A stroke occurs when blood flow to a part of the brain is interrupted. This interruption can happen either due to a blocked blood vessel (ischemic stroke) or bleeding within the brain (hemorrhagic stroke). When brain cells are deprived of oxygen and nutrients, they die, impacting abilities controlled by that region. Since the brain controls all bodily functions, including movement, a stroke can profoundly affect the muscular system.
The Brain-Muscle Connection
The brain orchestrates all voluntary muscle movements through a complex network of signals. The motor cortex, located in the frontal lobe of the brain, initiates these movements. Electrical signals from the motor cortex travel down specialized pathways, such as the corticospinal tract, through the brainstem and spinal cord.
These signals then reach motor neurons in the spinal cord, which transmit impulses directly to the muscles. This intricate communication pathway tells muscles when to contract or relax, enabling coordinated and precise movements. This system enables movements from walking to delicate hand movements.
Immediate Muscular Impairments
A stroke directly impacts the muscular system by damaging the brain areas responsible for motor control. This damage interrupts the nerve signals sent from the brain to the muscles. This results in a loss of voluntary control over affected muscles.
Initial effects include muscle weakness (paresis) or complete paralysis (plegia). These impairments often manifest on one side of the body (hemiparesis or hemiplegia), as one side of the brain controls the opposite side. The severity of these immediate impairments depends on the stroke’s location and extent of brain damage.
Chronic Muscular Changes
Over time, stroke recovery may involve chronic muscular changes. Spasticity is a common development, characterized by muscle stiffness and involuntary spasms. This occurs due to exaggerated reflexes and altered neural signals from the damaged brain, causing muscles to continuously fire or become overactive. Spasticity can make movement difficult and may worsen with faster movements.
Muscle atrophy, or muscle wasting, can also occur. This happens due to disuse of the muscles and altered nerve signals following the stroke. Muscle loss can increase significantly in the months following a stroke, impacting daily activities. If spasticity or prolonged immobility is not addressed, contractures may develop. These are fixed tightenings of muscles, tendons, or skin that prevent normal joint movement.
Restoring Muscular Control
Rehabilitation helps individuals regain or improve muscular function after a stroke. Physical therapy focuses on restoring strength, coordination, and balance through exercises and gait training. Occupational therapy helps individuals relearn fine motor skills and adapt daily activities for increased independence.
Other interventions, like constraint-induced movement therapy, encourage the use of the affected limb by restricting the unaffected one. The brain’s ability to reorganize and adapt, known as plasticity, is harnessed during rehabilitation. Consistent, intensive therapy is important for maximizing recovery and improving muscular control.