1. The document discusses the relationship between current and capacitance in physiological systems. It defines current as the rate of flow of charges and capacitance as the ability of a capacitor to store charges. 2. It explains that the plasma membrane of cells can be modeled as a capacitor, with charges separated by the lipid bilayer. Membranes allow the flow of ions through ion channels, conducting electrical signals. 3. Nerve conduction velocity is measured, representing the speed of current through a nerve. It depends on the nerve membrane's resistance and capacitance, with myelination decreasing capacitance and increasing speed.

1. ELECTROPHYSIOLOGY
Relationship of current and
capacitance for physiological system

2. CURRENT
♦ Electric current is define as the rate of flow
of charges passing through a point
or
 Amount of charges (Q) passing per unit
time (t)
and is given as
Equation 1

3. CAPACITANCE
• Is the ability of a capacitor to store charges
• A capacitor is made up of two conductive
plate that are separated by small distance or a
thin layer of dielectric (insulator) b/w two
conducting plates.

4. • The surface area of plates increases the
capacitance while the distance of dielectric
decreases the capacitance.
• When positive and negative ions are
separated by conducting substance a
potential difference generate across them
but when insulation is provided in between
them charges store there and do not flow.
Equation 2

5. RELATIONSHIP B/W CURRENT AND
CAPACITANCE
• Placing equation 2 (Q= CV)
in equation 1 (I= Q/t)
we get I = CV/t
• We can conclude that current is directly
proportional to voltage and capacitance but
inversely proportional to time.
• Nerve Conduction Velocity (NCV) is the
speed of current passing through a nerve
and is dependent upon capacitance.

6. ELECTRICAL PROPERTIES OF
CELL MEMBRANE
• Compare the plasma
membrane with a
capacitor , charges are
separated by lipid bilayer
through electrogenic
pump (Na+/K+ ATPase)
generating a voltage
across it
• The hydrophobic thin
layer of lipids act as an
insulator and membrane
become able to store
charges.

7. • Membrane of all cells in particular excitable
cells have many ionic gates which allow
flow of charges (current) through them after
receiving certain stimuli.
• Thus membrane is also a good conductor of
current.
• Depolarizing phase of Action potential is
similar to the flow of ions from a capacitor.
• While repolarizing phase is similar to the
restoring the charges for further impulses.

9. VARIOUS DIAGNOSTIC LAB TESTS TO
RECORD ELECTRICAL ACTIVITY OF
DIFFERENT ORGANS
• EEG (Electroencephalogram of brain)
• EMG (Electromyography of muscles)
• ECG (Electrocardiogram of heart)
• ENoG (Electroneurograpghy of nerves)
• NCV (Nerve conduction velocity of nerves)

10. NERVE CONDUCTION VELOCITY
• Is the rate of propagation of electric signal
through a nerve.
• Or the distance covered by AP per unit time.
• NCV = lambda /time

11. • From the equation we can see that NCV is
directly proportional to the Rm.
• While inversely proportional to the Cm.
• MYELINATION provide insulation and thus
decrease Capacitance although there is a
decrease in amplitude of current but impulses
are ensured to be very fast in ling nerves.
• Nodes of Ranvier after few millimeter
provide conduction and propagation of
impulse in forward direction
• Invertebrates have unmyelinated short
neurons that is why AP are very rapid .

14. Commonly used method for
Animal Model
1. Dissect the frog Schiatic nerve.
2. Or the median and lateral giant axon of
earthworm.
3. Set-up the instrument (stimulator,
electrodes, wires and oscillator and
plates) and chemical (such as Ringer
buffer).
4. Place the nerve over electrodes.
5. Record the electrical activity.
6. Calculate NCV.

15. Procedure for Human NCV
• Locate the nerve to be studied.
• Small electrode will be taped to the skin over the
nerve after applying conducting gel.
• An stimulating electrode will be placed at a known
distance away from recording electrode.
• The nerve will be stimulated by a mild and brief
electrical shock.
• The patient may experience discomfort or pain due
to the shock.
• The stimulation of the nerve and the electrical
impulse and current will be displayed on an
oscilloscope (a monitor that display electrical
activity).

17. Observations
• Any decrease in the NCV will indicate:
1.Extent of demyelination of nerve
2. Any Conduction Block
3.Axonopathy (damage to the long
portion of a nerve cell)
SIGNIFICANCE
•Diagnosis of various diseases
•Detection of source and location of conduction
block

18. References
• Neurophysiology:
3rdedition by R.H.Carpenter
Nerve Conduction studies:
• https://backyardbrains.com/experiments/comparingN
• https://Hmphysiology.blogspot.com
Thank you!