APK 2105C Lecture 23: Neurons Part 2

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Chapter 7, Lecture 2
Neurons
Electrical circuits in biology
o Neurons and muscle cells (all types) are electrically excitable
They function through electrical signals in the form of changes in
membrane potential
o Electrical forces exist between charged particles (ions like Na and K)
Opposites attract, likes repel
Separation of charges requires energy (they naturally want to be
together)
A function of the plasma membrane
More negativity inside the cell
Plasma membrane has lots of positive ions on outside, negative
ions on the inside
Greater the difference in charges, the more energy required to
keep them separate
When opposite charges are separated, energy is stored in the particles
Electrical potential
Voltage
When ions move, they carry their charge with them
Current (I) = movement of electrical charges
o How easily ions move depends on the properties of the substance through which
they move (i.e. plasma membrane)
Resistance (R) = measurement of the hindrance of the charge movement
Greater resistance = decreased current
Is the plasma membrane permeable to ions? NO not without
transporting channels/transmembrane proteins
o Generally plasma membrane is very resistance to current
Conductance (g) = inverse of R (measures what facilitates the movement
of ions)
g = 1/R
Conductance increases as plasma membrane gets more
permeable to ions
o Increased permeability = increased conductance
Water is a great conducter
o The relationship potential difference, current and resistance is defined by Ohm’s
Law = I = E/R
I = current
E = potential difference in voltage
R = resistance
o Ions are present in diff conc inside and outside the cell
Lots of Na outside the cellalways wants to come into the cell
Overall charge inside cell is negative
Separation of these ions contributes to potential for movement of them
Opening and closing ion channels allows for movement of the ions (and
their charges)
Which is an electrical signal at the cellular level
Membrane potential (Vm) = difference in voltage across the plasma membrane
o At rest, a neuron is not receiving or sending any signals
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