What is faster in electrophysiological analysis, many cells or single excitable cell?
single excitable cell (msec, sec)
Neurophys has been a study of what?
electrical activity of the brain at the global and cellular level
What does electrophysiological analysis of nervous system activity involve?
cathode ray oscilloscope recording of VOLTAGE-time displays
Macro electrode are good for what?
population responses
What are the diagnostic tools used for population responses?
- EEG, sEP, ERP (cortex & pathwways)
- compound whole nerve potential (peripheral nerve)
- EMG (group of muscle cells)
What doe micro-electrodes record?
single cell responses
What diagnostic tools are used for single cell recordings?
- single unit extracellular recording
- single unit Intracellular
- single unit patch-clamp
what is an ERP?
event related potential for cell population recording
what is an EEG?
electoencephalogram for recording potentials on the skull
On a graph for ERP, EEG and WNP what is recorded on the y-axis upward
ERP - positive up
EEG - negative up
WNP - negative up
in single unit recordings what charge is upward on y-axis?
positive up
How are EEG used clinically?
diagnostic tool to tell abnormal from normal
identifies where pathology located
What defines a normal EEG?
alpha rhythm average around midline
What defines an abnormal EEG?
“spikes” in multiple leads
**What is a problem with EEG?
the recording cannot tell us anything about what is wrong at the cellular level but can tell us grossly normal vs abnormal
What are ERPs triggered by?
sensory input (visual, auditory, somato)
What is receptotopic mapping?
map receptor sheets on to the brain (place-to-place mapping of r/c’s to cortex)
****What are ERPs used for?
used to evaluate the general viability/functional integrity of a sensory pathway
What are compound whole nerve potentials used for?
PNS electrodiagnosis
What is important about graduated electrical stimulation of PNS recordings?
- smallest currents activate large fibers only
- large currents activate all fibers, small and large
In thee PNS which fibers are myelinated and unmyelinated? what is their arrival during a CRO recording?
myelinated 1)Aalpha 2)Abeta 3)Adelta
unmyelinated 4) C
= order in which they appear in CRO
What does a abnormal PNS recording look like?
-diabetes/MS => demyelination and inability to produce myelinating cells => increased lag time in AP
***** What does peripheral neuropathy look like? significance of whole nerve potential?
- slowing, failure of conducting fibers
- doesnt tel what is happening at cellular level but rather what is happening with the nerve
What are the functional/ clnical significance of EEGs, ERPs, WNP?
- oldest brain recording tech.
- excellent temporal, poor spatial res
- used for differential diagnosis of CNS, PNS, sk mm.
- inability to monitor cell-level processes
What are the benefits of single cell neurophysiology?
very fast electrical membrane communication (less than 1 sec)
What is involved in single unit electrophys?
plasma membrane
What are electrical membrane signalling directly and indirectly coupled to in single unit electrophys?
ion channels and signal transduction pathways
Energy dependent
What type of potential do single unit recording have?
all-or-none
What encompass the graded potentials in a neuron and the electrogenic all or none membrane?
graded = dendrite and axon all-or-none = axon
Are graded potentials passive or active?
passive electronic spread
Are all-or-none active or passive regenerative propagation?
active
What are some characteristics of functional dynamic polarization?
highly ATP dependent
needs glucose & O2 to keep up (ionotropic = fast; melanotropic = slow)
What are the 3 tech. of single cell recording?
extracellular, intracellular unit recording & patch clamp
What is the resting membrane potential?
-70mV
What is important about patch-clamp?
single/group of ion channels
- can be resting, graded, all-or-none
What is the physiological sequence via neuronal chains?
electrical => chemical => electrical…etc.
What did Sherrignton discover?
stop and go synapses
What is synaptic delay?
2msec for synaptic signal to move across synaptic cleft
What controls the actions at the synapse?
go (excitatory) and stop (inhibitory) messages
What is the importance of Go and Stop?
contraction and relaxation of mm groups etc
What kind of n.t. is Acetylcholine?
inhibitory
How do you quiet down striated mm?
quiet down CNS (Ach)
What is an excitatory amino acid?
glutamate
What is an inhibitory amino acid?
GABA
What is thee membrane of excitable cells permeable to?
lipid-soluble substances, NOT charged ions
A thin unit membrane acts as a good battery plate & stacks electrical charge, what does it show?
capacitance
Electrically charged entities can only get across membrane via what?
- slow crossing via transport proteins
- rapidly via ion channels
Define leakage in p.m.
passive ion channels
always open
single ion selective
responsible for RMP or neurons, mm & glia
What are gated ion channels responsible for?
graded & all-or none AP for neurosecretion
What are the diffusional tendencies for Na, K, Cl, Ca?
Na, Cl, Ca = inward
K = outward
How are conc. differences maintained with Na, Cl, Ca, K?
pumped by ion exchange
What are the tendencies of Na?
transport = Na-K pump
Intracellular conc = low
Ion diffusion = inward
What are the tendencies of K?
transport = Na-K pump
intracellular conc = high
ion diffusion = outward
What are the tendencies of Ca?
Transport = Ca pumps
intracell conc = low
ion diffusion = inward
What are the tendencies of Cl?
transport = KCC2 co transport
Intracell conc = low
ion diffusion = inward
What does KCC2 K-Cl cotransport involve?
1 K and 1 Cl => outside cell = K moving with conc gradient and Cl against
What forces act on ions dissolved in solution?
- diffusional
- electrostatic
What is the electrochemical equilibrium?
diffusion stops when at equilibrium - dictated by NERNST equation
What is the rule for intracellular membrane voltage?
set closest to the equilibrium potential of the most permeant ion
- ion with the greatest # of open channels
What are the Eion for Ca, Cl, Na, K?
Ca = +246 Na = +60 Cl = -70 K = -90
What are the general features of RMP?
- always inside negative
- found throughout the unit membrane but vary across types of excitable cells
What are the RMP of small, large neurons and mm, glial cells?
small = -60mV large = -70mV mm = -80mV glial = -90mV
What is the significance of RMP?
- ***RMP in neurons & mm is the background against which all electrical signaling is produced
- glial cells have an RMP but do not generate electrical signals on cell membrane
What is the mechanism of RMP?
- RMP in glial cells is pure K diffusion potential
- neurons & mm = predominantly K diffusion but Na ion inward leakage very small contribution
Is there a leakage channel for Ca in skeletal mm.?
NO
What is the importance of Na?
takes away negativity => establishes -70mV
What are the functions of leak current ion channels?
- single ion selective
- open at rest
- produce the resting membrane potential
What is the structure of leak current ion channels?
2 pore, 4 sided tetramere topolgy
Alpha and Beta proteins make up leak current ion channels, what is their function?
- alpha helix (4) form the channel
- Beta form the anchoring protein
What are the importance of leak channels?
- expressed throughout entire excitable cell (K>Cl>Na)
- produce RMP
What are depolarizing excitatory effects?
loss of polarization => positive and continuation of AP
What are the pathways of graded synaptic potentials?
ionotropic and metabotropic signal transduction pathways
What are the hyperpoarization inhibitory effects?
excess negativity (negative) => arrest the AP
What are the processes through which information is sent through a cell?
transduction -> transformation -> propagation -> translation
What are the membrane domains and associated electrical events in a cell?
dendrites & soma = graded, synaptic potentials
axon hillock, impulse trigger zone = all-or-none
axon = impulse propagation/conduction
axon terminals = excitation secretion coupling
Match the processes with the appropriate membrane domain
transduction = dendrites & soma transformation = axon-hillock and impulse trigger zone propagation = axon translation = axon terminals
What happens when n.t release occurs at the synapse?
r/c binding => ion channels open or close => conductance change => postsynaptic potential changes => excited or inhibited postsynaptic cells
What are EPSPs?
excitatory postsynaptic potentials => voltage depolarization by excitatory n.t (neurotrophin), neuropeptide ligands, neuromodulator substance
What happens when 2 EPSPs elicited in rapid succession?
sum to produce a larger EPSP (temporal summation)
All excitatory synapses have 2 mechanisms, what are they?
ionotropic and metabotropic
What are all excitatory synapses calles?
Grey Type 1 synapses
What are some characteristics of Grey Type 1 Synapse (excitatory)?
- round presynaptic vesicles
- large presyn bulb with electron dense inside
- wide synaptic cleft
- dense postsyn basement membrane
- large extensive postsyn density
What are type 1 synapses known as beside Grey Type 1?
assymetrical junction
What are some functions, structure of ligand-gated ion channels?
- 1 pore, 4TM, 5 subunit pentameres
- gated open or closed by ligands
- especially like Na but selective to Cl, Ca, K too
What happens to the ligand-gated ion channel with glutamate presentation?
glutamate goes out = resting state = closed
glutamate attaches = open
ligand - gated channels have 5 subunits, whats the importance?
selective filter
What did Sutherland discover?
- signalling molecules that control nerve cell function do so via 2 types of membrane signal transduction mechanisms: 1) IONOTROPIC 2) METABOTROPIC
WHat is direct/ ionotropic synaptic action?
- direct, selective binding of n.t. to surface r/c of ion channel
- rapid & reversible change in electrophysiology
- new addition to the cellular control arsenal
- ***OPEN or CLOSE membrane ion channels
What is the difference between ionotropic vs. metabotropic?
ionotropic = ligand gated ion channel metabotropic = G protein coupled receptors
What is the system of activation for metabotropic r/c’s?
nt => binds r/c => G-protein activated => effector protein => intracellular messengers => ion channel opens => ions flow across membrane
What is the special about indirect/ metabotropic synaptic action?
- slower & indirect
- G-protein/ P coupled
- turn on slowly => dephospo => turn off slowly
Where is the metabotropic motif commonly employed in?
the neural networks of the brain
What are CAMs?
cell-adhesion “docking” molecules which bind the cells together (ie. Neurexins & Neurligans)
What is the postsynaptic organization?
1) CAM
2) Ionotropic STPs
3) Metabotropic STPs
What is the AP threshold in a cell?
-65mV
What happens when EAA - Gutamate is introduced to ionotropic - STP?
- AMPA-r => open => increase conductance permeability => Increase Na in => Icrease EPSc => Graded Depol fast EPSP
What happens when EAA - Gutamate is introduced to metabotropic - STP?
mGlu-r => close => decrease conductance permeability => Decrease K out => Increase EPSc => Graded depol slow EPSP
What happens if the summation between iono and metabo STP is greater than or equal to 5mV above RMP (-70mV)?
trigger zone impulse and AP begins
What happens with channel opening?
Increased ionic permeability (Pion), Increased conductance (G), decreased membrane resistance (Rm)
What happens when a channel closes?
Decreased Pion, Decreased G, Increased Rm
What happens with an indirect closing of K metabo channel?
rebound depol postsyn (EPSP)
What happens with an indirect closing of sodium metabo channel?
rebound hyperpol postsyn (IPSP)
Metabo ion channel closing “gating themes”show passive decay, which is?
the excitatory voltages/currents die out as they move away from the postsyn membrane region
What happens to depol of postsyn membrane?
+ charges cancel out negative charge which causes a pushing effect away from postsyn membrane (see pg 58)
Why is the location crucial for testing electronic decay of graded EPSP?
the closer to the synapse = more powerful current; therefore the more powerful the message
What is temporal summation in a neuron?
repeated impulse over a short period of time from a cell produces temporal summation EPSCs/ EPSPs at that synapse
What is spatial summation in a neuron?
sensory summation that involves stimulation of several spatially separated neurons at the same time
If >5mV graded potential, what does this trigger at the AH-IS/T.Z areas?
Transformation = all-or-none AP
What are the characteristics of EPSPs?
- graded in size
- summate both temporally and spatially
- display passive electronic decay
At the axon hillock what happens to the signal in terms of graded synaptic membrane response?
transduced => transformed
What are IPSPs?
inhibitory postsyn potentials = hyperpolarize (SILENCE EFFECT)
What are the events from n.t release to postsyn excitation/inhibition?
nt release => r/c binding => ion channels open or close => conductance change (ion current flow) => post syn potential changes (EPSPs, IPSPs) => excited or inhibited postsyn cells
What can happen with 2 IPSPs elicited in rapid succession?
sum to produce a larger (-‘ve) IPSP
What are Grey Type II Synapses?
inhibitory with IAA being GABAergic
Grey Type II Synapse are location specific, wher?
tend to cluster at specific locations toward axon hillock
What are some specifications of Inhibitory synapses?
- flattened oval presyn vesicles
- small, multiple presyn active zones
- narrow syn cleft
- modest postsyn basement membrane
- multiple, restricted postsyn densities
Are Inhibitory synapses asymmetrical?
NO, they are symmetrical (in terms of density)
Grey type I are asymmetric
Where is the binding site on GABAa r/c Cl complex?
2 alpha subunits
All the ionotropic site is how many sided?
5 - ion selectivity because of this
What is the difference between Greys Type I and II in terms of ionotropic and metabotropic at active zone?
Greys Type II uses GABAa for both metabotropic and ionotropic and ionotropic are direct but slow!
Metabotropic signal transduction in Inhibitory synapses utilize what 2 GABA subtypes which correlate to which ions?
GABAb -> K (-90mV)
GABAa -> Cl
How is the signal inhibitory when Cl- equilibrium is -70mV and GABAa is for above -70mV?
due to GABAb and the use of K efflux which equilibrium is -90mV (see pg 65) - essentially draws the equilibrium below -70mV
what is the neuropeptide for inhibitory synapses?
Eukephalin
What happens with GABA presentation for iono-STP?
GABAa => Increased conductance (open) => Increased Cl- IN => graded hyperpol FAST IPSP
What happens with GABA presentation for metabo-STP?
GABAb => Increased conductance (open) => Increased K+ OUT => graded hyperpol SLOW IPSP
Passive electronic decay for inhibitory synaptic voltages die out where?
prior to hillock, die out fast
IPSPs do what at the AH-IS trigger zone to suppress impulse production?
push voltages away from impulse threshold => postsyn inhibition
What happens if IPSP = EPSP; IPSP > EPSP; IPSP<EPSP?
IPSP = EPSP => cancel each other out and no AP
IPSP > EPSP => inhibitory effect (hyperpol) no AP
IPSP < EPSP => excitatory effect (depol) AP (>5mV)
What is neuronal integration?
IPSP + EPSP to determine whether an AP occurs
At the axon bulb what does the AP stimulate?
Ca to be released
What are the channels on the axon?
all or none impulse + voltage gated ion channel
What aa/nt stimulates excitatory actions? inhibitory? both?
excitatory = 75% Glutamate (E.A.A); 25% Ach, Adenosine, NA, serotonin inhibitory = 90% GABAa/GABAb (I.A.A) both = histamine, Ach
From threshold to peak what are the # in mV?
-65=>0=>+20
What is the Na dependent process in the all or none impulse?
rising depol phase
What is the K dependent process in the all or none impulse?
repol phase
What is the AP threshold?
-65mV
What causes the difference in AP from nerve to nerve?
axon hillock graded EPSP + summation time
What did Hodgkin and Huxley test on to prove ion movement through membrane pores?
squid giant axon
What causes the impulse that occurs at the TZ and subsequent opening of ion selective and voltage gated ion channels?
****positive, graded cationic generator currents supply the depolarizing voltage to trigger these events!
What happens when Na influx pushes charge inside the cell to positive?
inactivated state of r/c (AMPA) => refractory period
What happens when K efflux outside cell?
hyperpol. => cell need to repol to -90mV => refractory period
What is the spike freq upper limit?
800 spikes/sec
What can selectively block Na channel?
tetrodotoxin (TTX) & saxitoxin (STX)
What is saxidomus?
a specific toxin that inhibits depol of neuron (Na channel) therefore fatal to humans - from clams
What can selectively block K channels?
tetraethylammonium (TEA) from outside the cell & 4-Aminopyridine from inside after migration into the cell
Do the K and Na voltage gated channels differ in transmembrane segments?
No they both have 6TM, 1 pore and 4 sided tretramers
What is the difference between absolute and relative refractory periods?
absolute => no AP from second stimulus
relative => second impulse fails to elicit an impulse of normal size or amplitude
What does the Na influx during thee rising depol phase of the AP spike produce?
local cationic (+) circuit current (LCC)
What is LCC?
helps to depol the next patch of membrane with Na voltage gated channels until reaches end of axon or fiber
What happens to the speed of conduction when you increase/ decrease axonal size in small, unmyelinated axons?
Increase axon size => decrease resistance => Increase speed of LCC => faster conduction velocity
Decrease axon size => increase resistance => decrease speed of LCC => slower conduction velocity
What is the conduction velocity in small unmyelinated axons?
0.3-4.0m/s
What is the conduction velocity of large myelinated axons?
5-120m/s
What is salidatory conduction? where does it take place at?
hopping conduction at the Nodes of Ranvier in myelinated axons
What are the characteristics of All-or-None Law?
- threshold voltage
- magnitude from threshold to peak voltage
- duration
- voltage waveform
- conduct/ propagate
- electrogenic -> self-regenerative
What does a high freq stimulation lead to in the axon bulb in terms of Ca?
general increase of Ca => release of peptide nt from large dense-core vesicles, as well as small molecule nt from small clear-core vesicles
What are stored in small vesicles in axon terminal?
small mol transmitter (glutamate, aspartate, GABA, Ach)
What is the sequence of events of AP arriving at axon terminal in terms of Ca?
AP => LCC opens Ca voltage gated channel => Increase in Ca => glutamate release => Glutamate bind to postsyn => Glutamate reuptake by glial cells or presyn cells
What is the Katz’s Quantal Hypothesis of Transmitter Release?
- a single impulse forces many small vesicles to release their contents into synaptic cleft and then diffuse to postsyn and bind to recognition sites and open ligand-gated ion channels
What happens in silent chemical synapses, with no invading all or none impulse?
few “quanta” (small vesicles) release spontaneously and form a spontaneous miniature postsynaptic potential mPSP
What determines the amount of quanta released by the neuron?
Ca levels in the presynaptic terminal
where are neuropeptides generated and stored in a neuron?
generated in the neuron cell body from precursor molecules
stored in large dense-core vesicles
What happens once the NP of a dense-core vesicle enters the synaptic cleft?
diffuses to the postsyn cell, the NP binds to a r/c/ which INDIRECTLY activates a signal transduction pathway and coupled postsynaptic cellular response
What happens to the NP in the synaptic cleft with decreased amounts of Ca?
the peptide diffuses out of the synaptic cleft
altered by endopeptidases
What is Dales Rule?
a single neuron transcribes, constructs, packages, and releases the same chemical transmitter at ALL of its synaptic terminals (for both small and large vesicles)
What are the inhibitory NP for Glutamate and GABA?
Glu => Subs-P
GABA => Enkephalin
Which r/c’s do small molecule n.t. activate?
Iono & Metabo
What r/c’s do NPs activate?
metabo ONLY!
Is there retrograde signalling with impulse-based signal release?
NO
What r/c’s do non-impulse bases, continuous/constitutive signal release (growth factors) activate?
NGF, BDNF => Metabo-TrK-R
What are ways to terminate transmitter action?
- active transmitter re-uptake
- diffusion
- degradative processes
- autoreceptor inhibition of release
How are small molecule transmitters take up in the synaptic cleft? whats the effect?
- avid reuptake in glia & terminal via specific n.t. transporter
- rapid/fast decrease of conc. in the synaptic cleft which provides rapid termination of synaptic action
What Neuromodulator has different mechanism of termination of transmitter in the synaptic cleft than small molecule transmitter?
Ach = degradative enz - Ach-E in synaptic cleft
Dopamine, serotonin, noradrenaline have same mech and effect as small molecule transmitter (Glu, Asp, GABA, Gly)
How are neuropeptides terminated in the synaptic cleft?
- ednopeptidases in synaptic cleft and diffusion
- very slow breakdown and diffusion decreases # of NP in cleft - allows for prolonged action
What are special about autoreceptor actions in terms of n.t.?
provide negative feedback to decrease small mol n.t. release into snyaptic cleft - to stop synaptic action
- Glu comes back and binds to mGlu-R which inhibits release
- GABA binds to GABAb-R
What is presynaptic inhibition?
decrease n.t. release
What is presynaptic facilitation?
Increase n.t release
What is the mechanism of neuromodulation?
induced change in axon terminal Ca ion levels/ conc.
What n.t. is released from neuromusculare junctions?
Ach
Where is Ach released from in NMJ?
prejunctional component (active zone)
What are the 2 types of release from NMJ?
- spontaneous release
- evoked release
Is an AP evoked with spontaneous release at NMJ?
- small depol of the post-junctional end plate region do not spread beyond the end-plate and do not excite the mm cell = NO!; however do produce mEPPs (miniature end plate potentials)
What is special about an EPP?
20-40mV with 1 release; graded response; very big and dont usually summate
Do evoked release at NMJ form an AP?
YES! form an EPP (end plate potential) which gives rise to an AP => tension generation
Is the NMJ Ca dependent?
YES!
How is Ach blocked?
ACh-E degrades Ach in cleft
**The motor end plate of the NMJ has specific characteristics, what are they?
- direct, ionotropic system
- nicotinic-Ach ion channel
- ligand gated ion channel
- 5 sided pentamer
What cause an End Plate Potentials (EPP)?
- binding of 2 Ach => gates open
- Increased conductance => depol
- large (20-40mV) event
- 2 ion voltage (Na influx (mostly) K efflux)
What are the characteristics of an NMJ?
- high-fidelity and high safety factor chemical synapse
=> obligatory and reliable 1-1 transmission of motorneuron impulse leads to mm impulse (“twitch”)
What are special about electrical synapses in CNS?
- allows for unhindered passage of electrical ionic currents
- bidirectional communication
- mediates synchronized electrical activation of some cell types (neocortex, thalamus, brainstem (inhibitory) neurons, cardiac & smooth mm)
What is the structure of electrical synapses (gap junctions)?
6-seded hemi channels called connexons
4 alpha helixes per subunit
