ANATOMY OF THE SPINAL CORD in detail.pptx
- 2. SPINAL CORD • 18 INCHES LONG • CYLINDRICAL IN SHAPE • Occupies the upper 2/3rd of the VC. • Stretches from the upper border of the foramen magnum to the IVD between the L1 and L2. • Newborns-extends to the level of L3.
- 3. The tapered inferior end forms conus medullaris. It is connected to the coccyx by a non-neuronal cord called Filum Terminale. When the dorsal and ventral roots of the lower lumbar and sacral segments assume a longer course around the conus medullaris to reach the corresponding intervertebral foramina, the cauda equina is formed.
- 4. • Gives rise to 31 pairs of spinal nerves. • The bundle of spinal nerves extending inferiorly from lumbosacral enlargement and conus medullaris surround the filum terminale and form cauda equina. • Segmented 8 Cervical 12 Thoracic 5 Lumbar 5 Sacral 1 Coccygeal • Has two enlargements: • Cervical Enlargement: supplies upper limbs. • Lumbosacral Enlargement: supplies lower limbs.
- 5. • Due to the differential growth of the vertebral column relative to the spinal cord, the spinal cord segments do not always correspond to the vertebral levels. • Accordingly, the cervical spinal nerves exit above their corresponding vertebrae and the remaining spinal nerves emerge from the vertebral column below their corresponding vertebrae.
- 10. SPINAL MENINGES • is invested by the dura, arachnoid, and the piamater. • The dura mater is comprised of an inner meningeal and an outer endosteal layer. Dense, strong fibrous membrane. • Encloses the spinal cord & cauda equina. • Continuous above with meningeal layer of dura covering the brain. • Ends at the level of S2. • Separated from wall of vertebral canal by the extradural space.
- 11. • Contains loose areolar tissue & internal vertebral venous space. • The outer endosteal layer forms the periosteum of the vertebral canal and the epineurium of the spinal nerves at or slightly beyond the intervertebral foramina. • At the level of the second sacral vertebra the spinal dura joins the filum terminale to attach to the coccyx as the coccygeal ligament.
- 12. • The arachnoid mater is a loose, irregular, and trabecular layer that is continuous with cranial arachnoid mater. • Surrounds the spinal cord without following the sulci. • is pierced by vessels that supply the pia mater. • Separated from pia mater by subarachnoid space. • Ends on filum terminale at level of S2.
- 13. • The pia mater intimately adheres to the spinal cord, giving rise to the dentate ligaments. • These ligaments are triangular extensions that extend to the dura, coursing between the dorsal and ventral roots. • Act as suspensory ligaments for the spinal cord. • Thickened on either side between nerve roots to form the ligamentum denticulatum.
- 14. Cross Section of Spinal Cord • The spinal cord is incompletely divided into two equal parts, anteriorly by a short, shallow median fissure and posteriorly by a deep narrow septum, the posterior median sulcus. • Composed of gray matter in the center • surrounded by white matter supported by neuroglia.
- 15. • Commissures: connections between left and right halves. Gray with central canal in the center White • Roots: spinal nerves arise as rootlets then combine to form roots. • Dorsal (posterior) root has a ganglion • Ventral (anterior) • Two roots merge laterally and form the spinal nerve.
- 16. GRAY MATTER • H-shaped pillar with anterior & posterior gray horns. • United by gray commissure containing the central canal. • Lateral gray column (horn) present in thoracic & upper lumbar segments • Amount of gray matter related to the amount of muscle innervated. • Consists of nerve cells, neuroglia, blood Vessels.
- 17. • Consist of nerve cells & unmyelinated nerve fibers. • H-shaped formed of: Anterior horns: containing motor nuclei. Posterior horns: containing sensory nuclei Lateral horns: containing autonomic cells
- 18. WHITE MATTER • Consists of mixture of nerve fibers, neuroglia and blood vessels. • White color is due to high proportion of myelinated nerve fibers. • The white matter of the spinal cord is arranged in columns/funiculi; anterior, posterior and lateral. • The nerve fibers are arranged as bundles, running vertically through the cord. • A group of nerve fibers (axons) that share a common origin, termination and function form a tract or fasciculus • These tracts are formed by sensory nerve fibers ascending to the brain, motor nerve fibers descending from the brain and fibers of connector neurons. • Tracts are often named according to their points of origin and destination, e.g.Spinothalamic, Cortocospinal tract.
- 19. PATHWAYS IN WHITE MATTER The white matter contains 3 types of nerve fibres: • Ascending (sensory) tracts: carrying sensory impulses from the spinal cord to higher centers. • Descending or efferent tracts: carrying motor or autonomic impulses from higher centres to the spinal cord. • Associative tracts: containing short ascending & descending fibres which coordinate the function of the different regions of spinal cord.
- 22. • Descending pathway • A. Corticospinal Tract • Arises from the cerebral cortex • Pathways: is a large bundle of myelinated axons that descends through the brain stem via a tract called the medullary pyramid and then largely crosses over downward into the lateral white columns.
- 23. • The great majority of axons in the corticospinal system decussate in the pyramidal decussation within the medulla and descend within the lateral corticospinal tract. • These fibers terminate throughout the ventral gray column and at the base of the dorsal column. • - concerned with voluntary, discrete, skilled movements, especially those of the distal parts of the limbs.
- 24. • Ascending Pathways • 1.Lateral Spinothalamic Tract The pain and thermal receptors in the skin and other tissues are free nerve endings. Painful and thermal sensations ascend in the lateral spinothalamic tract. • 2.Anterior Spinothalamic Tract The axons enter the spinal cord from the posterior root ganglion and proceed to the tip of the posterior gray column where they divide into ascending and descending branches. These fibers of the first-order neuron terminate by synapsing with cells in the substantia gelatinosa. Transmit impulses from light touch & pressure receptor.
- 25. • 3. Posterior White Column: Fasciculus Gracilis and Fasciculus Cuneatus The axons enter the spinal cord from the posterior root ganglion and pass directly to the posterior white column of the same side. Here, the fibers divide into long ascending and short descending fibers. These short descending fibers are involved with intersegmental reflexes. For discriminative Touch, Vibratory Sense, and Conscious Muscle Joint Sense.
- 26. DERMATOMES • Dermatome is a segment of skin supplied by one spinal nerve. • Cutaneous areas supplied by adjacent spinal nerves overlap. • There is therefore little or sensory loss after interruption of a single spinal nerve or dorsal root.
- 28. MYOTOMES • Myotomes are used to assess the level of motor function. • Each segmental nerve root innervates more than one muscle, and most muscles are innervated by more than one nerve root.
- 30. EFFECTS OF LESIONS OF THE MOTOR PATHWAYS AT VARIOUS LEVELS • AT THE CEREBRAL CORTEX-localized paralysis eg.Monoplegia. • IN THE INTERNAL CAPSULE-widespread paralysis on the opp half of body-Hemiplegia. • IN THE BRAINSTEM- Above the level of pyramidal decussation-Contralateral Hemiplegia. • IN THE SC- LAT CST-UMN paralysis of muscles on same side of the body. ABOVE C5-Quadriplegia BELOW T1-Paraplegia
- 31. BLOOD SUPPLY OF THE SPINAL CORD • Three longitudinal arteries supply the spinal cord: • an anterior spinal artery • paired posterior spinal arteries. • The anterior spinal artery, formed by the union of branches of the vertebral arteries. • Sulcal arteries arise from the anterior spinal artery and enter the spinal cord through this fissure. • Each posterior spinal artery is a branch of either the vertebral artery or the posteroinferior cerebellar artery. • The posterior spinal arteries commonly form anastomosing channels in the pia mater.
- 32. • The anterior and posterior segmental medullary arteries . • The segmental medullary arteries are located chiefly where the need for a good blood supply to the spinal cord is greatest. • They enter the vertebral canal through the IV foramina.
- 33. VEINS OF THE SPINAL CORD • have a distribution similar to that of the spinal arteries. • There are usually three anterior and three posterior spinal veins . • The veins draining the spinal cord join the internal vertebral (epidural) venous plexus in the epidural space . • The internal vertebral venous plexus communicate with dural sinuses and vertebral veins in the cranium. • The internal vertebral plexus also communicates with the external vertebral venous plexus on the external surface of the vertebrae.