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94 Cards in this Set
- Front
- Back
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What is tetrodotoxin?
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A toxin from Puffer fish (only used in research). Selectively inhibits sodium ion channels - no affect on K channels or on ATP hydrolysis to ADP and energy.
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What is tetraethylammonium ion?
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Only used in research. Highly specific to inhibiting K ion channels. Does not interfere with sodium ion channels
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What is Ouabain?
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It is a cardiac clycoside used clinically. Inhibits hydrolysis of ATP but does not interfere with sodium and potassium channels
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What is the all or none principle in regards to action potentials?
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You can not tell from the size (amplitude) of the action potential what the strength of the stimulus was.
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What is a refractory period?
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The time it takes for an excitable membrane to be ready for a second stimulus once it returns to its resting state following an excitation.
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What is absolute refractory period?
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It coincides with Na+ permeability changes. Regardless of stimulus strength, another action potential can not be generated.
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What is relative refractory period?
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It coincides with K+ permeability. Another action potential can be generated if the stimulus is greater than the normal threshold. Essentially at the end of the action potential.
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What is a ligand-gated channel?
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Mediates local increases in ion conductance at synapses and either depolarizes or hyperpolarizes. Examples: nicotinic ACH receptor, GABA receptor)
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What is a voltage-gated channel?
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Mediates rapid voltage gated changes in ion permeability during action potential in excitable cells.
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What is the main function of myelin?
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To increase velocity of conduction
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What is the maximum conduction velocity in human nerve cells?
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Approximately 120 meters per second
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What is the relationship of velocity to fiber diameter?
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About 1:1
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What is the largest fiber diameter in humans?
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Approximately 20 micometers
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What two things determine the velocity of conduction in nerve cells?
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Diameter and myelination
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If nerve fibers were not myelinated, what would have to happen to the fiber in order to have the same velocity?
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The diameter would have to increase
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How does myelination save energy?
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It reduces the amount of ATP needed to carry a signal
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When is most myelin produced?
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Most myelin is laid during embryo stage
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On a nerve fiber, where does the action potential take place?
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Only in the Nodes of Ranvier (spaces between myelin) Would not take place under myelin
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What are three properties of the nodes of Ranvier?
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Membrane capacity of ability to hold a charge is low, resistance is high, Na+ channels are clustered at the nodes (1,000/mm2) - the more ion channels, the more the action potentials
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What is saltatory propagation?
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Action potentials along myelinated axons from one Node of Ranvier to the next node, increasing the conduction velocity of action potentials without needing to increase the diameter of the axon.
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What is the internodal area of an axon? What are two properties of that area?
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Internodal area is under the myelin. In this area, the ability to hold a charge is high and resistance is low (electrotonic potential)
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What happens to the electrotonic potential under myelin and at the nodes of Ranvier?
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Under myelin, electrotonic potential maintains at threshold level, then when entering the nodes with the Na+ channels, immediately goes into action potential
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What channels are present in internodal areas?
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Very few Na+ channels (approx 25 channels/mm2), large amount of K+ channels present which will block action potential
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What is a potential way of increasing conduction in a demyelinated fiber (i.e. in a patient with MS)?
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Block K+ channels - conduction will improve. An example of a K+ blocker is 4-aminopyridine
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What are 4 types of synapses?
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Axodendritic (synapse between axonal knob and dendrite), axosomatic (between axon knob and soma), Axoaxonic (between axonal knobs of two neurons), dendrodendritic (only in certain specialized neurons - not common)
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What are the two most common types of synapses?
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Axodendritic and axosomatic
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What are asymmetrical or Gray's type 1 synapse?
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Postsynaptic membrane is thicker. Usually excitatory
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What are symmetrical or Gray's Type 2 synapses?
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Pre and post-synaptic membrane are of equal dimension. Usually inhibatory
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What are the types of neurotransmitters?
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Excitatory, Inhibitory, Neuromodulatory (don't directly cause excitatory or inhibitory potentials - they change environment to help make excitation or inhibition easier)
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What are some examples of neurotransmitters?
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Acetylcholine, epinephrine, norepinephrine, serotonin, GABA, glutamate, glycine, B-endorphin, enkephalin, somatostatin
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What is the most common inhibitory neurotransmitter?
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GABA (gamma-Aminobutyric acid)
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What is the function of a neurotransmitter dependent on?
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The receptor. Most neurotransmitters can function as excitatory, inhibitory or neuromodulatory
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Where is a neurotransmitter synthesized?
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In the soma or in the synaptic knob (in or out of the synaptic vesicles). The final destination is going to be storage in the vesicles
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What types of neurotransmitters must be synthesized within the soma and why?
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Peptides must be synthesized in the soma because that is where the DNA, RNA, RER is located. They bind to proteins and move away from the cell body
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What does Antrograde mean?
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Movement away from the cell body
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What does Retrograde mean?
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Toward the cell body (or soma)
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What occurs at the neuromuscular junction?
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As action potential gets to synaptic knobs, Ca++ voltage gated channel open - cause release of NT, Under resting condition, Synapsin-I is dphosphorylated attached to synaptic vesicles leading to actin polymerization. Synaptic vesicles "caged" until neuron stimulated. Influx of Ca++ - binds to calmodulin - complex activates Kinase II which phosphorylates synapsin-I carboxyl terminal. Disruption of actin-synapsin-I vesicle complex. Vesicles move to pool of vesicles for release. Synapsin-I dephosphorylated. Whole process < 0.5 millisec
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What happens if neurotransmitters are released accidentally?
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Damage occurs
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What occurs at the release of excitatory neurotransmitters?
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It is released into synaptic junction - binds to receptor on post synaptic membrane. Until then, can be excitatory, inhibitory, or neuromodulary. Depolarization of post synaptic membrane (conductance of BOTH Na+ and K+) including action potential: excitatory postsynaptical potential - End plate potential. Lasts 1-2 millisecs
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What occurs at the release of inhibitory neurotransmitters?
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Same binding process on postsynaptic membrane as excitatory NT. Inhibitory postsynaptic potential. K+ moves out and Cl- moves in. Membrane potential becomes more electronegative. 1-2msec
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What are two ways that neurotransmitters are deactivated?
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Immediately on the postsynaptic membrane or reuptake mechanism
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How are neurotransmitters deactivated immediately on the postsynaptic membrane?
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ACH conversion to acetate and choline by the action of ACHesterase. So effective that nearly 70% of ACH is dactivated PRIOR to inducing its activity
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How are neurotransmitters deactivated by reuptake mechanism?
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Serotonin and Norepinephrine - reuptake into synaptic knob and deactivated on mitochondrial membrane by monoamine oxidase. NE also deactivated on postsynaptic membrane by catecholomethyl transferase.
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Why does norepinphrine have two mechanisms for deactivation?
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Because NE is not only produced in the neurons but also secreted by the adrenal medulla into the blood which goes to the tissue and needs to have reuptake by the tissues as well as by the neurons.
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What is the purpose of Serotonin reuptake inhibitors?
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Increases pool of serotonin at synapse. Helps control depression.
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What controls the autonomic nervous system?
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Hypothalamus
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What factors divide the autonomic nervous system into sympathetic and parasympathetic?
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Anatomic distribution and origin of the nerves, effects on organs (mostly antagonistic), neurotransmitter released by the POST ganglionic fibers, discharge pattern
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What kind of receptors to postganglionic neurons are in the autonomic nervous system?
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Nicotinic receptors
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What kind of receptors to all parasympathetic target organs are in the autonomic nervous system?
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Selective Muscurinic receptors
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What kind of receptors to all sympathetic target organs are in the autonomic nervous system?
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Selective alpha and beta receptors
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What kind of receptors does ACH bind to?
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Nicitinic or muscurinic
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What kind of receptors do epinephrine and norepinephrine bind to?
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Alpha and beta receptors
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What do preganglionic fibers secrete?
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They always secrete ACH (excitatory neurotransmitter)
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Where is the sympathetic chain located?
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Parallel to the CNS
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Where is the post ganglia located?
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Either within the sympathetic chain or just outside of it
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What are three characteristics of the long sympathetic post ganglionic fibers?
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Extend all the way into the tissues, secretes mostly NE (90%) or epinephrin (10%) (can bind on alpha or beta receptor), Adrenargic: secreting adrenaline and noradrenaline
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Where are the preganglia located in the parasympathetic nervous system?
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Cranial nerves 3,7,9,10; S2-4. Preganglionic fibers very long - to a cm away from tissue it is going to innervate. Secretes ACH (excitatory - binds to nicotinic receptor on post ganglion)
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Where are the postganglion located in the parasympathetic nervous system?
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Only about a cm away from tissue. Very short (opposite of sympathetic). Secretes ACH - binds to muscurinic receptors
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What is the discharge pattern for the sympathetic nervous system?
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Massive mechanisms to prepare for stressful conditions
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What is the discharge pattern for the parasympathetic nervous system?
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Discrete mechanisms - often to specific tissues/organs (i.e. vagel nerve - digestion)
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What are the cells of the adrenal medulla and what do they do?
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Modified sympathetic postganglionic fibers and chromaffin cells. Chromaffin cells secrete NE and Epi directly into circulation (as opposed to as a neurotransmitter)
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Where is the adrenal medulla derived from?
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The same neuronal crest line as the sympathetic system
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What is the pattern of secretion of NE and Epi by the adrenal medulla?
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At birth, secretes more NE until the sympathetic system develops. Epi is more dominant with age.
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Approximately how many neurons are in the CNS?
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Over 100 billion
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Approximately how many different types of nerve cells are ther?
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Approximately 1,000
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A typical nerve cell has how many synapses on its surface?
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1,000-10,000 and may communicate with as much as 1,000 or more other neurons
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What are the components of a typical neuron?
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Soma, dendritic extensions (for afferent [toward] input) and a single axon that is normally highly branched into hundreds of thousands of branches.
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What happens to myelination at the branching of the axon
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It stops
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What are the three classifications of neurons?
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Unipolar, Bipolar and Multipolar
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What are unipolar neurons?
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Contain a soma and axon (i.e. sensory and dorsal root ganglion). More common in fetal development than in adult.
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What are bipolar neurons?
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Contain a soma and a single dendritic extension and axonal extension. (i.e. interneurons and retinal bipolar neurons) Common in the CNS
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What are multipolar neurons?
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Contain a soma, many dendritic extensions and a single axon. Most common type of neuron (i.e. alpha motor neurons).
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What is the axon hillock?
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Junction between the cell body and axon. Allows output into the axon that originally comes from the dendrites
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What is Tau protein?
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Building block of proteins of the microtubules located in the axon.
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What is phosphorilation of microfilaments?
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Microtubules become tangled (neurofibrillary) - causes Alzheimers, dementia, parkinsons.
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What does antrograde mean?
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Down axon away from cell body
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What does retrograde mean?
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up axon toward cell body (may not happen properly in tangled microtubules)
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What are the most important function in establishing nerve membrane potential (though there are also other ions)
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Sodium, Potassium, Chloride
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What is the negative resting membrane potential for nerve cells?
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-60 to -90 mV
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What is the Nernst equasion?
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E(ion) = RT/zF In Co/Ci (All ions E = R(gas constant)T(temperatue)/z(charge) F(Faraday) natural law of concentration outside/concentration inside
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Nernst Equasion for a single ion
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Em (membrane potential) = -61log concentration in/concentration out
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In the coupled Na-K ATPase pump, what is the influx of ions?
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Na+ pumped outward while K+ is pumped inward, both move against concentration gradient , 3 Na+ pumped for every 2 K+ - causes inside to be more negative. At max, 200 Na+ and 130 K+ pumped/sec
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What are the two types of signals that nerve and muscles use through voltage changes for communication?
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Graded potential and action potential
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What happens in depolarization?
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Membrane permeability to Na+ increases several hundred fold post stimulation, Na+ rushes in, no significant change in K+ permeability, Na+ causes reversal of polarity, membrane potential approaches but doesn't reach E(Na+) (potential difference across membrane)
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Why does Membrane not reach E(Na+) in depolarization?
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Increase in Na+ conductance time is limited, depolarization of membrane and increase in Na+ permeability gives powerful boost to K+ conductance of the membrane w/ a delay of approx 1 msec, Increase permeability to Na+ stops
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What occurs in repolarization?
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Na+ permeability turned off in order to repolarize, permeability to K+ increases over its resting level, K+ moves out of neuron, Na/K pump restores resting membrane potential
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What causes hyperpolarization?
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K+ permeability greater than normal
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What are conditions like at the membrane threshold?
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Usually 5-15mV above resting membrane potential. Charge is unstable and dissipates rapidly and reverses its polarity resulting in rapid rise of action potential (depolarization). Unstable charge needed in order to create action potential without a really really strong stimulus.
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What happens during the absolute refractory period?
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Sodium dependent, cell is unexcitable, threshold 5-15mV above resting membrane potential (established with unequal distribution of ions)
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What is hypopolarization (depolarization) vs hyperpolarization?
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Hypopolarization is becoming less electronegative. Hyperpolarization (by way of inhibitory neurotransmitters) is going further from threshold - more electronegative. In hyperpolarization, sodium ion channels are not affected, but chloride channels are.
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Which of the following describes graded potential? A) varies in magnitude depending on stimulus strength, B) increase in magnitude with distance from site of stimulus, C) obeys all or none principle, D) all of the above
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A) varies in magnitude depending on stimulus strength
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Acetylcholine actions can best be described as: A) ligand-gated ion channel, B) voltage gated ion channel, C) GABA-gated ion channel, D) b&c, E) a&b
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A) ligand-gated ion channel
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Which of the following factors increases the number of quanta of neurotransmitter released? A) increase in extracellular calcium, B) decrease in extracellular calcium, C) acetylcholinesterase in presynaptic fiber, D) a&b, E) a&c
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A) Increase in extracellular calcium
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In relation to autonomic nervous system, what has long preganglionic fibers?
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Parasympathetic
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