part 8 Flashcards
the excitatory action of an EPSP is when?
membrane depolarizes closer to threshold of action potential, thus increasing excitability.
Describe Excitatory Postsynaptic Potentials (EPSP).
depolarization caused by an increase in permeability of Na+ and K+ channel
What leads to an Inhibitory Postsynaptic Potential (IPSP)?
hyperpolarization caused by increase in permeability of Cl- or K+ channel
– Influx of Cl- ions and efflux of K+ ions hyperpolarize membrane
describe the Inhibitory action of an IPSP?
membrane hyperpolarizes away from threshold, decreasing excitability.
Excitatory synapses usually occur on?
dendrites
inhibitory synapses usually occur on ?
cell bodies
simultaneous activation of excitatory synaptic potentials from different regions is known as ?
Spatial summation of psp’s
successive synaptic potentials from same synapse can summate to create overall excitation or inhibition. this is known as?
Temporal summation of PSP’s
what produces EEG waves?
Synchronization of PSPs among large populations of neurons
“analog” information processing of PSPs is done at what two regions of a neuron?
Dendrites and cell bodies
Axon potential initiation happens at the ?
Axon Hillock
“digital” information is processed by the ?
Axon
Non-gated channels have ___ ion channels and are located __?
K+
along whole cell except initial segment & nodes of Ranvier
Voltage gated channels have __, __, __ ion channels and are located __?
Na+, K+, Ca++
(Na+, K+) Initial segment, nodes of Ranvier (APs),
(Ca++) Axon terminal (transmitter release)
neruotransmitter/ ligand gated channels have __, __, __ ion channels and are located __?
Na+,K+, Cl-
(Na+,K+) Postsynaptic dendrite membranes (EPSP’s)
(Cl-) Postsynaptic cell body membrane (IPSP’s)
what does METABOTROPIC (INDIRECTLY) GATED TRANSMISSION involve?
Involves cell signaling systems that utilize enzymes and/or genomic regulation (“metabolism”)
Compare metabotropic and Ionotropic transmissions
ionotropic transmission: the receptor for the transmitter is on the ion channel itself. The response is fast, but of short duration
metabotropic transmission: the receptor is a membrane protein that activates a cascade of enzymes that stimulate synthesis of second messengers and/or alter gene activity.
These proteins are a complex of α, β, and γ units that dissociate from the receptor protein and activate other enzymes to produce second messengers.
G proteins
They utilize GTP (Guanosine triphosphate), hence the name G.
these Proteins are the most important signal transducing molecules in cells
G PROTEINS
two ways in which Ligand receptor activates G protein?
- Transmitter causes receptor to bind with inactive G protein
- GTP replaces GDP, activating the G protein
3 ways in which α, β, γ portions of activated G protein generate cell activity?
- Direct action on the permeability of ion channels
- Activation of second messengers (eg. cAMP)
- Gene transcription of proteins
Explain how Direct action of G proteins on ion channels works?
• β, γ portions G protein bind directly onto ion channels to alter its permeability
for example.. In heart deceleration, vagus nerve stimulates the SA node using Ach to open K channels and hyperpolarize the cell. This inhibits cardiac action potentials and decreases the heart rate
two primary examples of second messengers that occur in all body cells?
cAMP and IP3/DAG
explain the second messenger cascade?
G protein >Enzyme > 2nd messenger >Effector (kinase or other enzymes) >Cell function
