HBF-III LEC 21 Neuroscience Anatomy of Spinal Cord Notes 2025 PDF

Spinal Cord Organization Page 1 of 10 Dennis J. Goebel, Ph.D. Spinal Cord Organization Lecture Objectives I. Describe the anatomic boundaries and features of the spinal cord: wrt size, extent, and vertebral levels....

Spinal Cord Organization Page 1 of 10 Dennis J. Goebel, Ph.D. Spinal Cord Organization Lecture Objectives I. Describe the anatomic boundaries and features of the spinal cord: wrt size, extent, and vertebral levels. II. Describe the surface anatomy of the spinal cord: surface indentations, location of the enlargements, and the structure components that suspend it within the dural sac.. III. Describe the regions (grey and white matter) of the spinal cord in cross sectional views. IV. Describe the individual characteristics of each spinal cord level (cervical, thoracic, lumbar, and sacral) and be able to identify the spinal cord levels based on their characteristics and specific landmarks. Lecture Outline I. Spinal Cord A. Anatomical Boundaries B. Unique extrinsic CNS segmentation C. Spinal Cord enlargements D. Relationship of the spinal cord and anatomical features of the spinal cord with the dural sac. II. Surface anatomy of the spinal cord A. Ventral (anterior) surface of the spinal cord B. Dorsal Surface (posterior) of the spinal cord III. Cross sectional anatomy of the spinal cord A. White mater 1. Defining Funiculi 2. Defining Fasciculi B. Gray matter 1. Defining the dorsal horn, ventral horn and the intermediate zone C. Defining the grey and white commissures D. Somatotopic organization of the anterior grey horns IV. Unique anatomical characterizations of the cervical, thoracic, Lumbar and sacral levels of the spinal cord. Spinal Cord Organization Page 2 of 10 Dennis J. Goebel, Ph.D. I. Spinal Cord A. Anatomical Boundaries 1. Begins at caudal end of medulla, where it transitions into the spinal cord at the plane of foramen magnum. 2. Ends as the Conus medullaris at the interface between Lumbar vertebrae LV1 and LV2. B. The Spinal cord is the only "extrinsically segmented component of the CNS" 1. Gives rise to 31 pairs of spinal nerves (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal). Please review their relationships with the corresponding vertebral pairing (See Figure 1). C. Spinal Cord enlargements (See Figure 1) 1. Cervical enlargement (C5-T1) 2. Lumbosacral enlargement (L2-S3) D. Other components of the spinal cord (See Figure 2 on next page) 1. Lumbar cistern: The physical cord ends as the Conus medullaris at the level of LV1-2. The subarachnoid space defined by the dura sac that extends from LV1-2 to SV2 and is filled with cerebral spinal fluid (CSF). Clinically used as a site for a lumbar puncture to obtain CSF sample. 2. Cauda equina: contains elongated dorsal and ventral roots that give rise to lower lumbar, sacral and coccygeal nerves, that is located within the lumbar cistern. Figure 1 3. Filum terminale: Non-neuronal medial filament that (formed by pia mater), which extends from the conus medullaris to the terminal end of the dura sac. Spinal Cord Organization Page 3 of 10 Dennis J. Goebel, Ph.D. Figure 2: Netter 177 II. Surface Anatomy of the spinal cord A. Ventral (anterior) surface (See Figure 3, Figure 4 on the next page and Figure 8) 1. Anterior median sulcus/fissure 2. Anterior lateral sulcus/fissure (site where ventral spinal rootles (somatic motor) exit the cord) B. Dorsal (posterior) surface (See Figure 3, Figure 4 on next page, and Figure 8 on the last page of these notes) 1. Posterior median sulcus 2. Posterior lateral sulcus (site where dorsal spinal rootless (sensory) enter the cord) 3. Posterior intermediate sulcus (septum): Extends from spinal cord level C1 to spinal cord level T6. See Figure 4 on next page. Figure 3: Moore, Clinical Oriented Anatomy, 3rd Ed.  Spinal Cord Organization Page 4 of 10 Dennis J. Goebel, Ph.D. III. Cross Sectional Anatomy of the Spinal Cord: (Figure 4: taken from cervical level ~C7) A. White Matter: Composed of myelinated axons (ascending and descending) which are stained brown using osmium-tetroxide staining. 1. Funiculi: (Gross descriptive regions): See diagram in Figure 4a & 4b. a. Dorsal funiculus (also called “the dorsal columns”) blue filled region. b. Lateral funiculus (red filled region). c. Anterior funiculus (green filled region). 2. Fasciculi: (defined bundles of axons (tracts) within a funiculus: See Figure 4a & 4b. Fasciculi located within the dorsal funiculus (See Figure 4) a. Fasciculus gracilis (fGr): These are paired columns of white matter that are positioned within the dorsal funiculus. These columns extend the full length of the spinal cord. b. Fasciculus cuneatus (fCu): Paired, and laterally positioned within the dorsal funiculus (Spans CN1-TN6). Figure 4a C. Gray Matter: composed of neurons, glial, axons, and dendrites. 1. Horn or column (see Figure 4a & 4b) a. Dorsal horn: Provides sensory (afferent) input. The dorsal horn is subdivided into 3 regions (See Figure 4a). i. Head (substantia gelatinosa) ii. Neck iii. Base b. Ventral (anterior) horn: Provides (efferent) motor output. Spinal Cord Organization L11 Page 5 of 10 Dennis J. Goebel, Ph.D. c. Inter medial zone (or zona intermedia) containing the region of the lateral horn. i. Lateral horn (also known as the intermediate cell column (See Figure 4a & b). The lateral horn is prominently displayed in cross sections of the thoracic and upper lumbar levels of the cord), and also seen in cross sections of the sacral level of the cord as well. Preganglionic autonomic motor centers reside here as follows: 1. Preganglionic sympathetic motor neurons (at the level of T1-L2 of the spinal cord). 2. Preganglionic parasympathetic motor neurons (pelvic splanchnics, at the level of S2-S4 of the spinal cord). D. Commissures (See Figure 4 on previous page) 1. Ventral white commissure (contain heavily-myelinated axon fibers that cross to the opposite side through this bundle). See Figure 5b 2. Ventral gray commissure: Contains neuronal cell bodies and lightly myelinated fibers that cross to the opposite side through this bundle (Illustrated in Figure 4a). 3. Dorsal gray commissure: Contains neuronal cell bodies and lightly myelinated fibers that cross to the opposite side through this bundle (Illustrated in Figure 4a). E. Somatotopic Organization of the Anterior (Ventral) Horn (See Figure 5, on the next page) 1. Somatotopic arrangement of motor neurons within the ventral horn are diagramed in Figure 5a (on the next page). Motor neurons within the ventral horns are somatotopicly arranged within the grey matter of the ventral spinal cord into three regions (Flexors, Extensors and Axial (Trunk) musculature) and mapped to the body. Figure 5a illustrates the mapping of the cervical cord to the upper limb. Figure 5b (on the next page) is a cross-section though the lumbar sacral enlargement, which maps out the lower motor neurons to: flexors, extensors and axial musculature. a. Medial-axial muscles (left side of the body: Figure 5a & b, on the next page). b. Lateral-appendicular muscles (left side of the body: Figure 5a, on the next page). c. Dorsal-flexors (right side of Figure 5a & 5b, on the next page). d. Ventral-extensors (right side of Figure 5a & 5b, on the next page).  Spinal Cord Organization L11 Page 6 of 10 Dennis J. Goebel, Ph.D. Cervical enlargement Figure 5a Figure 5b IV. Regional variation of the 4 levels of the spinal cord: Cross sectional anatomy of the cervical, thoracic, lumbar, and sacral spinal cord can be identified by their individual characteristics as follows. A. Cervical Level (See Figure 6A, on page 7) 1. Oval shaped and large diameter. 2. Large amount of gray matter (resulting from motor neurons for the upper limbs making up the cervical enlargement). 3 Large amount of white matter. 4. Contains the posterior (dorsal) intermediate sulcus and septum, spanning spinal cord segments C1-T6. B. Thoracic Level (See Figure 6B, on page 7) 1. Spin cord is circular-shape and smaller in diameter than the cervical cord. 2. Decreased area of gray matter compared to the cervical level. 3. The ratio of white matter to grey matter is increased in the thoracic cord as compared to the cervical cord. 4. The dorsal horn is longer and narrower than in the cervical cord. 5. Unique characteristics of the thoracic cord: a. Nucleus dorsalis of Clarke (bilaterally located (between spinal segments C8-L2). b Lateral horn (also referred to as the intermediolateral cell column) contains pre-ganglionic sympathetic neurons). c. Posterior intermediate sulcus (T1-T6) Spinal Cord Organization L11 Page 7 of 10 Dennis J. Goebel, Ph.D. b. Posterior lateral sulcus (T1-T12) Figure 6 C. Lumbar Level (See Figure 6C) 1. Large diameter than thoracic cord. 2. More white and gray matter than thoracic levels above, and to the sacral levels below. 3. No posterior intermediate sulcus. 4. Large substantia gelatinosa. Spinal Cord Organization L11 Page 8 of 10 Dennis J. Goebel, Ph.D. D. Sacral Level (See Figure 6D, on previous page) 1. Round shape and small diameter 2. Quadrangular-shaped gray matter 3. More gray matter than white matter 4. Large substantia gelatinosa 5. Intermediolateral cell column area (contains preganglionic parasympathetic neurons). V. The Dorsal Columns (Fasciculus gracilis and Fasciculus cuneatus) A. Primary somatic (and visceral sensory) efferent axons from the cervical, thoracic, lumbar, sacral and coccygeal regions utilize the dorsal columns; in route to the caudal medulla (Dr. Walker will enlighten you on the details of these in a separate presentation shortly). The spinal level contribution to each pair of columns and their relationships to the posterior median, poster intermediate and posterior later sulcus (See Figures 7 & 8) to the and their anatomical boundaries for each pair of columns are as follows. 1. Fasciculus cuneatus (fCu): Contains primary sensory axons from the dorsal root ganglia arising from spinal cord segments C2-T6. The right and left fasciculus cuneatus are positioned lateral to the fasciculus gracilis (See figure 7) and are bounded medially by the posterior intermediate sulcus and laterally by the posterior lateral sulcus (See Figures 7, 8 and 9). Figure 7 Spinal Cord Organization L11 Page 9 of 10 Dennis J. Goebel, Ph.D. 2. Fasciculus gracilis (fGr): Contains primary sensory axons from the dorsal root ganglia arising from spinal cord segments T6-S5 & Co1. The right and left fasciculus gracilis are positioned on the dorsal surface of the spinal cord, medial to the fasciculus cuneatus (See figure 7), and are bounded medially by the posterior median sulcus and laterally by the posterior intermediate sulcus (See Figures 7, 8 Figure 2 and 9). Surface Anatomy of the Spinal Cord (Figure 8) A B Figure 8 Spinal Cord Organization L11 Page 10 of 10 Dennis J. Goebel, Ph.D. Figure 99 Figure 9 Dorsal (Posterior) view of the cervical spinal cord showing the dorsal columns. Rt & L Fasciculus cuneatus (FC) (Columns shaded red) and Rt & L Fasciculus gracilis (FG) shaded green. Dashed white line defines the border between cervical spinal cord below and the medulla of the brainstem above.