Term
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Definition
| Measures the strength of the contraction |
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Term
| Membrane of a resting Neuron |
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Definition
| In a resting neuron, the inner surface of the plasma membrane is negatively charged compared with its external surface. The membrane is then said to be electrically polarized |
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Term
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Definition
| The difference in electrical potential “voltage” between the two sides of the membrane is referred to as the resting potential or membrane potential. Typically, the resting potential is 60-100 milivolts |
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Term
| At resting, what is the membrane very permeable to? (and not permeable) |
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Definition
| The cell membrane is very permeable to K(+) and Cl (-), but is not very permeable to Na(+) and the large, negatively charged proteins and other organic molecules in the cell interior. These negatively charged molecules may be thought of as “fixed” negative charges. |
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Term
| ATP-driven pump in the membrane |
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Definition
| Pumps 3 sodium ions out of the cell and 2 potassium ions into the cell. The result is a highly unequal distribution of ions across the cell membrane, with a high concentration of sodium ions outside the cell and a high concentration of potassium ions inside the cell. |
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Term
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Definition
| The membrane potential depends on the distribution of ions on either side of the membrane. Therefore, it is essential that there is a supply of ATP to pump out any sodium ions that leak in. THe sodium ions are pumped against their concentration gradient. |
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Term
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Definition
| The resting membrane is very permeable to potassium ions caused by the presence of in membrane of large numbers of potassium leak channels. |
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Term
| Negatively charged proteins |
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Definition
| The resting membrane is impermeable to the negatively charged proteins and other large organic molecules inside the cell. They are too big to diffuse through the plasma membrane, and there are no pores in the membrane to allow them to pass through it. |
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Term
| Negatively charged proteins |
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Definition
| The resting membrane is impermeable to the negatively charged proteins and other large organic molecules inside the cell. They are too big to diffuse through the plasma membrane, and there are no pores in the membrane to allow them to pass through it. |
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Term
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Definition
At first, positively charged potassium start diffusing out of the cell through their leak channels. They diffuse outwards because their concentration is much higher inside the cell than outside.
But that cannot go on. THe negatively charged proteins inside the cell cannot diffuse out. The result is that the inside of cell becomes more and more negatively charged. |
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Term
| The negative charge caused by diffusion of potassium |
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Definition
| This negative charge creates a potential gradient that tends to draw positively charged potassium ions back into the cell. |
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Term
| Creation of Rest Potential |
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Definition
| When the electrical forces drawing potassium ions into the cell balance the diffusion forces driving potassium ions out of the cell, there is a potential (across the membrane called the resting potential, which corresponds to the potassium Nernst potential. |
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Term
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Definition
The resting membrane is slightly permeable to sodium ions, and so sodium is continually and slowly leaking into the nerve fiber. (If this were allowed to continue, the concentrations of potassium and sodium ions would equalize and the resting potential would be zero)
So the ATP-pump is used. |
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Term
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Definition
| Often a signal (either due to the neurotransmitter or a stimulus such as pressure, touch sound, etc.) will act to make the inside of the membrane less negative with respect to the outside, in which case it is said to depolarize the membrane. Depolarization events can occur in graded steps. |
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Term
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Definition
| When a depolarization changes the membrane potential to a value called the threshold, an action potential is generated. |
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Term
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Definition
| At threshold (usually about -55mV), the membrane, which has previously been almost impermeable to sodium ions, starts to become highly permeable to them. In fact, the permeability of the membrane of the membrane to sodium ions becomes much, much greater than the permeability of the membrane to potassium ions. |
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Term
| Voltage-gated sodium channels |
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Definition
| The sudden increase in permeability to sodium at action potential is due to the opening in the cell membrane of voltage-gated sodium channels. |
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Term
| From action potential to resting potential |
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Definition
| The return of the membrane potential back to its resting value is accelerated because the potassium permeability actually rises above its resting value for a short period of time |
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Term
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Definition
| `The transient rise of potassium permeability is due to the presence of slowly-opening voltage-gated potassium channels in the membrane. Since the potassium leak channels are always open, the membrane actually becomes more permeable to potassium than it was during resting potential. |
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Term
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Definition
| The rise of potassium causes a transient hyperpolarization or overswing at the terminal phase of the action potential. Finally, the voltage-geted potassium chanels close, and the membrane returns to the resting potential. |
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Term
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Definition
| During an action potential, the nerve will not respond to further stimuli, and is said to be in its refractory period. |
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Term
| Propagation of an Action Potential Along a Nerve Fiber |
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Definition
| When an action potential is triggered at the beginning of a nerve fiber, it causes the next region of the nerve fiber membrane to depolarize, also generating an action potential. This repeated continuously, and the wave of depolarization travels all the way along the fiber until it reaches the axon terminals. |
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Term
| Propagation of an Action Potential Along a Nerve Fiber |
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Definition
| When an action potential is triggered at the beginning of a nerve fiber, it causes the next region of the nerve fiber membrane to depolarize, also generating an action potential. This repeated continuously, and the wave of depolarization travels all the way along the fiber until it reaches the axon terminals. |
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Term
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Definition
| Nerve impulses travel along different nerve fibers at different speeds. The conduction velocity along a nerve fiber is determined by the diameter of the nerve fiber. Myelin is found in vertebrates. IN mammals, axon diameter seems to determine the degree of myelination |
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