ELM 4.2 Flashcards
Connexon subunits are called…
connexins
A key component of an electrical synapse is the
connexin - Connexin is a subunit of the gap junction channel that connects the cytoplasm of electrically synapsed cells together.
In a classic series of experiments (shown in the figure above) the German scientist Otto Loewi examined chemical transmission in isolated frog hearts. In one heart, he stimulated a nerve that regulates the heart beat (X). He them pumped buffer (Y) from the bath surrounding this heart into an organ bath with a second heart in it.
The buffer (Y) pumped into the second chamber contains high concentrations of which neurotransmitter?
Acetylcholine
What is a MEPP (miniature end plate potential)?
When the synapse occurs spontaneously so there is not as large a response
What is a quantum?
amount of transmitter per vesicle
What do quantums vary by?
A fixed step
What is the formula for quantal current?
EPP current / 1 quantum current
Properties of mini’s (3)
- occur spontaneously - even in zero extracellular Ca2+
- have amplitudes that are multiples of a quantal unit
- are due to release of one or a few quanta (= vesicles)
What does clathrin insure? (3 factors)
- constant vesicle size
- constant number of vesicles
- constant size of terminal
What is tetanus caused by?
anaerobic bacterium Clostridium tetani
What does anaerobic bacterium Clostridium tetani do?
cleaves snare proteins
What is the mechanism of action for anaerobic bacterium Clostridium tetani?
- tetanus toxin binds to and enters presynaptic nerve terminals in the skeletal muscle neuromuscular junction, and then travels back up the motor neuron axon into the CNS.
- it is released from the dendrites of the motor neuron and is taken up by inhibitory neurons. These neurons normally release GABA or glycine, which are inhibitory neurotransmitters. Once inside the inhibitory neurons, tetanus toxin destroys their SNARE proteins and stops them from releasing GABA or glycine.
(The normal function of these inhibitory neurons is to regulate the motor neurons that stimulate skeletal muscle contraction. When this regulation is lost, the skeletal muscle will go into uncontrollable spasms. This lead to breathing problems and it has a mortality rate of around 10%.)
Tetanus summary
Tetanus is caused by the anaerobic bacterium Clostridium tetani, which is related to Clostridium botulinum . Tetanus toxin enters motor neurons and travels up their axons to the spinal cord. In the spinal cord it is released by the motor neurons and is taken up by inhibitory neurons. Inside these neurons it breaks down proteins involved in transmitter release (similar to botulinum toxin). This results in a lack of inhibition in the spinal cord and uncontrollable muscle spasms occur. This is the disease we call tetanus.
What is a toxin that blocks voltage gated calcium channels?
Tetrodotoxin
(Omega conotoxins are produced by fish-hunting marine snails such as Conus magus (photograph below). They are small peptide toxins that block calcium channels.)
What is a toxin that destroys SNARE proteins?
Botulinum toxin
(Botulinum toxin disrupts neuromuscular transmission. The enzyme components of botulinum toxin are proteases. They cleave the SNARE proteins that are involved in the fusion of neurotransmitter-containing vesicles with the synaptic membrane. This means that ACh cannot be released and results in a (frequently) fatal paralysis. Alpha bungarotoxin acts on nicotinic acetylcholine receptors, omega conotoxin acts on voltage gated calcium channels and tetrodotoxin acts on voltage gated sodium channels.)
