A patient has suffered a cerebral hemorrhage that has caused dysfunction of the precentral gyrus of his right cerebral cortex. As a result:
a. He cannot voluntarily move his left arm or leg.
b. He feels no sensation on the left side of his body.
c. He feels no sensation on his right side.

Verified step by step guidance

1. Step 1: Identify the function of the precentral gyrus. The precentral gyrus is the primary motor cortex responsible for voluntary motor control of the contralateral side of the body.
2. Step 2: Understand the lateralization of brain function. The right cerebral cortex controls voluntary movements on the left side of the body, and the left cerebral cortex controls the right side.
3. Step 3: Analyze the symptoms related to motor function. Since the patient cannot voluntarily move his left arm or leg, this aligns with damage to the right precentral gyrus affecting motor control on the left side.
4. Step 4: Consider the sensory symptoms. The precentral gyrus is primarily motor, so loss of sensation (which is processed in the postcentral gyrus) on the left side is unlikely to be caused by damage to the precentral gyrus.
5. Step 5: Conclude which symptoms are consistent with the lesion. The inability to move the left side voluntarily (a) is expected, but loss of sensation on either side (b or c) is not directly caused by precentral gyrus dysfunction.

Key Concepts

Precentral Gyrus and Motor Function

The precentral gyrus, located in the frontal lobe, is the primary motor cortex responsible for voluntary movement control. Damage to this area disrupts motor commands, leading to paralysis or weakness on the opposite side of the body due to the crossing of motor pathways.

Contralateral Control of the Body

Each cerebral hemisphere controls the opposite side of the body. Therefore, injury to the right precentral gyrus affects motor function on the left side, explaining why voluntary movement of the left arm and leg would be impaired.

Distinction Between Motor and Sensory Functions

The precentral gyrus is involved in motor control, not sensory perception. Sensory information is processed in the postcentral gyrus; thus, damage to the precentral gyrus does not cause loss of sensation, only motor deficits.