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Gross Anatomy: Spinal Cord and Meninges Spinal Cord The spinal cord: • occupies the vertebral canal • in infants the spinal cord extends into the sacrum • in the adult the cord extends from the cranial border of the atlas to L2 • level of termination is slightly more superior in flexion Spinal Cord The spinal cord is: • part of the central nervous system. • segmental in nature What is a spinal cord segment? How many segments are there? Note the relationship of the “nerves” to the spinal cord: Dermatomes, Myotomes and Sclerotomes C5 C6 C7 Teres Minor Supraspinatus Rhomboids Infraspinatus Deltoid Teres Major Biceps Brachialis Serratus Anterior Subscapularis Pectoralis Major Pectoralis Minor Coracobrachialis Latissimus Dorsi Anconeus Triceps C8 T1 Spinal Cord Enlargements Cervical Enlargement • the larger and more pronounced of the enlargements • extends from about C3 to T2 Lumbar Enlargement • extends from L1 to S3 Below the lumbar enlargement, the cord tapers to the conus medullaris. “The Heavenly Seven” Nerve Roots Nerve Roots and IV Discs A 18-year-old female presents with pain in her neck and in her right arm. Physical exam reveals pain along the lateral arm, involving the thumb. Grip strength is normal. Her upper limb reflexes on the right side are: • biceps = 1/4 • brachioradialis = 0/4 • triceps = 2/4 What is the most likely etiology for these findings? CLINICAL CONCEPT Muscle Strength is measured on a scale of 0 to 5. > Normal strength is 5/5 > Paralysis is 0/5 Muscle Stretch Reflexes are measure on a scale of 0 to 4. > Normal is 2/4 > PNS lesions are 0 or 1/4 > CNS lesions are 3 or 4/4 Note the position of SPINAL CORD SEGMENTS relative to VERTEBRAL BODIES! Student Dr. Spencer? A compression fracture of the L2 vertebral body would most directly affect what level of the SPINAL CORD? A. T12 B. L1 C. L2 D. L4 E. Cx1 Blood Supply to the Spinal Cord • Branches from the Vertebral Artery - Anterior and Posterior Spinal Arteries • Segmental Spinal Arteries – anterior radicular – posterior radicular – variable segmental medullary arteries Blood Supply to the Spinal Cord Venous Drainage of the Spinal Cord Intervertebral veins: follow arteries and nerves. They are draining spinal veins Spinal Veins: Internal Venous Plexus: communicates with the external spinal venous plexus Venous Drainage of the Vertebral Column External Spinal Venous Plexus: Basivertebral Veins: they drain the vertebral bodies A 66-year-old male presents with the chief complaint of increased urinary frequency, back pain, lower limb weakness and numbness of two weeks duration. A digital rectal exam suggests prostate cancer. A gadolinium-enhanced MRI of the spine reveals: Think/Pair/Share A 12-year-old male presents with the chief complaint of fever, headaches, nuchal rigidity, nausea and lethargy of two days duration. History and physical exam leads to the suspicion of meningitis. You need to sample cerebrospinal fluid. Where is it? What layers do you need to go through to sample CSF? Where should you stick your needle? Spinal Meninges The spinal cord (in fact the entire CNS) is enclosed in three layers of tissue, the meninges. The meninges are from external to internal: 1. Dura mater 2. Arachnoid mater 3. Pia mater Spinal Meninges The dura mater: • is the outermost covering of the spinal cord • is a thick and dense inelastic membrane • is attached around the foramen magnum and bodies of the 2nd and 3rd cervical vertebrae • has tubular extensions for the roots of the spinal nerve as they pass thorough the IV foramen Spinal Meninges The epidural space: • is between the dura and the periostium of the vertebrae • extends to the skull - fluids put into the sacral hiatus can spread to the base of the skull The subdural space: • is a potential space between dura and the arachnoid that contains only a serous fluid • ends at the level of S2 Potential spaces can become REAL spaces when they fill with blood, air, etc. Spinal Meninges The arachnoid is a delicate membrane, that is separated from the dura by a potential subdural space. The arachnoid is not attached to the dura, but held to it by the normal pressure of CSF The subarachnoid space: • is between the arachnoid and the pia • contains cerebrospinal fluid (CSF), blood vessels and connective tissue • surrounds the cord and spinal nerves, ends at the level of S2 Spinal Meninges The arachnoid is only loosely related to the underlying pia mater. • the spinal cord ends at L2 • the dural sac and arachnoid end at S2 As a result there is a large space between the arachnoid and pia in the lumbar region: Lumbar Cistern: Sampling CSF: Lumbar puncture and intracranial pressure:What about a newborn? Lumbar Cistern Lumbar Puncture Spinal Meninges The pia mater: • faithfully invests the spinal cord and brain • is a vascular membrane (holds all the vessels like posterior and anterior spinal artery) Spinal Meninges Denticulate ligaments: • continuous with the pia on the cord, between the dorsal and ventral roots • tooth-like process, 21 in number, stops at the T12 level • serves to stabilize the cord within the dura Spinal Meninges The filum terminale: • is a fine filament of pia and connective tissue that descends from the conus medullaris • descends to the level of S2 where it is joined by dura (filum terminale internum) • descends to coccygeal levels and anchors the spinal cord in the dura sac (filum terminale externum) Spinal Meninges Spinal block: Epidural block: injecting anesthesia outside the dura