Term
| What is a resting membrane potential (RMP)? |
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Definition
| The RMP is the voltage that exists across a cell membrane when the cell is not transmitting electrical signals; polarity is such that the inside of the cell is negative with respect to the outside. |
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Term
| What are the nodes of Ranvier? |
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Definition
| They are the gaps in the myelin along axons. |
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Term
| What does the myelin sheath function to do? |
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Definition
| The myelin sheath functions to protect the axon, electrically insulate fibers, and increase nerve impulse transmission. |
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Term
| What cells form the myelin sheath in the peripheral nervous system? |
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Definition
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Term
| What cells form the myelin sheath in the central nervous system? |
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Definition
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Term
| What are the differences between saltatory and contiguous conduction? |
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Definition
Contiguous (continuous; lack myelination; grey matter)
Saltatory (myelinated; white fatty-matter; tissue is white) |
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Term
| What factors determine the velocity of nerve conduction? |
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Definition
1. Degree of myelination (contiguous or saltatory)
2. Axon diameter |
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Term
| What does the action potential frequency indicate? |
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Definition
| The AP frequency is an indication of stimulus intensity. |
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Term
| What is the "all or none" phenomenon? |
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Definition
| The phenomenon is a reference to the fact that a threshold must be crossed in order for an action potential to manifest. If a cell depolarizes slightly, but does not cross the threshold, it will not produce an action potential. |
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Term
| What ensures that an action potential is sent in only one direction along an axon? |
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Definition
| A refractory period ensures one-way travel of an AP. |
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Term
| In which direction do the action potentials flow? |
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Definition
| From the cell body, axon hillock, along the axon, and to the axon terminal |
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Term
| What initiates an action potential? |
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Definition
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Term
| What is the membrane threshold, and why is it important? |
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Definition
| Membrane threshold in an excitable cell, the critical value of the membrane potential to which the cell must be depolarized in order to trigger an action potential. |
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Term
| What is the total change in mV amplitude required to generate an action potential? |
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Definition
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Term
| Why are nerves and muscles considered to be "excitable" tissues? |
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Definition
| Muscle and nerve cells are considered to be "excitable" because they're capable of transmitting action potentials after electrical or chemical stimulation sufficient to depolarize the plasma membrane. |
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Term
| What does a membrane potential indicate? |
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Definition
| The difference in electrical potential or voltage that appears across the membranes of most cells |
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Term
| Which three ions are the major contributors to the resting membrane potential? |
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Definition
K+ Potassium (most permeable and, thus, most important)
Na+ Sodium
Cl- Chloride ions |
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Term
| What is the resting membrane potential for a typical nerve cell? |
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Definition
| -65mV to -85mV (usually -70mv) |
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Term
| Differentiate between a nerve cell and a glial cell. |
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Definition
Glial cells lack axons and dendrites, and they cannot generate action potentials. They support nerves.
Glial cells surround neurons, hold them in place, provide nutrition (nutrients and oxygen), help maintain homeostasis, provide electrical insulation, destroy pathogens, regulate neuronal repair and the removal dead neurons, and participate in signal transmission in the nervous system. |
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Term
| What are the major parts of a neuron? |
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Definition
| Cell body, dendrites, axon hillock, myelin sheath, axon terminal, node of Ranvier |
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Term
| Which part of the neuron has the lowest threshold? |
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Definition
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Term
| Name and describe the three classes of neurons of the nervous system. |
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Definition
1. Afferent neuron - generates AP from sensory receptors; long axon; found mainly in the PNS
2. Interneuron - found entirely within the CNS
3. Efferent neurons - generate AP from the CNS; has a long peripheral axon in the PNS |
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Term
| What are some of the purposes of glial cells in the CNS? |
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Definition
- support neurons
- insulate neurons
- guide young neurons
- promote health and growth |
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Term
| What is the primary function of each of the four glial cells that were discussed? |
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Definition
astrocytes - support and brace neurons; anchor neurons to their nutrient supplies; guide migration of young neurons during development; establish a blood-brain barrier (BBB); repair minor brain injuries; degrade neurotransmitter activity; take up excess K+ from the ECF
microglia - phagocytes; immune defense of the CNS
ependymal cells - line the central cavities of the brain and spinal column; help form the cerebral spinal fluid
oligodendrocytes - wrap CNS nerve fibers (to form myelin sheaths) |
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Term
| What are the contributors to the nerve cells' resting membrane potential? |
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Definition
| The sodium/potassium pump actively helps to contribute to the RMP, while "leaky" and ion gated channels passively contributes to the RMP. |
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Term
| How can ions move quickly across a membrane? |
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Definition
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Term
| What is the difference between a "leaky" ion channel and a gate ion channel? |
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Definition
| "Leaky" channels are always open, whereas gated ion channels must be opened via voltage, thermal, chemical, or mechanical stimulation. |
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Term
| What are the four types of gated ion channels discussed in class? |
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Definition
1. voltage gated - membrane potential
2. chemically gated - neurotransmitter
3. mechanically gated - physical deformation of receptors
4. thermally gated - local temperature |
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Term
| What must happen in order for a chemically gated ion channel to open? |
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Definition
| A neurotransmitter must bind to the receptor |
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Term
| A voltage gated ion channel will open under what conditions? |
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Definition
| when the intracellular fluid environment is less negative (positively charged) |
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Term
| How will ions move across membranes through open gated channels? |
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Definition
| down their electrochemical gradient |
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Term
| What contributes to the electrical changes in a neuron? |
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Definition
| ions moving in and out of the neuron |
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Term
| What are the biggest difference between a graded potential and an action potential? |
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Definition
GP travels short distances, where as AP travels farther
GP voltage intensity decreases with distance, whereas AP does not
GP is sub-threshold, whereas AP passes the threshold
GP is directly proportional to the triggering event, whereas AP impulses due to crossing the threshold |
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Term
| What is the difference in duration and intensity of change in membrane potential between a graded and action potential? |
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Definition
| GP - duration is directly proportional to the triggering event. In a typical nerve cell, the AP duration is approximately 1 ms. |
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Term
| Name and describe in detail what happens during the four polarization states during the generation of an action potential. |
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Definition
1. Depolarization - membrane potential becomes less negative than the RMP
2. Repolarization - Membrane returns to RMP after depolarizationi
3. Hyperpolarization - membrane becomes more polarized (more negative) than the RMP
4. ? |
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Term
| The net flow of cations changes the charge of a membrane at a particular location at the plasma membrane. Ions can get across a plasma membrane via several mechanisms. What are the two broad categories of how ions pass a plasma membrane? |
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Definition
| Active transfer vs. Passive transfer? |
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