Chapter 13 - Section 13.1 - The Spinal Cord - Before You Go On - Page 483: 4

A stroke in the right cerebral hemisphere can lead to the paralysis of the limbs on the left side of the body due to the way the nervous system is organized. To explain this, we need to understand the basic principles of brain anatomy and how it controls voluntary movement: 1. **Crossed Control:** The human brain is organized in a way that each hemisphere of the brain primarily controls the opposite side of the body. This is known as contralateral control. The right hemisphere primarily controls motor functions and sensory perception for the left side of the body, while the left hemisphere controls the right side of the body. 2. **Cortical Motor Areas:** The primary motor cortex, located in the precentral gyrus of the frontal lobe of each cerebral hemisphere, is responsible for initiating and controlling voluntary muscle movements. The left primary motor cortex controls the right side of the body, and the right primary motor cortex controls the left side of the body. When a stroke occurs in the right cerebral hemisphere, it can damage or disrupt the normal functioning of the right primary motor cortex. This damage may lead to a loss of motor control signals that would normally be sent to the muscles on the left side of the body. As a result: - The right hemisphere's inability to send motor signals to the left side of the body can result in weakness or paralysis in the left limbs. - Additionally, because the left hemisphere is relatively unaffected by the stroke, it can still control the right side of the body, which typically remains functional. In summary, the crossed control of the nervous system means that a stroke in one hemisphere of the brain can affect the motor function of the opposite side of the body. In the case of a stroke in the right cerebral hemisphere, this can result in paralysis or weakness in the left limbs, which is a classic symptom of a stroke affecting the motor cortex. Other stroke-related symptoms may also arise, depending on the location and extent of the damage within the right hemisphere.

A stroke in the right cerebral hemisphere can lead to the paralysis of the limbs on the left side of the body due to the way the nervous system is organized. To explain this, we need to understand the basic principles of brain anatomy and how it controls voluntary movement: 1. **Crossed Control:** The human brain is organized in a way that each hemisphere of the brain primarily controls the opposite side of the body. This is known as contralateral control. The right hemisphere primarily controls motor functions and sensory perception for the left side of the body, while the left hemisphere controls the right side of the body. 2. **Cortical Motor Areas:** The primary motor cortex, located in the precentral gyrus of the frontal lobe of each cerebral hemisphere, is responsible for initiating and controlling voluntary muscle movements. The left primary motor cortex controls the right side of the body, and the right primary motor cortex controls the left side of the body. When a stroke occurs in the right cerebral hemisphere, it can damage or disrupt the normal functioning of the right primary motor cortex. This damage may lead to a loss of motor control signals that would normally be sent to the muscles on the left side of the body. As a result: - The right hemisphere's inability to send motor signals to the left side of the body can result in weakness or paralysis in the left limbs. - Additionally, because the left hemisphere is relatively unaffected by the stroke, it can still control the right side of the body, which typically remains functional. In summary, the crossed control of the nervous system means that a stroke in one hemisphere of the brain can affect the motor function of the opposite side of the body. In the case of a stroke in the right cerebral hemisphere, this can result in paralysis or weakness in the left limbs, which is a classic symptom of a stroke affecting the motor cortex. Other stroke-related symptoms may also arise, depending on the location and extent of the damage within the right hemisphere.