N5315 Advanced Pathophysiology
Altered Cellular Function and Cancer
Module Core Concepts and Objectives with Advanced Organizers
Cellular Physiology
1. Analyze the steps of the action potential.
● Sodium permeability increases, sodium ions move into the cell increasing positivity,
depolarization is occurring, action potential threshold is reached as cell becomes more
positive, potassium permeability increases, potassium ions leave the cell, repolarization is
occurring, resting membrane potential is reestablished.
· The action potential carries signals along the nerve or muscle cell and conveys
information from one cell to another.
· When a resting cell is stimulated with voltage the membrane becomes permeable to
sodium.
· Movement of sodium into the cell, the membrane potential decreases, moves to a
negative or zero is known as depolarization. Depolarized cells are positively charged.
· To generate an action potential and the resulting depolarization is known as threshold
potential. It happens when the cell has depolarized by 15-20 millivolts. When the threshold is
met the cell continues to depolarize with no further stimulation. This makes the sodium rush
out of cell causing the membrane potential to reduce to zero and become positively
(depolarization). This rapid reversal in polarity results in action potential.
· Repolarization is negative polarity of the resting membrane potential. Membrane
permeability to sodium decreases, and potassium increases with outward movement of
potassium. This makes the membrane potential more negative.
· During most of the action potential the plasma membrane cannot respond to any
additional stimulus is known as absolute refractory period. Its related to changes in sodium.
· If potassium increases, a stronger stimulus can evoke an action potential is relative
refractory period.
· A membrane potential more negative than normal, requires a larger stimulus to reach the
threshold potential is hyperpolarized (less excitable). occurs when the membrane is
repolarizing.
· A membrane that is more positive than normal, needs smaller stimuli to reach threshold
potential is hypopolarized (more excitable than normal).
2. Discuss how the action potential is altered by calcium and sodium imbalances and the
clinical significance
· Na has a greater concentration in the ECF. When a neuron is excited by a stimulus, the
stimulus-gated Na+ channels open allowing Na+ to move intracellularly. This moves the
, resting membrane potential of -70mV more towards 0. Once the threshold potential is
reached (-59mV) the voltage gated Na+ channels open allowing for more Na+ to move into
the cell and complete the depolarization to a maximum of +30mV. If the depolarization does
not reach a minimum of -59mV (threshold potential) the voltage gated Na+ channels will not
open and the cell will simply repolarize to -70mV without generating an action potential.
· Hyponatremia: Cellular swelling and deficits of intracellular Na alter the ability of cells
to depolarize and repolarize normally. Causes neurological changes headaches, lethargy, and
seizures.
· Hypernatremia: Na is largely in the ECF, increase concentration of Na causes
intracellular dehydration and hypervolemia. Causes hypotension, tachycardia, thirst.
· Hypercalcemia decreases cell permeability to sodium. This causes the threshold potential
to become more positive and is further away from the membrane potential. It takes more of a
stimulus to initiate an action potential. The cells are far less excitable and do not initiate
action potentials. This leads to weakness, hyporeflexia, fatigue, lethargy, confusion,
encephalopathy, a shortened QT segment and depressed widened T waves on EKG.
· Hypocalcemia- calcium deficits causes partial depolarization of the nerves and muscle as
the threshold potential becomes more negative and approaches resting membrane potential
(hypopolarization). A smaller stimulus is needed to start the action potential. This means the
cells are more excitable. This results in tetany, hyperreflexia, paresthesias, prolonged QT
interval, seizures, muscle spasms, laryngospasm.
Topic Describe the How is the action How is the action
Action Potential potential altered by a potential altered by a
potassium imbalance? calcium imbalance?
Action Potential is the Hypokalemia causes a Hypercalcemia
Physiology membrane more negative resting causes a higher action
potential of an membrane potential potential threshold
active neuron. therefore the cell is more causing a more
One that is difficult to excite. difficult excitable
conducting an Because potassium action potential.
impulse. The contributes to the
process of repolarization phase of Hypercalcemia
conducting an the action potential, decreases the cell
impulse hypokalemia delays permeability to Na+
(action ventricular repolarization which makes the
potential) and the frequency of threshold potential
involves a action potentials more positive and
stimulus that further away from the
, activates the Causes: weakness, membrane potential.
neuron → the smooth muscle atony, Takes a stronger
neuron paresthesias, cardiac stimulus to initiate the
depolarizes → dysrhythmias action potential. Cells
then are less excitable.
repolarizes Hyperkalemia affects
the resting membrane Causes: weakness,
Once the cell is potential. the resting hyporeflexia, fatigue,
more positively membrane potential of lethargy, confusion,
charged, the the cell becomes more encephalopathy,
sodium channels positive. A normal RMP shortened QT
open and sodium of -90mv may now be segment, depressed
flows into the -80mv. The cell is said to widened T-waves.
cells. Membrane be hypo-polarized. The
potential is near cells are more excitable When the action
zero. The neuron and conduct impulses potential reaches the
repolarizes more easily and more axon ending, it causes
(becomes more quickly.; therefore, the another ion (calcium,
negatively person will have peak T Ca++) to en
charged), waves on EKG. As ter the cell, which in
potassium potassium rises the turn causes the
channels open. resting membrane vesicles—the tiny
potential will continue to bubbles full of
become more positive neurotransmitters—to
and it will eventually release their content
become equal to the into synaptic gap
threshold potential. The
threshold potential is the Hypocalcemia: there
point at which is an increase in cell
depolarization must reach permeability to Na+
in order to initiate an which causes
action potential (transmit progressive
the impulses). If the depolarization.
resting membrane Threshold potential
potential equals the more negative; closer
threshold potential, an to the resting
action potential will not membrane potential.
be generated and cardiac Cells are more
standstill will occur. excitable.
Paralysis and
Altered Cellular Function and Cancer
Module Core Concepts and Objectives with Advanced Organizers
Cellular Physiology
1. Analyze the steps of the action potential.
● Sodium permeability increases, sodium ions move into the cell increasing positivity,
depolarization is occurring, action potential threshold is reached as cell becomes more
positive, potassium permeability increases, potassium ions leave the cell, repolarization is
occurring, resting membrane potential is reestablished.
· The action potential carries signals along the nerve or muscle cell and conveys
information from one cell to another.
· When a resting cell is stimulated with voltage the membrane becomes permeable to
sodium.
· Movement of sodium into the cell, the membrane potential decreases, moves to a
negative or zero is known as depolarization. Depolarized cells are positively charged.
· To generate an action potential and the resulting depolarization is known as threshold
potential. It happens when the cell has depolarized by 15-20 millivolts. When the threshold is
met the cell continues to depolarize with no further stimulation. This makes the sodium rush
out of cell causing the membrane potential to reduce to zero and become positively
(depolarization). This rapid reversal in polarity results in action potential.
· Repolarization is negative polarity of the resting membrane potential. Membrane
permeability to sodium decreases, and potassium increases with outward movement of
potassium. This makes the membrane potential more negative.
· During most of the action potential the plasma membrane cannot respond to any
additional stimulus is known as absolute refractory period. Its related to changes in sodium.
· If potassium increases, a stronger stimulus can evoke an action potential is relative
refractory period.
· A membrane potential more negative than normal, requires a larger stimulus to reach the
threshold potential is hyperpolarized (less excitable). occurs when the membrane is
repolarizing.
· A membrane that is more positive than normal, needs smaller stimuli to reach threshold
potential is hypopolarized (more excitable than normal).
2. Discuss how the action potential is altered by calcium and sodium imbalances and the
clinical significance
· Na has a greater concentration in the ECF. When a neuron is excited by a stimulus, the
stimulus-gated Na+ channels open allowing Na+ to move intracellularly. This moves the
, resting membrane potential of -70mV more towards 0. Once the threshold potential is
reached (-59mV) the voltage gated Na+ channels open allowing for more Na+ to move into
the cell and complete the depolarization to a maximum of +30mV. If the depolarization does
not reach a minimum of -59mV (threshold potential) the voltage gated Na+ channels will not
open and the cell will simply repolarize to -70mV without generating an action potential.
· Hyponatremia: Cellular swelling and deficits of intracellular Na alter the ability of cells
to depolarize and repolarize normally. Causes neurological changes headaches, lethargy, and
seizures.
· Hypernatremia: Na is largely in the ECF, increase concentration of Na causes
intracellular dehydration and hypervolemia. Causes hypotension, tachycardia, thirst.
· Hypercalcemia decreases cell permeability to sodium. This causes the threshold potential
to become more positive and is further away from the membrane potential. It takes more of a
stimulus to initiate an action potential. The cells are far less excitable and do not initiate
action potentials. This leads to weakness, hyporeflexia, fatigue, lethargy, confusion,
encephalopathy, a shortened QT segment and depressed widened T waves on EKG.
· Hypocalcemia- calcium deficits causes partial depolarization of the nerves and muscle as
the threshold potential becomes more negative and approaches resting membrane potential
(hypopolarization). A smaller stimulus is needed to start the action potential. This means the
cells are more excitable. This results in tetany, hyperreflexia, paresthesias, prolonged QT
interval, seizures, muscle spasms, laryngospasm.
Topic Describe the How is the action How is the action
Action Potential potential altered by a potential altered by a
potassium imbalance? calcium imbalance?
Action Potential is the Hypokalemia causes a Hypercalcemia
Physiology membrane more negative resting causes a higher action
potential of an membrane potential potential threshold
active neuron. therefore the cell is more causing a more
One that is difficult to excite. difficult excitable
conducting an Because potassium action potential.
impulse. The contributes to the
process of repolarization phase of Hypercalcemia
conducting an the action potential, decreases the cell
impulse hypokalemia delays permeability to Na+
(action ventricular repolarization which makes the
potential) and the frequency of threshold potential
involves a action potentials more positive and
stimulus that further away from the
, activates the Causes: weakness, membrane potential.
neuron → the smooth muscle atony, Takes a stronger
neuron paresthesias, cardiac stimulus to initiate the
depolarizes → dysrhythmias action potential. Cells
then are less excitable.
repolarizes Hyperkalemia affects
the resting membrane Causes: weakness,
Once the cell is potential. the resting hyporeflexia, fatigue,
more positively membrane potential of lethargy, confusion,
charged, the the cell becomes more encephalopathy,
sodium channels positive. A normal RMP shortened QT
open and sodium of -90mv may now be segment, depressed
flows into the -80mv. The cell is said to widened T-waves.
cells. Membrane be hypo-polarized. The
potential is near cells are more excitable When the action
zero. The neuron and conduct impulses potential reaches the
repolarizes more easily and more axon ending, it causes
(becomes more quickly.; therefore, the another ion (calcium,
negatively person will have peak T Ca++) to en
charged), waves on EKG. As ter the cell, which in
potassium potassium rises the turn causes the
channels open. resting membrane vesicles—the tiny
potential will continue to bubbles full of
become more positive neurotransmitters—to
and it will eventually release their content
become equal to the into synaptic gap
threshold potential. The
threshold potential is the Hypocalcemia: there
point at which is an increase in cell
depolarization must reach permeability to Na+
in order to initiate an which causes
action potential (transmit progressive
the impulses). If the depolarization.
resting membrane Threshold potential
potential equals the more negative; closer
threshold potential, an to the resting
action potential will not membrane potential.
be generated and cardiac Cells are more
standstill will occur. excitable.
Paralysis and
