Synaptic Transmission and the Neuromuscular Junction Flashcards
What is a synapse
a specialized gap region that permits a neuron (or
nerve cell) to pass an electrical or chemical signal to another neuron or to the target effector cell
What is the difference between chemical and electrical synapses
eletric direct electrical continuity by gap junctions.
indirect chemical neurotransmitter that diffuse to other cell.
what is a gap junction made of?
vlakke arrays of connexons, each consisting of 6 connexin monomers.
how do the multiple connexons physically conncted two cells.
via multiple aqueous channels
What two kind of chemical syapses are there
ionotropic and metabotropic
What is the agonist of electrical and chemical synapses?
electrical none
chemical e.g ACh
membrane proteine of electrical synapse
connexon
membrane proteine of chemical synapse
ionotropic, receptro/channels
metabotropic: receptro/G protein
delay in transmission for each type of synapse
electrical, instant
ionotropic 1ms
metabotropic seconds to minutes
What kind of nerve is the vagus nerve and what does it do?
parasympathetic, produces a substance (ACh) responsible for depression of the heartbeat.
is ACh inhibitory or excitatory?
both
what are reciprocal synapses?
pass electrical current with equal efficiency in both directions
what are rectifying synapses?
Allow current only in one direction.
how can intrinsic rectification be altered?
gap junctions composed heterotypic channels
what are heterotypic channels?
a gap junction that is composed of two hemichannels, each made up of a different connexin monomer.
are chemical synapses reciprocal or rectifying?
rectifying
are chemical channels one or unidirectional for signal propogateion adn why?
unidurectional, because presynaptic cell can produce retorgade sygnaling molecules and receptors on presynaptic membrane can inhibit or facilitate the realse of a transmitter.
How do vescular transporters concentrate neurotransmitters inside?
energy on an H+ electrocehmical gradient
what does a increase of intracellular Ca2+ do at the presynapse
triggers the fusion of synaptic vesicles with the presynaptic membrane
How is the process of chemical synapses terminated?
enzymatic destruction of the transmitter (e.g., hydrolysis of ACh by acetylcholinesterase), (b) uptake of transmitter into the presynaptic nerve terminal or into other cells by Na + -dependent transport systems, or (c) diffusion of the transmitter molecules away from the synapse.
what are ligands.
agonists
what is the difference between ionotropic receptors and metabotropic receptors?
ionotropic aganist gated ion channels.
metabotropic. receptors coupled to G protein.
what are the subunits of a G protein?
α and βγ subunits
what do the α and βγ subunits produced by the Activation of a metabotropic G protein–linked receptor?
they iniate a wide variety of cell responses by direct interaction with either ion channel proteins or other second-messenger effector proteins.
what is the nicotonic AchR
ionotropic receptor
what is the muscarinic AchR?
metabotropic recptor at the atrial parasympathetic synapse of the heart
what does the activation of Muscarinic receptor do
activates the G protein, which opens an inward rectifier K+ channel, or GIRK. which leads to hyperpolarisation which leads to inhibition of cardiac excitation.
what does does the activation of the nictonic receptor do?
opens the AChR channel resulting in increase of permabilkty of NA and K., which leads to muscle contraction.
what does Acetylcholinesterase do?
breaks down acetylcholine.
what is a motor unit.
all the muscle fibers innervated by the axon from one motor neuron
what is the end plate?
neuromuscular junction
Where is the neuromuscular junction?
synaptic contact with a muscle fiber.
What are boutans
bulb-shaped ending that finally contact the muscle fiber.
what do the postjunctional folds do
increase increase surface area of muscle plasma.
what is the basal lamina
a extracellualr matrix in the synaptic cleft containing various proteins that mediate adhesion of the neuromuscular junction and play important roles in synapse development and regeneration.
what and where is AChE and what does it do
acetylcholinesterase in basal lamina , hydroplyses ACh to choline and acetate.
where are the vesicles produced
the cell bodies of motor neurons in the spinal cord.
how are the vesicels translocated to the nerve terminal
by microtubule-mediated process of fast axonal transport
what is choline acetyltransferase
enzyme that syntheses ACh from choline and acetyl outside the vesicle.
What does the ACh-H exchanger do
moves ACh inward the vesicle and H+ out
how is the process of the ACH-H exchanger driven?
vesicular proton electrochemical gradient (positive voltage and low pH inside), which is produced by the vacuolar-type H pump.
is vacuolar-type H pump passive or acxtive?
active, uses ATP
what are active zones
regions where vesicles fuse and ach is released
where are the most AChRs at neuromuscular joints
at the tops of postjunctional folds.
is the delevery of neurotransmitters to a location precise
yes
what is EPP
end plate potential
To what is the revarsal potential of end plate current close?
0mV
to what are AChR permeable
NA, K and Ca, not anions
What happens to Vm when nicotinic AChR channels open?
V m shifts to a value between E K (approximately −80 mV) and E Na (approximately +50 mV).
what kind of potential is EPP
excitory postsynaptic potential.
Whata re hyperpolarizing postsynaptuc responses called?
inhibtory postsynaptic potentials.
serotonin and glutamate are .. selective
and glycine and GABA are … selective
serotonin and glutamate are cation selective
and glycine and GABA are anion selective
what are depolarizing postsynaptic responses called
excitatory postsynaptic potentials.
What is dendrotoxin
K+ antagonist
what is tetanus and botulinum toxin
proteine toxins made by bacteria, ACh release antagonist
what is physostigmine and DFP
acetylcholinesterase antagonist
what is nicotine en acetylcholine
AChR channel agonist
what is d -tubocurarine and a-Bungarotoxin
AChR channel antagonist
what is tetrodotoxin, Saxitoxin and u-conotoxin
Muscle Na channel antagonist
what is ω-conotoxin
peptide toxin, Ca2+ channel antagonist
what is tetrodoxotin en Saxitotoxin
small guanidinium neurotoxins of neuronal Na+ channel antagonist
how does dendrotoxin facilitate ACh release?
Because it block K+ so the memrbane cant repolarise and more Ca2+ enters the cell.
What does tetanus do.
increase of muscle tension, (begint met kaak). these toxins inhibit synaptic transmission at the spinal cord, neurons that would normale inhibit muscle contraction.
what does botulism cause
paralysis of skeletal muscle, and a vierty of symptoms that are related to inhibition of cholinergic nerve endings in the autonomic nervous system.
what anatgonist is used to treath muscle spams.
botuliism
what antagonist is used to threath strabismus (a condition in which both eyes cannot focus on the same object because of abnormal hyperactivity of particular eye muscles).
botulism
what is botox and how long does it last
botulinium toxin, smooth wrinkles by local paralysis of facial muscles. to 6 months
what are carbamycholine and succinylcholine and what is difference with normale stof
agonist AChR
resistent to AChE so prolonged effect.
what molecule is used for sugery and why
succinycholine, to prevent excitation because of inactivation of Na channels.
what leads to desensitization of the AChR
agonising, a AChR for a long time.
how can d-Tuborcurarine be cured
increase in concentration of the natural agonist ACh by binding competition. which can be produced indirectly by an inhibitor of AChE such as neostigmine
what is pancuronium
stronger agonist of AChR than d-tubocuraine, used for surgery.
what is the difference between organophosphorus compounds and physostigmine/Neostigmine
organophosphorus is irreversible anti AChE drug
what are anatoxin and fasciculin?
natural organophosphorus (inhibitor of AChE)
