Spinal Cord Outline

Spinal Cord Outline - Chapter 13: The Spinal Cord, Spinal...

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Chapter 13: The Spinal Cord, Spinal Nerves, and Spinal Reflexes I. General Organization of the Nervous System, p. 422 In this chapter we will look at the spinal cord and spinal nerves, and their role in spinal reflexes -- the rapid, automatic responses triggered by certain specific stimuli. Spinal reflexes are controlled by the spinal cord alone. The brain is not involved. II. Gross Anatomy of the Spinal Cord, p. 423 The adult spinal cord ends between vertebrae L1 and L2. The groove on the posterior side is the posterior median sulcus . The deeper groove on the anterior side is the anterior median fissure . The amount of gray matter in any segment is related to its involvement with sensory and motor nerves of the limbs, forming enlargements of the spinal cord. The cervical enlargement is associated with nerves of the shoulders and upper limbs; the lumbar enlargement with the pelvis and lower limbs. The thin, conical part of the spinal cord below the lumbar enlargement is the conus medullaris , ending in a thin thread of fibrous tissue (the filum terminale ) which attaches to the coccygeal ligament. The nerve roots which extend below the conus medullaris are the cauda equina . The spinal cord is divided into 31 segments, based on the vertebrae where each spinal nerve originates (although the relationship between the spinal segment and the vertebrae it’s named for changes with age). A cervical nerve is named for the vertebra inferior to it. All other nerves are named for the vertebrae superior to them. Each spinal nerve associated with a segment is divided into 2 branches -- the ventral root , which contains axons of motor neurons, and the dorsal root , which contains axons of sensory neurons. Dorsal root ganglia contain the cell bodies of sensory neurons. On each side of the spine, the dorsal and ventral roots pass out of the vertebral canal through intervertebral foramen and join together to form a spinal nerve . Because they carry both afferent (sensory) and efferent (motor) nerves, spinal nerves are mixed nerves . Spinal Meninges, p.425 The spinal cord is physically isolated from its surrounding structures. Specialized membranes called spinal meninges protect the spinal cord and carry its blood supply. The spinal meninges continue upward into the skull, where they are continuous with the cranial meninges . A viral or bacterial infection of these membranes is called meningitis . The spinal and cranial meninges consist of 3 layers: 1. The Dura Mater The dura mater is the tough, fibrous outer layer of the spinal cord. Cranially, the spinal dura mater fuses with the periosteum of the occipital bone and becomes continuous with the cranial dura mater. Caudally, the spinal dura mater tapers to a dense cord of collagen fibers that joins the filum
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Spinal Cord Outline - Chapter 13: The Spinal Cord, Spinal...

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