Topic #1 - neuron & signaling [lecture]

what is a multipolar vertebrate neuron?

multiple projections growing from cell body , a single axon

what is included in the input body of a neuron?

cell body (soma) , apical dendrites, nucleus, basal dendrites

what does the input body conduct ?

Integrate Inputs

• chemical & electrical synaptic potentials

• sometimes conducts sensory info

• endogenous slow potential = in some cells in some chemical environments , some neurons produce rhythmic single Action potential regularly

what is included in conduction

axon:

- axon hillock [initial segment]

- myelin

-node of ranvier

what does conduction body conduct

conducts action potentials

what does the output body consist of

axon terminals

what does the output body conduct

-presynaptic terminals

- release of transmitter

what happens to isolated neurons ?

resting potential is usually flat "silence cell"

what does pacemaker activity mean

when theres spikes going up & down

what is an example of endogenous potential & what is it

generated endogenously by the cell but its array of ion channel's when activated can produce pacemaking or bursting

EX:

1. bursting behavior = rhythmic activation in membrane & in depolarized ways it typical "burst" of action potentials

2. cardiac muscle is able to produce pacemaker activity

what is sensory generated potentials

have touch sensitive axons that response to pressure or movement in the skin

what type of membrane is input body

passive or active

what type of membrane is conduction body

active

what type of membrane is output body

passive or active

what is an example of bursting & what 2 types of behavior does it have on

bursting behavior #1 = cells involved in rhythmic behaviors that are going on all the time such as breathing & you can find at the core , pacemaker

bursting behavior #2 = neuroendocrine that are cells that release hormones in bloodstream (R15 cell)

what is the R15 cell

in mollusk slug that have a single indefity nueron which is R15 & is involved in releasing cocktail peptide which is involved in whole system such as respiration, digestion, etc & most important in water balance

what happens in endogenous bursting

- ionic mechs vary in diff cell types

- interaction of inward Ica+ & outward IK+ causes Vm oscillations

what was the golgi silver stain technique

small fraction of tissue was stained & it was important bc only stains 5% of neurons in slice of tissue

what was the principle of dynamic polarization

- info flows in predictable & consistent direction within nerve cell

- info flows begins @ receiving [input] sites on dendrites & soma to trigger zone @ axon hillock (initial segment)

- @ axon hilllock, action potential is initiated & propagated unidirectionally along axon to presynaptic transmitter release sites @ axon terminal

- neurons differ greatly in form & function but most adhere to this patter of info flow

what does unipolar cell include, biopolar cells & pesude [unipolar cells]

Unipolar = cell body produces signal neurtire & occasionally more than 1 axon but usually 1

Biopolar cells {retina} = 2 main neutries merging in bipolar , composed of axon & apical dendrite

Pesude - unipolar cells = signle neutries emerging from cell body & emerges to peripheral axon & central axons

what is local grade potential

graded change in membrane potential (Vm) that varies continuously in amplitude w/ stimulus strength & decays exponentially over distance

* less than 100 microns

what is action potential

a transient, all or non reversal of Vm produced by a regenerative inward current in excitable membranes

- does not decay over distance

*more than 100 microns

what is the most general thing that happens in signal transduction in a typical vertebrate neuron

the more local graded potential depolarizes a neuron, the higher the action potential freq evoked, up to a point [the cells maximum spike freq]

what does local graded potential show

shows that it usually dies out in the axon bc its more than 100 microns so occurs in cell body & dendrites

why does spike transduction occur in the axon hillock

bc of ION CHANNELS

- @ axon hillock you have high concentration of Na+ & K+ but Na+ is important & acts as a trigger of Action potentials that responds to local grade potential

what type of code is the input body, conduction body & output body

input = local graded

- AM code

conduction = action & local graded

- FM code then AM code

output = action

- FM code

what does AM & FM code mean

AM = amplitude modulated

FM = freq modulated

what are motor neurons

"efferents"

- synapse onto muscle or gland tissue

- in vertebrates , all motor neurons are excitatory (produce excitatory postsynaptic potentials ) but in invertebrates, can either be either excitatory or inhibitory

what are sensory neurons & what are some examples

"afferents"

- transduce sensory info

EX: heat, cold, light, mechanical pressure or stretch, chemical energy

what are neuroendocrine cells

release neurohormones into circulation

• R15

what are interneurons

- are both postsynaptic & presynaptic to other neurons

- can be either local or projection type interneurons

what is an example of non spiking local interneuron w/ no axon & what technqiue can you use

starburst amacrine cell in mammalian retina

- Lucifer yellow dye "LY" = produced higher intensity of light & requires very little; diffuses through cell very fast

- if you see it spreading to adjacent cells then they have to be coupled by gap juntions

- transmission occurs local graded potentials from dendrites & communicate w/ each other by synaptic zones are in proximal side closer to cell body

what is an example of spiking projection interneurons w/ long axons & what is an example

reticulospinal cells in vertebrate brainstem

EX:

mauthner cell [M cell]

- involved in fast escape behavior in fish, the tail flip so if that cell gets turned on then that AP activates

what does reticulospinal cells mean

"reticulo" = location of cell bodies

"spinal" = target of cells

what is membrane potential (Em)

voltage or electrical potential (mV) across cell membranes, arising from a separation of charge

- typical Em in neurons is -60 or -70 mV [inside negative]

what is depolarization

decrease in Em (decrease inside negatively) or movement of Em in a positive direction

what is hyper-polarization

increase in Em (increased inside negatively) or movement of Em in a negative direction

what did the principle of dynamic polarization do ? ( ramon y cajal)

it was a uni-direction of information

what does channelrhodopsins (CHR) do & what do they let in?

Depolarization

- let in Na+

what does halorhodopsin do & what do they let in?

Hyperpolarization

- let in chloride

what are some recordings that involve electrical activity in the nervous system

• extracellular recording

• intracellular recording

• Optical recording

how does extracellular "differential" work

- "differential " extracellular recording from axons & whole nerves

- 2 active electrodes in contact w/ tissue

- subtracting 1 signal from the other & amplify what remains in the signal

- size of spike records determined by size of neuron producing activity

- reduces 60 Hz noise

how does extracellular "single ended" work

- single electrode recording from nerve cells & record relative to the ground

- record activity of single neurons or small groups of neurons in active brain or spinal tissue

electrodes usually carbon fiber

what are the 2 types of intracellular recording ?

sharp electrode & whole cell path

what are the differences of sharp electrode vs whole cell path

Sharp:

- electrode tip diameter = 0.01-0.1 um

- electrolyte solution inside is 3-4 M KCl or another K salt

- ruptures membrane & poking into cell making hole & some solution will go down in concentration gradient & go into cell & will change intracellular ion concentration

Whole cell patch :

- electrode tip diameter = 1-2 um

- electrolyte solution inside is isotonic artificial intracellular saline

- no impaling

- low noise recording

what are voltage sensitive dyes

can get recording of change in membrane potential that is very fast

what is easier to use , voltage sensitive or calcium sensitive dyes & why? & what happens

calcium sensitive dyes bc it changes fluorescent in response to changes in calcium levels

- whenever cell spikes = influx of calcium but that sodium mediated spike will trigger calcium influx

what is an intrinsic signal

actual change in light transmission through tissue that occurs during heightened activity & has time constant in seconds range so its a slow development, no dyes needed ; results of change in blood flow that occurs w/ increase of neural activity

what happens in calcium imaging & what does it indicate

cell goes from mostly blue to orange

- indicates of increase calcium levels associated w/ spike

what is another word for "hemodynamic response"

- neurovascular coupling or "roy Sherrington principle"

an increase of neural activity causes what

increase of local blood flow & increase of local blood oxygenation

what is an FMRI

FUNCTIONAL MAGENTIC RESONANCE

- detects the increased ration of O2/ de-O2 (deoxygenated) hemoglobin during "hemodynamic response" to increased neural activity

how does the FMRI affect all cells of the body

deoxygenated hemoglobin is more strongly attracted to this magnetic field than oxygenated hemoglobin

why do glia cells specifically astrocytes play a critical role in hemodyanamic

critical role in this function in hemodynamic response bc modulating local blood flow in response to neuronal activity

what was the neuron doctrine

cellular hypothesis of neurons

- using Golgi stain [invented by camillo & perfected by ramon y cajal]

what method was used for "photoinactivation" & what did it produce

exposure of lucifer yellow to blue/UV light

- prodcued free radicals that rapidly kill cell = photoinactivation

- used to delete cells from invertebrate neural circuits

- focused UV lasers can be used to "clip off" individual dendrites or axon branches w/ this technique

what are optogentics

use of light to excite or inhibit cells, usually neurons that have been genetically modified to express light sensitive ion channels or pumps

- expressed in a mouse or some other animal that lacks that protein

what are channelelrhodopsins (Ch1 & Ch2)

light -gated cation channels obtained from motile , single cell green algae (chalamydomonas )

how is Ch2 activated & what does it cause

activated by blue light & causes cell depolarization & excitation

how is halorhodopsin (ex; Halo-3) activiated

light activated chloride pump that drives Cl- into cells

how is archaerhodopsin (arch) activiated

light activated proton pump that drives H+ out of cells

how are halorhodopsin & archaerhodopsin obtained & how are they activated & what does it cause

- both obtained from "halobacteria" [Achaea]

- when activated by green/yellow light, cause cell hyper-polarization & inhibition

in a a channelrhodopsin in a vitro recording what kind of spiking does it cause from pyramidal neuron actiivty

- intracellular spiking in response of blue light pulses presented by micro light pipette

in a a channelrhodopsin in a vivo recording what kind of spiking does it cause from pyramidal neuron actiivty

- extracellular recording

- intensity of light pulse you can get 1 to 1 for every light pulse in action potential