After completing this unit, you should be able to: Describe the embryonic development of the spinal cord; describe the gross and microscopic structure of the spinal cord; list the major spinal cord tracts, and classify each as a motor or sensory tract; distinguish between flaccid and spastic paralysis, and between paralysis and paresthesia;. | 12 The Central Nervous System: Part D The Spinal Cord: Embryonic Development By week 6, there are two clusters of neuroblasts Alar plate—will become interneurons; axons form white matter of cord Basal plate—will become motor neurons; axons will grow to effectors Neural crest cells form the dorsal root ganglia sensory neurons; axons grow into the dorsal aspect of the cord Figure White matter Neural tube cells Central cavity Alar plate: interneurons Dorsal root ganglion: sensory neurons from neural crest Basal plate: motor neurons Spinal Cord Location Begins at the foramen magnum Ends as conus medullaris at L1 vertebra Functions Provides two-way communication to and from the brain Contains spinal reflex centers Spinal Cord: Protection Bone, meninges, and CSF Cushion of fat and a network of veins in the epidural space between the vertebrae and spinal dura mater CSF in subarachnoid space Spinal Cord: Protection Denticulate ligaments: extensions of pia mater that secure cord to dura mater Filum terminale: fibrous extension from conus medullaris; anchors the spinal cord to the coccyx Figure Ligamentum flavum Supra- spinous ligament Lumbar puncture needle entering subarachnoid space Filum terminale Inter- vertebral disc T12 L5 Cauda equina in subarachnoid space Dura mater L5 L4 S1 Arachnoid matter Figure Cervical enlargement Dura and arachnoid mater Lumbar enlargement Conus medullaris Cauda equina Filum terminale Cervical spinal nerves Lumbar spinal nerves Sacral spinal nerves Thoracic spinal nerves (a) The spinal cord and its nerve roots, with the bony vertebral arches removed. The dura mater and arachnoid mater are cut open and reflected laterally. Spinal Cord Spinal nerves 31 pairs Cervical and lumbar enlargements The nerves serving the upper and lower limbs emerge here Cauda equina The collection of nerve roots at the inferior end of the vertebral canal Cross-Sectional Anatomy Two lengthwise grooves divide cord into right and left halves Ventral . | 12 The Central Nervous System: Part D The Spinal Cord: Embryonic Development By week 6, there are two clusters of neuroblasts Alar plate—will become interneurons; axons form white matter of cord Basal plate—will become motor neurons; axons will grow to effectors Neural crest cells form the dorsal root ganglia sensory neurons; axons grow into the dorsal aspect of the cord Figure White matter Neural tube cells Central cavity Alar plate: interneurons Dorsal root ganglion: sensory neurons from neural crest Basal plate: motor neurons Spinal Cord Location Begins at the foramen magnum Ends as conus medullaris at L1 vertebra Functions Provides two-way communication to and from the brain Contains spinal reflex centers Spinal Cord: Protection Bone, meninges, and CSF Cushion of fat and a network of veins in the epidural space between the vertebrae and spinal dura mater CSF in subarachnoid space Spinal Cord: Protection Denticulate ligaments: extensions of pia mater that secure cord to dura
