Spinal CordThe Spinal Cord & Spinal NervesSlide 3Spinal Cord ProtectionStructures Covering the Spinal CordExternal Anatomy of Spinal CordInferior End of Spinal CordSpinal Cord & Spinal NervesGray Matter of the Spinal CordWhite Matter of the Spinal CordSpinal NervesA Nerve PlexusCervical PlexusPhrenic NerveBrachial PlexusBranches off Brachial PlexusLumbar PlexusBranches of Lumbar PlexusSacral PlexusBranches of Sacral PlexusSciatic Nerve BranchesDermatomes & MyotomesSlide 29Tracts of the Spinal CordLocation of Tracts inside CordFunction of Spinal TractsSlide 33Spinal ReflexesReflex ArcIllustration of the Stretch ReflexIllustration of Tendon ReflexFlexor (withdrawal) ReflexCrossed Extensor Reflex1Spinal CordI. AnatomyII. Physiology2The Spinal Cord & Spinal NervesTogether with brain forms the CNSFunctions1. spinal cord reflexes2. integration (summation of inhibitory and excitatory) nerve impulses3. highway for upward and downward travel of sensory and motor information3Spinal CordI. Anatomy1. Protective Structures2. External 3. Internal4. Spinal Nervesa. Coveringb. Distributionc. DermatomesII. Physiology4Spinal Cord Protection1. vertebral column5Structures Covering the Spinal Cord2. MembraneA. Dura mater - dense irregular CT tubeSubdural space filled with interstitial fluidB. Arachnoid = spider web of collagen fibersA. Subarachnoid space = CSFC. Pia materthin layer covers BVdenticulate ligs hold in place6External Anatomy of Spinal CordFlattened cylinder16-18 Inches long & 3/4 inch diameterIn adult ends at L2In newborn ends at L4Growth of cord stops at age 51. Cervical enlargementupper limbs2. Lumbar enlargementlower limbs7Inferior End of Spinal Cord1. Conus medullariscone-shaped end of spinal cord2. Filum terminalethread-like extension of pia materstabilizes spinal cord in canal3. Caudae equinae (horse’s tail)dorsal & ventral roots of lowest spinal nerves4. Spinal segmentarea of cord from which each pair of spinal nerves arisesFilum terminaleConus medullaris8Spinal Cord & Spinal NervesSpinal nerves begin as roots1. Dorsal or posterior root is incoming sensory fibersdorsal root ganglion (swelling) = cell bodies of sensory nerves2. Ventral or anterior root is outgoing motor fibersPosterior Root(Sensory)Anterior Root(Motor)10Gray Matter of the Spinal CordCentral canal continuous with 4th ventricle of brainGray matter is shaped like the letter H or a butterflycontains neuron cell bodies, unmyelinated axons & dendritespaired dorsal and ventral gray horns lateral horns only present in thoracic spinal cordgray commissure crosses the midline11White Matter of the Spinal CordWhite matter covers gray matterAnterior median fissure deeper than Posterior median sulcusAnterior, Lateral and Posterior White Columns contain axons that form ascending & descending tracts12Spinal Nerves31 Pairs of spinal nervesNamed & numbered by the cord level of their origin1. 8 pairs of cervical nerves (C1 to C8)2. 12 pairs of thoracic nerves (T1 to T12)3. 5 pairs of lumbar nerves (L1 to L5)4. 5 pairs of sacral nerves (S1 to S5)5. 1 pair of coccygeal nervesMixed sensory & motor nerves16A Nerve PlexusJoining of ventral rami of spinal nerves to form nerve networks or plexusesFound in neck, arm, low back & sacral regionsNo plexus in thoracic regionintercostal nn. innervate intercostal spacesT7 to T12 supply abdominal wall as well17Cervical PlexusVentral rami of spinal nerves (C1 to C5)Supplies parts of head, neck & shouldersPhrenic nerve (C3-C5) keeps diaphragm aliveDamage to cord above C3 causes respiratory arrest18Phrenic Nerve19Brachial PlexusVentral rami from C5 to T1Supplies shoulder & upper limbPasses superior to 1st rib & under clavicleAxillary n. = deltoid & teres m.Musculocutaneous n. = elbow flexorsRadial n. = shoulder & elbow extensorsMedian & ulnar nn. = flexors of wrist & hand20Branches off Brachial Plexus22Ventral rami of L1 to L4 Supplies abdominal wall, external genitals & anterior/medial thighInjury to femoral nerve causes inability to extend leg & loss of sensation in thighInjury to obturator nerve causes paralysis of thigh adductorsLumbar Plexus23Branches of Lumbar PlexusNotice: Femoral and Obturator nervesFound anterior and medial to hip joint24Sacral PlexusVentral rami of L4-L5 & S1-S4Anterior to the sacrumSupplies buttocks, perineum & part of lower limbSciatic nerve = L4 to S3 supplies post thigh & all below kneePeroneal nerve injury produces foot drop or numbnessTibial nerve injury produces calcaneovalgus (loss of function on anterior leg & dorsum of foot)25Branches of Sacral Plexus26Sciatic Nerve BranchesNotice: Common Peroneal nerve and Tibial nerve behind the kneeNotice: Sciatica pain extends from the buttock down the leg to the footmay be sign of herniated disc27Dermatomes & MyotomesEach spinal nerve contains both sensory & motor nerve fibersDermatomearea of skin supplied by one spinal nerveoverlap prevents loss of sensation if one damagedsensory anesthesia requires 3 spinal nerves to be blockedSkin on face supplied by Cranial Nerve V29Spinal CordI. AnatomyII. Physiology1. Tracts2. Reflexesa. Stretchb. Tendonc. Flexord. Crossed Extensor30Tracts of the Spinal CordFunction of tracts1. highway for sensory & motor information2. sensory tracts ascend3. motor tracts descend Naming of tractsindicates position & direction of signalexample = anterior spinothalamic tractimpulses travel from spinal cord towards brain (thalamus)found in anterior part of spinal cord31Location of Tracts inside CordMotor tracts Sensory tractspyramidal tract (corticospinal) spinothalamic tractextrapyramidal tract posterior columnspinocerebellar32Function of Spinal Tractstwo-point discrimination, pressure and vibrationpain, temperature, deep pressure33Function of Spinal Tractsvoluntary movements, posture & muscle tone, equilibrium34Spinal ReflexesAutomatic response to change in environmentIntegration center for spinal reflexes is gray matter of spinal cordExamplessomatic reflexes result in skeletal muscle contractionautonomic (visceral) reflexes involve smooth & cardiac muscle and glands.heart rate, respiration, digestion, urination, etcNote: cranial reflexes involve cranial nerves35Reflex ArcSpecific nerve impulse pathway5 components of reflex arc1. receptor 2. sensory
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