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CENTRAL NERVOUS SYSTEM, SPINAL NERVES, AND CRANIAL NERVES CHAPTER 10 SPINAL CORD STRUCTURE: PROTECTION AND COVERINGS • Meninges – 3 layers of con tissue around spinal cord and brain – Dura mater – extends to 2nd sacral disc – Arachnoid mater – Pia mater – Subarachnoid space – where cerebrospinal fluid circulates Gross anatomy of the spinal cord • • Lower part of brain to 2nd lumbar vertebrae Cauda equina – Nerves of lumbar, sacral, coccygeal regions of the spinal cord • Cervical enlargement – Nerves supply upper limbs • Lumbar enlargement – Lower limbs • • Each of 31 spinal segments give rise to a pair of spinal nerves Anterior median fissure and posterior median sulcus divide the spinal cord into right and left halves – White matters surrounds H shaped gray matter – Central canal – contains cerebrospinal fluid Internal structure of the spinal cord • Gray matter –cell bodies, dendrites, unmyelinated axons, axon terminals, neuroglia – Anterior horns – cell bodies Somatic motor neurons – Posterior gray horns – somatic and autonomic sensory neurons – Lateral gray horns – only in upper lumbar, sacral, thoracic segments; cell bodies of autonomic motor neurons Continued • White matter: myelinated axons – Columns – 1 or more tracts with bundles of axons • Sensory (ascending) tract • Motor (descending) tract • Name of tract indicates position in white matter, where it begins and ends, direction of impulse • Ex: anterior spinothalamic tract Spinal nerves • Roots – connect each spinal nerve to a section of the cord – Posterior root – contains only sensory axons • posterior root ganglion cell bodies sensory neurons – Anterior root – axons of somatic motor neurons and autonomic motor neurons – sensory and motor axon = mixed nerve • 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal Spinal nerve coverings • Endoneurium – individual axon • Fascicles – groups of axons wrapped in perneurium • Epineurium – covering over entire nerve fuses with dura mater of spinal meninges Plexuses • passes through it intervertebral foramen it divides into branches • form networks by joining with adjacent nerves = plexuses – From here nerves bearing names of the region they supply or course they take • Cervical – skin, muscles of posterior head, upper shoulder, diaphragm • Brachial – upper limbs, several neck and shoulder muscles • Lumbar – abdominal wall, external genitalia, parts of lower limbs • Sacral – buttocks, perineum, lower limbs Intercoastal nerves • T2-T11 do not form plexuses • extend directly to what they supply; – muscles between ribs, abdominal muscles, skin of chest and back Spinal cord functions • White matter – Highway for nerve impulse • Gray matter – Receives, integrates incoming and outgoing info – Spinal Reflexes • Inborn • Learned Reflex arc: patellar reflex Major parts and protective coverings of brain • • • • • Brain stem Diencephalon Cerebrum Cerebellum Protected by cranium and cranial meninges Brian blood supply and the bloodbrain barrier • Needs 20% body’s oxygen supply • Neurons with 0 oxygen for 4min or more permanently damaged • BBB – Protects brain cells from harmful substances, pathogens by preventing passage from blood to brain tissue – Consists Of: • Tightly sealed blood capillaries Cerebrospinal fluid (CSF) • clear • Carries O2, glucose, other need chemicals from blood – neurons, neuroglia and removes wastes, toxics • moves trough subarachnoid space and ventricles – 2 lateral, 3rd, 4th • Made by choroid plexuses • Reabsorbed into blood by arachanoid villi • Drains into superior sagittal sinus Meninges and ventricles Brain stem • Medulla oblongata – Wm: sensory and motor tracts between spinal cord and other parts of brain – Nuclei (gm) • • • • • Cardiovascular center Medullary rhythmicity area Touch and vibration Reflexes 5 pairs of cranial nerves Pons • Wm – Connects parts of the brain to each other • Nuclei (GM) – Signal for volunatary movements that originate in the cerebral cortex are relayed to the cerebellum – Help control breathing – Association with cranial nerves 5-8 Inferior aspect of the brain Midbrain • Connects pons to the diencephalon • Wm – Cerebral peduncles • MN from cerebrum – spinal cord, medulla, pons • SN medulla – thalamus – Nuclei (GM) • Substantia nigra • Right/left red nuclei – axons from cerebrum and cerebellum synapse • Association CN 3-4 • Superior colliculi • Inferior colliculli Midbrain Reticular formation • Small clusters of gray matter mixed with white matter • RAS – Sensory info upward to cerebral cortex = consciousness – Motor – regulating muscle tone