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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?
what is the voltage distribution across membrane based on?
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
which direction does sodium and potassium move?
sodium moves in, potassium moves out for nerve impulses through sodium and potassium channels
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
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)
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
what kind of axons are myelinated?
long axons in PNS and white matter in brain
what is in the cell body of a neuron?
ER, golgi, make synaptical vesicles (neurotransmitters)
what happens during depolarization?
sodium channels open
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
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
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
what protein acts as the ball on the ball on a chain model?
Raw3-IP on the cytoplasmic side
what is the declining phase of action potential mean?
Na channel inactivation and opening of voltage gated K channels
how is the threshold reached?
volrage channel trigger some Na channels to open which make other Na channels open
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
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
how can depolarizations be produced?
- electrical stimulation
- ions entering the cells in response to an excitatory neurotransmitter (Ache)
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
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
what is a synapse?
connection between domain signaling nerve to responding nerve cell
how do you get rid of extra neurotransmitters?
- enzyme that degrades it
- can be reused
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?
how do we know that action potential is unidirectional?
put in electrodes, shows the shift of electrical signal
what are the tasks of the nerve cells?
receive, conduct, and transmit signal through action potential without weakening; ensure that signal is reamplified
what opens in response to depolarization?
Na channels that further depolarize
what triggers the depolarization of membrane?
what makes up the refractory component?
6 pass transmembrane protein, domain of channel that will block channel
what can make signals conducted more rapidly?
in wider and myelinated axons
what axons have the most rapid signal transductions?
proprioception, touch, pan and temperature
what are nodes of ranvier?
spaces between glial cells, uninsulated segments of axonal membrane located at 1mm intervals
which cells are usually myelinated?
either inside brain glial cells or outside brain peripheral nervous system (schwann cells)
what kind of conduction results as a result of myelination?
what is the insulator of myelin called?
what does the declining phase of action potential involve?
inactivation of Na channels and continued entry of K ions through voltage gated K channels
what initiates an action potential?
binding of neurotransmitter to ligand gated channels in postsynaptic membrane initiates
what causes action potential to arise?
if the membrane potential at the axon hillock reaches threshold
how does the synaptic stimulation change the membrane potential?
what kind of synapses are excitatory and inhibitory?
- ligand gated cation channels-excitatory
- ligand gated Cl-channels -inhibitory
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
how does antidepressants create affect action potential?
target norepinphrine or serotonin uptake (block the reuptake)
how many synapses are in the CNS?
what are cajal bodies?
mRNA processing maturation of snRNP particles
what structures are found in the nucleus?
cajal bodies, PML bodies, speckles
what are speckles in the nucleus
clusters of interchromatin granules, involved in RNA processing, not transcription sites
what makes proteins function in the nucleus?
how can biochemists study the nucleus?
grounding cells up and doing differential centrifugation, in vitro look at function--no organelles found in nucleus
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
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
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
what is the major structure of nucleolus?
1-5 per nucleus; transcriptionally active rRNA gene clusters; nearly 700 proteins in involved in rRNA synthesis