Spinal cord lecture slides-1.pdf

Spinal cord Dr Siobhan McMahon Learning objectives - Understand the surface and internal features of the spinal cord - Understand the blood supply of the spinal cord - Understand the importance of tracts within the spinal cord Spinal cord Cylindrical shape Begins at foramen magnum Continuous wi...

Spinal cord Dr Siobhan McMahon Learning objectives - Understand the surface and internal features of the spinal cord - Understand the blood supply of the spinal cord - Understand the importance of tracts within the spinal cord Spinal cord Cylindrical shape Begins at foramen magnum Continuous with Medulla Average diameter 1-1.5cm Approx. 45cm in length Occupies upper 2/3 vertebral canal of vertebral column Protected by vertebral column, meninges, CSF Spinal cord Terminates at between L1-L2 in adult Terminates near L3 in young child Spinal cord surrounded by vertebral column • • • • • 7 cervical vertebrae 12 thoracic vertebrae 5 lumbar vertebrae 5 sacral vertebrae 4 fused vertebrae - coccyx 3 Meningeal Layers Dura mater Arachnoid Layer Pia Mater Between dorsal and ventral roots - Denticulate ligament A continuation of pia mater Spinal cord enlarged at : Cervical enlargement - origin to brachial plexus (C3-T2) Lumbar enlargement - origin to lumbosacral plexus (L1-S3) Inferiorly spinal cord tapers off into conus medullaris Extension of bundle of nerve roots beyond the cord is called the cauda equina (horse's tail) Filum terminale – a prolongation of pia mater - descends from Conus medullaris to attach to coccyx (anchor) 31 pairs of spinal nerves - Produces external segmentation (31 segments) 8 cervical 12 thoracic 5 lumbar 5 sacral 1 coccygeal Spinal nerves emerge from vertebral canal via intervertebral foramina Transverse section Posterior / Dorsal Spinous process Anterior / Ventral Spinal nerve attached by - ventral / anterior roots (motor) at ventrolateral aspect of spinal cord - dorsal / posterior roots (sensory) at dorsolateral aspect of spinal cord Each root attached to cord by series of rootlets Dorsal roots possess a dorsal root ganglion Dermatomal map Each spinal nerve carries sensory information for a part of the body surface Area of skin supplied by right and left dorsal roots of a single spinal segment Several dorsal roots innervate overlapping areas on skin - sensation lost in one dermatome only when approx 3 adjacent roots injured PNS spinal nerves Sensory information – afferent nerve fibers Bring information to the spinal cord – travel up to brain Motor information – efferent nerve fibers Send information from the spinal cord – out along nerves Somatic efferent Somatic afferent Visceral efferent Visceral afferent Gray matter White matter Spinal cord composed of inner core of Gray matter (nerve cell bodies, glia, blood vessels) - surrounded by outer covering of White matter (nerve fascicles, glia, blood vessels) Posterior / Dorsal Anterior / Ventral Gray Matter • Dorsal / posterior column • Ventral / anterior column • Lateral column (Intermediate zone) - Rexed’s laminae – ten zones In thick sections of spinal cord – nerve cells exhibit a laminar (layered) arrangement True lamination – confined to dorsal horn 10 laminae of Rexed defined in gray matter as a whole x Nerve cell groups in dorsal gray columns Substantia gelatinosa Apex of dorsal gray column throughout cord length Receives afferents related to pain, temp, touch from dorsal root Nucleus proprius Ventral to substantia gelatinosa throughout length Receives fibers from dorsal white columns Senses of position, movement (proprioception) Posterior / Dorsal x Anterior / Ventral Nerve cell groups in dorsal gray columns Nucleus dorsalis (Clarke’s column) Base of dorsal gray column C8 – L3/4 segments Proprioceptive signals – cells give rise to posterior spinocerebellar tract x Nerve cell groups in ventral gray columns Cell columns of lower motor neurons in ventral gray matter supply groups of muscles with similar functions Amount of gray matter present related to amount of muscle innervated at that level Gray matter largest within cervical and lumbosacral enlargements - Innervation of muscles in upper and lower limbs respectively White matter Divided into three regions/columns on each side: • Anterior (ventral) funiculus Between anterior median fissure and anterolateral sulcus • Lateral funiculus Between anterolateral sulcus and posterolateral sulcus • Posterior (dorsal) funiculus Between posterolateral sulcus and dorsal median sulcus White matter • Ascending tracts – carry impulses from pain, tactile, thermal, muscle and joint receptors (exteroeceptive and proprioceptive information) • Descending tracts – descend down from the cerebral cortex and brainstem Involved in control of movement, posture, muscle tone, etc • Intersegmental tracts – fibers carry information from one segment to another, important intersegmental spinal reflexes - Nerve fiber bundles with a common function Arterial supply to the spinal cord Blood is supplied to the spinal cord via THREE arteries: 1) One Anterior (median) spinal artery - Located along the anterior midline of the cord - Supplies most (75%) of the arterial blood supply to spinal cord 2) Two smaller Posterior spinal arteries - Lie on each side of the cord posteriorly - Supplies only 25% of the arterial blood supply to posterior region of spinal cord Posterior spinal arteries - arise directly from vertebral spinal arteries or indirectly from posterior inferior cerebellar arteries Anterior spinal artery - Formed by union 2 branches vertebral arteries Veins of the spinal cord Spinal cord veins drain into 6 longitudinal channels Anterior spinal vein posterior spinal vein Anterolateral veins Posterolateral veins Radicular veins drain into internal vertebral venous plexus Into anterior and posterior Radicular veins