Spinal Cord Morphology - Dr. Aylin AKTAR PDF

The Spinal Cord - Gross Anatomy Extent: From: Level of foramen magnum To: Btwn L1 & L2 vertebrae • Sometimes terminates as high as T12 or as low as intervertebral disc btwn L2 & L3 The Spinal Cord - Gross Anatomy • Cylindrical in shape about 40 - 45 cm long, weighs 30 grams • Roughly cylindric...

The Spinal Cord - Gross Anatomy Extent: From: Level of foramen magnum To: Btwn L1 & L2 vertebrae • Sometimes terminates as high as T12 or as low as intervertebral disc btwn L2 & L3 The Spinal Cord - Gross Anatomy • Cylindrical in shape about 40 - 45 cm long, weighs 30 grams • Roughly cylindrical • Circular/oval in x-section • Occupies superior 2/3rds of vertebral canal → Long vertebral column → Short spinal cord The Spinal Cord - Gross Anatomy • Superiorly, continuous w/ medulla oblongata • Inferiorly, conical, forming the conus medullaris (medullary cone) • Continuous with a fibrous cord called filum terminale which attaches to dorsum of coccyx – made from modified pia mater • Lower part of filum terminale extends down, gains layer of dura & attaches to dorsum of coccyx – coccygeal ligament • Filum terminale connects conus medullaris to back of coccyx • Provides a connection which stabilizes the entire spinal cord. The Spinal Cord - Gross Anatomy • Conus medullaris (1) (medullary cone) • Cauda equina (2) • Filum terminale (3) The Spinal Cord - Gross Anatomy • Cauda equina Termination of dural sac • Filum terminale • Coccygeal ligament Coccygeal ligament Coccyx The Spinal Cord - Gross Anatomy • 31 pairs of spinal nerves attached • After the spinal cord tapers out, the spinal nerves continue to branch out diagonally, forming the cauda equina The Spinal Cord - Gross Anatomy • 2 spindle-shaped intumescences C4 - T1 cervical intumescence L1 - S3 lumbosacral intumescence • Enlarged due to increased number of neurons contributing to innervation of the limbs The Spinal Cord - Gross Anatomy Spinal Meninges • 3 connective tissue coverings • Surround, protect & suspend spinal cord within vertebral canal • Spinal meninges continuous w/ cranial meninges • Carry blood supply • Dura mater: Outer layer • Arachnoid mater: Middle layer • Pia mater: Inner layer The Spinal Cord - Gross Anatomy Spinal Meninges Dura mater: Outer layer Arachnoid mater: Middle layer Pia mater: Inner layer Pia mater : Medieval Latin - "tender mother“ Figure 13–3 The Spinal Cord - Gross Anatomy Spinal Meninges Dura Mater : • Medieval Latin: “hard mother“ • Thickest, outermost membrane • Dense connective tissue • “Durable”: Able to withstand wear, pressure, damage; hard-wearing The Spinal Cord - Gross Anatomy Spinal Meninges Dura Mater : • Spinal dura mater differs from cranial dura: • Spinal dura is a single layer • Cranial dura is bilayer • Cranially: • fuses w/ periosteum of occipital bone • continuous w/cranial dura mater • Caudally: • tapers to dense cord of collagen fibers • joins filum terminale in coccygeal ligament for longitudinal stability Intact dur mater The Spinal Cord - Gross Anatomy Spinal Meninges Arachne: • Greek: “Spider“ • Arachnoid mater: Spider-web like • Thin, transparent, delicate The Spinal Cord - Gross Anatomy Spinal Meninges Filum terminale has 2parts: • Filum terminale internum: Extension of the pia mater after the conus medullaris (L2) which extends approximately to the coccyx • Anchors spinal cord to end of dural sac End of dural sac (S2) • Is opaque white compared to surrounding cauda equina. • Filum terminale externum: Dural part of the filum terminale. Often referred to as the coccygeal ligament Filum terminale externum (Coccygeal ligament) • After the dural sac terminates at S2, the externum envelopes the internum to attach to the coccyx Coccyx Spinal Meninges – Posterolateral View • Pia mater adheres closely to the spinal cord • Blood vessels of the cord lie on surface of the pia Filum terminale filum terminale: pia mater below L1 L1-S2: fil.term.internum S2-coccyx: fil.term.externum Note that: Pia mater terminates (closes) at the inferior limit of spinal cord (L1) Dura mater and arachnoid mater terminates at S2 level. The Spinal Cord - Gross Anatomy Spinal Meninges Epidural Space • Btwn spinal dura mater & walls of vertebral canal • Separates dura from periosteum of the vertebrae • Contains loose connective and adipose tissue • Anesthetic injection site Spinal Meninges – Posterolateral View Epidural space • Contains veins & fat Post. interior vertebral venous plexus Epidural fat Dura mater Spinal Meninges Subarachnoid Space • CSF • Arachnoid extends to S2 vertebra, but spinal cord ends at level of upper lumbar vertebra ➔ Lumbar Cistern formed below L2 vertebra • Lumbar puncture Spinal Meninges Denticulate Ligaments: • Double folds of pia that extend from lateral aspects of cord, penetrate the arachnoid, extend & fuse to inner surface of the dura • Attached on each side of dura as a series of 21 tooth-like extensions • Are extensions of the pia that allow the cord to “float” in the spinal canal • Points of attachment of the dentate ligaments alternate with the points of exit of nerve roots. • Opaque white compared to rootlets & roots of spinal nn Spinal Meninges Denticulate Ligaments: Spinal Cord – Central Canal • Extends throughout length of cord • A.k.a. ependymal canal • Filled w/ CSF • Continuous with ventricular system of brain • Helps transport nutrients & protects by cushioning against impact Spinal Cord Central Canal Sagittal MRI noting a normal central canal (arrows) Spinal Cord - Internal Structure Central Canal • At cervical & thoracic segments, situated nearer anterior (ant 1/3rd) • At lumbar segments in center • In conus medullaris in post. 1/3rd • Lined by ciliated, columnar epithelium, outside of which is an encircling band of gelatinous substance, - central gelatinous substance • Consists mainly of neuroglia (non-neuronal cells), a few nerve cells and fibers Spinal Cord - Internal Structure Terminal Ventricle A.k.a. 5th ventricle or ampulla caudalis • Fusiform, widest part of central canal • Positioned at transition from the tip of the conus medullaris to the origin of the filum terminale Saggital ultrasound scan • Visible in new borns and up to 5 years of age • Regresses during first weeks after birth Axial ultrasound scan The Spinal Cord - Gross Anatomy Fissures & Sulci • Anterior median fissure: Deep longitudinal • Posterior median sulcus: Shallow furrow • Divide spinal cord into R & L halves • R & L half joined by a commissural band of tissue which contains the central canal • Posterolateral sulcus: Lat. to each side of post. median sulcus. Dorsal roots of spinal nerves enter The Spinal Cord - Gross Anatomy Fissures & Sulci Posterointermediate sulcus • In cervical and upper thoracic segments only The Spinal Cord - Gross Anatomy • 31 pairs of spinal nerves attached • 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal • C1-7 exit above corresponding vertebra • C8 exits below C7 vertebra and above vertebra T1 • Thoracic, lumbar, and sacral are then numbered by the vertebra above • In the case of a lumbarized S1 vertebra (aka L6) or a sacralized L5 vertebra, the nerves are typically still counted to L5 and the next nerve is S1 The Spinal Cord - Gross Anatomy Spinal Nerves • Attached to cord by anterior (motor) roots & posterior (sensory) roots • Each root attached to cord by series of rootlets • Each posterior nerve root has a posterior root ganglion (a.k.a. dorsal root ganglion) • Roots penetrate the dura at the intervertebral foramen • The sleeve of dura, which envelops these roots, becomes continuous with the epineurium of the peripheral nerves. The Spinal Cord - Gross Anatomy Spinal Nerves • Spinal nerves are united ventral & dorsal spinal roots, attached in series to the sides of the spinal cord • Spinal ganglia are large groups of neurones on the dorsal spinal roots The Spinal Cord - Gross Anatomy Roots • Ventral root: • Contains axons of motor neurons • Dorsal root: • Contains axons of sensory neurons • Dorsal root ganglia: • Contain cell bodies of sensory neurons The Spinal Cord - Gross Anatomy Spinal Nerves • The dural and arachnoid covering of the dorsal and ventral roots extends outward into the intervertebral foramen as far as the point where the two roots themselves fuse to form a mixed spinal nerve. Spinal Cord - Internal Structure • In transverse sections, s. cord differentiated into: • central core of grey matter • surrounded by an outer covering of white matter. • Grey Matter : • Configured in characteristic H, or butterfly shape • Ventral & dorsal columns, a.k.a. horns • A.k.a. Anterior & posterior columns • Amount of grey matter present at any given level related to amount of muscle innervated at that level ➔ size greatest at cervical & lumbosacral enlargements, which innervate the muscles of upper & lower limb, respectively Spinal Cord - Internal Structure • At T1- L2 levels a small lateral horn is additionally present • R & L half of grey matter connected by the grey commissure • Grey commissure contains central canal • Part of grey commisure ant. to central canal referred to as ant. grey commisure • Part that is post. to central canal referred to as post. grey commisure Spinal Cord - Internal Structure • White matter: Ascending & descending axons • Link spinal cord segments to one another & the spinal cord to the brain. • White matter of R & L sides is continuous across midline through the white commissure which lies anterior to the grey commissure. Spinal Cord - Internal Structure - WHITE MATTER • White matter surrounds central core of grey matter • Composed mainly of myelinated fibres w/neuroglia & blood vessels • Divided into R & L halves, anteriorly by the deep anterior median fissure, & posteriorly by posterior median sulcus • In each half, divided into anterior, posterior & lateral funiculi / white columns Distinguishing Spinal Cord Segments • Rostral regions have more white matter because ascending fibers have accumulated from all cord levels and descending fibers have not yet dispersed to their terminations. Conversely, caudal regions have less white matter. • In regions supplying the limbs and digits (i.e., the cervical and lumbar enlargements), the gray horns are large because they provide a higher density of innervation of skin and muscle. This is because the limbs and digits have increased sensory acuity and discrete motor control. • The lateral horn is present only at thoracic and lumbar levels. • The posterior intermediate sulcus subdivides the posterior funiculus at levels above T6. Distinguishing Spinal Cord Segments • Shape: Cervical sections tend to be wide & squashed looking, like an oval. • Ventral horn enlargement: At segments that control a limb, motor neurons are large & numerous → enlarged ventral horns in 2 places: lower cervical sections (C5-C8) & lumbar/sacral sections. Distinguishing Spinal Cord Segments • Amount of white matter relative to grey matter decreases as you move down the cord • In white matter of cervical cord: All of the axons going to or from entire body • In white matter of sacral cord: Only axons going to or from last few dermatomes - all other axons have "gotten off" at higher levels ➔ sacral cord looks like it has a lot of grey matter – really it has just lost all of the white. Spinal Cord Segments - Summary • Wide flat cord, lots of white matter, ventral horn enlargements = cervical. • Round cord, ventral horn enlargements = lumbar. • Small round cord, almost no white matter = sacral. • And the remaining level, thoracic, has pointed tips which stick out between the small dorsal and ventral horns • This extra cell column is called the lateral horn, or intermediate horn, or the intermediolateral cell column. • It is the source of all of the sympathetics in the body, and occurs only in thoracic sections. Spinal Cord - Internal Structure • In general, neurons situated in dorsal horn are primarily concerned w/ sensory functions • Neurons in ventral horn are mostly associated w/ motor functions Summary The Spinal Cord - Gross Anatomy - Blood Supply Arterial from 2 sources: 1) Longitudinal vessels Arise sup. to cervical portion of cord & descend on surface (a) Ant. spinal a. (single) 75% of cord -Union of 2 aa, from vertebral aa. -Originate in cranium -App. paralell to ant. median fissure (b) Post. spinal aa. – R & L (paired) 25% of cord -Originate in cranium, from terminal branch of each vertebral a. -Descend along posterolateral sulcus The Spinal Cord - Gross Anatomy - Blood Supply 2) Segmental (Radicular) Spinal Aa. • Reinforcement by branches of arteries neighbouring the spinal cord • Branches of: • ascending cervical artery • deep cervical artery • intercostal arteries • lumbar arteries • lateral sacral arteries • These pass thru intervertebral foramen & divide into ant. & post. radicular aa • Have variable anastomoses w/ the spinal arteries & form an arterial vasocorona around the spinal cord. Vasocorona supply peripheral lateral aspect • Artery of Adamkiewicz: Largest ant. segmental medullary artery – L- thoracolumbar The Spinal Cord - Gross Anatomy Blood Supply Artery of Adamkiewicz • Largest ant. segmental (radicular) artery • Arises from L post. intercostal a. (9th to 12th T) • Major supply to lower thoracic & upper lomber parts of spinal cord • A.k.a. Major anterior segmental medullary a. of the lumbar enlargement, Great anterior radiculomedullary a. Great anterior segmental medullary a. The Spinal Cord - Gross Anatomy - To Cauda Equina & Conus Medullaris • Arise from lumbar, iliolumbar, and median & lateral sacral a.a. • Ascending branches from these tributaries supply the conus medullaris • Anterior & posterior spinal arteries coalesce at conus medullaris Blood Supply The Spinal Cord - Gross Anatomy - Blood Supply Venous Drainage Anterior spinal vein: • Runs along ant median fissure Posterior spinal veins • Runs along post median sulcus 4 lateral segmental (radicular) veins (ant & post) • Run behind the nerve roots. • They end in the intervertebral veins 1: Posterior spinal vein – median longitudinal 2: Anterior spinal vein – median longitudinal 3: posterolateral spinal vein 4: radicular (or segmental medullary) vein 5: posterior spinal arteries 6: anterior spinal artery 7: radicular (or segmental medullary) artery • Valveless • Situated in the pia mater • Form an anastamotic network along surface of spinal cord (venous vasocorona) • Drain into the internal and external vertebral plexuses Spinal Cord Venous Drainage External verterbal venous plexus (Epidural) • Consists of ant. & post. plexuses which anastomose freely with each other. • Ant. external plexus lies in front of the bodies of the vertebræ • Post. external plexus partly on post. surfaces of vertebral arches & their processes, & partly between the deep dorsal muscles Spinal Cord Venous Drainage Ant & Post Internal Vertebral Venous Plexus: • Also empties into dural venous sinuses superiorly (vertebral v, sigmoid sinus, occipital sinus) • Also has connections with: • Thoracal, abdomibal, intercostal vv • Ant & post external vertebral venous plexus • Prostatic venous plexus • Pelvis venous plexus The Spinal Cord - Gross Anatomy The Spinal Cord - Gross Anatomy • 2 The Spinal Cord - Gross Anatomy • 3 The Spinal Cord - Gross Anatomy