Upper Motor Neuron (UMN) lesions Flashcards
Adaptive physiological changes to muscle that occur after brain lesion
> Loss of fx motor units.
Changes in muscle fibre type and size.
Length-associated changes, including reduction in muscle fascicle length, with shortened muscle fibre and contracture.
Cellular atrophy that may be load dependent.
Changes in muscle mechanical properties including increased muscle stiffness.
Increased sensitivity of muscle spindles in short, stiff muscles.
Proliferation of extracellular connective tissue with increased amount of collagen associated with resistance to passive stretch, muscle stiffness and contracture.
Increased connective tissue reduces muscle compliance and increases the spindles’ responses to stretch.
Increased intramuscular fat.
Changes in muscle metabolism such as reduced oxidative capacity.
Reduced capillary density compatible with endurance de-training or inactivity.
Major impairments interfering with functional motor behaviour
> Impaired muscle activation and weakness.
> Impaired motor control including slowness of movement.
> Prolonged rise to peak force.
> Adaptive changes to muscles and other soft tissues.
Summary points
> Major primary impairments are failure to activate motor units due to disruption of the corticospinal pathway, resulting in reduced ability to generate and time muscle forces and to control synergic (intersegmental) muscle coordination. They are the major cause of functional disability.
> Secondary adaptations to immobility and disuse are structural and fx changes to muscle, including increased intrinsic stiffness, reduced extensibility, contracture and increased sensitivity of muscle spindles.
> The functional effects of spasticity (reflex hyperactivity) are unclear. No relationship has been found between spasticity and extent of motor disability. Decreasing hyperreflexia does not result in improved fx. Strength training and exercise do not increase spasticity.
> Repetitive active and task-specific exercise and fx strength training can increase fx strength and fx performance, decrease spasticity and muscle stiffness and actively preserve the length of muscle.
