101_11AI-neuro2_extrac_fluid

101_11AI-neuro2_extrac_fluid - topic set #2: interstitial...

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topic set #2: interstitial fluids in CNS & PNS choroid plexus blood-brain barrier recall that the nervous system… a) transduces environmental stimuli into electrical signals b) sends electrical signals to various tissues rationale for today’s lecture : a) these signals result from changes in the permeability of nerve cell membranes to ions inside & outside these cells. b) before studying how these signals are generated, & because incorrect ion concentrations can result in abnormal electrical activity, let’s look at how extracellular fluid is formed . npb101-w2011-ishida similar to Figs 9-1 & 10-1 imagine Na + & glucose enter your blood (after a meal). how would these reach the fluid surrounding your brain , spinal cord , & nerves in your arm ? 1) first, notice the blood flow from the heart to capillaries in the “head & brain” and “arms” 2) next, ask yourself “hmm… what happens at capillaries?”
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Fig 10-18 in the arm, leg, torso: a) small ions (inorganic and organic), sugars, and amino acids are physically small enough to diffuse through small openings (“ fenestrae ”) between neighboring endothelial cells that form the walls of the capillaries. b) these materials can diffuse freely between the blood and the fluid surrounding these capillaries. c) these capillaries are therefore said to be “ leaky ”. leaving capillary entering capillary npb101-w2011-ishida thus, there are 2 ways material can leave fenestrated capillaries: a) water-soluble species diffuse through the fenestrae (labeled “pores” here) b) lipid-soluble species can diffuse through the endothelial cell membranes Fig 10-18 cross-section thru capillary
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how does material leave the capillaries & reach peripheral nerves? 1) materials leak out of fenestrated capillaries ( labeled “blood vessels here ) 2) both lipid- and water-soluble materials diffuse through a leaky connective tissue ( “perineurium” ) to the extracellular space around nerve fibers. we will see a similar connective tissue in the brain. Fig 5-30 npb101-w2011-ishida circulatory system extracellular fluid summary:
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Netter’s Atlas of the Human Body (2006), p.90 in the head: 1) 2 major arteries carry blood to the brain : one passing in front of the bones of the neck (internal carotid artery) & one passing along the side of these (basilar artery). this allows them to enter the skull and extend upwards into the brain. 2) there, they branch into arterioles, then into capillaries . back side basilar artery internal carotid artery Perez’s Atlas of Human Anatomy (2006), p.163 npb101-w2011-ishida unlike the arm, etc: 1) most capillaries in the brain are not fenestrated : the neighboring endothelial cells are fused together at “tight junctions” 2) because the membranes block the free diffusion of water-soluble
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This note was uploaded on 07/09/2011 for the course NPB 101 taught by Professor Fuller,charles/goldberg,jack during the Winter '08 term at UC Davis.

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101_11AI-neuro2_extrac_fluid - topic set #2: interstitial...

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