APK 2105C Lecture 23: Neurons Part 2
5 Jun 2018
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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 cell—always 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
