Academic Half Day Dec 2008 Haythum O. Tayeb Chapter 9: The Spinal Cord

Outline Review of: Highlights on embryology of the spinal cord Structure of the spinal cord (anatomy) Regional charecteristics Blood supply Functional consideration of the pathways The spinal nerves (input and output) Grey matter columns White matter columns Spinal Reflexes

Embryology of the Spinal Cord

The neural plate and caudal eminence Day 18: Neural plate formation of neuro-ectoderm Caudal portion  cervical, thoracic and lumbar cord. Day 20 (to 42): Appearance of caudal eminence Sacral and coccygeal levels

Neural tube formation Day 21: the edges of the neural plate (neural folds) enlarge posteromedially to meet at midline.

Neural tube formation Neural fusion, starting at the adult cervical spinal cord. Anterior neuropore closure: day 24. Posterior neuropore closure: day 26. Neural crests detach.

Cells of the neural tube Ventricular zone  ependyma of central canal Subventricular zone  macroglia Intermediate zone  basal and alar plates (grey horns) Marginal zone  axonal tracts (white matter)

Neural tube derivatives Basal plates  venral horns. Alar plates  dorsal horns. Interface  intermediolateral column. Neural crest cells  DRG.

Last points Somites: Vertebrae (sclerotomes) Dermatomes (skin and dermis) Myotomes (muscles) Relation of the spinal cord to the vertebral column By end of 1 st trimester: both formed and have equal length Both grow caudally but vertebral column faster Spinal cord seems drawn rostrally. Intervertebral foramina move caudally. Hence the cauda equina, the lumbar cistern…

Structure of the Spinal Cord

Regional Charecteristics

Blood Supply of the Spinal Cord

Functional consideration of pathways

ModalityReceptorsFiber types Exteroceptive (GSA) Pain and temperature Bare nerve endings A δ (thin myelinated) C (non myelinated) Superficial touch Meissner’s Corpuscles Merkel’s receptors Aβ (Medium, myelinated) Proprioceptive (GSA) Proprio- ception Muscle Spindle Golgi Tendon Organ A α (large melinated) Aβ (medium myelinated) Deep touch, Pressure, Vibration Pacinian corpuscles Ruffini ending AβAβ Interoceptive (GVA) Viscero- sensory Visceral receptors for nociceptive stimuli C

Grey Matter Laminae

The white matter Tracts Ascending Descending Propriospinal

White matter - Ascending tracts Posterior column tracts The anterolateral system Spino- cerebellar tracts Posterior: from Clark’s (dorsal) nucleus (lamina 6,7) Anterior: from “spinal border cells” (lamina 5-8)

Posterior column tracts (gracile and cuneate fasciculi) T6

The anterolateral system Spinothalamic Spinomesencephalic (spinotectal, spinoperiaqueductal) Central pain modulation Spinoreticular fibers Arousal with pain Spinohypothalamic Autonomic and limbic responses to pain

The anterolateral system

White matter – Descending Tracts Lateral Faniculus Lateral corticospinal tracts Rubrospinal Reticulospinal Fastigiospinal Raphespinal Hypothalamospinal Anterior Faniculus Anterior corticospinal tract Vestibulospinal tracts Retiulospinal tracts Medial longitudinal fasciulus

Lateral corticospinal tract

Anterior corticospinal tracts

Rubrospinal tract Present in cervical levels Stimulates flexor tone and inhibits extensor tone Possible role in decorticate flexor posturing Uncertain role in humans

Reticulospinal and tectospinal tracts Reticulospinal: uncrossed Pontine (anterior faniculus) Medullary (lateral faniculus) “Extensor tracts” Tectospinal: direction of head and eye movements

Vestibulospinal tracts Lateral (uncrossed) Medial (bilateral) Extensor

Spinal Reflexes

Muscle Stretch Reflex

Flexor reflex

Crossed extension reflex

Quick clinical refresher - 2 slides

Spinal cord syndromes

Spinal Cord Syndromes

In conclusion The spinal cord develops from the caudal portion of the neural plate and the caudal eminence. The structure of the spinal cord differs according to the level due to the varying degrees of grey and white matter The spinal cord constitutes the major conduit and a relay station from and to the brain, conveying afferent and efferent somatic and visceral information. The spinal cord also functions in spinal reflexes Knowledge of the various pathways of the spinal cord is both fun and important in localization in clinical neurology.

Thanks for listening!!

References Haines Blumenfeld Snell’s neuroanatomy Gray’s anatomy