neuro final exam

what is the cell theory

individual cells are the basic building block of life

two types of stains

nissl stain and golgi stain

the nissl stain stains…

the nucleus and rough ER

the golgi stain stains

the entire neuron

what were the two prominent theories for how cells communicated with each other?

reticular theory and neuron doctrine

reticular theory states…

individual neurons are all continuous with each other

neuron doctrine states…

neurons are distinct cells that come close to each other but are not continuous (extension of cell theory)

which theory ended up being correct, reticular theory or neuron doctrine?

neuron doctrine, as proven by electron microscopy in the 1950s

before chemical synapses were visualized using electron microscopy, what biological lines of evidence pointed to their existence?

• adrenal gland extract mimics electrical stimulation of the sympathetic nervous system

• applications of acetylcholine has the same effect as electrically stimulating motor neurons

• motor neurons can be excited or inhibited by electrically stimulating spinal cord axons

what are the overarching parts of the neuron?

soma (cell body) and neurites (axons and dendrites)

soma contains

all the organelles that are common to any cell

axon contains

• axon hillock

• axon collateral

• recurrent collateral

• axon terminal (terminal bouton)

dendrite contains

• dendritic tree (arborization)

• dendritic spines

synapse

• vesicles

• receptors

• presynaptic density

• postsynaptic density

• synaptic cleft

what is the presynaptic density?

contains proteins needed for exocytosis

what is the synaptic cleft?

the space between the axon and dendrite

what is the law of dynamic polarization

information flows from dendrite to soma to axon

what are different methods for classifying neurons?

• number of neurites

• shape of the soma/dendritic tree

• function

• axon length

• neurotransmitter secreted

how are neurons named by number of neurites?

unipolar have 1 neurite, bipolar have 2 neurites, multipolar have 3+ neurites

what are two ways neurons are named by shape of soma/dendritic tree?

stellate, pyramidal

how are neurons named by function

motor neuron, sensory neuron, interneurons

what are motor neurons

neurons that contact muscle cells

what are sensory neurons

neurons that perform some sort of signal transduction process

what are interneurons

neurons that receive and send signals to neurons

how are neurons named by axon length

local circuit neuron, projection neuron

what are local circuit neurons?

short, signals an axon within the same structure

what are projection neurons?

long, communicates with a distant structure

what is transcription?

a process through which DNA is copied into mRNA

what does transcription?

RNA polymerase

what is the promoter region?

part of the RNA sequence that tells the RNA polymerase where to start reading

how do transcription factors, promoter regions, and RNA polymerase work together?

if the appropriate transcription factor is interacting with the promoter region, then the RNA polymerase would read that particular gene to produce RNA and it will be spliced into the final mRNA transcript

what is the stop sequence?

part of the RNA sequence that tells the RNA polymerase where to stop reading

what is translation?

a process through which mRNA is copied into protein, which is separated based on whether the protein is cytosolic or membrane-bound

what are cytosolic proteins?

proteins that wind up floating around in the side of the cell and thus can be translated at a free ribosome

what are membrane-bound proteins?

proteins that have to be embedded in the membrane in order to take the correct shape, so they have to be translated by ribosomes on the rough ER so the protein can be folded into the membrane as it is

how many ribosomes are present in the axon?

very few; therefore, proteins destined for the axon are transported from the soma

transport machinery involves…

the cytoskeleton, such as microtubules, and proteins like kinesin and dynein that travel on these paths

what is kinesin?

walks along the microtubule from the soma to axon terminal: anterograde

what is dynein?

walks from axon terminal to soma: retrograde transport

in addition to neurons, the nervous system also includes…

glia

types of glia

• astrocytes

• myelinating cells

• microglia

what do astrocytes do?

regulate the extracellular concentrations (such as removing NT from the EC fluid to terminate signaling, ion concentration to generate voltage)

what do myelinating cells do?

wrap along an axon, which allows for signals to travel down that axon much more rapidly

what are the different types of myelinating cells and how are they differentiated?

oligodendrocytes (CNS) and schwann cells (PNS)

what do microglia do?

macrophages of the CNS

what is cre-lox recombination?

a research method that can be used to selectively alter DNA in only the cells that express a specific gene of interest

what are the 3 main types of membrane proteins?

• channels

• transporters

• pumps

what are channels?

pore through the membrane that allow for free diffusion, bidirectional

what are transporters?

bidirectional protein that changes conformation. can be uniporter, symporter, or antiporter

how are the different types of transporters distinguished from each other?

uniporter allows one ion to cross, symporters let two ions cross in the same direction, and antiporters can let two ions cross in opposite directions

what are pumps?

atpases: unidirectional, can move against concentration gradient because of ATP energy source

what does selectivity mean in terms of membrane proteins?

describes which ions can pass

what does gating mean in terms of membrane proteins?

conditions for opening/closing the membrane protein

what is C?

capacitance; the ability to carry charge; measured in farads

what is I?

current; the movement of charge; measured in amps

what is V?

voltage (electrical potential); difference in charge; measured in volts

what is G?

conductance; how easily charge can move; measured in siemens

what is R?

resistance (1/G); how difficult it is for charge to move; measured in Ohms

what are the conditions for creating an electrical potential difference (voltage)?

ionic concentration difference and selective ion permeability

when is electrochemical equilibrium (Eion) reached?

when the electrical and chemical forces are equal

ionic concentration differences in neurons are established by…

the Na/K pump, which moves K+ in and Na+ out

selective ion permeability is established by…

leak channels, which are selective for K+ and open all the time

the magnitude of Eion depends on…

ionic concentrations

what can be calculated from ionic concentrations?

equilibrium voltage

what are the equations for calculating equilibrium voltage?

Nernst equation and Goldman equation

nernst equation

calculates Eion when the membrane is permeable to one ion

goldman equation

calculates Eion when the membrane is permeable to multiple ions

for a membrane permeable to many ions, the equilibrium voltage will fall…

between Eion for the individual ions

what do leak channels make the neuron (in terms of ion permeability)?

very permeable to K+ and slightly permeable to Na+

what does Ohm’s Law describe?

the relationship between voltage (V), current (I), and resistance (R)

what is Ohm’s Law?

V = IR

ionic currents depend on…

membrane voltage, ion’s equilibrium voltage, and ion’s conductance

equation for ionic current

I(ion) = G(ion) * (Vm - E(ion))

for a specific ion, when is there no net current?

when the membrane voltage is equal to the ionic equilibrium voltage

what is I(Na), and what does it mean?

I(Na) < 0. negative currents are inward, so Na+ positive charge moves into the cell

what is I(K) and what does it mean?

I(K) > 0. positive currents are outward, so K+ positive charge moves out of the cell

when are action potentials generated?

when conductance for Na increases

what happens at the start of the AP?

Na+ channels open, so G(Na) increases, causing I(Na) to also increase. I(Na) > I(K), so voltage increases

magnitude of depolarization is proportional to…

current and resistance

rate of depolarization is inversely proportional to…

capacitance and resistance

what is the time constant?

measure of how fast a system responds to a change in input. also the time where the voltage has risen 63% of its overall increase

how do you get time constant

R*C

voltage changes fastest when time constant is…

small

what are variables that affect resistance?

• # of open ion channels (inversely proportional)

• cell size (inversely proportional)

• channel conductance/permeability (inversely proportional)

what are variables that affect capacitance?

• cell size (proportional)

• myelination (inversely proportional)

what are the discrete phases of an action potential?

• rest

• generator potential

• rising phase

• overshoot

• falling phase

• undershoot

what happens during resting phase?

• Vrest established by unequal ion concentrations and selective ion permeability

• at rest, PK >>> PNa

• negative voltage is stabilized by Na/K pump

what is generator potential?

a small increase in voltage that makes the membrane potential rise toward the threshold

what is rising phase?

depolarization; the entire period of time that voltage is rising

what is overshoot?

the entire period of time where the voltage is more positive than 0

what is falling phase?

repolarization; the entire period of time that voltage is dropping

what is undershoot?

hyperpolarization; the entire period of time where voltage is more negative than rest

ionic current and permeabilities depend on

membrane proteins

types of membrane proteins

• Na+/K+ pump

• Passive K+ channel (leak channel)

• Voltage-gated Na+ channel

• Voltage-gated K+ channel

properties of the voltage-gated Na channel

• determine I(Na)

• open during rising phase

• single polypeptide

• four domains form a pore

• voltage sensitivity derives from positively charged S4 alpha helix

• Na+ sensitivity derives from pore loop within a given domain

• blocking particle mediates inactivation

Na+ channel conformational changes depend on

voltage and time

Na+ channels go from closed to open because of…

an increase in voltage

Na+ channels go from open to inactivated because of…

time passing

Na+ channels go from inactivated to closed because of…

voltage dropping

properties of the voltage-gated K channel

• determine I(K)

• open during falling phase

• four polypeptides form a pore

• sensitive to voltage

• does not inactivate

• slow to open and close