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38 Cards in this Set
- Front
- Back
Transmembrane Potential |
The potential difference, measured across a plasma membrane and expressed in millivolts, that results from the uneven distribution of positive and negative ions across the plasma membrane |
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Five main membrane Process in Neural Activities |
1) Resting potential 2) Graded potential 3) Action potential 4) Synaptic activity 5) Information processing |
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Resting Potential |
The transmembrane potential of resting cell |
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Graded Potential |
1) Temporary, localized change in resting potential 2) Caused by stimulus |
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Action Potential |
1) Is an electrical impulse 2) Produce by graded potential 3) Propagates along surface of axon to synapse |
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Synaptic Activity |
1) Releases neurotransmitters at presynaptic membrane 2) Produces graded potentials in postsynaptic membrane |
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Information Processing |
Response (integration of stimuli) of postsynaptic cell |
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Three requirements for transmembrane potential: |
1) Concentration gradient of ions (Na+, Cl-, K+) 2) Selectively permeable through channels 3) Maintains charge difference across membrane (Resting potential -70mV) |
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Passive forces acting across the membrane; Chemical gradients: |
Concentration gradients of ions (Na+ & K+) |
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Passive forces acting across the membrane; Electrical gradients: |
1) Separate charges of positive & negative ions 2) Result in potential difference |
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Electrical currents and Resistance |
1) Electrical currents; movement of charges to eliminate potential difference 2) Resistance; How much the membrane restricts ion movement |
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Electrochemical Gradient |
For a particular ion (Na+ & K+) is the sum of chemical and electrical forces acting on the ion across a plasma membrane. A form of potential energy. |
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Equilibrium Potential |
The transmembrane potential at which there is no net movement of a particular ion across the cell membrane |
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Equilibrium Potential values: |
K+ = -90mV Na+ = +66 mV These values are in the membrane were freely permeable, but it is not! |
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Active forces across the membrane |
Sodium-potassium ATPase (exchange pump) 1) Is powered by ATP 2) Carries 3 Na+ out & 2 K+ in 3) Balances passive forces of diffusion |
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Resting Potential |
Plasma membrane is highly permeable to K+ ions, so resting potential is fairly close to -90mV (this represents the equilibrium potential for K+ |
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Resting potential, even though the electrochemical gradient for Na+ ions is very large, membrane permeability to these ions is very low. |
1) Therefore Na+ has a small effect on normal resting potential 2) This makes it just slightly less negative than it would normally be |
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Resting potential Na+/K+ exchange pump ejects 3 Na+ ions for every 2 K+ ions it brings in. |
Thus stabilizing resting potential when ration of entry/exit |
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At normal resting potential, these passive and active mechanisms are in balance. |
Resting Potential |
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Resting potential varies widely depending on the cell type |
Typical neuron has resting potential of -70mV |
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Changes in Transmembrane potential , transmembrane potential rises or falls in response to? |
Temporary changes in membrane permeability, resulting from opening or closing specific membrane channels. |
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Transmembrane potential Sodium & Potassium channels |
Membrane permeability to Na+ and K+ determines transmembrane potential |
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Transmembrane Potential are either, what? |
Passive or Active |
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Transmembrane Potential passive channels also called leak channels are? |
Always open and permeability changes with conditions. |
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Transmembrane Potential active channels also called gated channels are? |
Open and close in response to stimuli & at resting potential, most gated channels are closed |
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The conditions of gated channels are? |
1) Closed, but capable of opening 2) Open (activated) 3) Closed, not capable of opening (inactivated) |
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Three classes of gated channels are? |
1) Chemically gated channels 2) Voltage gated channels 3) Mechanically gated channels |
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Chemically gated channels |
Open in presence of specific chemical (ACh) at a binding site and found on neuron cell bodies and dendrites |
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Voltage gated channels |
1) Respond to changes in transmembrane potential 2) Have activation gates (opens) and inactivation gates (closes) 3) Characteristic of excitable membrane 4) Found in neural axons, skeletal muscle sarcolemma & cardiac muscle |
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Mechanically gated channels |
1) Respond to membrane distortion 2) Found in sensory receptors: Touch, Pressure & Vibration |
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Transmembrane potential exists across plasma membrane because? |
1) Cytosol and extracellular fluid have different chemical/ionic balance. 2) The plasma membrane permeability in response to chemical or physical stimuli |
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Graded potential also called local potentials: |
1) Changes in transmembrane potential (That cannot spread far from site of stimulation 2) Any stimulus that opens a gated channel (Produces a graded potential) |
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The resting state, opening sodium channel produces graded potential such as: |
1) Resting membrane exposed to chemical 2) Sodium channel opens 3) Sodium ions enter the cell 4) Transmembrane potential rises 5) Depolarization occurs |
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Depolarization is a shift in transmembrane potential toward 0mV: |
1) Movement of Na+ through channel 2) Produces local current 3) Depolarizes nearby plasma membrane (graded potential) 4)change in potential is proportional to stimulus |
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Repolarization |
When the stimulus is removed, transmembrane potential returns to normal. |
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Hyperpolarization |
1) Increasing the negativity of the resting potential 2) Result of opening a potassium channel 3) Opposite effect of opening a sodium channel 4) Positive ions move out, not into cell |
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Transmembrane potential is most affected at the site of stimulation: |
The effect decreases with distance and spreads passively (owed to local currents) |
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Effects of graded potentials at cell dendrites or cell bodies: |
Trigger specific cell functions |