Download Electrical Signals in Neurons

Electrical Signals in Neurons
Ch. 12-3
Mini-Physics Lesson
• Potential energy – energy
stored in a system (the body)
as a result of its position or
chemical composition
• Kinetic energy – energy being
used for motion or force
Physics to Anatomy
• Neurons are excitable because of a voltage
difference across the membrane - potential
• “Potential” will initiate an impulse that can
travel through the nervous system
• Graded potentials – used for short-distance
communication
• Action potentials – allow communication over
short and long distance within the body
Potential
• Membrane potential – electrical voltage
difference across the membrane
• Resting membrane potential – membrane
potential in an excitable cell
– Like voltage stored in a battery
– If + and – ends connect, electrons flow in a current
• Current
– Flow of charged particles
– For the body – these are ions instead of elecrons
Ion Channels
• Gradient – difference
• Electrochemical gradient – difference in
charge and concentration
• Positive cations move toward negative areas,
negative anions move toward positive areas
• Ion location can be controlled with gates that
can open or close the pore
Ion Channels
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•
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•
Leakage channels
Voltage-gated channels
Ligand-gated channels
Mechanically gated channels
Ion Channels
• Leakage channels
– Randomly open and close
– most cells leak more potassium (K+) than sodium
(Na+)
• voltage-gated channels
– Opens in response to a change in voltage
(membrane potential)
– Generate and conduct action potentials
Ion Channels
• Ligand-gated channels
– Opens and closes in response to chemical stimulus
(nts, hormones, other ions – ligand molecule)
– Ex: Ach opens channels that allow Na+ and Ca2+
to go in and K+ to go out
– Work in 2 ways
• ligand molecule can open or close the channel itself by
binding
• Ligand molecule activates another chemical messenger
to open the channel
Ion Chanenls
• Mechanically gated
– Opens or closes in response to stimulation by:
• Vibration: sound waves
• Pressure: touch
• Tissue stretching
– The channel is physically disrupted and opens
Ion Channels
Resting Membrane Potential
• Exists due to negative ions in cytosol (ICF) and
equal positive ions in ECF
• The greater the difference in charge, the larger
the potential
• Example:
– 5 Na+ on outside, 4 Cl- on inside – small potential
– 25 Na+ on outside, 4 Cl- on insdie – great
potential
RMP
• Most cells have potential between -40 to -90
mV; typical is -70mV
• Minus sign means the cell is negative – not
negative potential!
• Any cell with potential is polarized
– The potential varies between +5 to -100 mV
How does the potential get there?
• ECF
– Rich in Na+ and Cl-
• ICF
– Rich in K+
– Also has P-, amino acids,
RMP
• Ion interaction
– There are many K+ leakage channels, so K+ diffuse
out
– + ions exit, inside becomes more negative
– - ions can’t leave because they are bound to
molecules
– - charges attract the K+ back in toward the cell
– Few Na+ ions leak inward
– This would destroy the membrane potential, so
there are pumps that take care of this
Na+/K+ pump
• To keep the RMP
– Pump out Na+ as it leaks in
– Pump in K+ as it leaks out
– 3 Na+ for each 2 K+ - this still maintains a negative
charge in the cell
RMP - Draw