rotation that is being tested on the body.