Anatomy Chapter 14 Notes

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The Brain and Cranial Nerves
Chapter 14 Notes

14.1 Brain Organization, Protection, and Blood Supply
* brain: a portion of the CNS made of neurons and neuroglia * control center for registering sensations and correlating them together and with stored information to make decisions and take action * center for intellect, emotions, behavior and memory * neural tube: brain and spinal cord develop from the ectodermal tube * anterior part expands

* inner part constricts to form three regions
* primary brain vesicles: prosencephalon, mesencephalon, and rhombencephalon * secondary brain vesicles: formed by the subdivided prosencephalon and rhombencephalon * prosencephalon: forebrain that gives rise to the telencephalon and diencephalon and the rhombencephalon * rhombencephalon: hindbrain that develops into the metencephalon and myelencephalon * brain vesicles five rise to the following adult structures: * telencephalon: develops into the cerebrum and lateral vesicles * diencephalon: forms the thalamus, hypothalamus, epithalamus, and third ventricle * metencephalon: becomes the pons, cerebellum, and upper part of fourth ventricle * myelencephalon: forms the medulla and lower part of the fourth ventricle * mesencephalon: gives rise to the midbrain and aqueduct of the midbrain * walls of brain regions form the nervous tissue of the brain * hollow interior of the tube transform into the ventricles (fluid filled spaces) of the brain * protective structures of the brain arise from the expanded neural crest tissue

Major Parts of the Brain
* brain stem: continuous with the spinal cord ad is made of the medulla, pons, and midbrain * cerebellum: posterior to the brain stem
* diencephalon: superior to the brain stem and consists of the thalamus, hypothalamus, and epithalamus * cerebrum: the largest part of the brain supported on the diencephalon and brain stem

Protective Coverings of the Brain
* cranium and cranial meninges surround and protect the brain * cranial meninges: continuous with the spinal meninges and have the same basic structure * dura matter: outer
* arachnoid matter: middle
* pia matter: inner
* cranial dura matter has two layers that are fused together except where they separate to enclose the dural venous sinuses that drain venous blood from the brain and deliver it to the jugular veins (no epidural space around brain)

* periosteal layer: external
* meningeal layer: internal
* blood vessels enter brain tissue and pass along the surface then penetrate inwards and are sheathe by a loose-fitting sleeve of pia matter * three extensions of the dura matter separate parts of the brain * falx cerebri: separates the two hemispheres of the cerebrum * falx cerebelli: separates the two hemispheres of the cerebellum * tentorium cerebelli: separates the cerebrum from the cerebellum

Brain Blood Flow and the Blood-Brain Barrier
* blood flows to brain mainly via the internal carotid and vertebral arteries * dural venous sinuses drain into the internal jugular veins to return blood from the head to the heart * brain uses 20% of the oxygen and glucose used by the body * if the activity of neurons and neuroglia increases in a region of the brain the blood flow to that area also increases * slowing of brain blood flow may cause disorientation or lack of consciousness * 1-2 minutes impairs neuronal function and 4 minutes causes permanent injury * supply of glucose must be continuous due to lack of brains production * low glucose levels lead to confusion, dizziness, loss of consciousness, etc. * blood brain barrier: tight junctions that seal together the endothelial cells of the brain blood capillaries and a thick basement membrane that surround the capillaries *...
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