Nervous System - Neurons, Neurotransmitters, Receptors

what is a membrane potential

difference in electrical energy between ICF and ECF due to the electrochemical gradients of ions

what is the membrane potential at rest

lots of Na outside (+ outside), lots of K inside (- inside)

what is repolarization and what is the membrane potential then

inside of the cell is negative, outside of the cell is positive. K flows out of the cell. Happens as a recovery after depolarization

what is depolarization and what is its membrane potential then

inside of the cell is more positive, outside of the cell is more negative. Na flows into the ell. Triggered during contraction/signals

what channels are open and closed at resting membrane potential (-70mL)

Voltage-gated Na and voltage-gated K channels are closed 

what is a threshold potential

level of membrane potential that a neuron needs to reach to trigger an action potential 

what is the membrane potential at threshold potential

Voltage gated NA channels opened, allowing NA to flow into cell and changing the resting potential of -70mV to –55mV  

what channels are open/closed at repolarization

Voltage-gated Na channel close and are inactivated, voltage-gated K channels open, allowing for K ions to flow out of the cell (losing + ions and decreasing the membrane potential (going from a more positive to a more negative membrane potential) 

what is hyperpolarization

when all the K+ ions are flowing out and the cell is losing + ions, the membrane potential will dip below the normal –70mV for a little bit before restabilizing 

what happens to the membrane potential after hyperpolarization

Afterwords, voltage-gated K channel will close up, allowing Na+/K+ ATPase Pump to restabilize the inside of the cell (going back to the resting membrane potential) 

Afterwords, voltage-gated K channel will close up, allowing Na+/K+ ATPase Pump to restabilize the inside of the cell (going back to the resting membrane potential) 

what is a refractory period

time intervals after an action potential when a cell is unable/harder to fire a new impulse 

what is a relative refractory period

a new actional potential CAN be triggered, but you need a super strong stimulus to do so 

• From late repolarization to hyperpolarization phase 

• Happens due to voltage-gated K+ channels remaining open 

what is an absolute refractory period

no new action potential can be generated, no matter how long the stimulus 

• From depolarization - repolarization

• Happens due to voltage-gated Na channels are inactivated 

what are the states of the voltage gated na channel during different states

resting: closed

depolarization: open

repolarization: inactivated

hyperpolarization: closed

dendrites have a ___ that ___ and ___

local graded potential, starts at dendrites, moves to axon hillock

what is the difference between local graded potential and normal action potential

Intensity and distance of the action potential can change, unlike action potentials where they have a set intensity and cannot be decreased (aka, as the local graded potential travels from the dendrites to the axon hillock, that distance can change and the signal can lose its intensity as it goes down

local graded vs action potential

local: short distance, strength change

action: long distance, uniform potential

what are the 2 types of local graded potentials

• excitatory: depolarizes

• inhibitory: hyperpolarizes

this means that the potential can start with either depolarization or hyperpolarization

what is summation

Because there are many dendrites on a neuron, all of the incoming graded potentials get added up and it MAY or MAY NOT reach the threshold potential to fire an action potential 

what is temporal summation

postsynaptic neuron (the neuron that has the incoming graded potentials) is adding up multiple graded potentials coming from 1 singular presynaptic neuron (the neuron sending the info to the postsynaptic one) at different times 

what is spatial summation

postsynaptic neuron is adding up multiple graded potentials from multiple presynaptic neurons at the same time

can an action potential start with either depolarizaiton or hyperpolarization

only depolarization

what is the difference between how an action potential vs local graded potential is triggered

a local graded potential uses gated channels on the dendrites and soma, while an action potential uses voltage-gated channels on a certain zone and the axon

diameter of axon: how does it affect the velocity

larger diameter = faster

myelin sheath thickness: how does it affect the velocity

thicker = faster

Saltatory vs continuous conduction: how does it affect the velocity

saltatory = faster, continuous = slower

length of itnernodes: how does it affect the velocity

longer = faster

size of nodes of ranvier: how does it affect the velocity

smaller = faster

density of ion channels: how does it affect the velocity

higher density = faster

what is isochronicity

nerve signals arrive at different parts of the body at the exact same time, even if some signals have to travel further than others

types of nerve fibers; group A

largest diameter, heavily myelinanted.  

• Ex: motor neurons 

• fastest

types of nerve fibers: group B

intermediate diameter, lightly myelinated 

• Ex: visceral afferents, preganglionic Sy autonomic 

• medium speed

types of nerve fibers: group c

smallest diameter, unmyelinated 

• Ex: postgangionic autonomic fiber 

• slowest

step 1 of how the action potential only flows one way

When depolarization happens (voltage gated Na channel opnes and lets Na in), it goes in both directions. BUT one side will encounter a closed voltage-gated Na channel as it travels to the axon terminal while the other side will hit an inactivated voltage-gated membrane channel that doesn't allow anything to go through (the ones that go to the inactivated channel are lost, which makes you lose some intensity of the action potential) 

step 2 of how the action potential only flows 1 way

As the action potential flows to the axon terminal, the previous voltage-gated channel will become inactivated as the other opens 

what do lidocaine and mepivacaine do

voltage-gated sodium channel blockers, stops action potential and numbs person

what does saxitoxin do

selective, reversible (slow) voltage-gated sodium channel blocker 

stops action potential from happening, paralyzes a person temporarily

what does cyanobacteria and its specfic inhibitors do

agonist of acetylcholine, irreversible binding to ACh receptors 

• Anatoxin A: irreversibly binds to ACh receptor 

  • ach channel is kept open, locking Na channels shut and cannot repolarize (stuck in a depolarizing state)

• Anatoxin A(S): AChesterase inhibitor  

  • ach channel is kept open, locking Na channels shut and cannot repolarize (stuck in a depolarizing state)

causes a lot of sporadic movement then paralysis