Spinal Cord and Spinal Nerves

Spinal Cord Runs through the vertebral canal Extends from foramen magnum to second lumbar vertebra Regions Cervical Thoracic Lumbar Sacral Coccygeal Gives rise to 31 pairs of spinal nerves All are mixed nerves Not uniform in diameter Cervical enlargement: supplies upper limbs Lumbar enlargement: supplies lower limbs Spinal Cord

Meninges of Spinal Cord Connective tissue membranes Dura mater: outermost layer; continuous with epineurium of the spinal nerves Arachnoid mater: thin and wispy Pia mater: bound tightly to surface Forms the filum terminale anchors spinal cord to coccyx Forms the denticulate ligaments that attach the spinal cord to the dura Spaces Epidural: external to the dura Anesthestics injected here Fat-fill Subdural space: serous fluid Subarachnoid: between pia and arachnoid Filled with CSF

Cross Section of Spinal Cord Anterior median fissure and posterior median sulcus deep clefts partially separating left and right halves Gray matter: neuron cell bodies, dendrites, axons Divided into horns Posterior (dorsal) horn Anterior (ventral) horn Lateral horn White matter Myelinated axons Divided into three columns (funiculi) Ventral Dorsal lateral Each of these divided into sensory or motor tracts Cross Section of Spinal Cord

Cross Section of Spinal Cord 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 dorsal and ventral roots Dorsal and ventral roots merge laterally and form the spinal nerve

Organization of Spinal Cord Gray Matter Recall, it is divided into horns Dorsal, lateral (only in thoracic region), and ventral Dorsal half – sensory roots and ganglia Ventral half – motor roots Based on the type of neurons/cell bodies located in each horn, it is specialized further into 4 regions Somatic sensory (SS) - axons of somatic sensory neurons Visceral sensory (VS) - neurons of visceral sensory neur. Visceral motor (VM) - cell bodies of visceral motor neurons Somatic motor (SM) - cell bodies of somatic motor neurons

Gray Matter: Organization

White Matter in the Spinal Cord Divided into three funiculi (columns) – posterior, lateral, and anterior Columns contain 3 different types of fibers (Ascend., Descend., Trans.) Fibers run in three directions Ascending fibers - compose the sensory tracts Descending fibers - compose the motor tracts Commissural (transverse) fibers - connect opposite sides of cord

White Matter Fiber Tract Generalizations Most consist of a chain of two or three neurons All pathways are paired one on each side of the spinal cord

White Matter: Pathway Generalizations