Unit 2 : Chapters 3 and 4 Flashcards
what do atoms do?
gain or lose electrons
- if they gain, it is more negatively charged
-if they lose, it is more positively charged
cations
positively charged
anions
negatively charged
hydrophobic
does not mix with water
-lipids are hydrophobic
hydrophilic
mix well with water
- polar molecules and ions are hydrophilic
what kind of layer is the cell membrane?
lipid bilayer
- anything that mixes with water will not pass the cell membrane
Diffusion
process of a movement of a substance from a region of higher concentration to the region of lower concentration until particles are evenly spread out
- molecules move down a concentration gradient
concentration gradient
the difference in concentration of a substance from one place to another
protein channels
allow certain molecules (water molecules) to pass through the membrane, but most chemicals are unable to cross
semipermeable membranes
only certain substances can pass through
electrostatic forces
like charges repel each other and opposite charges are attracted to each other
voltage
measure of stored or potential energy
current
flow of energy (active energy)
potential energy
energy being held
intracellular fluids
fluid inside cell
extracellular fluids
fluid surrounding the cell
what happens when recording electrode is placed in a neuron?
it creates a negative charge
- inside of axon is more negative
what should be more negative; inside or outside of cell?
the inside of the cell should be more negatively charged
what is the measure of the resting membrane potential?
-65mV
- inside the cell is more negative than the outside
resting membrane potential
voltage between inside and outside of the cell when the cell is resting
factors contributing to negative membrane potential
- selective membrane permeability (ion channels, negative proteins)
- diffusion (equilibrium potential)
- electrostatic forces (equilibrium potential)
- Na-K pump
what is the ratio of Na-K pump?
3 Na+ ions are pushing out while 2 K+ ions are pushing into the cell
steps of resting membrane potential
- Na-K pump pumps 3 sodium ions out of the cell and 2 potassium ions into the cell which requires considerable energy
- potassium ions go down into the concentration gradient through ion channels and out of the cell because there is too much potassium which leaves the inside of the cell more negative than the outside
- sodium can not reenter the cell because the sodium gates are closed, therefore the outside of cell becomes positive which creates electrostatic force
- the concentration gradient pushing K out and and the electrostatic force pulling K back inside of the cell creates a balance
- Resting potential is the equilibrium of potassium
- key driver for cell resting potential
are potassium channels selectively permeable?
yes, they are open and selectively permeable
can proteins easily leave the cell?
no
does the Na-K pump require a lot of energy?
yes, and it is responsible for maintaining the cell’s membrane potential
are neurons polarized?
yes, because there is potential across the cell membrane.
- specifically it has negative resting membrane potential (-65mV) because of the seperation of ions across the cell membrane which is caused by the Na-K pump
hyperpolarize
more negative (less than -65mV)
depolarize
more positive (greater than -65mV)
at resting potential, what are K+ ions doing?
they are at equilibrium across the membrane
Action Potentials process
- input from the presynaptic neuron causes the neuron to depolarize
- when the neuron reaches the threshold (about -40mV), the voltage gated Na+ channels open and Na+ rushes into the cell, causing it to rapidly depolarize
- Na+ channels close and voltage gated K+ channels open, K+ rushes out of the cell causing it to rapidly repolarize and causing afterpotential (hyperpolarization)
- cell returns to resting potential
absolute refractory periods
no amount of stimulation can induce another action potential
- because voltage gated Na+ channels are inactivated
relative refractory periods
only a strong stimulation can produce another action potential
- because the flow of K+ ions have temporarily hyperpolarized the neuron
3 states of sodium channels
- channels are closed but ready to open
- open
- inactivated
All or None Property of Action Potentials
neuron either fires/strikes causing an action potential or it doesn’t
-there is no half action potential
action potentials
electrical message a neuron sends along its axon to the presynaptic axon terminals
- flowing of ions across the membrane (first sodium, then potassium)
what potentials decay and which do not?
action potentials do not decay, they regenerate and graded potentials do decay over time and distance
how does an action potential regenerate?
sodium channels keep opening as the action potential spreads along the axon
- after the action potential passes, the sodium channels inactivate and the action potentials spread in one direction towards the axon terminals
what is conduction velocity affected by?
diameter of axon and myelination
- larger diameters = faster conduction
-myelination produces saltatory conduction, which is faster
saltatory conduction
action potentials jump from one node of Ranvier to the next node
-faster because myelin insulates axon and reduces decay depolarization of cell and passive spread of depolarization is faster than waiting for sodium channels to open
what are the two types of graded potentials?
EPSPs and IPSPs
graded potentials
-spread passively meaning the neuron is not regenerating the potential
- passive spread of electrical current
- decays over time and distance
postsynaptic potential types
- graded potentials
- local potentials
local potentials
change in the membrane potential is local to the synapse and can only spread passively from there
EPSP
synaptic potential that INCREASES the chance that a future action potential will occur in a postsynaptic neuron
- causes depolarization
IPSP
synaptic potential that DECREASES the chance that a future action potential will occur in a post synaptic neuron
- causes hyperpolarization
how do neurons communicate with each other?
- through electrical synapses
- synapses where neurotransmitters are released onto postsynaptic cells
what do neurotransmitters briefly alter?
resting potential of postsynaptic cells which creates postsynaptic potentials (aka graded potentials)
what determines excitation or inhibition?
neurotransmitter plus its receptor
- some neurotransmitters can cause excitation or inhibition depending on which receptor is present
what determines where a cell fires?
whether the membrane potential reaches threshold at the axon hillock
- this happens from the summation of excitatory and inhibitory inputs
process of graded potential
when all the EPSPs and IPSPs reach axon hillock, an action potential will occur if the threshold is reached
- the longer the distance the synapse is from the axon, the smaller the EPSP/IPSP will be when it arrives at the axon hillock
spatial summation
MULTIPLE presynaptic cells fire SIMULTANEEOUSLY
Neurotransmitter Release Process
- depolarization of presynaptic terminal -> Ca2+ flows into cell through voltage gated calcium channels
- synaptic vesicles fuse with membrane and release neurotransmitters into synapse
- neurotransmitter binds to receptors on postsynaptic membrane, which triggers EPSP and IPSP
temporal summation
SINGLE presynaptic cell rapidly fires multiple signals in quick succession
Two Methods for Neurotransmitter Removal
degradation and reuptake
exogenous substance
results in no synaptic signaling
tetradoxin toxin
blocks voltage gated sodium channels which results in no action potentials
how are neurons identified?
by their neurotransmitter because most neurons use one major neurotransmitter at their synapse
what causes EPSPS?
due to the opening of SODIUM channels
- these channels are ligand gated
what causes IPSPs?
due to the opening of CHLORIDE channels
- these channels are ligand gated
Ionotropic Receptors
FAST ion channels that are typically responsible for EPSPs and IPSPs, typically sodium (EPSP) and chloride (IPSP) channels
Metabotropic Receptors
SLOW GPCRs (active G proteins) that increases concentration of second messenger, which then communicates to areas within cell through various ways
Second Messengers
communicates to areas within the cell
- may open or close ion channels, alter production of activating proteins or active chromosomes
GPCRs (G protein coupled receptors)
activate intracellular signaling mechanisms through second messengers
agonists
increases activation of receptors
antagonists
blocks activation of receptors
EEG
process - electrodes on scalp (use a “cap”) to record electrical activity
purpose - measures brain potentials on a large level
-good temporal resolution, poor spatial resolution
ERP
process - electrodes on scalp (use a “cap”) to record electrical activity
purpose - measures brain potentials but time-locked to a particular stimulus
- better temporal resolution than EEG
optogentics
process- inject a virus into brain that contains an opsin (inhibitory or excitatory) which can then be manipulated by light in non human animals
purpose- can manipulate regions and pathways during behavior of interest
what makes a neurotransmitter?
- exists in presynaptic axon terminals
- presynaptic cell contains enzymes for synthesis
- released when action potentials reach terminals
- has specific receptors that recognize it on postsynaptic membrane
- experimental application produces changes in postsynaptic cels
- blocking release prevents presynaptic cell from affecting postsynaptic cell
