Lecture 5 Flashcards
What is synaptic transmission?
-The process which neurons sends signals to target cells.
What is a synapse?
A special zone where one neuron communicates with another. Its a discrete specilaized junction that transfers electrical or chemical signal (Intracellular signal) that could be either inhibitory or excitatory.
What are the characteristics of the electrical synapse?
- Presynaptic cell
- Gap-junction channel
- Post synaptic cell
Physically connected
What is the characteristic of the chemical synapse?
Presynaptic terminal (Vesicles
- synaptic cleft
- the postsynaptic site (receptors)
How is electric synpase mediated?
Its mediated by structural contacts called gap junctions. electrical transmissions are usually excitatory.
What type of transmission do chemical signals mediate?
They mediate Excitatory or Inhibitory. They release chemical transmitter (T) which is a secretory event.
In chemical synapse; how does it take action?
-Action potential opens Ca2+ channels and that causes vesicle fusion and release into the synaptic cleft. Then the postsynaptic receptors will generate a response whether its depolarization or hyperpolarization of Plasma membrane.
What is an NMJ? How does its size effect its function? Does it have another name?
Neuromuscular junction which is a special synapse between neurons and skeletal muscles. Its a giant excitatory synapse.
- The other name is the endplate region.
- Its giant size makes it more reliable for transmission.
In absence of disease, how many muscle actions can 1 nerve Action potential performs?
1 action potential to generate a muscle action.
What is a motor unit? How does a motor unit interact with a muscle fiber?
- A motor unit is an alpha motor neuron and all the muscle fibers it innervates.
- Each muscle fiber is innervated by one alpha motor neuron but each motor neuron could innervate multiple muscle fibers.
How is the NMJ organized?
the axons end with presynaptic terminal boutons. these cells lie in gutter-like invaginations of the muscle fiber surface. These infoldings lead to primary and secondary synaptic clefts.
How many T units does each vesicle contain?
about 1 quantum which is about 5000-10000
How are vesicles divided in the presynaptic junction?
They’re divided into 2 pools.
1) readily releasable pool near the presynaptic plasma membrane
2) Large stationary pool or slowly releasable pool away from the PM.
How does a post synaptic AChRs channel functions?
2 acetycholine molecules bind to the AChR of the channel and that triggers the activation of the channel.
How long is a synaptic transmission delay?
about .5 msec.
So how does a Muscle action potential happens?
1) Neuron action potential deplorizes the cell which activates voltage-dependent Ca 2+ channels
2) Ca 2+ triggers exocytosis
3) The release of (T) into the synaptic cleft.
4) each neuromuscular junction has 200-300 receptors and each AP releases 1 quanta of T for each receptor.
5) Muscle End plate potential is activated which results in Muscle action potential.
- The more NAP the more Ca2+ concentration into the cell so it will release cells from the stationary pool.
What type of potential is EPP?
its a form of graded potential that relies on the amounT of acetylcholine transmitted.
What is the fate of the AcH after its release?
1) ACh is the only example of a neurotransmitter where its hydrolyzed by an enzyme (Hydrolysis by acetylcholinesterase) AChE.
2) diffused out of the cleft
3) bind to the postsynaptic receptor
How does the cell recycle synaptic vesicles?
Via endocytosis:
1) vesicle membrane attaches to clathrin via adapter proteins.
2) Dynamin is also involved in the fission of the invaginated pits.
How can toxins block neuromascular transmission?
it can block it from a presynaptic prespective or a post synaptic prespective
What is the function of Botulinum toxin?
it goes into the cell via endocytosis and blocks exocytosis of the cell.
What is the function of a-Bungarotoxin?
its a venom which is composed of a small peptide that attaches to the AChRs irreversibly and blocks activation by ACh.
how does Myasthenia gravis disease causes muscle weakness?
-It’s an autoimmune postsynaptic disease where antibodies attack AChRs and cause an inflammation in the cleft that ends up widening it.
How does Lambert disease lead to muscle weakness?
its a presynaptic autoimmune disease where antibodies attack specific Ca2+ channels.
