Exam 4: February 6-10 Flashcards
what is a neuron?
a highly specialized cell – it doesn’t look like the other cells in our body – it has strange arms going off of it
it’s still one of our cells! it still has a cell body and everything
what happens in the nucleus?
the nucleus is where we re-ferment DNA to make proteins so that the cell can do the jobs it has to do
this happens in neurons too because they’re just like the other cells in our body!
how big is the cell body of a neuron? what does it do?
cell body is not as big an area as in other cells because it has all the arm extensions off of it
lots of neurotransmitters that get used by these cells are proteins that get made in this cell body area in the nucleus
what are processes?
the projections/extensions/arms sticking off – they aren’t very long but there’s typically one that’s much longer than the others – processes allow the cell to make specific connections to and from other cells – so some processes gather info from other cells and other send information to other cells
what are the two types of processes?
dendrites and axons
what are dendrites? what do they do?
a process on a neuron and they are all across the cell body and they receive information
upwards of 400K from one neuron
why are there so many dendrites?
we have so many of them because they receive information with membrane bound receptors so therefore we need to have enough space for all those receptors
if we increase the number of receptors we increase the likelihood of communication – so the more SA for the receptors the more communication possibilities and the more information can be received
we also want our neurons to be collecting information from lots of places!
what are axons? what do they do?
they send information
they are a single, elongated tube that comes off of the neuron cell body
they are much wider and longer than dendrites, up to 1 meter long!
where are processes located?
all processes come off of the cell body
why are axons so long?
they’re long because we need them to be able to go from our spinal cord all the way to our big toe and the tips of our fingers – one cell is covering this whole distance! It goes from the cell body and send information out like going out to the fingers to tell the muscles to move
what is the axon terminal?
an axon doesn’t stay as one elongated tube but instead it spreads itself out which is referred to as the axon terminal which is where we release the neurotransmitters so we can have our message be passed on to our neighboring neuron or effector like a muscle or a gland
when our proteins are made in the cell body and get carried in the tube on the inside all the way to the axon terminal the entire 1 m distance and the release point is the axon terminal
what does it mean if an axon is myelinated? what does myelin do?
myelin protests the axon from the extracellular fluid and the interstitial fluid aka they’re giving the axon insulation
it looks like when you wrap an ace bandage around a knee when it’s injured – there are sections of myelin around our axon
what type of communication system is our nervous system?
Our nervous system is an electrical communication system, which needs insulation just like the wires in your house! Insulation helps our electrical activity
electrical communication is how we communicate with our axons
what are Schwann cells?
glial cells of the PNS that make myelin
they cover a single section of a single axon - so what you see is sections of myelin that are made one spot at a time, one cell covering one section of the axon
what are oligodendrocytes?
glial cells of the CNS that make myelin
the myelin that they make is created by cells that can cover multiple sections of axons and even multiple axons from different neurons
cover many axons and many sections of the axons
what kind of coverage do Schwann cells and oligodendrocytes provide? is it sufficient coverage?
Schwann cells and oligodendrocytes do not do complete coverage, they both leave openings and breaks in the “insulation”
we actually need those breaks –these breaks are called the nodes of Ranvir and give us access to the interstitial fluid and extracellular fluid
what are the nodes of ranvir?
breaks in the myelin sheaths around our axons
they give us access to the interstitial fluid and extracellular fluid
what are glial cells?
connective cells!!
they’re a group of connective cells that help the neurons to do their job
their job is to provide support for the neurons – the support is happening physically, structurally and functionally, metabolically, providing the right environment
what is the ratio of neurons to glial cells?
for every 1 neuron you would see 9 glial cells so the CNS is 90% glial cells
BUT the split is equal by volume/mass so this tells you that neurons weight a lot more and are a lot bigger than glial cells
neurons = upper management
glial cells = workers
what are the types of glial cells in the CNS?
oligodendrocytes, ependymal cells, astrocytes, and microglial cells
what are the types of glial cells in the PNS?
Schwann cells
what do ependymal cells do?
they’re glial cells of the CNS
they create a boundary between the interstitial fluid that’s around our neurons and the rest of the interstitial fluid
so we’re creating a special area of interstitial fluid that’s just around our brain and our spinal cord called the cerebral spinal fluid
analogous to our epithelial cells in the sense that they create a boundary
what is the cerebral spinal fluid?
the interstitial fluid immediately around our brain and spinal cord that is sectioned off by our ependymal cells
what are the functions of our ependymal cells?
1) regulate what can get into cerebral spinal fluid area
2) regulate amount of cerebral spinal fluid
3) serve as stem cells
4) cilia
how does the cilia on the ependymal cells help its function?
cilia allows them to move and create movement in the cerebral spinal fluid
things move in interstitial fluid by diffusion but we know diffusion has a problem with distance so if we can give those things that need to move a bit of help by creating some flow movement we can fix the distance/diffusion problem and the cilia generating flow movement does that for us
what are stem cells?
ependymal cells can be stem cells
they’re cells that can generate themselves but also other cells – can serve to make more ependymal cells AND they can generate more neurons!!!
what are astrocytes?
type of glial cell of the CNS and they’re our big workers, they’re doing the daily interaction in helping our neurons
they regulate what’s inside the cerebral spinal fluid
how do astrocytes play a part in the potassium gradient?
there’s more K inside a typical cell so astrocytes make sure that that gradient remains so that we can do electrical messages better so it actually takes away K from the cerebral spinal fluid
how do astrocytes regulate the level of neurotransmitters?
takes away neurotransmitters from cerebral spinal fluid because a neurotransmitter is kind of like sending a note to someone but once you get the job done you throw the note away
we want to make sure things only happen once and not linger on later so we want to clean up neurotransmitters quickly
how do astrocytes regulate glucose?
they make sure there’s a good level of glucose around our neurons so that our neurons can uptake glucose and do self metabolism pathways and start glycolysis so that they can always make ATP
how to astrocytes ensure that we make the most ATP possible?
to get the most ATP, neurons need O2 so you need a blood supply so astrocytes also participate in blood supply component to provide O2 so that neurons can make the most ATP possible
capillaries are our smallest blood vessels: we have tons of them in association with our brain – however you don’t want the pathogens in our blood to get across and get to your neurons – it’s okay for pathogens to attack viruses in our body but we don’t want viruses to reach our neurons
what is the blood brain barrier? how to astrocytes play a roll in the blood brain barrier?
it’s difficult to move things from the blood to the cerebral spinal fluid because the astrocytes are doing their job by enhancing the blood brain barrier
how to astrocytes play a roll in the blood brain barrier?
they enhance the blood brain barrier by keeping the tight junctions between the endothelial cells and create our capillary walls and keep everything tight so that stuff can’t move from the blood to the interstitial fluid and that way pathogens can’t get out
what is the trade off of astrocytes sealing off the blood brain barrier?
the trade off is that if we don’t let things out of our blood, hello oxygen, glucose, endocrine system, and your immune system use your blood
your white blood cells are moving in your blood so that they can get to spots where there’s some sort of pathogen outside of your blood, they leave your vascular system and go to that point
so now our WBC warriors can’t leave the blood and get to our CSF to fight because of the astrocytes
what do astrocytes have to do with the growth of neurons? at what time in our life are they very important?
they help with the development and growth of neurons both structurally in giving them locations to grow into and with metabolic support so that they can become the biggest neurons they can be
so astrocytes are critical during fetal development so that the brain can develop the way it should
how do astrocytes help with communication?
astrocytes have gap junctions that exist between astrocytes which can help with direct communication through those channels
they also have gap junctions with our neurons so they can communicate with our neurons
they also impact our neurotransmitters and how much of them are around and how long they’re around so when neurons are communicating with other neurons they can impact that communication by how long the neurotransmitter is around
what are microglial cells?
glial cells of the CNS that are in our cerebral spinal fluid and are the immune cells in the cerebral spinal fluid
they’re phagocytic cells so if they come across something that’s not supposed to be there they engulf it and destroy it
what if microglial cells are doing their job?
they aren’t always doing battle – when they aren’t doing battle they’re in their resting mode
in their resting mode they look like mini neurons because they have a cell body with lots of little processes coming off of it – in this resting mode they still serve an important function = in this highly branched form they’re releasing chemicals that insure that the neurons are able to do their job properly and can grow and develop properly = sort of assisting the astrocytes
what happens to microglial cells when a pathogen is detected in the CSF?
• When a pathogen is detected in the CSP, the microglial cells change from resting to phagocytic form and they pull in all the projections and become a classic looking round cell which will aid them in having to move because now they’re smaller
they also need to be able to effectively endocytose the pathogen and so they need more straight off surface area so they bring in projections
now the chemicals that they release are not for the neurons development anymore, they’re chemicals that make a not hospitable environment for pathogens so that the pathogens can’t function and not survive
what are the types of neurons?
1) afferent neurons
2) efferent neurons
3) interneurons
what are afferent neurons? what are their parts?
bring information to our CNS from receptor which is the first part of our reflex arc
a separate cell can be acting as the receptor or the afferent itself could be picking up the signal
they don’t have dendrites, there’s an axon terminal on both sides that does the gathering and carrying out information function
located in the PNS except the axon terminal is in the CNS so it can communicate to it
what are efferent neurons? where are their parts located?
take information from the CNS - it serves as our efferent pathway in our reflex template
the dendrites are in the CNS while the axons are in the PNS because you have to connect up to the effectors to get us a response through the reflex template
what connects our neurons to the effector like hour heart, lungs muscles, gland
?
what’s an interneuron?
act as integrator – connect A to E
entirely within CNS
the CNS is the area where we draw a circle around our interneurons and the interneurons define the CNS
what’s the ratio of all the types of neurons?
for every 1 afferent neuron, we have 10 efferent neuron
for every one afferent neuron there’s 200,000 interneurons
what’s a synapse?
synapse is the space where a neurotransmitter gets released into interstitial fluid to get to the next cell
what kinds of synapses are there?
1) chemical synapses
2) electrical synapses
what are chemical synapses?
like when neurotransmitters release sites – slower than electrical synapses
what are electrical synapses?
based on our gap junctions
we’re going to be able to keep an electrical activity as an electrical message and move it from cell A to cell B
faster than chemical synapses
which type of synapse is innately faster?
electrical
in our nervous system which synapse is faster?
chemical synapses are what’s dominantly found
the tradeoff is that electrical activity is bidirectional while chemical is unidirectional - when we’re talking about communication we want it to go as fast as possible in one direction
when communication turns around and goes back the other way actually makes it slower
what’s a focus neuron?
the tan one and it’s connecting up to 4 neurons and communication is happening from left to right
what are pre and post synaptic neurons?
any synapse is about two cells; one cell connecting to another – so there’s always one neuron communication with another
since it’s chemical synapses and the message only goes in one direction – they’re referred to as pre and post synaptic neurons
pre synaptic is releasing neurotransmitters and post synaptic is receiving the neurotransmitters/message
defining a neuron as pre and post isn’t a thing because most times it’s both
how do neurotransmitters travel?
they move through interstitial fluid so it can diffuse over and reach post synaptic cell – membrane bound receptors receive the message
what is convergence?
five different pre-synaptic neurons come together and all talk to one post-synaptic focal neuron
more pre talking to fewer post (4:1)
what is divergence?
dividing, making more
focus neuron communicating with four other neurons – the number of pre is less than the number of post (1:4)
how is potential energy created?
we have a variety of electrical potentials associated with our cells
we created potential energy with our gradients – our potential energy is our electrical energy
what is membrane potential?
this is the main type of potential because the rest are based off/rely on membrane potential - it’s the potential that makes all the others possible
is there electrical charge separation across the PM?
we can have a separation of ions on either side of the membrane
electrical charge separation across PM due to distribution of charged components – the membrane stops the ions from moving relative to their gradient
Na/K/ATPase pump made a electrical gradient because more + went out than came back in because 3 Na went out and only 2 K got brought back in so most cells end up being a little bit more negative inside = a little more positive on the outside – more sodium on the outside and more potassium on the inside
is potassium happy with its location relative to the membrane?
potassium on the inside is happy being near negative charge but the sodium on the outside next to the positive charge isn’t happy and wants to move away from it
this means we have to pay attention to both chemical (concentration) and electrical gradient and what they’re tell the cell to do
what is the net G?
Net G = conc. G + electrical G
what is the net G of sodium?
concentration gradient tells Na to go into the cell and the electrical gradient is also telling sodium to go into the cell to get closer to the negative charged inside so sodium will go into the cell
what is the net G of potassium?
concentration gradient tells K to go out of the cell but the electrical gradient tells K to go into the cell towards the negatively charged inside so the gradient directions are opposite of each other
if these are vectors, the only way you know which way K goes you need more information: you have to know the sizes of the arrow – you know how to calculate concentration (#/volume)
do all cells have membrane potentials?
yes!
every cell has a membrane potential so every cell can experience a graded potential
what is Vm?
voltage across the membrane
what is Vm at rest in most cells?
at rest, most cells Vm = -70 mV since cells are usually negative on the inside
how does your membrane potential change?
due to all charged components like Na, K, Cl, Ca, etc. what’s the distribution of all of these? If you change the distribution for one of those you’re going to change your membrane potential
what is the relationship between PM permeability and Vm? what is created by a change in permeability?
if permeability stays the same, Vm doesn’t change
increased permeability causes ions to move which causes a change in membrane potential (delta Vm) = graded potential**
ex. if permeability changes, like opening a channel for Na, then Na will go into the cell and our Vm will change
what kind of change is a graded potential?
LOCAL
local change in ion flow only! Sodium is moving because it’s diffusing into the cell following its electrochemical gradient
the change in graded potential is therefore also dependent on diffusion – we know diffusion has a problem with distance so therefore, so does graded potential!
Vm of the entire membrane doesn’t change, just the area around the Vm change – like when you open a window in a hot room, you feel the cold air near the window but the other side of the room doesn’t feel anything
what is SS for a membrane potential?
resting potentials
are cells polarized or depolarized at rest?
cells are polarized at rest
what does depolarized mean?
depolarized means make it less negative and decrease the potential and bring it closer to zero since we started at -70 mV
what does hyper polarized mean?
hyperpolarized means making it more negative and increasing the potential
what is a stimulatory stimulus in terms of membrane potential? what is an inhibitory stimulus?
cells are more likely to do things when they’re depolarized so depolarizing is a stimulatory stimulus
cells are less likely to do things when they’re hyperpolarized so hyperpolarized is an inhibitory stimulus
what is depolarization?
going back to rest
what are traits of Vm?
1) size variable: change in number of ions – if more ions move there’s a bigger change
2) decrease with distance: these are local events – graded potentials are related to diffusion
what can open a voltage gated channel?
a change in electrical distribution opens a voltage gated channel – change in potential can open voltage gated channel
what can cause an action potential?
graded potentials can cause an action potential
where do action potentials happen? what are they?
action potentials only happen in special cells in your body called excitable cells such as neurons, muscle cells, etc
they are quick, large delta s in Vm
last 1 to 2 milliseconds
we’re changing our Vm so it really is a Vm, it’s just a special case of GP so everything from GP still applies to AP
what is a major characteristic of action potentials?
they are very stereotyped
one of the traits of grated potentials is that they can be different sized, they can be depolarizations or hyperpolzarization
however when we look at AP, they always look the exact same = same time → as a result it’s an all or none event = we either meet the conditions and it stays as a normal GP and we see no AP
whats an example of an action potential?
shooting a gun is an all or none event = squeeze the trigger the bullet comes out – squeeze the trigger three times harder, the bullet doesn’t come out any faster – once you reach the threshold you get the AP to happen
pregnancy
what if a grated potential is next to a voltage gated channel?
action potential
what are the requirements of an action potential?
1) voltage gated Na channels
2) voltage gated K channels
the same Vm opens both channels!
what’s an inactivator? what does it do?
it doesn’t close the Na channel, it just blocks the channel so you don’t see Na move with its gradient
like Bronson opening her garage door opener but there’s a car in the way so she can’t get into her garage because there’s a car in the driveway
don’t need anything to bind to them to get this to happen, you just need the right membrane potential to cause a change in voltage
voltage that causes the channel to open also causes the inactivator to swing over and block the entrance
what is the speed of Na channels in an AP? how about the inactivator?
Na channels are incredibly quick to open
inactivator is slower to swing over so Na will flow in until the inactivator gets the chance to move over – same amount of Na will go through every time because the rate of the inactivator is the same each time
what are the three possible states of the channel?
open, closed, inactivated
what is the speed of voltage gated K channels?
slower to respond than Na
like an automatic door that doesn’t open by the time you get there and you have to jerk back – it’s the same signal as the Na channel telling it to open, it just takes longer to open
what causes the Na and K channels to open during an AP?
the same Vm opens both Na and K channels!
so therefore channels have to be near each other
first see Na channel go from closed to open –> then the inactivator moves over some period of time later and the K channel open kind of at the same time but K channel technically opens up after the inactivator gets to it’s position
what are the conditions of an AP at -70 mV?
this is at rest
Na channel is closed and K channel is closed
this is redundant because duh the same Vm activates both of them –> we know there are gradients for both Na and K so if we open the channels we know they’ll both want to move
what is our threshold potential?
-50 mV
what gets us to our threshold potential during an AP?
depolarization gets us up to the TP - we have to get Vm up to this spot
what are the steps that get us to our threshold potential during an AP?
1) Na channels open → Na will go into the cell due to chemical concentration gradient reasons and electrical reasons since inside of the cell is negative
2) with positive Na going in, the cell becomes less negative and we further the depolarization → the huge peak in the graph is due to the influx of Na
positive feedback
what kind of feedback is the depolarization event of an AP?
positive feedback
some stimulus causes us to vary from steady state and we continue to move away
what happens at the peak of an AP?
inactivator swinging over will stop the depolarization which causes us to hit a peak in the graph → Na is inactive
K channel opens → by concentration K wants to go out of the cell AND by charge K wants to go out of the cell since at the peak of the graph we’re at +30 mV and the inside of the cell is actually positive
now we’ll have less positive charges on the inside when K goes out of the cell and we are now repolarizing the cell to make it polar again which is the downhill part of the graph
we will cross the threshold again on the way down which is also the trigger to close the channels so Na closes (there’s a slight period where they’re closed and inactivated but it’s super small)
what voltage are you at at the peak of an AP?
+30 mV
what happens during the hyperpolarizaiton event of an AP?
just like how K opens slow, they also close slow so they’ll stay open a little longer even after we cross the TP
so what ends up happening is too much K ends up leaving the cell and it becomes hyper polarized (super negative like -80 mV)
eventually K will close and we’ll end up back at the resting potential of -70 mV
what is the threshold potential?
this is the Vm where we see the immediate opening of our Na channels – also the same Vm that opens K channels but there’s just a lag
what is a stimulus?
initial stimulus is some grated potential that happened
once we hit the threshold, it’s the influx of Na into the cell that takes over the driving force of what’s changing our Vm
what is a sub threshold potential?
when a graded potential occurs but it doesn’t depolarize enough to reach he TP and thus it is sub-threshold potential and an action potential will not occur because it is all or none
the initial stimulus doesn’t get us to the threshold
the subthreshold potential stays as a grated potential, it’s not an AP
the size of the grated potential doesn’t matter, as long as you hit the threshold it doesn’t matter if it was exact or 700 times bigger
what is the amplitude of an action potential?
the amplitude won’t change as long as we reach threshold which is why they’re stereotyped
it’s independent of original grated potential that caused the threshold potential and triggered it
no change in size since they’ll all look exactly the same→ unlike grated potentials which can vary in size
what do we use AP for?
local anesthetics that block Na channels
litocaine that kill pain in the mouth block Na channels that are voltage gated so no action potential
