ANATOMIA MACROSCÓPICA DA MEDULA ESPINAL - PARTE 2
Understanding Spinal Segments and White Matter
Overview of Spinal Cord Segments
- The presentation discusses cross-sectional representations of spinal cord segments, specifically highlighting cervical segment C5 and lumbar segments L1 to S3.
- It raises the question about variations in white matter across different spinal segments, emphasizing the importance of understanding these differences.
Intumescences and Neuronal Population
- The speaker explains that regions like the cervical and lumbosacral intumescences have a higher neuronal population, leading to thicker anterior and posterior columns in these areas.
- As one moves inferiorly down the spinal cord, there is a noticeable decrease in white matter density segment by segment.
White Matter Density Variation
- The reduction in white matter is attributed to fewer ascending and descending fiber tracts as one approaches lower spinal regions.
- Higher segments contain more fibers projecting from the cortex to the spinal cord or vice versa, indicating greater complexity at upper levels.
Connections with Spinal Nerves
- The discussion transitions to connections between spinal nerves and medullary segments, emphasizing their significance for understanding segmentation.
- Filaments radiculares (root filaments) are introduced as key components connecting medullary segments with peripheral nerves.
Formation of Spinal Nerves
- These root filaments combine to form anterior (ventral) and posterior (dorsal) roots, which then unite to create mixed spinal nerves carrying both sensory and motor information.
- Each spinal nerve consists of an anterior root (motor function) and a posterior root (sensory function), highlighting their dual role.
Implications of Nerve Injury
- An avulsion or rupture near the origin of a spinal nerve can lead to significant sensory and motor repercussions due to its mixed nature.
- This injury may manifest as peripheral lesions affecting both sensory perception and motor control.
Segmental Organization of Medulla
- Each pair of spinal nerves corresponds directly with specific medullary segments; thus, understanding this relationship is crucial for clinical assessments.
- A segment is defined by where radicular filaments connect within the medulla, reinforcing how each segment relates back to its corresponding nerve pair.
Testing Segment Integrity
- To assess integrity within a specific medullary segment, testing associated pairs of spinal nerves is essential.
Medullary Segments and Their Structure
Overview of Medullary Segments
- The spinal cord is formed from pairs of spinal nerves connecting to the medulla, totaling 31 segments.
- These segments are divided into: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal segment.
Cervical Segment Clarification
- There are eight cervical medullary segments despite having seven cervical vertebrae; the first segment emerges between the atlas (C1) and the occipital bone.
- This segment is associated with innervation of posterior neck muscles that facilitate head movement.
Topographical Regions of the Spinal Cord
- The spinal cord is divided into five topographical regions that share names with corresponding vertebral regions.
- These regions include: cervical (8 segments), thoracic (12 segments), lumbar (5 segments), sacral (5 segments), and a single coccygeal segment.
Vertebro-Medullary Topography
Understanding Vertebro-Medullary Relationship
- The term "vertebro-medular topography" refers to the relationship between vertebrae and the spinal cord.
- In adults, the spinal cord does not occupy the entire vertebral canal; it typically ends at L1-L2 level.
Structure of Spinal Cord
- The spinal cord is a cylindrical mass composed of white and gray matter with 31 medullary segments.
- The vertebral canal is formed by overlapping vertebrae from different regions including cervical, thoracic, lumbar, and sacral areas.
Growth Discrepancies Between Spine and Spinal Cord
Adaptations During Development
- During intrauterine life, there’s a near-perfect correspondence between spinal cord length and vertebral column length.
- However, postnatally, bone growth occurs more rapidly than spinal cord growth leading to adaptations in nerve root lengths for proper innervation.
Understanding the Spinal Cord and Its Correspondence with Vertebrae
Observations on Spinal Cord Trauma
- The speaker discusses how the nervous system adapts, referencing a clinical observation of trauma that lacks direct correspondence between vertebrae and spinal cord segments.
- It is noted that there is no one-to-one correlation between vertebral levels and spinal cord segments, which complicates clinical assessments.
Clinical Implications of Spinal Injuries
- A hypothetical scenario is presented where a trauma at vertebra T10 could lead to confusion regarding the corresponding spinal segment due to anatomical differences in growth rates between the spine and spinal cord.
- The speaker emphasizes that the spinal cord does not grow at the same rate as the vertebral column, leading to discrepancies in injury assessment.
Rules for Determining Segmental Correspondence
- An important rule introduced by a clinician involves observing spinous processes to determine corresponding spinal segments through a specific calculation method.
- The process involves adding two to the identified spinous process level to find its related medullary segment, highlighting an innovative approach for clinicians.
Application of Segmental Rules
- The speaker explains how this rule can be applied across different regions of the spine, including cervical (C), thoracic (T), lumbar (L), sacral (S), and coccygeal segments.
- For example, identifying T11 or T12 leads to recognizing lumbar segments L1 and L2 based on established rules for calculating segmental relationships.
Meninges and Protection of the Spinal Cord
- Discussion shifts towards protective structures surrounding the spinal cord—meninges—which consist of three layers: dura mater being the outermost layer.
Meninges and Their Spaces
Overview of Meninges
- The outermost layer of the meninges is called dura mater, which translates to "hard mother." It serves as a protective covering.
- In living individuals, there exists a virtual space filled with cerebrospinal fluid (CSF) between the arachnoid membrane and the dura mater. This space disappears upon death.
- The pia mater, or "soft mother," closely adheres to neural tissue, including the spinal cord.
Structure and Function of Arachnoid Membrane
- The arachnoid membrane has extensions resembling spider legs that connect it to the underlying pia mater.
- There are three main spaces surrounding the spinal cord: epidural space, subdural space, and subarachnoid space.
Epidural Space
- The epidural space lies between the dura mater and the periosteum of the vertebral canal. It contains adipose tissue and veins.
- This area can be visualized as having significant amounts of adipose tissue along with venous plexuses.
Subdural Space
- The subdural space is a potential cavity containing a small amount of cerebrospinal fluid (CSF), which helps cushion structures in this region.
Subarachnoid Space
- The subarachnoid space is larger than both previous spaces and is located beneath the arachnoid membrane above the pia mater.