Test 1: Review/Membrane and Synaptic Physiology Flashcards
Where does info transfer in neuron?
synapse
What leads to complex neural control system?
convergence and divergence
what does Intracellular recording electrode measure?
measure membrane electrical potential
What is the ground?
extracellular space
What is the electric potential?
Between electrode and ground
What is resting potential?
Potential at equilibrium
If equal on both sides, then zero. But if stuff has to cross, it will change
What is the transmembrane potential?
A function of cell’s ability to maintain concentration gradients of different ion species across cell’s membrane.
A rest membrane potential primarily determined by
K+ ions, tend to flow OUT along concentration gradient
As K+ flow out
other cations in. Electrical gradient
Equilibrium potential is a
linear function of the log of the concentration ratio
Nerst Equation: getting equilibrium with 1 ion only
E(ion) = Transmembrane voltage at equilbirum
RT/zF ln (ion out)/(ion in)
Cations on top.
2 chamber: where do ions flow?
For K+
if greater than -58, go left
if lower than -58, go right
Why is the resting membrane potential not the equilibrium potential for K+?
Because determined by multiple ions
E (Na+)
E (K+)
E (Cl-)
E (Ca2+)
E(Na+)= +56mV
E (K+)= -102mV
E (Cl-)= -76mV
E (Ca2+)= +125mV
Goldman Equation
Em = RT/F ln (p(ion) + p(ion)/p(ion) + p(ion)
Cations have “out” on top
PK: PNA: PCL is 1: 0.04: 0.045
Membrane potential function of relative permeabilities
Na/K+ pump
main gradients ATPase convert ATP to ADP and phosphate restores ion concentration gradients maintains resting potential electrogenic - 3Na+ out, 2K+ in 20-40% energy consumption
Hyperkalemia
high K+ depolarized excitable membrane
cardiac muscle become hyperexcitable, fibrillation- uncontrolled contraction.
Hypoxia/stroke: ATP runs down, cell can’t maintain differential gradient, depolarized, increased excitotoxicity.
The time required to reach __% o final voltage is membrane time constant tau
63%
resistance * capacitance
why are membranes SLOW to depolarize?
capacitance properties
Time constant is time when voltage response rise to
1-(1/e) or 63% of Vinfinity (steady state membrane charge)
You need a (longer/short) tau to fire AP.
Longer
What is ^?
Length constant
Depends on membrane resistance
Calculate ^
SQRT(membrane resistance) /
SQRT(intra r + extra r)
best passive current: lower intra/extra r and higher membrane resistance
Increase strength of depolarization: does this make bigger AP?
no, more AP but not bigger
Passive responses
below thershold
active response/conductance
above threshold
negative current
hyperpolarization
Rising phase
rapid depolarization
overshoot
positive to 0 mV
Falling phase
repolarization
undershoot
hyperpolarization following the spike
Voltage Clamp Technique
studies AP
clamp amplifier injects current to axon through 2nd electrode
By measuring the current injected, determine amp. and time of ionic current across membrane `
What happens in squid axon if you replace Na+ with choline?
only outward current now
Does K+ activate faster or slower than Na+?
Slower
Block Na+
TTX
Block K+
TEA
Steps of AP
- activate Na+ = Na+ ions into cell, depolarize, activates K+ channels
- Inactive Na+
- Hyperpolarize K+
- Na+ inactive portion removed
Patch clamp allows for
individual or small numbers of ion channels
Cell-attached recording
response of channels/channels pipette has covered
Whole-cell recording
more suction, membrane disrupted
electrode interior continuous with cell interior
Inside-out recording
intact membrane, suction away from cell
Outside-out recording
pull back some membrane, and have it reform such that cytoplasmic side frees electrode.
Na+ conductance
rapid onset (activation) rapid offset (inactivation)
K+ conductance
slow onset/offset
after hyperpolarization (undershoot)
Refractory period: absolute refractory period
Na+ channel inactivation
relative refractory period
afterhyperpolarization
higher threshold
If AP travels in both directions, what stops it from going back and forth?
refractory period
AP travels at specific rate.
_______ measures the rate at which electrical impulses move along a nerve.
Used to diagnose disorders of the _______
nerve conduction study (NCS)
peripheral nerves and muscle
Action Potential Propagation: Conduction of AP
combine passive, active currents
passive spread of cations depolarizes next segment of membrane. Next segment crosses threshold. AP generation occurs, causing passive current spread to next segment: Regeneration of AP.
____ inactivation produces refractory period and prevents backpropagation
Na+
______ repolarize membrane.
voltage-gated K+ currents
Faster axons are
big and myelinated
Why are larger axons faster?
less internal resistance
Why myelin faster?
less capacitance
insulates axon
restriction to nodes of ranvier
capacitive and ionic currents are highest at ____
nodes of Ranvier
higher capacitance at unmyelinated nodes …
slows AP
Loss of myelin means local circuits must charge…
larger areas, and reduce r means less change in V membrane.
Structure of voltage gated channels
integral proteins may have several spanning domains pore voltage sensor - internal domain selective permeability
What makes and maintains ion gradients?
ATPase PUMPS
Channelopathies - small but critical alteration in ion channel gradients
Familial Hemiplegic Migraine (FHM)
migraine attacks the last 102 days, sever headaches vomiting
**Ca2+ Channel
Channelopathies small but critical alteration in ion channel gradients
Episodic ataxia type 2 (EA2)
recurrent attacks of abnormal limb movements and severe ataxis (incoordination), headache, nauseas (stomach distress)
usually attacks are triggered by emotional stress, exercise, or alcohol and last for a few hours
**Ca2+ Channel
Channelopathies small but critical alteration in ion channel gradients
X-linked congenital stationary night blindness (CSNB)
recessive retinal
night blindness, decrease acuity, myopia, nystagmus, strabismus, rod photoreceptors not functional
paralysis: decreased electrical excitability in muscles
**Ca2+ Channel
Channelopathies small but critical alteration in ion channel gradients
Episodic ataxis type 1 (EA1)
brief episodes of ataxis (incoordination)
increased electrical excitability due to impaired AP repolarization
**K+ Channel
Channelopathies small but critical alteration in ion channel gradients
Benign familial neonatal convulsion (BFNC)
frequent brief seizures during first week of life and disappearing spontaneously within a few months
Decreased K+ efflux through v-gated K+ channels and increased electrical excitability
**K+ channel
Generalized epilepsy with febrile seizures
increase Na+ influx and INCREASED electrical excitability in the brain
Myotonia
increase Na+ influx and INCREASED electrical excitability and muscle stiffness (muscles)
DECREASE in Cl- conductance (muscles)
Paralysis
decreased Na+ influx that causes DECREASE in electrical excitability (muscles)
Paper: SCN9A channelopathy causes congenital inability to experience pain
nociceptive neurons.
mutations alpha subunit of Na 1.7
No pain
Each family had slightly different mutation
nonsense and frame shift mutations in the families.
na+ channels expressed HEK cells
Why? NOT SENSITIVE TO MEMBRANE VOLTAGE, SO THEY DON”T FIRE AP
Electrical synapse characteristics
faster than chemical
connected cells make electrical syncytium.
Gap junctions. Synchronize neurons.
6 connexins = 1 connexon
open and close randomly, increased probability of opening under specific conditions, elevated Ca2+, depolarization
using reflex pathways
Chemical synapse characterisitics
no direct contact, neurotranmitters in cleft
Methionine Sulfoximine
inhibits glutamate synthesis (limit stroke damage)
Carbidopa
inhibits dopamine synthesis (used in Parkinson’s)
- How would you stop AP arriving at terminal?
Novacaine, Na+ channel blocker
3-5. How do you stop depolarization and influx of Ca+ and vesicle stuff?
alpha latrotoxin- causes ca2+ independent transmitter release, convulsant
- How do you block transmitter release?
Tetanus toxin, blocks GABA release, convulsant
- Receptor binding interference
1) Mirapex- binds and activates dopamine receptors, Parkinson’s treatment
2) Diazepam (valium)- GABA agonist treatment for epiespy, anxiety
3) Clozapine- serotonin receptor agonist, antipsychotic
- Example that stops reuptake
SSRIs, antidepressants
- Degradation
cholinesterase, inhibitors, neostigmine
Experimental setup: voltage clamp of presynaspe membrane: what did we learn about calcium and shit?
cadmium block and no EPSP.
SO calcium is needed for transmitter release
SNARE:
Presyn
Postsyn
pre: SNAP25 and syntaxin
post: synaptobrevin
Synaptotagmin
Ca2+ sensor
triggers membrane transmitter release
Clostridium bactira
c. TETANUS
Botulism
PROTEASE. cleaves SNARE
block synaptic transmission
Alpha-latrotoxin
binds to synaptotagmin causes calcium independent transmitter release
Botulism
food bourne.
blurry vision, dry mouth, paralysis
fix with antitoxins
floppy baby
botox
Tetanus
bacteria through puncture
blocks release of inhibitory NT, loss of inhibition on spinal motor neurons.
Descending pattern of symptoms
Synthesis of DEN (Catecholamines)
Phenylalanine
PHENYLALINE HYDROXYLASE
L-tyrosine
TH- RATE LIMITING
3,4, dihydroxyphenylanine (DOPA)
L-AADC
Dopamine
DOPAMINE-BETA-h AND VMAT TO VESICLE
norepinephrine
PMNT
Epinephrine
Reserpine
treats high blood pressure/psychosis
block catecholamine transmission
stops it getting in vesicles
VMAT1
adrenal glands
VMAT2
catecholamine and 5HT neurons
3 ways of inactivation
- diffusion
- reuptake
- enzymatic inactivation
MAO -A
affinity for NE and 5HT
inhibited by clorgyline
slow acting
MAO -B
dopamine / o-phenylethlamine
inhibited by deprenyl (MPPP)
antidepressant, neuroprotective effects
Parkinson’s
sexual dysfunction
COMT
inhibitors used to prevent inactivation of DOPA
Tricyclic antidepressants target
NE
Serotonin synthesis
Tyrptophan
Enzyme: Tryptophan hydroxylase (rate limiting)
5-hydroxytryptophan (5-HTP)
Enzyme: AADC
5-HT
Serotonin facts
accumulated in vesicles by _____
inactivated by reuptake through ____
degraded by ____
Treaptuic effect slower, probably tied to downregulation of __________ on presynaptic membrane.
accumulated in vesicles by VMAT2
inactivated by reuptake through EXOCYTOSIS
degraded by MAO
Therapeutic effect slower, probably tied to downregulation of 5-HTA1 autoreceptors on presynaptic membrane.
JAMA on antidepressants
good if severe depression
Histamine synthesis and facts
Histidine
Histidine decarboxylase
Histamine
Transport by VMAT
degraded by histamine methyltransferase and MAO
mediate attention/arousal.
Receptors G-coupled.
antihistamines cause sedation.
antagonists used for motion sickness
gamma-aminobutyric acid (GABA)
GAD requires pyridoxal phosphate cofactor, derived from vitamin b6
alpha-ketogluatarate
GABA-T (mitochondria)
glutamate
GAD (cytosol)
GABA
Vesicle transport: VIAAT
reuptake: GAT
* ***degraded by : GABA-T (makes GHB)
GABA receptor subtypes
A/C: ionotropic, increase Cl- conductance
B: metabotropic, increase K+ conductance
Benzo: antianxiety
Barb: hypnotics, anesthesia, epilepsy `
Glutamate
excitatory amino acid
responsible for most fast excitatory neurotransmission in mammalian brain
derived from alpha-ketoglutarate
transported by VGluT
inactivated by reuptake EAA transporters located on neurons and glia
Acetylcholine
CAT makes it (Chat transfers acetyl to choline)
ACE degrades it
vesicles by VAChT
Cholinesterase inhibitors
sarin, malathion, neostigmine
Block ACE, prolong Ach
Ionotrophic
large, multisubunit
complex
fast onset/reversal
[N]
AMPA, Kainate, NMDA
Metabotrophic receptors
single polypeptide
7 transmembrane domain
activated leads to binding and activating of G proteins
Slow onset/duration
[M]
beta-adrenergic
[N]
2x alpha subunits
4 different subgroups
snake venom
5 subunits - 2 alpha, 1 beta, 1 gamma, 1 delta
ring and central poor
N-terminus in Extraceullar space
Each subunit has 4 transmembrane spanning segments
TM2 regions line the pore
Rings of - charge act as selective filter
Leucine residues in TM2 block ion channel
How are nACh [N] blocked?
Leucine residues in TM2 segments form ring, block central pore
Ach binds to receptors in pore, TM2 rotates
ion flow through expanded central pore and through hole in lateral walls of intracellular portion of receptor
Metabolic G protein coupled receptors
single polypeptide
transmitter binding leads to g protein activation
activated G protein couples to downstream effectors
slow onset longer duration
7 transmembrane domains
extraceullar N terminus
intracellular c terminus
long 3rd intracellular loop interacts with G protein, specificity
GTP bond = activation
How are G proteins activated?
1) Collision coupling - transient association between the activated receptor and the G protein. Subsequent collision coupling can occur between one activated receptor and several G proteins leading to amplification of signal
2) interaction of i3 of GPCR with g protein causes conformation change allowing exchange GDP for GTP
3) activated GTP-bound G proteins interact with effector proteins
4) activity of G protein is limited by GTPase activity that breaks down GTP for GDP
Ligand bind on TMS and TM6 –> Cleavage in i3
G protein active state
beta and gamm
alpha-GTP
What turns off alpha subunit: GAP
E3 binds to alpha subunit
G protein: when NT binds to receptor, ______ activates receptor
conformation change in i3 loop
Over 1/2 of all prescription drugs work through
G ptrotein coupled receptors
G protein couple receptors effects
ion channels cAMP/cGMP
intracellular enzymes
gene transcription
Second messengers
downstream of effector molecule
cAMP, phosphoinositol metabolites, calcium
target kinases that change activity of enzymes, metabolism, and ion flow
2nd messengers and receptors are held in close proximity by proteins that bind to specialized domains
Excitation of skeletal muscle
brain: upper MN
spine: lower MN –> release Ach to get PSPs
Motor unit = motor neuron and group of skeletal muscle fibers in innervates
finer control = smaller motor unit
induces Ca2+ influx. (CHEMICAL SYNAPSE)
troughs with receptors inside
increase Na+ permeability, depolarization causes +
end plate potential in the post synaptic muscle
