chapter 5 Flashcards
gap junctions
where electrical synapses occur. interconnect non neural cells like smooth cardiac muscle, liver and glia
connexins
proteins that make up gap junction
connexon
made from 6 connexin sub units
how many connexons form a gap junction channel
2
difference between electrical and chemical synapse
electrical are faster
pore of gap junction is larger
electrical synapse is bidirectional
step after incoming signal depolarizes membrane above threshold, travels down axon and then reaches the axon terminal
synaptic transmission
synapse
a specialized junction where one part of a neuron contacts and communicates with another neuron or cell type
what does it mean to be electrically coupled
cells that are connected by a gap junction
in electrical synapses, can the first neuron have a PSP induced by the second?
yes, they are bidirectional
where are electrical synapses often found in the brain
where normal function requires that the activity of neighboring neurons is highly synced
inferior olive
neurons in brain step nucleus that can generate small oscillations of membrane voltage and action potentials. they send axons to cerebellum and are important in motor control
when are gap junctions prominent?
early in development. it helps with growth and maturation
synaptic cleft
what pre and post synaptic membranes are separated by in chemical synapse
what is the synaptic cleft filled with?
extracellular protein. it serves as a “glue” that binds membranes together
what is usually the presynaptic element
axon terminal
synaptic vesicle
stores neurotransmitters
secretory granule
larger vesicles that contain soluble protein. also called dense-core vesicle since it appears dark
membrane differentiations
accumulation of protein adjacent to and within membranes on EITHER SIDE of synaptic cleft
active zones
actual sites of NT release
where are synaptic vesicles clustered?
cytoplasm adjacent to active zone
post synaptic density
protein thickly accumulated in and under postsynaptic membrane. contains NT receptors
what do neurotransmitter receptors do?
convert intercellular chemical signal to an intracellular chemical signal
if a post synaptic membrane is a dendrite
axodendritic
is a postsynaptic membrane is a cell body
axosomatic
when presynaptic membrane is on another axon
axoaxonic
when presynaptic axon is on a postsynaptic dendritic spine
axospinous
dendrodendritic
when its a dendrite/dendrite synapse. only happens in specialized neurons
grays type I
asymmetric post synaptic side is thicker. its also called asymmetrical synapses
is grays type I usually excitatory or inhibitory
excitatory
grays type II
symetrical. usually inhibitory
neuromuscular junction
chemical synapses that occur between axons of motor neurons of spinal chord and skeletal muscle
what always happens in neuromuscular junction?
action potential in motor axon always causes action potential in muscle cell it innervates
what has the largest synapse in the body?
neuromuscular junction
motor end plate
contains series of shallow folds in neuromuscular junction. also called post synaptic membrane
structure of motor end plate
folds of post synaptic membranes are packed with receptors
presynaptic active zones are aligned precisely with junctional folds
why are neuromuscular junctional folds inportant
ensures that many neurotransmitters are released onto a large surface of chemically sensitive membrane
what do amino acids and amines contain?
at least one nitrogen atom
where are amino acids and amines stored and released
synaptic vesicles
where are peptides stored and released
from the large secretory granules. this is because they are large molecules (chains of amino acids)
what are most CNS synapses usually mediated by?
amino acids
what mediates fast synaptic transmission at all neuromuscular junctions?
ACh
gaba is made primarily by…
the neurons that release them
what concentrates NTs inside vesicle?
transporter proteins
where are transporter proteins located
in vesicle membrane
peptides are formed when…
amino acids are strung together by ribosomes of cell body. occurs in rough ER
steps of peptide synthesis
peptide synthesized in rough ER
chain split in golgi apparatus- one of the smaller fragments is NT
secretory granules containing peptide bud off from golgi apparatus
secretory grandules transport down axon to terminal where peptide is stored
steps of amine and amino acid synthesis
enzymes connect precursor molecule into NT molecule in cytosol
transporter proteins load the NT inyo synaptic vesicle where they are stored
where are voltage gated calcium channels located
in active zone
why will Ca2+ flood into cytoplasm as long as they are open?
resting calcium concentration is low….0.0002 mM
exocytosis
when synaptic vesicle fuses to presynaptic membrane @active zone allowing contents of vesicle to spill out into synaptic cleft
steps of exocytosis
synaptic vesicle is loaded with NT
influx of Ca2+ through channel
release of contents into cleft by fusion of vesicle membrane
eventually recycled by process of endocytosis
endocytosis
when vesicle membrane is recovered and recycled vesicle is refilled with NT
what happens during prolonged periods of stimulation?
vesicles are mobilized from a “rescue pool” that is bound to cytoskeleton of axon terminal. release is triggered by elevations of Ca2+
step one of chemical synapse (synthesis)
some NT are transported from cell nucleus to terminal buttons…others are made from building blocks imported into the terminal, they are packaged into vesicles there
step two of chemical synapse (release)
in response to an action potential, the neurotransmitter is released across the membrane by exocytosis
step three of chemical synapse (receptor action)
the transmitter crosses the synaptic cleft and binds to a receptor
step four of chemical synapse (inactivation)
the transmitter is either taken back into the terminal or inactivated in the synaptic cleft
why are peptides not released in response to every action potential
sites of grandual exocytosis occur at a distance from Ca2+ entry. release requires high frequency trains of action potentials so that Ca2+ throughout the terminal can build to the level required to trigger release away from active zones. takes longer
are peptides released in active zones
no
post synaptic density
protein dense specialization attached to post synaptic membrane
neurotransmitters affect the postsynaptic neuron by…
binding to specific receptor proteins in the post synaptic density
what are the two types of NT receptors?
transmitter gated ion channels
g-protein coupled receptors
in transmitter gated ion channels, what happens when NT binds to specific site on extracellular region?
slight twist of subunits which causes the pore to open
how many subunits make a channel
4-5
what channel does not show much ion selectivity?
transmitter gated ion channel ex Ach gated channel is permeable to both Na+ and K+
ionotropic
acts quickly. ionic receptors change shape when bound by a ligand.
this channel changes shape to allow ions to flow through
metabotropic action
takes longer depending on the number of steps required to produce a response
they do not have channels
activate g-protein that in turn activates a secondary messenger, that in turn will activate something else
when is channel classified as excitatory?
if it is permeable to Na+
excitatory post synaptic potential
transient post synaptic depolarization caused by presynaptic release of NT
when is channel inhibatory
if it is permeable to Cl-, it hyperpolarizes postsynaptic cell from resting membrane potential
steps of g-protein coupled receptors
NT binds to receptor proteins in post synaptic membrane
receptor proteins activate g-proteins which are free to move along the intracellular face of the post synaptic membrane
activated g-proteins activate “effector” proteins
what makes g-protein receptors special?
they have seven transmembrane alpha helices
what does it mean that g-protein receptors have seven transmembrane alpha helices
they span the membrane seven times
g-proteins have the ability to bind…
GTP and GDP
guanosine triphosphate and guanosine diphosphate
example of ionotropic receptor
nicotinic receptor at neuromuscular junction
example of metabotropic
acetylcholine at neuromuscular junction (longer lasting)
what can effector proteins be?
g-protein gated ion channels in the membrane or enzymes that synthesize molecules called second messengers that diffuse away in cytosol
what else can g-protein receptors be referred to?
metabotropic receptors because they trigger widespread metabolic effects
the same NT can have different effects based off of….
what kind of receptor it binds to
autoreceptor
presynaptic receptors that are sensitive to neurotransmitter released. it acts as a safety valve to reduce release when NT gets too high
what allows a pre synaptic terminal to regulate itself?
autoreceptors
autoreceptors are usually…
g protein coupled receptors and a common dffect is inhibition of NT release or synthesis
what happens after NT release?
reuptake into presynaptic terminal
enzymatical degradation and recycled
glial cells help with NT removal by..
containing NT transporters
how is ACh terminated from neuromuscular junction
enzamatic destruction happens in cleft itself
what happens if transmitter removal sucks? (from drugs n shit)
desensitization despite continued presence of NT, channels will stay closed
neuropharmacology
the study of the effect of drugs on nervous system tissue
inhibitors
drugs that inhibit normal function of specific proteins involved in synaptic transmission
receptor antagonist
inhibitors of T receptors that bind to receptors and block (antagonize) the normal action of the transmitter
receptor agonist
drugs that mimic the actions of the naturally occuring neurotransmitter
nicotinic ACh receptors
located in muscles and uses this name to distinguish them from other types
what ACh receptors are involved with addictive effects of tobacco use
nicotinic receptors in the CNS
what do second messengers do?
activate additional enzymes in the cytosol that can regulate ion channel function and alter cellular metabolism
ACh effect on heart
slows rhythm of contractions by causing slow hyperpolarization of cardiac muscle cells.
metabotropic ACh receptor is coupled by g-protein to a potassium channel
opening of k channel hyperpolarizes cardiac muscle fibers and reduces the rate at which it fires action potentials
ACh effect on skeletal muscles
induces contraction by depolarizing muscle fibers.
receptor is a transmitter gated ion channel, specifically ACh channel permeable to Na..opening of this channel depolarizes the muscle fibers and makes them more excitable
generation of ISPS steps
action potential arriving in the presynaptic terminal causes the release of neurotransmitter
molecules bind to transmitter gated ion channel in post synaptic membrane..if Cl- enters postsynaptic cell through open channel, membrane will become hyper-polarized
binding of NT to receptor leads to activation of g-proteins.
activated g-proteins activate effector proteins which may be..
ion channels or
enzymes that generate intracellular second messenger
what is the elementary unit of neurotransmitter release
epsp
how many transmitter gated channels are activated depend on….
how much NT is released
the amplitude of EPSP is based on…
the number of transmitter molecules in a single synaptic vesicle
number of post synaptic receptors available at the synapse
why is there a difference between EPSP at neuromuscular junction and CNS
neuromuscular junction has to ensure that it is fail safe and generates EPSP at a huge size.
if every EPSP can capable of generating action potential in post synaptic cell, then a neuron would be little more than a relay situation. it needs to preform more sophisticated computations
what is integration of EPSP
many EPSP add together to produce significant post synaptic depolarization
spatial summation
adding together of EPSP generated simultaneously at many different synapses at the dendrite
temporal summation
adding together of EPSP
temporal summation
adding together of epsp generated at the same synapse
what does the effectiveness of EPSP triggering action potential depend on
how far the synapse is from the spike initiation zone
properties of dendritic membrane
miniature post synaptic potential
generated by transmitter contents of one of the vesicles in ABSENCE of an action potential
what two paths can synaptic current take
down inside dendrite
across the membrane
how do dendritic cable properties contribute to synaptic integration
internal resistance depends on diameter of dendrite
as current proceeds down the dendrite and to the synapse, the esps amplitude will deminish bc of the leakage of ionic currents through membrane channels
length constant
where depolarization is about 37% of that at the orgin.
when will an esps be more likely generated
if it has a longer length constant
internal resistance
resistance to current flowing longatudially
membrane resistance
resistance to current flowing across the membrane
what does internal resistance depend on
diameter of the dendrite and electrical properties of cytoplasm
what does membrane resistance depend on
of open ion channels
voltage gated channels in dendrites can act as important amplifiers of..
small PSP generated far out on dendrites
inhibitory synapse
job is to take the membrane away from action potential threshold. they exert a powerful control over a neurons output
what NTs bind to inhibitory synapse
GABA and glycine
similarities and difference between inhibitory snapse and excitatory snypse
both use transmitter gated ion channels
inhibitory is only permeable to Cl-
what is shunting inhibition
when snypse acts as an electrical shunt and prevents current from flowing through soma to axon hillock
where are inhibitory snypses clustered
on soma or near axon hillox
