Spinal Cord Anatomy and Function Quiz

Spinal Cord Anatomy and Function

• Central Nervous System (CNS): Comprised of the brain and spinal cord; spinal nerves connect to the CNS
• Peripheral Nervous System (PNS): Includes 31 pairs of spinal nerves and 12 cranial nerves
• Conus Medullaris: The tapering end of the spinal cord, located between vertebrae L1 and L2
• Lumbosacral Enlargement: Widening of the spinal cord in the lumbar and sacral regions, important for supplying the lower limbs
• Medulla Oblongata: The inferior part of the brainstem, continuous with the spinal cord and located at the foramen magnum
• Meninges: Protective membranes surrounding the spinal cord (dura mater, arachnoid mater, pia mater)
• Dura Mater: Outermost meninx; ends at approximately S2
• Subdural Space: A potential space between the dura and arachnoid mater; it becomes apparent during infection
• Arachnoid Mater: Middle meninx; located above pia mater
• Subarachnoid Space: Contains cerebrospinal fluid (CSF); spinal tap performed here (below L2)
• Pia Mater: Innermost meninx, tightly adheres to the spinal cord; avascular
• Epidural Space: Located outside the dura mater; filled with fat; used for epidural anesthesia during childbirth
• Cerebrospinal Fluid (CSF): Located in the subarachnoid space; produced by the choroid plexus; used in testing for meningitis
• Spinal Tap: A procedure to collect CSF for diagnostic purposes; performed below the level of L2 to avoid injuring the spinal cord
• Vertebrae vs Spinal Nerves: There are 33 vertebrae and 31 pairs of spinal nerves; the numbering system for nerves doesn't directly match that of vertebrae.
• Spinal Nerve Emergences:
  • Cervical nerves emerge superior to corresponding vertebrae
  • Thoracic and lumbar nerves emerge inferior to corresponding vertebrae

Spinal Nerve Formation and Function

• Intervertebral Foramina: Openings where spinal nerves exit the vertebral column
• Mixed Nerves: Spinal nerves carry sensory, motor, and autonomic (sympathetic) signals
• Ventral Roots: Carry motor signals; Do not contain ganglia
• Dorsal Roots: Carry sensory signals; contain the dorsal root ganglion (where sensory neuron cell bodies reside)
• Spinal Nerves: Formed by the combination of ventral and dorsal roots
• Rootlets: Small branches that join to form roots; 14-15 rootlets combine to form a ventral root.
• Ganglia: Clusters of nerve cell bodies in the PNS
• Dermatomes: Specific areas of skin innervated by a single spinal nerve
• Clinical Correlations:
  • Intervertebral Disk Herniation: Protrusion of the nucleus pulposus between vertebrae; affects spinal nerves.
  • Spinal Cord Location for Herniation: e.g., L4-L5 herniation affects the L5 spinal nerve.
  • Spinal Nerves Associated with Specific Body Parts: L4-L5 herniation will affect the L5 spinal nerve; causing pain along the lateral thigh, leg and dorsum of the foot; weakness in dorsiflexion of the foot and toes. L5-S1 herniation will affect the S1 spinal nerve; causing pain along the posterior thigh, calf, lateral foot; weakness in plantarflexion and reduced Achilles reflex.

Autonomic Nervous System

• Sympathetic Nervous System: "Fight-or-flight" response; ganglia located in the thoracic and lumbar regions
• Parasympathetic Nervous System: "Rest and digest" response; ganglia located in different areas
• White Ramus: Pre-ganglionic sympathetic neurons; carries sympathetic signals from the spinal cord to the sympathetic ganglia.
• Gray Ramus: Post-ganglionic sympathetic neurons; relays sympathetic signals from the ganglia to other nerves
• Sympathetic Ganglia: Located in the thoracic and lumbar regions; communicate with spinal nerves through white and gray rami

Cauda Equina

• Cauda Equina: Collection of nerve roots extending from the conus medullaris; responsible for the sensory and motor innervation of the lower limbs and the pelvic organs
• Spinal segments: a segment of the spinal cord that correlates with a spinal nerve.