Lesson 16 An Introduction to the Spinal Cord Spinal Nerves and Spinal Reflexes Spinal Reflexes Controlled by spinal cord alone not the brain Rapid automatic nerve responses triggered by Can involve a single spinal segment or multiple specific stimuli segments Figure 13 1 An Overview of Chapters 13 and 14 CHAPTER 14 The Brain Sensory input over cranial nerves Sensory receptors Reflex centers in brain Motor output over cranial nerves Effectors Muscles CHAPTER 13 The Spinal Cord Sensory input over spinal nerves Sensory receptors Motor output over spinal nerves Reflex centers in spinal cord Glands Adipose tissue 13 2 Spinal Cord Gross Anatomy of the Spinal Cord About 18 inches 45 cm long 1 2 inch 14 mm wide Ends between vertebrae L1 and L2 Bilateral symmetry Grooves divide the spinal cord into left and right Posterior median sulcus on posterior side Anterior median fissure deeper groove on anterior side 13 2 Spinal Cord Enlargements of the Spinal Cord Caused by Amount of gray matter in segment Involvement with sensory and motor nerves of limbs Cervical enlargement Nerves of shoulders and upper limbs Lumbar enlargement Nerves of pelvis and lower limbs 13 2 Spinal Cord Gross Anatomy of the Spinal Cord The distal end Conus medullaris Filum terminale Thin conical spinal cord below lumbar enlargement Thin thread of fibrous tissue at end of conus medullaris Attaches to coccygeal ligament Cauda equina Nerve roots ventral and dorsal extending below conus medullaris and into sacrum Figure 13 2 Gross Anatomy of the Adult Spinal Cord Dorsal root Dorsal root ganglion Central canal Posterior median sulcus White matter Gray matter Cervical enlargement Spinal nerve Ventral root Anterior median fissure C3 KEY Spinal cord regions Cervical Thoracic Lumbar Sacral C1 C2 C3 C4 C5 C6 C7 C8 T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12 L1 L2 L3 L4 L5 S1 S2 S3 S4 S5 Cervical spinal nerves Thoracic spinal nerves Lumbar spinal nerves Sacral spinal nerves Coccygeal nerve Co1 Posterior median sulcus Lumbar enlargement Conus medullaris Inferior tip of spinal cord Cauda equina T3 L1 S2 Filum terminale in coccygeal ligament b Inferior views of cross sections through representative segments of the spinal cord showing the arrangement of gray matter and white matter a The superficial anatomy and orientation of the adult spinal cord The numbers to the left identify the spinal nerves and indicate where the nerve roots leave the vertebral canal The adult spinal cord extends from the brain only to the level of vertebrae L1 L2 the spinal segments found at representative locations are indicated in the cross sections Figure 13 2 Gross Anatomy of the Adult Spinal Cord Part 1 of 4 Dorsal root Dorsal root ganglion Central canal Posterior median sulcus White matter Gray matter Cervical spinal nerves C1 C2 C3 C4 C5 C6 C7 C8 Cervical enlargement Ventral root Spinal nerve a The superficial anatomy and orientation of the adult spinal cord The numbers to the left identify the spinal nerves and indicate where the nerve roots leave the vertebral canal The adult spinal cord extends from the brain only to the level of vertebrae L1 L2 the spinal segments found at representative locations are indicated in the cross sections Anterior median fissure C3 b Inferior views of cross sections through representative segments of the spinal cord showing the arrangement of gray matter and white matter Figure 13 2 Gross Anatomy of the Adult Spinal Cord Part 2 of 4 Thoracic spinal nerves T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12 Posterior median sulcus Lumbar enlargement Conus medullaris T3 a The superficial anatomy and orientation of the adult spinal cord The numbers to the left identify the spinal nerves and indicate where the nerve roots leave the vertebral canal The adult spinal cord extends from the brain only to the level of vertebrae L1 L2 the spinal segments found at representative locations are indicated in the cross sections b Inferior views of cross sections through representative segments of the spinal cord showing the arrangement of gray matter and white matter Figure 13 2 Gross Anatomy of the Adult Spinal Cord Part 3 of 4 Lumbar spinal nerves Conus medullaris Inferior tip of spinal cord Cauda equina L1 L2 L3 L4 L5 a The superficial anatomy and orientation of the adult spinal cord The numbers to the left identify the spinal nerves and indicate where the nerve roots leave the vertebral canal The adult spinal cord extends from the brain only to the level of vertebrae L1 L2 the spinal segments found at representative locations are indicated in the cross sections L1 b Inferior views of cross sections through representative segments of the spinal cord showing the arrangement of gray matter and white matter Figure 13 2 Gross Anatomy of the Adult Spinal Cord Part 4 of 4 Inferior tip of spinal cord Cauda equina Sacral spinal nerves S1 S2 S3 S4 S5 Coccygeal nerve Co1 Filum terminale in coccygeal ligament b S2 Inferior views of cross sections through representative segments of the spinal cord showing the arrangement of gray matter and white matter a The superficial anatomy and orientation of the adult spinal cord The numbers to the left identify the spinal nerves and indicate where the nerve roots leave the vertebral canal The adult spinal cord extends from the brain only to the level of vertebrae L1 L2 the spinal segments found at representative locations are indicated in the cross sections 13 2 Spinal Cord 31 Spinal Cord Segments Based on vertebrae where spinal nerves originate Positions of spinal segment and vertebrae change with age Cervical nerves Named for inferior vertebra All other nerves Named for superior vertebra 13 2 Spinal Cord Roots Two branches of spinal nerves 1 2 Ventral root Contains axons of motor neurons Dorsal root Contains axons of sensory neurons Dorsal root ganglia Contain cell bodies of sensory neurons Note the cell bodies of the motor neurons that extend axons through the ventral root are located in the gray matter of the spinal cord 13 2 Spinal Cord The Spinal Nerve Each side of spine Dorsal and ventral roots join To form a spinal nerve Mixed Nerves Carry both afferent sensory and efferent motor fibers Figure 13 3a The Spinal Cord and Spinal Meninges White matter Ventral rootlets of spinal nerve Ventral root Dorsal root Dorsal rootlets of spinal nerve Gray matter Dorsal root ganglion Spinal nerve Meninges Pia mater Arachnoid mater Dura mater a A posterior view of the spinal cord showing the meningeal layers superficial landmarks
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