Stuff for Exam 1

santiago ramon y cajal contributions

revealed most of CNS structure using silver nitrate stain, correct idea of neuron theory

camillo golgi contributions

invented golgi (silver nitrate) stain and was really the first to use histology to study neuroscience; incorrect idea of reticular theory

reticular theory

neurons are continuous with one another, the nervous system is an uninterrupted network (reticulum)

neuron theory & its elements

neurons are individual units that communicate across intercellular gaps - proven with electron microscopes definitively in 1950 when you could observe synapses/gap junction

• brain made of individual units = cells = neurons

• units/cells may differ in size, shape, structure

• center of cells is nucleus, nerve fibers built from outgrowth/processes

• cells connected via contact and synapses allow transmission

• there is a preferred direction of transmission bw cells = polarization

• transmission is excitatory or inhibitory, not both

• Dale’s law → each terminal releases single type of transmittor

main parts, functions of neurons

dendrites receive info, directed to soma/cell body (has nucleus and organelles), axon propagates electrical signals via action potentials, axon terminals send out chemical signals/release neurotransmittors

plasticity

idea that experience can modify neuronal activity

unipolar neurons

one process

pseudounipolar neurons

typically have continuous axon with central (CNS) and peripheral (PNS) axon that goes into skin/muscle → often sensory

bipolar neurons, common location, what its structure tells us

axon and one main dendrite stem; ex: in retina, limited inputs and low surface area therefore each input contributes more to firing action potential or not

multipolar neurons, what its structure tells us

several processes - large surface area and multiple inputs so can be involved in many neural networks, each input contributes less to ap or not

polarity of axon proceedings

primarily in one direction: axon → dendrite → soma (back propagation does exist though)

nucleus in soma contains…

lots of euchromatin → loosely packaged DNA that is accessible and active in transcription

what is present in soma/functions

rough er with ribosomes to form proteins

golgi apparatus to modify and package proteins

neuronal structures most relevant to axon

myelin sheath (typically present) allows faster ap conductance

nodes of ranvier = gaps in myelin sheath

axon hillock/axon initial segment is where aps originate from

major components of cytoskeleton/structure

microtubules

neurofilaments

microfilaments

microtubules’ function

carry info, bases for protein transport (‘walked’ along them)

neurofilaments’ function

primarily make up axon’s structure

microfilaments’ function

responsible for cell shape and movement

axon means of communication, morphology

fairly uniform with branches at axon terminal, uses neurotransmitters within synaptic vesicles to send signals

dendrite means of communication, morphology

variety of branched patterns, diameter decreases towards end, receives/propagates info via postsynaptic receptors (have varying densities)

segments of neuron & what’s in them

somatodendritic - dendrites, soma

axonal -axon

terminal - axon terminal

where are action potentials initiated and why

at the AIS, because there is a high density of low voltage-activated channels there, allowing the depolarization required for AP firing

how was action potentials originating at AIS experimentally confirmed

electrodes were placed in various neuronal regions (axon, soma, dendrites) and mv was recorded in electrodes when ap was fired; increase in mv was first seen in axon, then soma, then dendrites

major proteins at AIS are…, allow…

ankyrin-G proteins, visualization of multiple types of channels and locations via fluorescence

types of channels around AIS, visualized with ankyrin-G proteins

Nav1.2 channels → clustered closer to soma, promotes its own back propagation to soma (proximal)

Nav1.6 channels → clustered farther from soma (distal)

general structure and elements of microtubules

tube-like structure made of 13 protofilaments; each protofilament is a heterodimer of alpha tubulin and beta tubulin, slightly slanted

microtubules are associated with…

unique microtubule-associated proteins (MAPs) - MAP2 is a dendritic marker, and Tau is associated with alzheimer’s

microtubule-disrupting agents (for exps)

nocodazole

colchicine

microtubule-stabilizing agent (for exps)

paclitaxel (AKA taxol)

actin general structure, made of

contains many genes that remain conserved, gamma and beta actin

has globular subunits made of G-actin and filament subunits made of F-actin

G v. F actin

F-actin is a double-helixed filament made of G-actin subunits

proteins associated with microfilaments

spectrin, ankyrins, dystrophin

F-actin disrupting agents

latrunculin A

cytochalasin D

microfilaments associated with what protein family?

Myosin family of motor proteins

general steps of axonal transport

1) proteins synthesized in rough ER in soma

2) nascent proteins transferred to Golgi apparatus, packaged into membrane-bound organelles or integrated into membrance

3) proteins slowly move down membrane (100-400 mm/day)

4) proteins specially localized → reach final location and stay there to carry out a specific function in that specific location

5) proteins recycled via endocytosis

6) proteins sorted for recycling or retrograde transport, occurs at cell body

(also vesicle trafficking in dendrites)

what is epifluorescence

uses fluorophores to visualize phenomena → one of the most important and common modern molecular biology techniques

requirements for epifluorescence

contrast agent (fluorescent molecule = fluorophore)

light source (for excitation)

optics for imagine

emission detector

most common fluorophore

green fluorescent protein, GFP (from jellyfish)

generally how epifluorescence works, machinery

only things with GFP (or whatever fluorophore) will show up

lambda emission

energy change from molecule’s excited state to its spontaneously reduced almost ground state

lambda absorption

change in energy from ground to excited state from light source

GFP lambda a, lambda e

absorption: 490 nm

emission: 509 nm

what is stokes shift

lambda emission - lambda absorption

how to calculate energy from epifluorescence

E = hc (plank’s constant * speed of light) / stokes shift

stochastic expression

3+ fluorescent proteins are expressed in an image to visualize multiple types of cellss/interactions, sometimes called brainbow

FRAP means…

fluorescence recovery after photobleaching

what is FRAP

a small section of fluorescently labeled cells is photobleached with lasers which removes their fluorescence, and it is then tracked how quickly/if at all surrounding fluorescent cells will infiltrate that bleached section - helps track cell spread/growth

‘filter’ at AIS

experimental evidence suggests this ‘filter’ restricts diffusion of certain proteins and may play a role in neuronal polarization

experimental evidence for AIS ‘filter’

FRAP bleached area in axon showed greater movement of small proteins than large ones to come replace area, suggesting that small proteins may have more success travelling through a ‘filter’ at the AIS than large ones

action potentials occur when? what does this rely on?

when membrane potential reaches threshold → mv relies on ions, channels, pumps

extracellular fluid is…

the same for all neurons

typical ion concentrations in/out of neurons, mV

high Na+ outside, high K+

cytoplasm. is relatively negative compared to extracellular fluid

type of transport through ion channels

passive → along concentration or voltage gradients, but various factors will cause these channels to open/close (ex, voltage gated or leak channels)

sodium potassium pump

3 Na+ out

2 K+ in

require ATP → active transport, against concentration gradients

general info about ion pumps

are active and require ATP, create concentration gradients againt electrochemical gradient by allowing ion movement across membrane → this causes mV

membrane potential definition and equation

comparison of intra v. extracellular voltage

mV = Vin - Vout

neuron RMP

-60 - -80 mV

4 ions that determine RMP of neuron

Na+, K+, Ca2+, Cl-

what causes hyperpolarization

- ion into cell, + ion out of cell

what causes depolarization

+ ion into cell, - ion out of cell

types of potentials

graded → voltage remains subthreshold, no AP

AP → triggers neurotransmitter release

ionic movement is determined by…

permeability, concentration gradient, electrical potental across membrance

permeability?

if ion channels are open for ions to travel through

concentration gradient?

an ion will try to flow to the side of membrane with a lower concentration of that type of ion

ex, Na+ prevalent outside cell so wants to come in

electrical potential across membrane?

an ion will try to flow to the side of membrane with the opposite charge as itself

ex, negative inside cell so positive ions want to go in, positive ones want to go out

ATPase cycle for sodium-potassium pump is important because…?

about 2/3 of neuron energy expenditure is due to this, generates outward current

ATPase cycle for sodium-potassium pump inhibited by?

Oubain

Digoxin

ATPase cycle for sodium-potassium pump looks like/steps

where is equilibrium potential

where opposing forces of concentration gradient and voltage gradients are balanced

concentration gradient equation

RT * ln ([ion outside]/[ion inside]

R is gas constant 8.314 J/kmol

T is temp (K)

voltage gradient equation

ZFV

Z is valence/charge of ion

F is faraday const 96485 C/mol

equation for equilbrium potential

ZFV = RT * ln ([ion outside]/[ion inside])

Veq will be reached for an ion if…

the ion channel remains open and the ion’s effect is unimpeded

what does Nernst eq potential tell us

Ek, reversal potential, tells us ion’s movement/direction (in or out)

generally if Vm < Ek, inwards net ion flow

Vm > Ek, outwards net ion flow

what is nernst equation

Ek = V = RT/ZF * ln ([ion outside]/[ion inside])

Veq of Na+

+56 mV

Veq of K+

-100 mV

Veq of Cl-

-76 mV

Veq Ca2+

+125 mV

typical mV for neuron

-60 → -75 mV

Goldman equation for overall membrane potential

P is…

permeability of membrane for each ion

permeability ratio of ions in squid giant axon

-Pk:PNa:PCl → 1.0 : 0.04 : 0.45

Ohm’s law, general

delta V = IR = I/G

Ohm’s law for neurons

Ix = G * (Vm - Ex)

Ix = current

G = conductance

Vm = membrane potential

Ex = Ek = reversal potential

general parts of RC circuit, neuron equivalents, values

capacitor (membrane capacitance → capacitative current)

resistor (membrane resistance → due to leak channels)

battery (membrane potential → potential to generate current)

membrane time constant eq

tau = R * Cm

membrane current eq

= Ic + I ionic

general characteristics of Na+ channels

transient, persistent, resurgent

Ca2+ and K+ channel types, general characteristics

can be high-voltage activated (HVA → L, N, P/Q channels)

can be low-voltage activated (LVA → T)

can be intermediate-voltage activated (R)

What are L, N, P, T, R channels

L: long-lasting

N: neural

P: purkinje

T: transient

R: residual

some nonselective cation channels

TRP

• mGluR

• photoreceptor

• possibly hair cells

some cyclic nucleotide-gated channels

HCN (Ih or If)

Cl- channels

H+ channels

variation involtage-gated potassium channels due to

over 80 mammalian genes encode K+ channel alpha subunits that form conductance pore, and can see more variability with alternative splicing; most diverse ion channel family

general parts and their purpose in v-gated K+ channels

various alpha subunits, form conductance pore

beta subunits → auxiliary proteins that associate with alpha subunits and modulate Kv channel activity

similarity in v-gated K+ channels

similar mechanism of hyperpolarization/decreasing cell excitability; kinetics is what mainly varies between channels

generally what a v-gated K+ channel looks like

step currents

channels gradually open, causing a slight inc/dec in mV until certain mV met and suddenly many channels open at once → sudden inc/dec in mV

sub v suprathreshold depolarization

subthreshold under threshold, no AP

suprathreshold meets threshold, AP fired