midterms i guess idk cymbalta is frying my brain Flashcards
What does the permeability of the cell membrane depend on
molecular size, lipid solubility, and charge
What can cross the membrane and what cannot
Gases can go across, polar molecules and ions need help of proteins
The relative rate of simple diffusion is () to the gradient across the membrane
roughly proportional
What type of transporter is a Na+ K+ pump? What does this type of transporter do
ATPase, it moves both molecules against their concentration gradients
What is secondary active transport
When something is moved down concentration gradient and something else uses that energy to move up
How are protein channels made and how do they filter
Made of 4-5 subunits that form a central pore. The physical properties determine the size and electric charge of things that can go through
Where do ligand gated channels trigger events
at the membrane because they are on the membrane lol
What part of voltage gated channels sense the potential difference across the membrane, and how does it work
The S4 segment acts as the voltage sensor. In the resting state (polarized), the inside of the membrane is negatively charged, attracting the positively charged S4 segment inward. Upon depolarization, the reduced negative charge inside the cell causes the S4 segment to move outward, triggering the opening of the channel.
What usually mediates endocytosis and why?
Usually receptor mediated to capture proteins
What are some reasons for exocytosis
Bulk transmembrane transport of molecules, such as neurotransmitters
What are the two types of exocytosis? Explain how they work and in what instances are they used
Exocytosis 1, dubbed kiss and run, and 2, full exocytosis. For 1, the vesicle can disconnect many times before contents are emptied. Only part of the contents go into interstitial fluid, and it is used for low rates of signalling. For 2, it is used for high levels of signalling and membrane proteins.
What creates a concentration gradient
enzyme ion pump, 3 Na+ are pumped out and 2 K+ are pumped in. Uses a shit ton of energy (1/3 of energy needs).
Why is the resting potential of the membrane not the same as the estimated resting potential of Na/K inequality (-10mV)?
Because the membrane is more permeable to K+ than Na+ and because there’s like no K+ outside, the K+ pumped in all want to go out. So they go out, until its wayyyy too positive outside, then they stop. At this point, its -70 mV
What does the Nernst equation describe and under what circumstances can you use it
It describes the balance between chemical force of diffusion and electrical force of repulsion (charges). You can only use it if there is only one ion species diffusing across the membrane
You use the Nernst equation to find the equilibrium potential for K+. What does this value mean
Its what the membrane potential would be if there were only K+ ions in the cell. Or, its what K+ wants the membrane potential to be (but it doesn’t get what it wants because the other ions are there to fuck shit up lol)
What is Eion
membrane potential that exactly opposes the concentration gradient (positive value)
What are the membrane potentials of K+ and Na+, and why is the actual membrane potential closer to that of K+’s?
K+ is -90, Na+ is +60. Its closer to K because K is more permeable, and according to the Goldman Equation (basically more overpowered Nernst Equation), the permeability of an ion is proportional to the resting membrane potential
Where are the Cl- ions concentrated and why
Outside the cell because theres a shit ton of big proteins and they are negative for some reason and the Cl-s are like fuck this shit im out. It’s not actively pumped out. They just don’t like being inside
What is conductance
How easy stuff (e.g. Na+) goes through a protein channel in the membrane
How is a Na+ channel opened
It is a voltage gated channel so the membrane needs to depolarize to -55, which then opens the activation gate. Shit ton of Na+ enters, and the cell depolarizes rapidly. Inactivation gate closes, then no more Na+. In order to remove the inactivation gate, you need the membrane potential to be lower than -55
What do you need for an action potential
A shit ton of Na+ channels, so the membranes can depolarize
What causes the repolarization part of an action potential
Na+ channels are now closed and K+ leaks out of the cell, hyperpolarizing it.
When the membrane potential is positive, what force drives Na+ into the cell?
Concentration, not electrical forces. Electrical forces is only when the membrane potential is not positive
Draw an action potential graph, labelling key points and explain
Check membrane 2 slide 24
What are the two types of refractory periods, explain them
Absolute and relative. Absolute is when none of the channels are reconfigured, relative is when some but not all are reconfigured, If you want to fire during relative refractory period, you need a stronger depolarization, and these action potentials will be of lower amplitude because the cell is EXTRA negative due to the K+ still leaving the cell.
You have your worst enemy strapped to a vivisection table, and you are about to inject a lethal injection you lawfully stole from a high security prison. What does the lethal injection do to your enemy’s cells
It prevents the cells from producing an action potential by keeping it above 20 mV, and the Na+ will be permanently inactivated. So the lethal injection puts a ton of K+ in extracellular space so the resting potential is no longer negative. (wow imagine uoft telling us how to kill ourselves, its like they actually want some of us to die off to reduce the load on their facilities while still milking our money)
Why is there a hyperpolarization after the action potential
Because K+ is leaving the cell to repolarize, and they overshoot a little
What is impulse conduction
When an action potential passively spreads because of the local changes in membrane potential
Can unexcitable cells depolarize?
Yes, they can conduct passive currents but cannot generate action potentials because they don’t have axons to carry the action potential elsewhere
What is a length constant for excitable cells
It measures how quickly a potential difference goes to zero as a function of distance. So, the bigger, the better (if you want the signal to send). It is the distance you can travel until the voltage drops to 37% of the original value.
How do you increase the length constant
Increase membrane resistance so you basically wrap duct tape around a pipe so you get less leakage. Increasing diameter so there is less internal resistance. However the best way is myelination
Express the length constant in terms of membrane an internal resistance
square root of membrane resistance over internal resistance
What are glial cells
cells that assist the nervous system, required for nutrition and increased membrane resistance. specialized glial cells form a myelin sheath.
What are the two types of specialized glial cells that myelinate?
Schwann cells that wrap all around a part of one axon. Oligodendrites streak out like octupus tentacles and wrap a bunch of axons separately
What is saltatory conduction
When action potentials jump from Nodes of Ranvier because they spread passively through myelinated regions. Only exposed membranes at nodes are excitable
What does one action potential at a node of ranvier do for the following nodes? Why is this helpful for not fucking up action potentials?
It brings the next 10 nodes to -55mV to generate action potentials. This is to prevent action potentials dying if a few nodes are poisoned.
What is a remak bundle
When a schwann cell surrounds a bunch of axons with only one layer, slightly insulating them
Why are refractory periods important
Because it prevents the action potential from going backwards, and makes it die out at the end of the cell.
What is a synapse
Association of a neuron with another neuron or muscle or gland
What is an electrical synapse and what cells are they present
At gap junctions bridged by connexins that allow small ions and depolarization to happen. There are no neurotransmitters. This is common in neurons and glial cells as well as cardio contractile muscles
How does exocytosis happen at the bouton
Ca++ is the ion that always triggers exocytosis. It is ingested when action potentials open the voltage channels for Ca++, and exocytosis happens. Some kiss and run, some full fusion. Vesicles are normally docked and ready to go
What are the chances of vesicle release at synapses
10-90%
What are the two different types of post synaptic receptors, explain the similarities and differences
The binding of neurotransmitter causes a change in shape of the receptor protein for both. A metabotropic receptor initiates a metabolic cascade to activate enzymes, and molecules that bind to it are considered neuromodulators. An ionotropic receptor directly opens channels, and molecules that bind to it are considered neurotransmitters
Binding of neurotransmitters to the post synaptic membrane for ionotropic receptors causes what
Excitatory or inhibitory post synaptic potentials, or respectively known as EPSPs and IPSPs. EPSPs happen when the ion channel caused by the ligand lets in positive ions, such as Na+ and K+, which depolarizes the membrane. IPSPs happen when the ion channel lets in Cl- or lets K+ out, which hyperpolarizes
What are the four common ionotropic ligands
Acetylcholine, Glutamate, GABA, Glycine
How does the metabotropic pathway work
Binding of the ligand activates an enzyme that is usually g protein coupled, this produces second messengers, which then activate other proteins. Until it phosphorylates a membrane protein.
What are the three 2nd messengers for metabotropic pathways
cAMP, cGMP, and lnP3s
explain how the b-adrenoreceptor works, what is the ligand, what type of pathway does it go through
It is a metabotropic pathway, the ligand is noadrenaline, which activates adenyl cyclase via g-protein alteration, and that phosphorylates the membrane Ca++ channel, increasing Ca++ influx. This is an EPSP
What are ligands for metabotropic receptors
ACh, peptides, catecholamines (noadrenaline and dopamine), serotonin, purines (ATP, adenosine), gases (NO, CO)
What parts of a neuron are not excitable and where PSPs occur
Dendrites and cell body
What is the trigger zone
The nearest excitable membrane at the beginning of the axon
How do post synaptic potentials (PSPs) travel
Through passive conduction
What are the two types of PSP summation
Spatial summation, when 10-30 PSPs at different synapses add up. Temporal summation is when there are only a few active synapses but they generate EPSPs at a high frequency and the summed potentials reach the threshold
Draw spatial summation and temporal summation as a function of membrane potential (mV) and time.
Check answers in membrane 04 pages 24-25
Where are IPSPs located and why are they there
They are between EPSPs and the trigger zone, so they can shunt the signals. It’s like casting counterspell in BG3 but instead of casting it whereever the fuck you want, you need to be positioned between the enemy and their target.
How does the IPSP shunt the signals provided by the EPSPs (how does your neuron cast counterspell, esentially)
It opens the Cl- channel, which has a resting membrane potential around -70mV. This does nothing at resting membrane potential, but when the membrane is depolarized, it clamps the membrane potential back down to resting, inhibiting the signal
Which are more common, IPSPs and EPSPs
IPSPs. Imagine if you had no inhibition. that would be very bad. you would drink vodka almost every day and lick your self harm scars until your tongue pushed past your epidermis and you would think of strade all the same
How do spike trains form for action potentials. What does this tell the brain
You have refractory periods, and hyperpolarization. The Na+ channels reconfigure because the cell is too polarized (it is voltage gated). The voltage gated K+ channels also close when membrane is repolarized. With all the right things closed, the membrane can go through diffusion back to resting MP, and fire again considering the EPSP still persists. This spike train tells the brain it is a big signal
What is a receptor potential, does it depolarize or hyperpolarize
a change in membrane potential when an external sensory que is recieved. This generally causes depolarization, except for photoreceptors
Where are sensory receptor proteins, and how do they work
they are in the cell membrane like the receptor proteins for post synaptic potentials (PSPs). They can either directly open ion channels or activate an enzyme with g-protein coupling, producing a secondary messenger, and amplifying the signal (like in a metabotropic pathway)
What is a PSP
post synaptic potential
Where are olfactory neurons located
At the olfactory epithelium, high in the nasal cavity
Write out the pathway for olfactory neuron signalling
Specific receptor proteins bind to specific odorants, g-protein is activated, adenyl cyclase activated, secondary messenger (cAMP) released, cAMP bind to ion channels, allow Na+ and Ca++ through, depolarizing the membrane
What are the two types of sensory cell transmission
- action potential generated at a branch point. the receptor potential will need to be summed at the branch point for an action potential 2. no AP produced, the depolarizing current goes through the membrane and causes influx of Ca++ which triggers exocytosis (vescicle release)
How does the taste receptor signal
Influx of Ca++, the depolarizing current reaches the other end of the cell, and vescicles are released.
What is adaptation for membrane potentials
When the membrane potential is not sustained even though the stimulus is present
What are the two types of membrane potential adaptations
Slow, where the receptor potential (i.e. depolarization) is sustained throughout the stimulus, but declines slightly. It is interested in the magnitude of stimulus. Rapidly adapting is where the receptor potential is zero when the stimulus is constant. It is kind of like a f’(x) of the stimulus. It only cares when there is a change in magnitude. It can be positive and negative
What is habituation
When repeated stimuli get weaker and weaker responses over time. This depends on the cell, some exhibit this a lot, others do not
If a stimulus is very strong, what will happen? What concept explains this
Coding of stimulus intensity. It says that receptor potential varies depending on stimulus strength. Strong stimuli cause greater receptor depolarization, and more neurotransmitter is released or the action potentials are at a higher frequency.
How do higher threshold sensory neurons help with coding of stimulus intensity
It allows the neurons to bypass the refractory period, and can sense sensations stronger than refractory periods allow
