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 Protect blood vessels and enclose venous sinuses Contain Cerebrospinal fluid Form partitions in the skull Superficial to Deep: Dura Mater, Arachnoid Mater, Pia Mater
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
Arachnoid Mater Middle Meninx Loose covering Does not dip into sulci Subdural Space Subarachnoid space arachnoid villi
Pia Mater (gentle mother) delicate highly vascularized tissue only meninx that clings to brain tissue
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
CSF circulation
Blood Brain Barrier Maintains stable environment for brain bloodborne substances must pass through three layers to reach the fragile neurons 1. endothelium of capillary wall 2. thick basal lamina surrounding each capillary 3. bulbous feet of the astrocytes missing in places underdeveloped in newborns and younger
Traumatic Brain Injuries Leading cause of accidental death in north america coup, countrecoup Concussion Contusion Subdural/Subarachnoid hemorrhage cerebral edema
Cerebrovascular Accidents 3rd leading cause of death in N.A. Most common Nervous system disorder Ischemic strokes Hemorrhagic strokes TIA s
Degenerative Brain Disorders Alzheimer s Disease Parkinson s Disease Huntington s Disease
Check Your Understanding pg 464
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
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
Cross Sectional Anatomy
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
Spinal Cord White Matter Ascending Descending Transverse
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
Ascending Pathways to the Brain First order neurons Second order neurons Third order neurons
Ascending Pathways to the Brain Dorsal Column Medial Lemniscal pathways Spinothalamic pathways Spinocerebellar pathways
Descending Pathways Upper Motor Neurons Lower Motor Neurons
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
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
Spinal cord disorders Spinal cord trauma Flaccid Paralysis Spastic Paralysis Poliomyelitis Amyotrophic Lateral Sclerosis
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Check your understanding page 473