Transcript Origin of Bio Potential

Unit I
Chapter -The Origin of Bio potentials
Anotomy
Cell membrane and resting potential
electro-chemical activity and equilibrium, permeability, active a passive
transport, channels, osmosis
Excitable cell
neuron: properties, action potential, signal integration, muscle cell
Nervous a muscle excitable tissue
ElectroEncefaloGraphy, ElectroCardioGraphy, ElectroMyoGraphy,
ElectroRetinoGraphy, ElectroOculoGraphy, ElectroHysteroGraphy,
ElectroGasteroGraphy, MagnetoEncefaloGraphy
Another types biosignals
synaptic potentials, unit activity, population response, evoked potentials
Cell membrane
Na-K pump
Vm
Membrane Current
im
membran current im
t
time / ms
distance / mm
Cytoplasmic membrane (or plasmalema)
Function:
• selective transport between cell and vicinity
• contact and mediation of information between cell and vicinity
Structure:
• thin semi-permeable cover surrounding the cell
• consists from one lipid double-layer and proteins anchored in there
lipid double-layer … gives basic physical features to plasmalema
… on / in: floating or anchored proteins (ion channels)
proteins … anchored in lipid double-layer in different ways
… give biological activity and specificity to plasmalema
glykokalyx … protective cover of some cells formed of oligosacharides,
… there are receptors, glykoproteins and other proteoglikans
… protects against chemical and mechanical damage
Material transport across the cytoplasmic membrane
Passive transport
Difusion
- free transport of small non-polar molecules across membrane
Membrane channel
- transmembrane protein
- transport is possible without additional energy
- cell can regulate whether it is open or not (deactivated)
- channel is specific for particular molecule
Osmosis
-solvent molecules go through semipermeable membrane from low concentration
site to the higher concentration site  development of chemical potential
Aktivní transport
- cell has to do a work (in form of chemical energy, mostly ATP) for
transportation
- it’s done by pumps, plasmatic membrane protein anchored in both lipid layers
(e.g. Na+-K+-ATPase)
- result of ion transport  different ion concentration in/out cell  electric
potential
Action Potential = ALL x NOTHING
Action Potential
Action Potential = opening of sodium and potassium channels
Action Potential
excitable cell
Vm
Na+ -channels
K+ -channels
time
resting potential
equivalent Current Dipole
Active and Passive Transport 
 chemical (concentration) + electric gradient 
 electro-chemical
potential on membrane
!!! Cell INSIDE is NEGATIVE compare to OUTSIDE
(in rest usually –75mV)
Excitable cell: NEURON
structure:
 dendrites with synapses
 body
 axon with myelin and synapses
function:
 thresholding of input signals
 integration (temporal and
spacial) of input signals
 generation of action potentials
Synapse
Synapse
HOW to measure potentials ?
by electrodes - intracellular,
- extracellular,
- superficial
indirectly – by recording of charge spread ... probes
(e.g. fluorescence)
FROM WHERE to measure potentials ?
- from whole body, organ, tissue slices, tissue
culture, isolated cell
Types of biosignals
Synaptic potentials –
excitatory pre- / post-synaptic potentials,
inhibitory pre- / post-postsynaptic potentials mostly they don’t cause
AP because of weak time and spacial summations
(correlation) … they don’t reach threshold for AP
Unit activity – activity of one neuron, ACTION POTENTIALS
Population response – summary response of neuronal population
APs of thousands of neurons
Evoked potentials – response of sensory pathway to the stimulus
Synaptic potentials
EPSP a IPSP
Synaptic potentials
Unit activity vs. Population response
Evoked potentials
… averaged signal of many cells
… recorded from:
Cerebral cortex
Brainstem
Spinal cord
Peripheral nerves
…
Excitable cell: NEURON and MUSCLE CELL
Striated muscles
skeletal muscle – controlled by CNS via moto-neurons
heart muscle - not controlled by CNS
- refractory phase is longer than contraction
(systolic) a relaxation (diastolic) time
Smooth muscles – not controlled by CNS, but by autonomic system
Heart
Heart
Atrial systole
Ventricular systole
Heart
cardiac dipol added up the local dipols:
Heart
cardiac cycle
Heart
cardiac vector field in transverse plane
M
Heart
cardiac vector field
j =const
Heart
ElectroCardioGram
Change of electric potential
 heart muscle activation
 atrium depolarization
3 diff. recording schemes:
Einthoven, Goldberger, Wilson
Frequency = 1-2 Hz !
Heart
2-dimensional recording
Heart
Eindhoven’s triangle
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Brain
ElectroEncefaloGram
Waves:
•Delta: < 4 Hz
... sleeping, in awakeness pathological
•Theta: 4.5 -8 Hz
... drowsiness in children, pathological in aduls
(hyperventilation, hypnosis, ...)
•Alfa: 8.5 -12 Hz
... relaxation physical / mental
•Beta: 12 - 30 Hz
... wakefulness, active concentration
•Gama: 30–80 Hz
…higher mental activity including perception and
consciousness
Biosignals Recording:
ElectroMyoGraphy – electric activity of skeletal muscles
ElectroRetinoGraphy – electric activity of retina
ElectroOculoGraphy – electric activity of eye movements
ElectroHysteroGraphy – electric activity of hystera (uterus)
ElectroGasteroGraphy – electric activity of stomach
MagnetoEncephaloGraphy – electric activity of brain
...
Electroneurogram (ENG)
Recording the field potential of an excited nerve.
Neural field potential is generated by
- Sensory component
- Motor component
Parameters for diagnosing peripheral nerve disorder
- Conduction velocity
- Latency
- Characteristic of field potentials evoked in muscle supplied by the
stimulated nerve (temporal dispersion)
Amplitude of field potentials of nerve fibers < extracellular potentials
from muscle fibers.
Field Potential of Sensory Nerves
Extracellular field response from the sensory nerves of the median or
ulnar nerves
To excite the large, rapidly conducting
sensory nerve fibers but not small pain
fibers or surrounding muscle, apply
brief, intense stimulus ( square pulse
with amplitude 100-V and duration 100300 sec). To prevent artifact signal
from muscle movement position the
limb in a comfortable posture.
Figure 4.8 Sensory nerve action potentials evoked from median nerve of a healthy subject at elbow and
wrist after stimulation of index finger with ring electrodes. The potential at the wrist is triphasic and of
much larger magnitude than the delayed potential recorded at the elbow. Considering the median nerve
to be of the same size and shape at the elbow as at the wrist, we find that the difference in magnitude and
waveshape of the potentials is due to the size of the volume conductor at each location and the radial
distance of the measurement point from the neural source.
Reflexly Evoked Field Potentials
Some times when a peripheral nerve is stimulated, a two evoked
potentials are recorded in the muscle the nerve supplies. The time
difference between the two potentials determined by the distance
between the stimulus and the muscle.
Stimulated nerve: posterior tibial nerve
Muscle: gastrocnemius