Physiology 206 Lecture 4 Outline of Last Lecture I. OsmosisII. Van’t HofIII. OsmolarityIV. Nervous SystemV. Classify NeuronsOutline of Current Lecture I. NeuronsII. Glia cellsIII. Action potentialsIV. Voltage Gated Ion channelsCurrent Lecture1/22/14- Sensory=afferent (in)- Motor=efferent (out)- Interneurons: transmit information between sensory and motor neurons- Glia cells (glia=’glue’)o Oligodendroglia: wrap around axons of neurons in CNS and insulate them Multiple branches that wrap around one neuron Forms myelin sheath in CNSo Schwann cells: one Schwann cell wraps around one axons and insulates it from other axons and extracellular fluid (ECF) Forms myelin sheath in PNSo Astroglia: looks like stars, has cell body with many projections Some terminate on cell body of a neuron, some on the surface of a capillary Form bridge between neurons and capillariesThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute. Facilitate transfer of materials between the two- Neuron->capillary: carries waste- Capillary->neuron: carries nutrientso Microglia: very small, not very many When there’s an injury microglia accumulate at the site of injury- Potentialo Potential=voltageo Driving force that makes charges moveo Exist where there are unequal amounts of chargeo Unequal distribution of ions across membraneso When charges move: voltageIN OUTK+ k+Na+ Na+- The differences between “in” and “out” are the differences in concentration of charges- 2 factors that affect action potentialo Greater concentration difference=greater potentialo The mobility of particles (ions) across membranes Net voltage(total) across membrane (potential)- The sum of charges moving (add up all the ions)- Voltage across the cell membrane is such that if the inside of the cell is negative, then the outside of the cell is positive- Lskrjl- Resting potential: ~75mVo the absolute value of the resting potential is never really known we would have to put electrodes inside and outside the cell to measure the ion concentration we can’t do this because it causes the ions to leak(punch holes in cell membranewhen testing), so whenever we test it isn’t exactly accurateo microelectrodes: used to measure membrane potentials the smaller the electrode the more accurate the reading- If you continuously increase the graded stimulus, the membrane potential will go to zero then return to normalo once you reach a threshold value, the responses will always be the sameo get an ‘all or nothing’ response: if the threshold value is reached, there will be an action potentialo graded potentials: stay within somao action potentials exit the soma and travel along the axon- In the milliseconds after the action potential has been stimulated, another action potential can’t be stimulated: this is called the refractory periodo Relevant refractory period: at the end of the refractory period, the action potential can be stimulated during this timeo Duration of refractory period sets a standard of how many action potentials can be generated Sets an upper limit on the frequency of the action potentials- Cell membranes have ion channels through which ions can passo Can be “closed” or “open” (Voltage Gated Channels, ~50mV)o Closed: in resting state, ions can only cross membrane slowly Ion concentration difference is large Membrane potential is smallo Open: ions can easily cross the membrane  Ion concentration difference small Membrane potential=0o When the voltage across the membrane is greater than -50mV, the channels are closedo When the voltage across the membrane is less than -50mV, the channels are open (pass the threshold