Ageing Effects on Motor Control
Original Editor - Wendy Walker
- Abnormal tone
- Fractionated movement deficits
- Perceptual deficits
- Somatosensory deficits
Motor System Impairments
Muscle tone = the resistance of muscle to passive elongation or stretch.
Hypertonicity, increased muscle tone, occurs as a result of loss of supraspinal inhibition to the spinal cord and is usually caused by damage to either the corticospinal tract or to the parietal lobe (from where 40% of the fibres of the corticospinal tract originate).
Hypotonicity, ie. reduced muscle tone, is defined as a decreased resistance to passive movement, and reduced or absent stretch reflex response.
It occurs as a result of decreased or absent neural drive to the muscles, and is seen in a number of conditions affecting elderly people including degenerative neuromuscular diseases and the early stages of stroke, in addition to peripheral nerve damage.
This is the single most common motor impairment; it is defined as the reduced ability to voluntarily activate the spinal motorneurons. It occurs primarily as a result of damage to the corticospinal system (ie. the motor cortical areas, the corticospinal tract and the spinal cord.
Paresis occurs in a wide range of neurological disorders common in the older population, including stroke, multiple sclerosis and peripheral neuropathy.
This is a lack of coordination between movements and/or body parts, e,g, during gait, and occurs as a result of damage to the cerebellar inputs, outputs, and/or cerebellar structures. Tone is usually reduced and reflexes may be pendular e.g. lower limb oscillates when patellar tendon reflex is tested.
This is primarily associated with Parkinson's and sometimes with dementia, and is characterised by slow movement (bradykinesia) or absence of movement (akinesia) and is usually caused by damage to the basal ganglia. Typically, people with hypokinesia struggle with the onset of movement, and can freeze during movement.
Fractionated movement deficits
Conditions which cause motor impairments frequently also cause sensory impairments.
- Somatosensory loss: this can have either a central or peripheral nervous system origin. The main effect on motor control is a reduction in the accuracy of the ongoing monitoring of movement. In many people with somatosensory loss, there is increased reliance on the visual system to plan and monitor movements.
- Perceptual deficits: eg. "pusher syndrome" where a person who has had a stroke or brain injury pushes with the unaffected limbs toward the affected side.
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