Lesson 16 The Spinal Cord and Spinal Nerves I Describe the gross anatomy of the spinal cord a The spinal cord is about 18in 45cm long and 1 2in 14mm wide The spinal cord ends between the L1 and L2 vertebrae b The spinal cord is bilaterally symmetrical Two grooves divide the spinal cord into left and right portions i The posterior median sulcus divides the spinal cord on the posterior side ii The anterior median fissure is a deeper groove on the anterior side c Enlargements of the spinal cord i Enlargements care caused by the amount of gray matter in a segment and the amount of involvement with the sensory and motor nerves of the limbs ii The cervical enlargement consists of the nerves of the shoulders and upper limbs iii The lumbar enlargement consists of nerves of the pelvis and lower limbs d The distal end of the spinal cord i The conus medullaris is a thin conical part of the spinal cord below the lumbar enlargement ii The cauda equina consists of nerve roots extending below the conus medullaris iii The filum terminale is a thin thread of fibrous tissue at the end of the conus medullaris attaching to the coccygeal ligament provides longitudinal support to spinal cord e Is it symmetrical along the entire length i Yes II Explain how spinal nerves are numbered a The spinal cord segments are based on vertebrae where spinal nerves originate The positions of the spinal segments and vertebrae change with age b Cervical nerves are named for their inferior vertebra c All other nerves are named for their superior vertebra III Describe the difference between the ventral and dorsal root a The ventral root contains axons of motor neurons i The cell bodies of the motor neurons that extend axons through the ventral root are located in the gray matter of the spinal cord ii The ventral root carries information away from the CNS b The dorsal root contains axons of sensory neurons i The dorsal root ganglia contains the cell bodies of the sensory neurons ii The dorsal root carries information to the CNS c The dorsal and ventral roots join to form a complete spinal nerve d Mixed nerves carry both afferent sensory and efferent motor fibers IV Describe the meninges covering the spinal cord a The spinal meninges are specialized membranes that isolate the spinal cord from its surroundings c Functions b Spinal meninges are continuous with cranial meninges i Protect the spinal cord ii Carry blood supply d Meningitis is the viral or bacterial infection of meninges Spinal or cerebral meningitis can disrupt CSF flow damaging or even killing neurons and neuroglia e The three meningeal layers i Dura mater the outer layer of the spinal cord 1 Tough and fibrous 2 Cranially the dura mater fuses with periosteum of the occipital bone and is continuous with the cranial dura mater 3 Caudally the dura mater tapers off to a dense cord of collagen fibers joining the filum terminale in the coccygeal ligament 4 The epidural space is located between the spinal dura mater and walls of vertebral canal It contains loose connective and adipose tissue with the adipose tissue acting as a protective padding a The epidural space is the site of anesthetic injection where an epidural block results in a temporary sensory loss and motor paralysis This is typically used at the inferior lumbar sacral region for pain control during childbirth These epidural blocks only affect spinal nerves in the immediate area ii Arachnoid mater the middle meningeal layer 1 The arachnoid mater covered by the arachnoid membrane which is composed of simple squamous epithelia 2 The subdural space is located between the arachnoid mater and the dura mater 3 The subarachnoid space is located between the arachnoid mater and the pia mater It contains a collagen elastin fiber network known as arachnoid trabeculae extending into the filum terminale It is filled with CSF 4 The CSF carries dissolved gases nutrients and wastes A lumbar puncture or spinal tap withdraws CSF iii Pia mater the inner meningeal layer 1 The pia mater is composed of a mesh of collagen and elastic fibers bound to underlying neural tissue 2 Blood vessels serving the spinal cord run along the surface of the spinal pia mater within the subarachnoid space f How is it anchored to prevent lateral movement i Paired denticulate ligaments extend from the pia mater to the dura mater stabilizing side to side movement V Describe the difference between the gray and white matter found in the spinal cord a White matter is superficial containing myelinated and unmyelinated axons i Organization 1 Tracts fasciculi are bundles of axons in white columns that relay information in the same direction a Ascending tracts carry information to the brain b Descending tracts carry motor commands to the spinal cord b Gray matter surrounds the central canal of the spinal cord It contains neuron cell bodies neuroglia and unmyelinated axons Gray matter has projections known as gray horns i The cell bodies of neurons form functional groups called nuclei whereas ganglia are clusters of cell bodies in the PNS 1 Sensory nuclei are located posteriorly dorsally and connect to peripheral receptors effectors 2 Motor nuclei are located anteriorly ventrally and connect to peripheral VI Explain the function of the gray horns of the spinal cord a Posterior gray horns contain somatic and visceral sensory nuclei b Anterior gray horns contain somatic motor nuclei c Lateral gray horns are in thoracic and lumbar segments containing visceral motor nuclei d Gray commissures are axons that cross from one side of the spinal cord to the other before reaching the gray matter VII Explain the function of the white columns of the spinal cord a The posterior white columns lie between posterior gray horns and the posterior median sulcus fissue b The anterior white columns lie between anterior gray horns and the anterior median i The anterior white commissure is an area where the axons cross from one side of the spinal cord to the other side c Lateral white columns are located on each side of the spinal cord between the anterior and posterior columns VIII Describe the connective tissue layers covering the spinal nerves a Each spinal nerve is surrounded by three connective tissue layers that support structures and contain blood vessels b Epineurium c Perineurium d Endoneurium i Outer layer made up of a dense network of collagen fibers i Middle layer that divides the nerve into fascicles axon bundles i Inner layer that surrounds individual axon IX
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