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in a cell with 30 million sodium ions, the movement of how many ions can set up a membrane potential of 100mV?
6000 ions
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what is the voltage distribution across membrane based on?
charge distribution
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what is a membrane potential?
the electrical potential required to balance the flux of an ion through a selective channel driven by its concentration gradient
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which direction does sodium and potassium move?
sodium moves in, potassium moves out for nerve impulses through sodium and potassium channels
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what is the basis of the membrane potential
- ion channels control the membrane potential
- membrane potential is determined by unequal distribution of charge on two sides of the membrne (capacitor-like)
- b/c of potassium leak channels, resting membrane potentials are near the K+ equilibrium potential
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what are the common features of a neuron?
- dendrites (receive signals)
- cell bodies (synthetic center)
- axons (relay signal and can be myelinated)
- synapse (release new signal)
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what do you call a highly reliable synapse between a motor neuron and a skeletal muscle cell?
neuromuscular junction: stimulates an action potential in the muscle plasma membrane
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what kind of axons are myelinated?
long axons in PNS and white matter in brain
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what is in the cell body of a neuron?
ER, golgi, make synaptical vesicles (neurotransmitters)
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what happens during depolarization?
sodium channels open
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what happens in an action potential?
voltage gated Na channels open, which changes membrane potential; K channels open based on electrochemical gradient (voltage gated) Na goes into cell, K goes out. K leaks
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what is the rising phase of action potential mean?
- due to opening of voltage gated sodium channels
- closed sodium channel=membrane polarized
- open sodium channel (membrane depolarized)
- channels close to inactivated state that is refractory to activation of 1msec
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what is the structure of voltage gated channels?
- have six helices (S5 and S6 line pore)
- charged S4 helix acts as a voltage sensor
- nonhelical segments ling pore provide selectivity filter
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what protein acts as the ball on the ball on a chain model?
Raw3-IP on the cytoplasmic side
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what is the declining phase of action potential mean?
Na channel inactivation and opening of voltage gated K channels
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how is the threshold reached?
volrage channel trigger some Na channels to open which make other Na channels open
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what happens during the action potential?
- action potentials involve a coordinated series of channel openings
- small depolarizations trigger self-reinforcing openings of voltage gated sodium and potassium channels
- peak of action potential approaches Na equilibrium potential
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how can tetrodoxtoxin kill you?
- binds voltage gated sodium channels
- first isolated from fish of the order tetraodontidae (fish with 4 strong teeth); has a high dissociation constant (binds really tightly to sodium channels, blocks sodium channels from working
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how can depolarizations be produced?
- electrical stimulation
- ions entering the cells in response to an excitatory neurotransmitter (Ache)
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why is partial depolarizations necessary?
to open voltage gated channels; opening and closing of ion channels produces electrical signals that can be sent rapidly down
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describe propagation of an action potential
- Ca is outside cell, rushes in when voltage changes, through gated channels, Ca release causes synaptic vesicles to fuse with membrane, releasing neurotransmitter into synaptic cleft, which binds to receptors
- sodium channels leaks, propagates and stimulates voltage gated Na channels next to it to propagate signal
- K channels activated, goes out of cell, convert ligand gated channel to potential change, initiate new action potential on other side
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what is a synapse?
connection between domain signaling nerve to responding nerve cell
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how do you get rid of extra neurotransmitters?
- enzyme that degrades it
- endocytosized
- can be reused
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what does Na entry do to membrane potential? what is the purpose of inactivation?
Na entry depolarizes adjacent membrane, but inactivation prevents action potential from spreading in reverse?
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how do we know that action potential is unidirectional?
put in electrodes, shows the shift of electrical signal
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what are the tasks of the nerve cells?
receive, conduct, and transmit signal through action potential without weakening; ensure that signal is reamplified
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what opens in response to depolarization?
Na channels that further depolarize
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what triggers the depolarization of membrane?
electrical impulse
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what makes up the refractory component?
6 pass transmembrane protein, domain of channel that will block channel
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what can make signals conducted more rapidly?
in wider and myelinated axons
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what axons have the most rapid signal transductions?
proprioception, touch, pan and temperature
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what are nodes of ranvier?
spaces between glial cells, uninsulated segments of axonal membrane located at 1mm intervals
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which cells are usually myelinated?
either inside brain glial cells or outside brain peripheral nervous system (schwann cells)
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what kind of conduction results as a result of myelination?
saltatory conduction
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what is the insulator of myelin called?
myelin sheath
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what does the declining phase of action potential involve?
inactivation of Na channels and continued entry of K ions through voltage gated K channels
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what initiates an action potential?
binding of neurotransmitter to ligand gated channels in postsynaptic membrane initiates
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what causes action potential to arise?
if the membrane potential at the axon hillock reaches threshold
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how does the synaptic stimulation change the membrane potential?
locally
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what kind of synapses are excitatory and inhibitory?
- ligand gated cation channels-excitatory
- ligand gated Cl-channels -inhibitory
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how does cocaine affect the transmission of action potential?
targets dopamine transporter (prevent dopamine from being transported back to signaling neuron, keep sending signal in the synaptic cleft
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how does antidepressants create affect action potential?
target norepinphrine or serotonin uptake (block the reuptake)
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how many synapses are in the CNS?
10^15
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what are cajal bodies?
mRNA processing maturation of snRNP particles
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what structures are found in the nucleus?
cajal bodies, PML bodies, speckles
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what are speckles in the nucleus
clusters of interchromatin granules, involved in RNA processing, not transcription sites
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what makes proteins function in the nucleus?
transcription factors
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how can biochemists study the nucleus?
grounding cells up and doing differential centrifugation, in vitro look at function--no organelles found in nucleus
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how do geneticists study the nucleus?
mutagenesis in yeasts, look for secretion mutants in ER, Golgi pathway; identify proteins in the secretory pathway by doing mutagenesis
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how do we see where components of nucleus lie?
use antibodies that are made to differnt components of nucleus and see that idff component within nucleus are localized differently
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what is the function of the nucleolus?
genes that encode ribosomes are concentrated there; these genes are most likely duplicated; different copies of ribosomal genes whose job is to make ribosomal RNA
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what is the major structure of nucleolus?
1-5 per nucleus; transcriptionally active rRNA gene clusters; nearly 700 proteins in involved in rRNA synthesis
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