Nervous System:Spinal Cord and Spinal Nerves(Chapter 13)Lecture MaterialsforAmy Warenda Czura, Ph.D.Suffolk County Community CollegeEastern CampusPrimary Sources for figures and content:Marieb, E. N. Human Anatomy & Physiology 6th ed. San Francisco: Pearson BenjaminCummings, 2004.Martini, F. H. Fundamentals of Anatomy & Physiology 6th ed. San Francisco: PearsonBenjamin Cummings, 2004.Nervous System Organization: CNS = brain and spinal cord PNS = all other neural tissueStructures in the PNS: -Ganglia = collection of somas together inone place -Nerves = bundles of axonsStructures in the CNS: -Center = collection of somas with acommon function -Nucleus = a center with a visible boundary -Neural cortex = gray matter (somas)covering the brain -Tracts = bundles of axons with commonorigins, destinations and functions -Columns/funiculi = large tracts in thespinal cord -Pathways = centers and tracts that link thebrain with the bodySensory pathways: receptor ! CNSMotor pathways: CNS ! effectorSpinal Cord-45cm (18”) from brain to L2-inside vertebral canal (stacked vertebralforamen)-surrounded by CT: Spinal Meninges-support and protect spinal cord -three layers (on handout)Amy Warenda Czura, Ph.D.1SCCC BIO130 Chapter 13 Lecture NotesSpinal cord cross sectional anatomy(on handout)-spinal roots exit vertebral canal throughintervertebral foramen-dorsal and ventral roots combine to formspinal nerveSpinal Nerves-31 pair-exit via intervertebral or sacral foramen-name for location of exit on spine, beginningbetween skull and C1Nerves: C1-C8, T1-T12, L1-L5, S1-S5, Co1-cord and column grow together until age 4; after column continues but cord does not: roots “stretch” to reach foramen-adult: cord ends at L1-L2-“stretched” spinal roots after L2 = cauda equinaLumbar puncture = “spinal tap”, at L3-L4, draw CSF from subarachnoid spaceAmy Warenda Czura, Ph.D.2SCCC BIO130 Chapter 13 Lecture Notes-intervertebral foramen maintained byintervertebral discs between vertebraeHerniated disc = nucleus pulposus rupturesthrough anulus fibrosis, compressesnerves in intervertebral foramen and/orspinal cord in vertebral canalSlipped disc = intervertebral disc distorted ordisplaced, causes pressureNerve structure(on handout)-axons repair if cut if follow original path-severed nerves do not usually repair: axonsdo not line up correctly-spinal nerves branch off cord near to whatthey innervate-cervical and lumbar enlargements of cordhouse cell bodies of motor neuronsfor muscles of appendages-Dermatome = region of skin surfaceinnervated by one pair spinal nerves-most spinal nerves do not go directly totarget: axons from multiple nervesintermingle in a nerve plexus(on handout)Amy Warenda Czura, Ph.D.3SCCC BIO130 Chapter 13 Lecture NotesTrauma and disorders:-often result from damage or pressureParalysis = loss of motor function: disorder ofventral root or anterior gray hornParesthesias = sensory loss: disorder of dorsalroot or posterior gray horn-complete transection results in loss of bothmotor and sensory below injuryParaplegia = sever between T1 and L4, loss oflower limb functionQuadriplegia = sever in cervical, loss of alllimb function (above C5 can kill)Organization of Neural Pathways10 million sensory neurons (receptor to CNS)500 thousand motor neurons (CNS to effector)20 billion interneurons (coordinate sensoryand motor)Interneurons organized into neuronal pools = functional groups with limited input sources (sensory) and output locations (motor)-spread of info organized into neural circuits-5 neural circuits: (on handout)Reflexes = rapid automatic response to specific stimuli-used to maintain homeostasis-simple reflex = sensory perception in, motorresponse out-simple reflexes can be grouped together forcomplex actionsReflex arc = single reflex (on handout)-reflex arcs = negative feedback: action opposes stimulus as form of defense, fast response, but not always coordinatedReflex Classification-four ways to classify (on handout)Superficial somatic reflex = stimuli originate at skin or mucous membraneStretch reflex = stimuli from overstretched tendonresponse delayed by each synapse but capable of more complex outputAmy Warenda Czura, Ph.D.4SCCC BIO130 Chapter 13 Lecture NotesExamples of common spinal reflexes1. Patellar Reflex-monosynaptic stretch reflex-carried on type A fibers-sudden stretch of patellar ligament activatesmuscle spindles ! signal quadricepsgroup to contractMuscle spindle = specialized muscle fiber-constantly signal CNS-relaxed = signal less-stretched = signal more ! threshold, triggerreflex arc-prevent overstretching of muscles andtendons-aid in maintaining upright position2. Withdrawl reflexes-complex polysynaptic spinal reflex-consists of three parts: a. Flexor reflex = flex to withdraw b. Reciprocal inhibition = inhibit extensors c. Crossed extensor reflex = maintain balancePain ! flexor muscles pull limb away ! extensors same limb inhibited toprevent opposition to flexion ! limbs on opposite side extend to provide balance for sudden flexionReflexes automatic but can be impacted byhigher brain centers:-fine tune or combine reflexes-take cues from reflex for coordinatedvoluntary movements-facilitate or inhibit reflexesReflexes serve as diagnostic tool to assess health and function of spinal cord and brain*Individual spinal nerves and theirinnervations and plexus origins will beexamined in detail in lab along with selectreflexes!Amy Warenda Czura, Ph.D.5SCCC BIO130 Chapter 13 Lecture