S. Mukherji, IIT-Bombay ([email protected]) Ground Rules • Lectures as scheduled • Tutorials as scheduled – there might be a quiz in one of the tutorial sessions (10 minute quiz). o No repeats of class lectures in tutorials. o If you have doubts – post on moodle by Sunday – answers will be posted or discussed in all the tutorial sections of that week. o Material covered in tutorials will be associated with the lectures and will be part of the exam syllabus. • Quiz o Strict about time… land up by 0815 • Mid Sem o End sem for tis part will be short answer type and small numericals.
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The famous radiograph made by Roentgen on 22 December 1895. This is traditionally known as "the first X-ray picture" and "the radiograph of Mrs. Roentgen's hand. "
The great breakthroug came in 1913 when William Coolidge and Lilienfeld made there first hot filament Cathode X-Ray tube. They replaced the cold Cathode with a heated spiral filament Cathode and tungsten Anode. The third anticathode disappeared, the angle of the Anode in his tube was set at 45º. X-Ray's could now be better controlled and were more reliable. The only practical problem was cooling the Anode, (which got extremely hot) this was a huge problem due to it's small size. New designs were developed, a heavy copper base to the Anode, sometimes with water or air cooling, this conducted the heat away and therefore increased the capacity of the tube to withstand a high current.
• Eindhoven was a physiologist… was interested in the electrical activity of the heart.
• Although electrical recordings of the heart were made earlier (Waller, 1887), in 1903 Einthoven demonstrated the first recordings of the ECG using an ingeniously built system with a high sensitivity Quartz filament for detecting ECG current.
• The muscle cell has made contraction its specialty. Its cytoplasm is packed with organized arrays of protein filaments, including vast numbers of actin filaments and mitochondria.
• The nerve cell stimulates the muscle to contract, conveying an excitatory signal to the muscle from the brain or spinal cord.
• Schwann cells are specialists in the mass production of plasma membrane, which they wrap around the elongated portion of the nerve cell, laying down layer upon layer of membrane like a roll of tape, to form a myelin sheath that serves as insulation.
• The nerve cell has to be extraordinarily elongated o After all it is carrying a signal from the brain to a “far off” muscle. o The main body, containing the nucleus, may lie a meter or more
from the junction with the muscle.
• The cytoskeleton has to be well developed so as to maintain the unusual shape of the cell and to transport materials efficiently from one end of the cell to the other.
• The plasma membrane, which contains proteins that act as ion pumps and ion channels, causing a movement of ions that is equivalent to a flow of electricity.
o All cells contain such pumps and channels in their plasma membranes, however the nerve cell has exploited them in such a way that a pulse of electricity can propagate in a fraction of a second from one end of the cell to the other, conveying a signal for action.
The Equilibrium Potential across a membrane arises from the balance between electrical forces and mechanical (i.e. diffusion) forces. We can derive it either from the Fick’s laws of diffusion or from the energetics point of view.
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For sodium ions at 37qC this translates to 61.5 mV per decade gradient.
Obviously since all these ions (and more) are present, there has to be effect by each one of them in developing the RMP. Nernst Equation does not explain it all
Mammalian muscle (rmp = -75 mV) ECF ICF
Cations Na+ 145 mM 12 mM K+ 4 mM 155 mM Anions Cl- 120 mM 4 mM
Frog muscle (rmp = -85 mV) ECF ICF
Cations Na+ 109 mM 4 mM K+ 2.2 mM 124 mM Anions Cl- 77 mM 1.5 mM
Two solutions having different concentrations of a highly dissociating salt separated by:
A completely permeable (allows everything) membrane. A semi-permeable, i.e. allows only one ionic species, membrane An impermeable (i.e. allows nothing through) membrane.