What is secreted by sebaceous glands?

Sensory information from the body is transmitted to the central nervous system through afferent nerve pathways. In many of these pathways, sensory fibers decussate (cross over) to the opposite side of the spinal cord or brainstem before reaching the cerebral cortex. This organization is important for integrating sensory input with motor control and higher brain processing. The result is a contralateral representation of the body in the brain, meaning each hemisphere processes sensory input from the opposite side of the body.

A. Brain cannot tell from which side of the body a sensory impulse originated: the brain is highly organized in its processing of sensory input and can precisely localize the origin of stimuli. Even though sensory fibers cross over, the central nervous system maintains a detailed somatotopic map of the body (e.g., sensory homunculus). This allows accurate identification of the side and location of a stimulus. Crossover does not impair localization.

B. Each cerebral hemisphere receives sensory impulses from its opposite side of the body: most major sensory pathways, such as the spinothalamic and dorsal column-medial lemniscus pathways, decussate either in the spinal cord or brainstem. As a result, the left hemisphere processes sensory input from the right side of the body, and the right hemisphere processes input from the left side. This contralateral organization is a fundamental principle of neuroanatomy and allows coordinated integration of sensory and motor function.

C. Each cerebral hemisphere receives sensory impulses from its own side of the body: This describes ipsilateral processing, which is not the typical arrangement for major sensory pathways. While some limited pathways may remain ipsilateral, most conscious sensory pathways cross to the opposite side of the CNS. This does not reflect the general organization of sensory nerve fibers.

D. Sensory impulses are blocked at the level of the spinal cord: sensory crossover does not block signal transmission. Instead, it allows signals to be redirected to the appropriate contralateral brain region for processing. The spinal cord serves as a conduit and integration center, not a barrier. Therefore, sensory impulses are actively transmitted, not blocked, during decussation.

The marked structure is the sagittal suture, a fibrous immovable joint (synarthrosis) located between the two parietal bones along the midline of the superior skull. It runs anteroposteriorly from the coronal suture anteriorly to the lambdoid suture posteriorly. The sagittal suture plays a key role in skull growth during childhood by allowing expansion of the cranial vault to accommodate brain development. It later ossifies progressively in adulthood, becoming more rigid.

A. Coronal suture: The coronal suture is located between the frontal bone and the paired parietal bones. It runs transversely across the skull from side to side, separating the anterior cranial vault from the superior region. It allows growth of the skull in the anterior-posterior direction during early development. Unlike the sagittal suture, it is not located along the midline but rather forms a horizontal junction.

B. Lambdoid suture: The lambdoid suture is found at the posterior aspect of the skull, where the parietal bones meet the occipital bone. It has a characteristic inverted “V” or lambda shape. It plays a role in posterior cranial expansion during development. Compared to the sagittal suture, it is posterior and not located along the midline of the skull.

C. Squamous suture: The squamous suture is located laterally between the temporal bone and the parietal bone. It is curved and relatively flat, forming part of the lateral skull wall. It allows articulation between these bones and contributes to cranial stability. It is not midline like the sagittal suture and is instead positioned on the sides of the skull.

D. Sagittal suture: The sagittal suture is a fibrous joint located along the midline between the two parietal bones. It extends from the coronal suture anteriorly to the lambdoid suture posteriorly. It is a key growth site during infancy and childhood, allowing expansion of the skull to accommodate brain growth. Since the circled structure lies centrally between the parietal bones, it corresponds to the sagittal suture.