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Brain Protection and Support
1. Cranium - made up of 8 skull bones that are fused together along zig-zag joints called sutures; brain fits into the cranial cavity
2. Meninges - three layers of protective tissue that provide a tough outer protection to the brain and spinal cord
3. Cerebrospinal Fluid (CSF) - clear fluid that buffers the brain and spinal cord from shock
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Brain Protection and Support (cont.)
4. Blood and Oxygen Supply - delivered to brain through the bloodstream
5. Blood-Brain Barrier - glial cells form a protective covering around blood vessels to prevent toxic substances from entering the brain
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Meninges, Layer #1
Dura Mater ("hard mother"); tough, leather-like outer layer; pain sensitive
Long channels ("sinuses") serve as veins and drain used blood and CSF
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Meninges, Layer #2
Arachnoid
Looks similar to a spider web
Separated from Dura mater by the tiny, fluid-filled sub-dural space
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Meninges, Layer #3
Pia Mater ("soft mother"); barely visible, close to brain and spinal cord; its many blood vessels carry oxygen and nutrients to the CNS and plays a key role in removal of waste products
Separated from the Arachnoid by the sub-arachnoid space
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Cerebrospinal Fluid (CSF)
Clear, colorless fluid that buffers the brain and spinal cord from shock; circulates constantly between subarachoid space and ventricles (4 large brain cavities)
Ventricle walls form a network of capillaries called the choroid plexus, which is covered in glial that produce 3/4 liter of CSF per day from blood plasma
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Functions of CSF
1. Provides protective cushion
2. Protects against injury
3. Diffuses waste material
4. Maintains a "special environment" for the brain
5. Penetrates between brain cells to deliver nutrients, hormones, and neurotransmitters
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Brain Nourishment
Brain requires at least 20% of the body's energy
Neurons cannot store energy, and are very particular about what they can use as energy - only glucose
Glucose is delivered by blood to the brain; if the bloodflow is cut off for as little as 3 minutes, neurons begin to die and permanent damage can occur
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Blood-Brain Barrier (BBB)
1. Protects the Brain: works as a filter by tightly sealing capillaries, overlapping the cells that form the capillaries, and by special glial cells that surround walls
2. Neurotransmitters: unable to pass through BBB, so must rely on substances than can
3. Neurotoxins: more than 440 harmful substances can pass through BBB
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Ischemic Strokes
Most common
Occurs when blood supply to part of the brain is blocked
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Types of Blood Clots
Cerebral thombosis: blood clot forms in a cerebral blood vessel and blocks blood flow
Cerebral embolism: an embolus ("wandering" blood clot) travels from the heart/arteries to the small vessels of the brain and creates a sudden blockage
Transient ischemic attack ("mini-stroke"): temporary blockage of blood flow to part of the brain
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Hemorrhagic Strokes
Most common type = anerurysm; occurs when an artery in the brain leaks or ruptures; can be caused when a wakened or diseased spot in the wall of an artery/vessel bursts
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