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The central nervous system consists of ______.
A. the brain and motor nerves. B. the brain and sensory nerves. C. the brain and spinal cord. D. the motor and sensory nerves. E. the spinal cord and all nerves.
The sympathetic division of the nervous system ______.
A. controls voluntary motor activity. B. conserves energy. C. mobilizes body systems. D. promotes non-emergency functions. E. includes the sensory nerves.
The ________ nervous system carries brain and spinal cord signals to other organs.
A. autonomic B. peripheral C. central D. craniospinal E. efferent
5
6
1. ___________
2. ___________
3. ___________
4. ___________
• ___________
Membrane Potentials
I. What is a Membrane Potential?
II. Ions in Neurons
III. Resting Membrane Potential
What is a Membrane Potential?Separation of charges across a cell membrane.
Stated more simply…
Difference in number of cations and anions across a membrane
+-+-
Membrane
+-+-
++++
----
+++++++
-------
Charge Separation in a Battery
• Membrane potential is analogous to a battery
• Battery sends electrical signal down a wire
• Neuron sends electrical signal down an axon
Neurons have a Membrane Potential
IN CELL OUTSIDE CELL PERMEABILITY
Sodium (Na+) 15 mM 150 Mm 1
Neurons have a Membrane Potential
IN CELL OUTSIDE CELL PERMEABILITY
Potassium (K+) 150 mM 5 mM 75
Neurons have a Membrane Potential
IN CELL OUTSIDE CELL PERMEABILITY
Protein (A-) 65 mM 0 mM 0
Neurons have a Membrane Potential
• iNside = Negative
• Outside = POsitive
Oh no!!!! Not diffusion again!!
AGHHHHHH!!!!!!
And now for some review…
HighHigh HomogeneousHomogeneousLowLow
Diffusion Across a Concentration Gradient
Time 1Time 1 Time 2Time 2
Membrane Potentials
I. What is Membrane Potential?
II. Ions in Neurons
III. Resting Membrane Potential
Plastics Make it Possible!
Ions
Plastics Make it Possible!Ions
Ion Diffusion in Neurons
1. Passive Channel
Ion Diffusion in Neurons
1. Passive Channel
2. Voltage-gated Channel
High Na+Low Na+
Diffusion of Na+ through Membranes
Which way will Sodium move?
High Na+
Ion movement based on concentration gradient
Low Na+
Diffusion of Na+ through Membranes
High Na+
Ion movement based on concentration gradient
Low Na+
Diffusion of Na+ through Membranes
X
High Na+
Ion movement based on concentration gradient
+60 mV
Low Na+
Diffusion of Na+ through Membranes
Na+ Ion Channel
High Na+
Ion movement based on concentration gradient
+60 mV
Low Na+
Diffusion of Na+ through Membranes
Na+ Ion Channel
Positively charged substances other than Na+ are in the cell
High Na+
Ion movement based on concentration gradient
Ion movement based on electrical gradient
+60 mV
Low Na+
Diffusion of Na+ through Membranes
Inward concentration gradient counterbalanced by the outward electrical gradient
Na+ Ion Channel
Positively charged substances other than Na+ are in the cell
Low K+High K+
Diffusion of K+ through Membranes
Which direction will Potassium move?
Low K+
Ion movement based on concentration gradient
High K+
Diffusion of K+ through Membranes
Low K+
Ion movement based on concentration gradient
High K+
Diffusion of K+ through Membranes
X
Low K+
Ion movement based on concentration gradient
-90 mV
High K+
Diffusion of K+ through Membranes
K+ Ion Channel
Low K+
Ion movement based on concentration gradient
-90 mV
High K+
Diffusion of K+ through Membranes
K+ Ion Channel
As K leaves it creates a negative charge that pulls it back in.
Low K+
Ion movement based on concentration gradient
Ion movement based on electrical gradient
-90 mV
High K+
Diffusion of K+ through Membranes
K+ Ion Channel
Outward concentration gradient counterbalanced by the inward electrical gradient
As K leaves it creates a negative charge that pulls it back in.
Concurrent Diffusion of Na+ and K+
Low K+High K+
Low Na+ High Na+
Concurrent Diffusion of Na+ and K+
Low K+High K+
Low Na+ High Na+
Concurrent Diffusion of Na+ and K+
Low K+High K+
Low Na+ High Na+
K+ exerts dominating effect on RMP (greater permeability)
Concurrent Diffusion of Na+ and K+
Low K+High K+
Low Na+ High Na+
K+ exerts dominating effect on RMP (greater permeability)
Na+ neutralizes some of the potential created by K+
Concurrent Diffusion of Na+ and K+
Resting Membrane Potential (RMP) = -70 mV
Low K+High K+
Low Na+ High Na+
K+ exerts dominating effect on RMP (greater permeability)
Na+ neutralizes some of the potential created by K+
Membrane Potentials
I. What is Membrane Potential?
II. Ions in Neurons
III. Resting Membrane Potential
Movement of Na+ and K+ at RMP
• Na+ and K+ are not at equilibrium
Movement of Na+ and K+ at RMP
• Na+ and K+ are not at equilibrium
• Both move DOWN concentration gradient
Movement of Na+ and K+ at RMP
• Na+ and K+ are not at equilibrium
• Both move DOWN concentration gradient
• Why doesn’t intracellular K+ concentration continue to fall?
Movement of Na+ and K+ at RMP
• Na+ and K+ are not at equilibrium
• Both move DOWN concentration gradient
• Why doesn’t intracellular K+ concentration continue to fall?
• Why doesn’t intracellular Na+ concentration continue to rise?
Na+
K+
Outside
Inside
Diffusion
Sodium-Potassium Pump
• Counterbalances diffusion of Na+ and K+
Na+
K+
Outside
Inside
Diffusion
Sodium-Potassium Pump
• Counterbalances diffusion of Na+ and K+
• No net movement of Na+ and K+
Ion Movement through Resting Neurons• Sodium pumped OUT
Ion Movement through Resting Neurons• Sodium pumped OUT
• Potassium pumped IN, but diffuses out easily
Ion Movement through Resting Neurons• Sodium pumped OUT
• Potassium pumped IN, but diffuses out easily
• Sets up Ions that are ready to move
Summary
• Charge separation between the inside and outside of a neuron, referred to as a membrane potential.
• Resting membrane potential (RMP) caused by concentration of Na+, K+, and protein anions.
• At rest, neurons have a RMP of -70 mV.
• Neuron will stay at RMP until stimulated, creating an Action Potential
