Chapter 13: The Spinal Cord, Spinal Nerves, and Spinal Reflexes13-1 Describe the basic structural and organizational characteristics of the nervous system.- The brain and spinal cord make up the central nervous system, and the cranialnerves and spinal nerves constitute the peripheral nervous system p. 417- The CNS consists of the brain and spinal cord; the remainder of the nervous tissue forms the PNS (Figure 13-1).1. Name the components of the central nervous system and of the peripheral nervous system. The central nervous system is made up of the brain and spinal cord, while cranial nerves and spinal nerves constitute the peripheral nervous system. 2. Define spinal reflex. A spinal reflex is a rapid, automatic response triggered by specific stimuli. Spinal reflexes are controlled in the spinal cord. 13-2 Discuss the structure and functions of the spinal cord, and describe the three meningeal layers that surround the central nervous system. - The spinal cord is surrounded by three meninges and conveys sensory and motor information p. 418. - The adult spinal cord includes two localized enlargements, which provide innervation to the limbs. The spinal cord has 31 segments, each associated with a pair of dorsal roots and a pair of ventral roots. (Figure 13-2). - The filum terminale (a strand of fibrous tissue), which originates at the conus medullaris, ultimately becomes part of the coccygeal ligament. (Figure13-2). - Spinal nerves are mixed nerves: They contain both afferent (sensory) and efferent (motor) fibers. - The spinal meninges provide physical stability and shock absorption for neural tissues of the spinal cord; the cranial meninges surround the brain. (Figure 13-3).- The dura mater covers the spinal cord; inferiorly, it tapers into the coccygeal ligament. The epudural space separates the dura mater from the walls of the vertebral canal. (Figures 13-3, 13-4).- Interior to the inner surface of the dura mater are the subdural space, the arachnoid mater (the second meningeal layer), and the subarachnoid space. The subarachnoid space contains cerebrospinal fluid (CSF), which acts as a shock absorber and a diffusion medium for dissolved gases, nutrients, chemical messengers, and waste products. (Figures 13-3, 13-4). - The pia mater, a meshwork of elastic and collagen fibers, is the innermost meningeal layer. Denticulate ligaments extend from the pia mater to the dura mater. They prevent side-to-side movement of the spinal cord. (Figures13-3, 13-4). - Sulcus, means groove or forrow. There’s a posterior median sulcus, and ventral lateral sulcus, dorsal lateral sulcus where the dorsal rootlets.- What effect does the stimulation of a sensory neuron that innervates an intrafusal muscle fiber have on muscle tone? Stimulation of the sensory neuron will increase muscle tone. 3. Identify the three spinal meninges. The three spinal meninges are the dura mater, arachnoid mater, and pia mater. 4. Damage to which root of a spinal nerve would interfere with motor function? Damage to the ventral root of a spinal nerve, which is composed of both visceral and somatic motor fibers, would interfere with motor function. 5. Where is the cerebrospinal fluid that surrounds the spinal cord located? The cerebrospinal fluid that surrounds the spinal cord is located in the subarachnoid space, which lies beneath the epithelium of the arachnoid mater and superficial to the pia mater. 13-3 Explain the roles of white matter and gray matter in processing and relaying sensory information and motor commands. - Gray matter is the region of integration and command initiation, and whitematter carries information from place to place. P. 422- The white matter of the spinal cord contains myelinated and unmyelinatedaxons, whereas the gray matter contains cell bodies of neurons andneuroglia and unmyelinated axons. The projections of gray matter toward theouter surface of the cord are called horns. (Figure 13-5). - The posterior gray horns contains somatic and visceral sensory nuclei;nuclei in the anterior gray horns function in somatic motor control. Thelateral gray horns, located only in the thoracic and lumbar segments,contain visceral motor neurons. The gray commissures (commissural, ajoining together) contain axons that cross from one side of the spinal cord tothe other (Figure 13-5) p. 422. - The white matter can be divided into six columns (funiculi), each of whichcontains tracts (fasciculi). Ascending tracts (sensory tracts) relay informationform the spinal cord to the brain, and descending tracts (motor tracts) carryinformation from the brain to the spinal cord. (Figure 13-5).6. Differentiate between sensory nuclei and motor nuclei. Sensory nuclei receive and relay sensory information from peripheral receptors. Motor nuclei issue motor commands to peripheral effectors. 7. A person with polio has lost the use of his leg muscles. In which area of his spinal cord would you expect the virus-infected motor neurons to be? The polio virus-infected neurons would be in the anterior gray horns of the spinal cord, where the cell bodies of somatic motor neurons are located. 8. A disease that damages myelin sheaths would affect which portion of the spinal cord? A disease that damages myelin sheaths would affect the columns in the white matter of the spinal cord, because the columns are composed of bundles of myelinated axons. 13-4 Describe the major components of a spinal nerve, and relate the distribution pattern of spinal nerves to the regions they innervate.- Spinal nerves form plexuses that are named according to their level ofemergence from the vertebral canal p. 424- There are 31 pairs of spinal nerves. Each has an epineurium (outermostlayer), a perineurium, and an endoneurium (innermost layer). (Figure 13-6).- Ramus/Rami = a branch- A typical spinal nerve has a white ramus (containing myelinated axons), agray ramus (containing unmyelinated fibers that innervate glands andsmooth muscles in the body wall or limbs), a dorsal ramus (providingsensory and motor innervation to the skin and muscles of the back), and aventral ramus (supplying the ventrolateral body surface, structures in thebody wall, and the limbs). Each pair of nerves monitors a region of the bodysurface called a dermatome. (Spotlight Figure 13-7; Figures 13-8, 13-9)- SENSORY INFORMATION: A spinal