Nervous System 2 - The Brain and the Cranial Nerves DR WAFAA SHUNNAQ Principal Parts of the Brain The adult brain consists of about 85 billion neurons

Nervous System 2 - The Brain and the Cranial Nerves DR...

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The Brain and the Cranial Nerves DR. WAFAA SHUNNAQ
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Principal Parts of the Brain The adult brain consists of about 85 billion neurons and 10-50 trillion neuroglia; it can be divided into four major regions: i. brain stem (continuous with the spinal cord), which consists of: a. medulla oblongata b. pons c. midbrain ii. cerebellum (posterior to the brain stem) iii. diencephalon (superior to the brain stem), which consists of: a. thalamus b. hypothalamus c. epithalamus iv. cerebrum (spread over the diencephalon like a mushroom cap)
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Protection of the Brain The brain is protected by: i. cranial bones ii. cranial meninges (that are continuous with the spinal meninges): a . outer dura mater consists of an external layer called the periosteal layer and an internal layer called the meningeal layer that are mostly fused together b. middle arachnoid mater c. inner pia mater iii. cerebrospinal fluid
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Extensions of the dura mater three extensions of the dura mater separate parts of the brain: 1 . falx cerebri separates the two cerebral hemispheres 2 . falx cerebelli separates the two cerebellar hemispheres 3. tentorium cerebelli separates the cerebrum from the cerebellum
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Cerebrospinal Fluid The cerebrospinal fluid (CSF): i. is a clear, colorless liquid that protects the brain and spinal cord against chemical and physical injuries; it carries oxygen, glucose, and other needed substances from the blood to neurons and neuroglia ii. circulates through the subarachnoid space and four ventricles which include: a. right and left lateral ventricles located in the two cerebral hemispheres b. third ventricle located between the right and left halves of the thalamus c. fourth ventricle located between the brain stem and the cerebellum
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Cerebrospinal Fluid iii. is formed as blood flows through choroid plexuses located in the walls of ventricles; these networks of capillaries are covered by ependymal cells which produce the CSF from blood plasma by filtration and secretion. iv. does not contain harmful blood-borne substances due to the presence of the blood-cerebrospinal fluid barrier formed by tight junctions located between the ependymal cells v. contributes to homeostasis by performing three major functions: a. mechanical protection by serving as a shock-absorbing liquid in which the brain floats b. chemical protection by providing an optimal chemical environment c. circulation, i.e., by exchanging nutrients and wastes between the blood and adjacent nervous tissue
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Brain Blood Flow and the Blood-Brain Barrier Blood supply to the brain is provided primarily by the internal carotid and vertebral arteries . 2. The blood-brain barrier (BBB) regulates the passage of substances from the blood into brain tissue and thereby protects brain cells from harmful substances and pathogens; it is formed by: i. tight junctions that seal together the endothelial cells of brain capillaries ii . a thick basement membrane that surrounds the brain capillaries iii. processes of astrocytes that press up against the capillaries
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Brain stem Brain stem (continuous with the spinal cord), which consists of: a. medulla oblongata b. pons c. midbrain
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