Chapter 13: The Spinal Cord, Spinal Nerves, and Spinal Reflexes.
CNS – The Spinal Cord, Spinal Nerves & Spinal Reflexes
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Transcript of CNS – The Spinal Cord, Spinal Nerves & Spinal Reflexes
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CNS – The Spinal Cord, Spinal Nerves & Spinal
Reflexes
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Spinal Cord & Spinal Nerves
Spinal cord Truly the pathway between body and mindConducts impulses to and from the brainCarries out spinal reflexes
Spinal nerves31 pairsAll are mixed nerves
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Mixed Nerves?
Dorsal rootsGanglion containing axons of sensory neurons (afferent)
Ventral rootsAll motor fibers (axons) leave the cord by the ventral roots (efferent)
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General Organization
Highly organized, very efficient
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Spinal Reflexes
Rapid, automatic nerve responses triggered by specific stimuli Controlled by spinal cord alone; not the brain
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Gross Anatomy of the Spinal Cord
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The Adult Spinal Cord
About 18 inches (45 cm) long1/2 inch (14 mm) wideEnds between vertebrae L1 and L2
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Bilateral Symmetry
Grooves divide the spinal cord into left and right
Posterior median sulcus:Shallow
Anterior median fissure:deeper groove on anterior side
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Enlargements of the Spinal Cord
Caused by:amount of gray matter in segmentinvolvement with sensory and motor nerves of limbs
Cervical enlargement:nerves of shoulders and upper limbs
Lumbar enlargement:nerves of pelvis and lower limbs
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The Distal End
Conus medullaris: thin, conical spinal cord below lumbar enlargement
Filum terminale:thin thread of fibrous tissue at end of conus medullarisattaches to coccygeal ligament
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Meninges of the Spinal Cord
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The Meninges
Specialized membranes isolate spinal cord from surroundingsSpinal meninges:
protect spinal cordcarry blood supply continuous with cranial meninges
Meningitis:viral or bacterial infection of meninges
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The 3 Meningeal Layers
Dura mater:outer layer of spinal cord
Arachnoid mater:middle meningeal layer
Pia mater:inner meningeal layer
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Spinal Dura Mater
Are tough and fibrousCranially:
fuses with periosteum of occipital boneis continuous with cranial dura mater
Caudally:tapers to dense cord of collagen fibersjoins filum terminale in coccygeal ligament
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The Epidural Space
Between spinal dura mater and walls of vertebral canalContains loose connective and adipose tissueAnesthetic injection site
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Arachnoid Mater
Middle meningeal layerArachnoid membrane:
simple squamous epitheliacovers arachnoid mater
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Inter-Layer Spaces
filled with cerebrospinal fluid (CSF)
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Cerebrospinal Fluid (CSF)
Is found in subarachnoid spaceCarries dissolved gases, nutrients, and wastes Spinal tap:
withdraws CSF
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Pia Mater
Is the innermost meningeal layerIs a mesh of collagen and elastic fibersIs bound to underlying neural tissue
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Spinal Cord Meninges
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Sectional Anatomy of the Spinal Cord
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Consists of….
White matterGray matterGray horns
Posterior gray hornscontain somatic and visceral sensory nuclei
Anterior gray hornscontain somatic motor nuclei
Lateral gray hornsare in thoracic and lumbar segmentscontain visceral motor nuclei
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Spinal cord is so highly organized:
it is possible to predict results of injuries to specific areas
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Spinal NervesThe roots unite into the spinal nerve
Spinal nerves exit through intervertebral foramen
Split into branches, or rami.
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DermatomesSpecific bilateral region of the skin surface monitored by a single pair of spinal nerves
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Nerve PlexusesPlexus = “braid”Nerves supplying the limbs form plexuses when they leave the spinal cord
Cervical plexusBrachial plexusLumbar plexusSacral plexus