Cloned from: Nervous System

by dr

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Central Nervous System
Brain & spinal cord
Peripheral Nervous System
Cranial & spinal nerves and the peripheral components of the autonomic nervous system
- Primary functional unit of nervous system - Nonmitotic, not replicating or replacing themselves if irreversibly damaged - consists of cell body, axon & several dendrites
- glial cells: provide support, nourishment & protection to neurons - 5 to 10 times more numerous than neurons - mitotic & can replicate - when neurons are destroyed, the tissue is replaced by proliferation of neuroglia cells
Neuroglia: Different types of glial cells = Oligodendrocytes
- specialized cells that produce myelin sheath of nerve fibers in CNS [Schwann cells myelinate nerve fibers in periphery] & are primarily found in white matter of CNS
Neuroglia: Different types of glial cells = Astrocytes
- provide structural support to neurons & their delicate processes form the blood-brain barrier w. endothelium of blood vessels, & play a role in synaptic transmission - found primary in gray matter - injury, acts as phagocytes for neuronal debris - proliferation = formation of scar tissue [gliosis] in CNS
Neuroglia: Different types of glial cells = Ependymal Cells
- line brain ventricles & aid in secretion of CSF
Neuroglia: Different types of glial cells = Microglia
- type of macrophage, relatively rare in normal CNS tissue - are phagocytes & are important in host defense
Nerve Impulse
- neurons initiate, receive, & process msgs about events both & outside body - initation of neuronal msg [nerve impulse] involves generation of an action potential
Action Potential
- cells @ resting state: [-] electric charge inside compared to outside of cell. - Na+ are high outside - K+ are high inside - depolarization: inside becomes + - repolarzation: inside becomes negative - metabolic process accomplished by Na+K+ pump [requires energy:ATP]
Resting Membrane Potential
- difference in electric charge across cell memebrane
- insulating capacity - myelination of nerve axons facilitates conduction of action potential - white, lipid substance
- chemical agent involved in transmission of an impulse across synaptic cleft - either Excitatory or Inhibitory
Excitatory Neurotransmitters
- cause an increase in Na+ permeability at postsynaptic cell membraine = action potential generated
Inhibitory Neurotransmitters
- cause an increase in permeability of K+ & Cl- ions, decreasing likelihood of generation of action potential
Spatial Summation
presynaptic input can be summed by the number of presynaptic cells firing
Temporal Summation
Frequency of firing of a single presynaptic cell
Cerebral Circulation
- blood supply of brain arises from internal carotid arteries [anterior circulation] & the vertebral arteries [posoterior circulation]
Internal Carotid Arteries
Supplies the ipsilateral hemisphere
Vertebral Arteries
- Basilar artery, formed by the junction of the 2 vertebral arteries, supplies structures the posterior fossa [cerebellum & brainstem]
Circle Of Willis
- arises from basilar artery & two internal carotid arteries - acts as a safety valve when differential pressure are present in these arteries - also acts as an anastomotic pathway when occlusion of a major artery on one side of brain occurs
2 Anterior Cerebral Arteries
supply the medial & anterior portions of frontal lobes
2 Middle Cerebral Arteries
supply the outer portions of the frontal, parietal, & superior temporal lobes
2 Posterior Cerebral Arteries
supply the medial portions of the occipital & inferior temporal lobes
Where does Venous Blood drain from in the brain?
through the dural sinuses, which form channels that drain into the 2 jugular veins
Blood-Brain Barrier
- astrocytes form the BBB - a physiologic barrier btwn blood capillaries & brain tissue - allows nutrients & gases to enter - only certan drugs can enter CNS from bloodstream [NOT ALL CHEMO DRUGS!] - lipid-soluble compounds enter brain easily - water-soluble & ionized drugs enter brain & spinal cord slowly
- protective structure - 3 layers that surround the brain & spinal cord: 1. Dura Mater = thick, outermost layer 2. Arachnoid Layer = Middle. Delicate, impermeable membrane 3. Pia Mater = Inner
Subarachnoid Space
- lies between arachnoid layer & pia mater; filled with CSF - All cerebral arteries & veins & CNs lie in this space - larger SA space is in region of 3rd & 4th lumbar vertebrae [area penetrated to obtain CSF during lumbar puncture] - anything that passes to & from brain & skull or its foramina, must pass through subarachnoid space
Spinal Cord
Ends between 1st & 2nd Lumbar Vertebrae
Tentorial Herniation
Expansion of mass lesions in cerebrum forces brain to herniate through the opening created by the brainstem [FORAMEN MAGNUM?]
- protects brain from external trauma - composed of 8 cranial bones & 14 facial bones - top & sides are smooth; bottom surface is uneven [many ridges, prominences, & foramina]
- largest hole is FORAMEN MAGNUM, which brainstem extends to spinal cord - this foramen offers the only major space for expansion of brain contents when increased ICP occurs
Vertebral Column
- protects spinal cord, supports head, & provides flexibility - made up of 33 individual vertebrae: 1. 7 cervical 2. 12 thoracic 3. 5 lumbar 4. 5 sacral [fused into 1] 5. 4 coccygeal
Vertebral Column
- each vertebra has a central opening for spinal cord - vertebrae held together by a series of ligaments - intervertebral disks occupy spaces btwn vertebrae
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