Motor cortex
This region of the brain's outer surface directly controls voluntary movement on the opposite side of the body, and damage here commonly produces the weakness seen in hemiparesis.
The physical effects of a stroke depend heavily on which brain region and blood vessel territory were affected, since different areas of the brain control different combinations of movement, sensation, vision, speech, and cognition.
Recovery is driven substantially by neuroplasticity, the nervous system's ability to reorganize itself by forming new neural connections and, to some degree, recruiting alternative pathways to perform functions previously handled by damaged tissue.
Key structures
Internal capsule and corticospinal tract
This densely packed pathway carries movement signals from the brain to the spinal cord, and even a small area of damage here can produce significant weakness due to how tightly fibers are packed together.
Cerebellum
Damage to this structure, though less common in typical stroke presentations, can produce significant coordination and balance difficulties distinct from muscle weakness.
Basal ganglia
These deep brain structures help regulate movement smoothness and muscle tone, and their involvement can contribute to changes such as spasticity or movement initiation difficulty.
Language areas (Broca's and Wernicke's areas)
Damage to these typically left-hemisphere regions can produce aphasia, affecting speech production, comprehension, or both, depending on the specific area involved.
Peripheral neuromuscular system (secondary effects)
Following the initial brain injury, secondary changes such as muscle shortening, joint stiffness, and deconditioning can develop in the affected limbs without targeted rehabilitation.
Planes & range
Rather than a single joint range, post-stroke assessment typically tracks functional movement quality and range across multiple joints of the affected side, since weakness, spasticity, and altered movement patterns can each limit range differently.
Understanding which brain systems were affected helps explain the specific pattern of physical, speech, or cognitive changes seen after a stroke, and helps guide a rehabilitation program tailored to the individual's particular deficits.