1. The origin of biopotentials
FYS 4250
Chapter 4
The origin of biopotentials
Many forms
Electrocardiogram ECG
Electroneurogram ENG
Electroencephalogram EEG
Electromyogram EMG
Electroretinogram (ERG)

2. Biopotentials
Produced as a result of electrochemical activity in excitable cells that are components of nervous, muscular or gland tissue
When cells are stimulated, an action potential will bring the cells out of the resting potential and trig a change in the electrical potential
Cell potential -40 to -90 mV relative to external medium

3. Axon in invertebrate animals
Resting membrane is slightly permeable to Na+, freely permeable to K+ and CL-. Sodium

4. Action potential, ekcitable cell
an adequate stimulus depolarizes the cell membrane so that the treshold level is exceeded, triggering an action potential. Constant speed along the membrane, polarised membrane.
Depolarizing of the cell membrane will increase the Na transport into the cell, which will yield a further depolarization and even more Na transport into the cell

5. Membrane potential
Nernst equation for potassium K (Nor - Kalium):
across a cell membrane with active channels pumping K ions into the cell.

6. muscle-fibre or axon

7. Dipoles in the axon
Signal propagation relatively small compared to the fiber length. Myelinated nerve cell is about 20 times faster potential propagation.
When an action potential is produced, there is no ability to respond to a second stimulus (absolute refractory period)
Relative refractory period, action potential can be elicited by an intense supertreshold stimulus.
A nerve axon with an absolute refractory period of 1 ms has upper limit of 1000 repetitive discharges per second.
Reversal of polarity in the active region because of depolarization, membrane behind is repolarized. No attenuation.
Vertebrate neurons are myeliniated, insulated by a sheath of myelin. (Lipoprotein complex.
Interupted at regular intervals, -> action potentials are not uniformly distributed along the membrane-> reduce leakage current, decrease membrane capacitance and improves transmission properties, esp. Speed.
Incidence of multiple scleroris (MS) disintegration om myelinated layer, is increased by 0.7% for each latitude northwards

8. Summing up in the nerve-cell
Both motorical and sensorical fibers are excited simultaneously by electrical stimulus.
Dorsal root is sensoric
Ventral root is motoric, dorsal root is nervous
Stimulation of the many large diametric motoric fibers will give the largest extracellular response.
Stimulation of sensoric fibers will excite two groups of sensoric fibres.

9. Muscle control Reflex arc Sense organ
Sensory nerve, sending information
CNS, integratorstation. Evaluated -> Motoric decision can be implemented
Motor nerve, communicating with peripheral muscle
Effector organ, like skeletal muscle fibers.
Spindle er lengdereseptorer

10. Neural velocity
Nerve stimulation at two different sites, subtraction of the shorter latency from the longer latency gives conduction time

11. Neurography
The potential is transferred through the median nerve, which is the same size and diameter all the way through the arm. The difference is due to the size of the volume conductor at each location and the radial distance of the measurement point from the neural source.

12. H-reflex
When a mixed peripheral nerve is stimulated with low intensity, only fibers with big diameter will be stimulated because they have the lowest treshold = sensoric fibers. (Spinal reflex). When stimulus is increasing, smaller motor fibers in the mixed nerve are stimulated in addition to the sensory fibers, short latency motoric contraction is produced. (M-wave). Even stronger stimuli, production of H-wave is interfered due to the refraction period of the motor fibers

13. EMG
Cross sectional view of the spinal cord

14. EMG
SMU = Single motor unit

15. The heart

16. Syncron-
ism in myo-
card

17. Myocard anatomy

18. Isokrone linjer for ventrikkel- aktivering
Mange regioner kan være aktive samtidig!

19. The heart dipole

20. The current dipole
H = iL
J = sE
v = H . r / 4psr3

21. Atrioventricular-block

22. Ectopic beat

23. Tachycardia flutter= increased regular frequency

24. flimmer (norsk) = fibrillation (eng) = = uregelmessig rytme

25. Ischemia
No S-T segment shift prior to coronary occlusion, but after

26. ERG
Electroretinogram

27. ERG A - Early receptor potensial ERP + late receptor potensial LRP
B- Bipolare og ganglion celler i innerste lag av retina
C – pigment epitel-celler
D- av-respond til retina
Early receptor potential (ERP) light-induced changes in photopigment molecules
Late receptor potential (LRP) output of the photoreceptors

28. EEG

29. Cerebrum

30. Signalpaths in
cortex

31. Fysisk institutt - Rikshospitalet
EEG waves 1
FYS4250
Fysisk institutt - Rikshospitalet 31

32. Fysisk institutt - Rikshospitalet
EEG waves 2
FYS4250
Fysisk institutt - Rikshospitalet 32

33. EEG electrodes

34. Sleep
EEG