11. Nervous Tissue and Nervous System
,11. Nervous Tissue and Nervous System
TOPIC: IONS: SODIUM AND POTASSIUM
Electrochemical Gradient
⚫ A combination and balance of two components:
1. Electrical gradient: Ions move toward area of blank charge.
2. Concentration gradient: Ions move from area of blank concentration to area of blank concentration.
⚫ If opposing, whichever gradient is blank drives net flow of ions.
EXAMPLE: Draw an arrow in each box to indicate in which direction the Electrical Gradient and the Concentration
Gradient would direct the flow of potassium ions through the K+ Channel.
PRACTICE: Suppose the extracellular fluid has a chloride (Cl-) concentration of 120mM, while the concentration of
chloride (Cl-) inside the cytosol is 60mM. Also suppose that the total net charge of the cytosol is more negative than
the extracellular fluid. Given this information, which statement is correct regarding the movement of Cl- ions?
a) The electrical and concentration gradients both favor movement into the cell.
b) The concentration gradient favors a net movement out of the cell, the electrical gradient favors movement into
the cell.
c) The electrical and concentration gradients both favor movement out of the cell.
d) The concentration gradient favors a net movement into the cell, the electrical gradient favors movement out of
the cell.
Page 2
, 11. Nervous Tissue and Nervous System
TOPIC: IONS: SODIUM AND POTASSIUM
Standard Sodium and Potassium Concentrations
⚫ Sodium (Na+): ⚫ Potassium (K+):
◼ Intracellular concentration relatively blank. ◼ Intracellular concentration relatively blank.
◼ Extracellular concentration relatively high. ◼ Extracellular concentration relatively low.
EXAMPLE: Given what you know about Na+ and K+ concentrations, draw an arrow in each box to indicate which
direction the Concentration and Electrical Gradients would direct the flow of both sodium and potassium ions.
PRACTICE: In a neuron at rest, the concentration of blank is higher outside the cell than in the cell, whereas the
concentration of blank is greater inside the cell than outside.
a) Sodium; potassium. b) Potassium; sodium.
PRACTICE: Which of the following statements is true regarding how the concentration gradient affects sodium ions
when a cell is at rest?
a) When a cell is at rest the concentration gradient has no effect on sodium ions.
b) The concentration gradient drives sodium ions into the cell.
c) The concentration gradient drives sodium ions out of the cell.
d) In a cell at rest the electrical gradient moves ions into the cell.
Page 3
,11. Nervous Tissue and Nervous System
TOPIC: IONS: SODIUM AND POTASSIUM
Electrochemical Gradient
⚫ A combination and balance of two components:
1. Electrical gradient: Ions move toward area of blank charge.
2. Concentration gradient: Ions move from area of blank concentration to area of blank concentration.
⚫ If opposing, whichever gradient is blank drives net flow of ions.
EXAMPLE: Draw an arrow in each box to indicate in which direction the Electrical Gradient and the Concentration
Gradient would direct the flow of potassium ions through the K+ Channel.
PRACTICE: Suppose the extracellular fluid has a chloride (Cl-) concentration of 120mM, while the concentration of
chloride (Cl-) inside the cytosol is 60mM. Also suppose that the total net charge of the cytosol is more negative than
the extracellular fluid. Given this information, which statement is correct regarding the movement of Cl- ions?
a) The electrical and concentration gradients both favor movement into the cell.
b) The concentration gradient favors a net movement out of the cell, the electrical gradient favors movement into
the cell.
c) The electrical and concentration gradients both favor movement out of the cell.
d) The concentration gradient favors a net movement into the cell, the electrical gradient favors movement out of
the cell.
Page 2
, 11. Nervous Tissue and Nervous System
TOPIC: IONS: SODIUM AND POTASSIUM
Standard Sodium and Potassium Concentrations
⚫ Sodium (Na+): ⚫ Potassium (K+):
◼ Intracellular concentration relatively blank. ◼ Intracellular concentration relatively blank.
◼ Extracellular concentration relatively high. ◼ Extracellular concentration relatively low.
EXAMPLE: Given what you know about Na+ and K+ concentrations, draw an arrow in each box to indicate which
direction the Concentration and Electrical Gradients would direct the flow of both sodium and potassium ions.
PRACTICE: In a neuron at rest, the concentration of blank is higher outside the cell than in the cell, whereas the
concentration of blank is greater inside the cell than outside.
a) Sodium; potassium. b) Potassium; sodium.
PRACTICE: Which of the following statements is true regarding how the concentration gradient affects sodium ions
when a cell is at rest?
a) When a cell is at rest the concentration gradient has no effect on sodium ions.
b) The concentration gradient drives sodium ions into the cell.
c) The concentration gradient drives sodium ions out of the cell.
d) In a cell at rest the electrical gradient moves ions into the cell.
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