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The CNS Part II

The CNS Part II. pg. 455-474. Protection of the Brain. Objectives Describe how the meninges, cerebrospinal fluid, and the blood brain barrier protect the CNS. Explain how Cerebrospinal fluid is formed, and describe its circulatory pathway. Meninges. Cover and protect the CNS

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The CNS Part II

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  1. The CNS Part II • pg. 455-474

  2. Protection of the Brain • Objectives • Describe how the meninges, cerebrospinal fluid, and the blood brain barrier protect the CNS. • Explain how Cerebrospinal fluid is formed, and describe its circulatory pathway

  3. Meninges • Cover and protect the CNS • Protect blood vessels and enclose venous sinuses • Contain Cerebrospinal fluid • Form partitions in the skull • Superficial to Deep: Dura Mater, Arachnoid Mater, Pia Mater

  4. Dura Mater (tough mother) • Strongest Meninx • Fibrous bilayer: • Periosteal layer (absent in spinal cord) • Deeper meningeal layer • Fused together except in dural venous sinuses • Dural Septa • Falx Cerebri, Falx Cerebelli, Tentorium Cerebelli

  5. Arachnoid Mater • Middle Meninx • Loose covering • Does not dip into sulci • Subdural Space • Subarachnoid space • arachnoid villi

  6. Pia Mater (gentle mother) • delicate highly vascularized tissue • only meninx that clings to brain tissue

  7. Cerebrospinal fluid (CSF) • Suspends CNS • Reduces brain weight be 97% • Protects CNS from trauma • Similar to blood plasma, but less protein and different ion concentrations • Choroid plexuses

  8. CSF circulation

  9. Blood Brain Barrier • Maintains stable environment for brain • bloodborne substances must pass through three layers to reach the fragile neurons • endothelium of capillary wall • thick basal lamina surrounding each capillary • bulbous feet of the astrocytes • missing in places • underdeveloped in newborns and younger

  10. Traumatic Brain Injuries • Leading cause of accidental death in north america • coup, countrecoup • Concussion • Contusion • Subdural/Subarachnoid hemorrhage • cerebral edema

  11. Cerebrovascular Accidents • 3rd leading cause of death in N.A. • Most common Nervous system disorder • Ischemic strokes • Hemorrhagic strokes • TIA’s

  12. Degenerative Brain Disorders • Alzheimer’s Disease • Parkinson’s Disease • Huntington’s Disease

  13. Check Your Understanding • pg 464

  14. The Spinal Cord • Describe the gross and microscopic structure of the spinal cord. • list the major spinal cord tracts, and classify each as a motor or sensory tract

  15. Gross Anatomy and Protection • Foramen Magnum to L1-L2 Vertebrae level • Major Reflex Center • Composed of Ascending and Descending tracts • Protected by bone, meninges, and CSF • Epidural space, meninges extend to S2. • Conus Medullaris, Cuada Equina, Filum terminale, denticulate ligaments. • 31 Spinal nerves • Cervical and Lumbar Enlargements

  16. Cross Sectional Anatomy

  17. Gray Matter and Spinal Roots • Mirror image lateral gray masses • gray commissure • posterior horns • anterior horns • lateral horns • Ventral roots • Dorsal roots • Dorsal root ganglion • 4 zones • somatic sensory, visceral sensory, visceral motor, somatic motor

  18. Spinal Cord White Matter • Ascending • Descending • Transverse

  19. Neuronal Pathways • All spinal tracts are part of multineuron pathways that connect the brain to the body’s periphery • 4 key generalizations • Decussation • Relay • Somatotopy • Symmetry

  20. Ascending Pathways to the Brain • First order neurons • Second order neurons • Third order neurons

  21. Ascending Pathways to the Brain • Dorsal Column Medial Lemniscal pathways • Spinothalamic pathways • Spinocerebellar pathways

  22. Descending Pathways • Upper Motor Neurons • Lower Motor Neurons

  23. Descending Pathways • Direct (Pyramidal) Pathways • Originate from neurons in the pre central gyro • impulses are sent through the brain stem via large pyramidal (corticospinal) tracts • No synapse until ventral horn motor neurons

  24. Descending Pathways • Indirect Pathways • all other motor pathways • complex, multi synaptic • control axial muscles, coarse limb movements, head, neck, and eye movements • reticulospinal and vestibulospinal tracts maintain balance, rubrospinal tracts control flexor muscles, tectospinal/superior colliculi mediate head movements in response to visual stimuli

  25. Spinal cord disorders • Spinal cord trauma • Flaccid Paralysis • Spastic Paralysis • Poliomyelitis • Amyotrophic Lateral Sclerosis

  26. Study Guide • AandPonline.com

  27. Check your understanding • page 473

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