Neurophysiology - Hu Flashcards
Electric Synapse
Uses ionic currents as the main method of communication with other cells. Here the synapses are mechanically connected via a gap junction, so current can be exchanged.
Chemical Synapse
Synapse that uses neurotransmitters as a messenger to talk to each other and pass a signal
Metabotropic Receptor
Couples with G-proteins
Ionotropic receptor
functions as a ligand-gated (activated) ion channel
Presynaptic heteroreceptor
located on presynaptic terminals
Presynaptic autoreceptor
located on presynaptic terminals, serves as a negative feedback mechanism to regulate firing and neurotransmitter release
Postsynaptic receptors
Located on postsynaptic target cells
Excitatory postsynaptic current (EPSC)
positively charged ions flow into a postsynaptic cell during membrane depolarization
Excitatory postsynaptic potential (EPSP)
membrane potential (Vm) depolarization in postsynaptic cell (in response to excitatory impulses)
Inhibitory postsynaptic current (IPSC)
Negatively charged ions flow into a postsynaptic cell during membrane hyperpolarization
Inhibitory postsynaptic potential (IPSP)
Vm hyperpolarization in postsynaptic cell (in response to excitatory impulses)
Acetylcholine (ACh)
Memory, sensory processing, motor coordination, neuromuscular junction, ANS and PANS function
Norepinephrine (NE)
CNS sensory processing, cerebellar function, sleep, mood, learning, memory, anxiety, and SANS
Dopamine (DA)
Motor regulation, mood, addiction, reinforcement, olfaction, hormone control concentration, and hypoxic drive
Serotonin (5-HT)
Emotional processing, mood, appetite, sleep, pain processing, hallucinations, and reflex regulations
Histamine (H)
Sleep, sedation, and temp regulation
Gamma amino butyric acid (GABA)
Major inhibitory neurotransmitter in the CNS
Glutamate (Glu)
Long-term potentiation, memory, major excitatory fxn in the CNS and PNS
Glycine (Gly)
Major inhibitory fxn in the CNS
Monamine Pathways in CNS
Norepinephrine (NE) - Locus Coeruleus–> cerebral cortex, limbic sys, cerebellum, and spinal cord
Serotonin (5-HT) - Raphe nuclei (RN)–> whole brain and spinal cord
Dopamine (DA) - Ventral tegmental area and Substantia nigra pars compacta (SNPC)–> basal ganglia, limbic system, and prefrontal cortex
Acetylcholine (ACh)–> Septal nuclei, nucleus basalis—>brain regions
G-Proteins/Second messengers
Bind GDP and GTP, coupled with metabotropic receptors (GPCRs), activate or inhibit activity of effectors,
Gs
Stimulatory, Active during high levels of cAMP
Gi
Inhibitory, Active during low levels of cAMP
Gq
Hydrolyzes, Second messenger is IP3 and DAG
Go
Second Messenger is Arachidonic Acid
Gap junction
A type of synapse that mechanically connects the cytoplasm of two cells allowing for the conductance of electrical signal as the messenger. Can be conducted bi-directionally and are smaller in the postsynaptic cell than in the presynaptic originating cell
Formed by connexon, made up of 6 connexin units - 4 membrane spanning regions, and the opening is smaller than a chemical synapse 3.5 nm v.s 20-40 nm
Resting Membrane Potential (RMP)
cell is at equilibrium and the net current (I) = 0
RMP depends on equilibrium potential (Ek) of K+, membrane at rest is primarily permiable to potassium
Ohm’s Law
The strength of a direct current (I) is directly proportional to the potential (voltage) different (^E, ^V and inversely proportional to the resistance (R) or reciprocal of the conductance R= 1/C) of the circuit.
V = IR
or
I = V/R
Nernst Equation
Relates the concentration gradient to the electric (potential) gradient that balances it. Determine equilibrium potential of a cell.
Es = E1 - E2 = RT/zsF(ln)[S]2/[S]1
S: arbitrary ion
S2 and S1: external and internal concentration of ion
E1-E2: membrane potential difference
R: universal gas constant
T: absolute temperature (kelvin) 273.15 + degrees in C
z: valence of the arbitrary ion (elementary change Na+=1 Ca2+=2 etc)
F: the Faraday constant
ln: natural log
Voltage Gated Ion Channels
Na, K, Ca
alpha1 subunit: “pore-forming” protein that has 4 homologous transmembrane domains (TM), each TM is a helix with 6 transmembrane spannings
Selective filter SS1-SS2 connects S5 and S6 to form pore
S4 segment fxns as a voltage gated sensor
Ligand gated Ion channels (Ionotropic receptors)
clustered in the postsynaptic membrane and open rapidly after binding with selective agonists.
Activation of ligand-gated ion channels induced Vm change
Ex: Nicotinic ACh receptor, Glutamatergic N-methyl-D-aspartate receptor (NMDAR), y-aminobutyric acid A-receptor (GABAaR)
Nicotinic Acetylcholine (ACh) Receptor (nAChR)
17 subunits, belongs to the superfamily pentametric ligand gated receptors (GABAaR, GlyR, 5-HT3R)
Positive ion channel, Na and others, but does not allow passage of anions. Depolarizes Vm and causes muscle contraction or neuron firing.
Agonists: ACh, nicotine, choline, cabachol, etc
Antagonists: alpha-bungarotoxin (venom) and tubocuraine (arrow poison) = irreversible binding of ACh receptors causing paralysis, respiratory failure, and death.
Prolonged or repeated exposure to ACh reduces nAChR conductance, sensitivity recovers only when ACh is removed.
Used in motor neurons for transmission of AP signal to muscles at the neuromuscular junction, also in the release of dopamine in the brain from nicotine stimulus.
Glutamatergic NMDA Receptor (NMDAR)
ligand gated, ionotropic receptor; belongs to the glutamate receptor family.
Non-specific cation channel (highly conductive for Ca2+) found only in CNS of vertebrates.
Tetramer of homologous subunits, at least 7 genes
Agonist and co-agonist: Requires simultaneous binding of glutamate (agonist) and glycine (co-agonist). Interacting with AMPA receptor
Antagonist: selectively blocked by AP5 and memantine
Mediates excitatory synaptic activity, acts as a coincidence detector for presynaptic glutamate release and postsynaptic Vm depolarization
Critical in synaptic plasticity; can induce excitotoxicity.
Phosphorylation increases its activity and Ca influx
GABAa Receptor
Are ion channels
Belong to the superfamily of pentameric ligand-gated ionotropic receptors. Has 5 subunits, each with 4 helical membrane spannings
15 different subunits in 7 families, combinations may alter function in regulating Cl opening (hyperpolarization of Vm)
Agonist: GABA
Function: a binding substrate for the major inhibitory neurotransmitter GABA in the CNS. Regulates inhibitory neuronal responses by conducting Cl influx via activating GABAaR/Cl channels = Vm hyperpolarization.
Mutation of GABAaR is related to Huntington’s disease, Epilepsy, and alcoholism
