pre midterm 1 Flashcards
resting membrane potential
constant voltage across a membrane when the cell is at rest (-40 to-90 mV, usually -60)
receptor potential:
change in membrane potential when sensory neurons are stimulated.
passive vs active flow in an axon
passive conduction decays over distance and active conduction is constant over distance.
K, Na, Cl, and Ca concentrations inside and outside the cell? what does this mean?
K: high inside, low outside
Na- low inside, high outside
Cl- low inside high outside
Ca- low inside high outside.
this means there is a slow potassium leak from the cell.
hodgekin and huxley
used a squid giant axon to study neurobiology. found when potassium concentration was changed, the membrane potential changed therefore potassium drives membrane potential.
voltage gated sodium channels and APs.
sodium channels don’t open until the threshold potential is reached. sodium channels open quickly during depolarization during the rising phase. they inactivate for the absolute refactory period. then the channels must be de-inactivated to generate another AP.
voltage gated potassium channels and AP
channel is sensitive to voltage changes and subunits undergo shape conformation to open the pore with depolarization. there is a 1 ms delay.
key properties of action potentials (repeat card until i understand)
- membrane voltage is at threshold when sodium channels open.
- during the rising phase membrane voltage is negative and Na influx leads to depolarization
- overshoot phase causes membrane voltage to rise above 0mV and approach the equilibrium for Na
- falling phase: Na channels inactivate and the K channels open with a delay and K efflux causes the membrane voltage to be negative.
- undershoot phase: when membrane voltage approaches equilibrium for K, there is hyperpolarization until K channels close.
- absolute refractory period: Na channels inactivate.
active and passive flow in action potentials
active: local inward movement of Na, outward movement of K. depolarization and hyperpolarization
passive: movement of current produced in active phase
tetrodotoxin
blocks Na channels and inhibits depolarization
alpha toxins
prolong action potentials and scramble information flow
beta toxins
cause Na channels to open at lower potentials causing uncontrolled action potential firing
dendrotoxin
blocks K channels
ion slectivity
each ion channel has a sleectivity filter that allows a particular ion to travel through. acheived by amino acids at the mouth of the pore.
voltage gated ion channels
larger than other channel types
transmembrane structures have structures with oppisite charges to their ion that act as voltage sensors.
depolarization pushes sensors outwards openening the channel and hyperpolarization pushes the sensors inwards closing the channel
ligand gated ion channels
respond to chemical signals, less selective that voltage gated,
electrical vs chemical synaptic transmission
electrical: direct neuron-neuron current flow, is passive, bidirectional, and uses gap junctions as ion channels
chemical: signals are mediated by neurotransmitters at the synapse. are slower, unidirectional, and use neuriotransmitters and their receptors.
where is electrical synaptic transmission found and why is it used
found in areas where neuron activity is highly synchronized in mammalian CNS. in non-neuronal cells like epithelial and heart muscle ceclls. 6 connexin units form 1 connexon channel and pores allow for bidirectional ion flow. the generation of AP in one neuron results in the synchronized firing of AP in the adjacent neuron, stimulating entire tissues at once.
presynaptic structures that guide neurotransmitter
pools of vesicles, voltage gated calcium channels, SNARE proteins to bring vesicle and membrane together.
postsynaptic structures for neurotransmitter purpose
help to anchor postsynaptic receptors in their membrane. prevent lateral diffusion of receptors, involved in synaptic plasticity.
neurotransmitter release
depolarization causes voltage gated calcium channels to open causing calcium influx. calcium causes vesicles to fuse with the presynaptic membrane and release neurotransmitter into synaptic cleft
postsynaptic path of neurotransmitter
transmitter binds to receptor molecules in the postsynaptic membrane. polysynaptic channels will either open (depolarize) or close (hyperpolarize). neurotransmitter either has excitatory or inhibitory effect on the postsynaptic neuron.
criteria for classical neurotransmitter
- substance exists in presynaptic neuron
- substance is released in response to presynaptic depolarization and mediated by calcium.
- specific receptors for the substance exist in the postsynaptic cell
what is the clinical significance of the neuromuscular junction? what is it?
neuromuscular junctions are synaptic junctions outside the brain or spinal chord. neuron-muscle. fast and reliable transmission and a large synapse size make there junctions pharmacologically significant.
