Unit 2 + Unit 3: spinal anatomy Flashcards
what other ion channel is similar in structure to a VG Na+ channel?
VG Ca2+ channel
also termed SLOW calcium channels
slow VG Ca2+ channels are blocked by:
dihydropyridine calcium channel antagnoists
Cl- permeability is adjusted to _____ or _____ electrical activity in excitable cells
hyperpolarize; suppress
these receptors typically open up Cl- channels in neurons
GABA receptors
Cl- influx typically makes the cell membrane more ____ and more ____ to excite
negative; difficult
permeability of Na+ _____ via opening of membrane Na+ channels; membrane potential becomes closer to nernst for Na+ during ______
increases; depolarization
why would a 2-way signaling process for depolarization along a cell be considered beneficial
if the AP can move in both directions, there would be a shorter time required to excite a cell
how is propogation of an AP in a VG Na+ channel considered a positive feedback loop?
the initial stimulus causes Na+ to come in, which then activates fast Na+ channels to allow more Na+ to come in until repolarization initiates
how does the motor neuron communicate with skeletal muscle if there is a “gap” between the two structures?
neurotransmitters
the gap is termed the neuromuscular junction (NMJ)
nicotinic-ACh receptor
found on skeletal muscles
(also on brain; think nicotine)
receptor has 2 binding sites
NT: ACh released from motor neurons and 1 receptor needs 2 ACh to bind
the inside of the receptor is negatively charged but the channel is specific for positively charged ions
which type of ions can pass through the nicotinic-ACh receptor?
the majority of the current is Na+ current; this means there is more Na+ influxing vs K+ effluxing (and Ca2+ influxing)
Ca2+ can also influx and depolarize the cell, but the majority of the influx is Na+
Ca2+ is a larger ion, which is why there isn’t as much Ca2+ influxing through the channel as there is Na+
aside from the n-ACh receptors found on skeletal muscle, how else do the skeletal muscles cells become more positively charged during depolarization?
after the initial depolarization through n-ACh receptors, nearby fast Na+ channels can open up to allow more Na+ to influx into the cell
paralytics work here
the neuromuscular junction
list out the steps to “excite” a nerve cell to cause skeletal contraction
- the brain sends “signal” to motor neuron to communicate with skeletal muscle cell
- the signaling molecules are the ACh neurotransmitters
- 2 ACh NTs bind to the nicotinic-ACh receptors
- the postively charged ion selective channel allows an influx of Na+ to flow into the cell
- depolarization occurs and activates nearby fast VG Na+ channels nearby to help propogate the AP across the skeletal cell leading to muscle contraction
which receptor types cause hyperpolarization in cardiac cells?
hyperpolarization makes cells more NEGATIVELY charged; this will suppress electrical activity in the cell
ex) muscarinic-ACh receptors
muscarine stimulates muscarinic-ACh receptors
where are m-ACh receptors found on the heart?
the “pacing centers”
SA and AV nodes
the RIGHT vagus nerve communicates with the ____ node
SA
the LEFT vagus nerve primarily communicates with the ____ node
AV
the vagus nerves communicate with the SA/AV nodes via this NT
ACh
the mACH-R has this type of protein structure
7TM (GPCR)
list out the mechanism of hyperpolarization in cardiac cells
- ACh binds to 7TM m-ACh-R
- alpha subunit and communicates with potassium channels (the effector protein) in the cell wall
- K+ channels now activated and effluxes K+ out of the cell
- increased EN makes the cell much more difficult to excite
- hyperpolarization (making the cell more negative past vrm) will make it so that it takes longer for the cell to become excited enough to fire off another AP
- this in turn will “keep the pace” of the heart (“70-72” BPM)
how does a vagal response cause a bradycardic response?
massive vagal stimulation causes potassium permeability to INCREASE, causing more K+ to efflux, causing hyperpolarization of pacemaker cells and causing the HR to slow down
describe what happens when an antimuscarinic drug inhibits pacemaker cell hyperpolarization
- antimuscarinic (antagonist) binds to active site of m-ACh-R
- alpha subunit is not active
- potassium channels close and cause cell to become more POSITIVE
- vrm is now more positive, and since our vrm has approached the threshold potential, it will take a SHORTER time to fire an AP
- shorter time to fire an AP means more APs fired AKA an elevated HR
give an example of a muscarinic-ACh-R antagonist
atropine
these two GPCRs antagonize each other in terms of keeping pace of the HR
m-ACh-R and beta receptors
how does physical pressure activate a neuron
- a stimulus causes a change in electrical activity
- once pressure (stimulus) is applied pressure sensitive Na+ channels will elongate the walls of the channels
- Na+ influx will be even greater (because the Na+ channel walls are wider)
- if there is enough Na+ current through the cell, an AP is depolarized and propogated through the neuron to the brain
nernst potential and ohm’s law
the nernst potential gives us polarity of the cell
ohm’s law states that if you have current going over some kind of resistance, you should have VOLTAGE
ex) if you have a bunch of Na+ channels open, there is a lot of Na+ current coming in, the current changes the resting membrane potential
you don’t have to have current; you just need POTENTIAL to influence the resting membrane potential
ex) 9V battery has stored voltage but doesn’t have any current going across the electrodes
what is the difference in a weak stimulus vs a very strong stimulus on an action potential graph
a weak stimulus barely gets over the threshold and it takes longer to fire an AP vs a very strong strong stimulus will fire an AP almost immediately
why is an AP sustained in the heart
it will give the heart time to contract and for the heart to fill
what are the effects of Cl- on a cell’s permeability
chloride “pumps the breaks”; the nervous system uses Cl- to control electrical activity in the heart
Cl- will hyperpolarize the cell and will make the cell much more difficult to excite
what are the extracellular effects of Ca2+
if ECF Ca2+ is increased, Ca2+ can block Na+ leaky channels, which will limit resting Na+ permeability
Ca2+ is a very large ion compared to Na+, so it will block Na+ from entering the cell
this is why Ca2+ is useful in treating hpERkalemic patients – hyperkalemia causes the cell to become more POSITIVE by not leaking out as much K+ and Ca2+ will esentially counteract this by making the cell more NEGATIVE by blocking Na+ channels
how are Mg2+ and Ca2+ dissimilar? how are they alike?
Mg2+ will function in the same way as Ca2+ will in terms of decreasing cell electrical excitability (Mg2+ is more specific to the heart); however, Mg2+ is a smaller ion than Ca2+
ICF/ECF Mg2+ can influence cell membrane potential vs ECF Ca2+
how does muscular tetany develop in a patient? (Trousseau/Chvostek’s sign)
hypocalcemia –
this will cause increased electrical activity at the motor neuron because hypocalcemia will allow much more leaky Na+ channels to diffuse more Na+ into the cell, making the cell much more excitable
rate of AP propogation in nerve dependent on:
- length of nerve (shorter = faster)
- diameter of nerve (wider = faster)
- insulation of the nerve (myelin sheath) – more insulation = faster AP
how does a Schwann cell (comprised of Schwann cell cytoplasm) end up myelinating an axon on a nerve fiber?
over time the Schwann cell will spiral around the nucleus, wrapping its lipid body around the axon, and will “squeeze” out the water, which it will then become a good insulator of the neuron
4 benefits to an insulated/myelinated neuron
- helps speed up AP
- reduces amt of energy consumed by cell (covering over more Na+/K+/ATPase pumps)
- less prone to ischemia
- prevents Na+ from leaking out neuron during AP
how do the Nodes of Ranvier assist with AP conduction?
they have a high density of Fast VG Na+ pumps localized in the node to ensure that there’s enough Na+ influx to propogate the AP futher along the axon
what is meant by “saltatory conduction”?
the AP is quickly “jumping/leaping” across a myelinated neuron
“saltatory” means to “jumping or leaping”
name 3 demyelinating disease and list their characteristics
1. multiple sclerosis
+autoimmune attacking of the myelin sheaths; causes issues with AP conduction
+lifelong/chronic disease
2. optic neuritis
+loss of vision d/t inflammation of optic nerve; associated with MS
+acute or chronic
3. Guillain-Barré Syndrome
+prevalent s/p COVID; autoimmune disease attacking myelin sheaths originating s/p viral infection/immunization/etc.
+acute
all can lead to progressive loss of function
all can be associated with genetics, infection, autoimmune hyperreactivity, polyneuropathies
explain the mechanism of demyelinated areas and how it affects AP conduction
demyelinated areas of the axon will not be able to regenreate ion channels, BUT, Na+/K+/ATPase pumps can remain in these areas
if the Nodes of Ranvier are intact close to these demyelinated areas, the INFLUX of Na+ from the fast VG Na+ channels will ultimately get EFFLUXED out of these remaining Na+/K+/ATPase pumps in the demyleinated areas, causing issues with AP conduction
why would an area with myelinated neurons require a higher than normal dose of local anesthetic?
harder to “block” because of the high density VG Na+ channels at the nodes
what makes up a gap junction?
6 connexin proteins = 1 connexon
2 connexons = 1 gap junction
how do gap junctions depolarize neighboring cells?
one cell can be depolarized via sodium influx and that sodium can travel into a neighboring cell to depolarize that cell via a gap junction; gap junctions allow small ions to pass through very easily and very quickly to a neighboring cell
what determines the signal resistance associated with electrical synapses?
the signal resistance is dependent on how many gap junctions are present
+the higher the # of gap junctions, the least amount of resistance there is to send ions across, thus creating a very fast current flow
where are gap junctions located in the body?
myocardium
smooth muscles
a few neurons
how can the bidirectionality of gap junctions cause issues in a tissue?
in the heart, if there is a “rogue” AP floating around, this can cause electrical disturbance on the tissue since there will be current flowing across the tissue much more quickly due to its bidirectionality, versus if there was a chemical synapse where it is a bit more controlled in signal conduction
in the heart, where would there be less amounts of gap junctions?
at the SA/AV nodes
these pacing areas of the heart have a built in system to cause delays to incorporate the “functional pause” needed for the heart to pump correctly
what are glial cells?
where are these glial cells located?
glial cells are the “support cells” in the nervous system
oligodenrocytes: location and characteristics
located in the CNS
are not good at regenerating myelin
the CNS is comprised of?
brain
spinal cord
CN II
retinas
Schwann cells: location and characteristics
located in the PNS (everything outside of the spinal cord)
can usually regenerate myelin if its not extensively damaged
how do chemical synapses assist in cell to cell communication?
presynaptic terminal will release chemicals (NTs) to bind to post-synaptic terminal to elicit communication
ex) ACh release to communicate between cells