Bellringer: Water Intoxication

• What is hyponatremia?• Symptoms? • What is brain edema? • What can it lead to? • What is vasopressin and what does it do?

• http://www.nbcnews.com/id/16614865/ns/us_news-life/t/woman-dies-after-water-drinking-contest/• http://www.scientificamerican.com/article/strange-but-true-drinking-

too-much-water-can-kill/?print=true

Action Potentials

• Neuron’s signaling device• Brief reversal of membrane potential• Excitable membranes only – nerve and muscle• SODIUM!

Propagation of the signal

• Sent/transmitted• Local patch of axonal membrane• Local current flows are established• Depolarization of adjacent membrane areas – which way? • Voltage-gated channels open, impulse is regenerated – self-

propagating at a constant velocity• Every action potential is identical• “spread of local depolarizing currents”

Role of myelin

Saltatory Conduction

• “leaping/jumping” electrical signal • Current can only pass through the membrane at the nodes, myelin

insulates• Dramatically increases speed of signal

No sodium entry – no action potential• Alcohol• Sedatives• Injected anesthetics block nerve impulses by reducing membrane permeability to ions

Cold and continuous pressure

• Interrupt blood circulation to neuronal processesImpair ability to conduct impulses

Ice to numbFoot goes “to sleep” when you sit on it

Exit Slip: What is multiple sclerosis? Impacts? • http://www.youtube.com/watch?v=qgySDmRRzxY