Neurophysiology L4: Synaptic Neurotransmission Flashcards
What is an electrical transmission?
When an action potential gets to a terminal, it has to transmit the electrical signal across the cell
What are 3 features of electrical transmission?
- Gap junctions allow direct electrical coupling between neurons.
- Generally rare in neurons.
- Common in cardiac and smooth muscle
Gap junctions allow direct __________ between neurons. ______ transmission is the main way of neurons communicating with each other or muscles
electrical coupling; chemical
Electrical transmission is generally rare in ______.
neurons
Main way of transmission in cardiac and smooth muscle is ______ transmission.
Electrical
Why is electrical transmission advantageous in cardiac muscle?
Advantageous in cardiac muscle because you want contraction in unison.- No stimulation happens. Electrical signals is generated at the SA node. Whole signal is transmitted very quickly to the rest of the cardiac muscle and and the whole cardiac muscle contracts in a unison. Mainly caused by electrical signals travelling from one cell to the other - coupled together.
How does electrical transmission work in smooth muscle?
In blood vessels (only in arterial smooth muscle) Only the surface of the smooth muscles are innervated by varicosities (nerve endings), deeper smooth muscles cells are not innervated. An electrical signal is generated on the surface and the signal is transmitted through the smooth muscles (because they’re coupled together) and the blood vessel constricts to reduce or increase the blood flow in a particular bed.
A pool of motor neurons (particular muscle) _____ (are/aren’t) coupled together. When stimulated –> _______ (all/none) stimulated –> muscle contracts (uniform way) - useless if controlled movement.
are; all
You loose that communication between _______ neurons in development, but they still work together and contract in ______ (not at the spinal cord level, but at the brain). The pattern is established on the _____ of the brain.
motor; unison; motor cortex
What are electrical synapses in relation to synaptic transmission?
Originally thought by some to be the main type of connection between “excitable” cells such as neurons
What are chemical synapses in relation to synaptic transmission?
What is a synaptic cleft?
- Synaptic clef/gap - neurons don’t make contact with each other.
- Contains recognition molecules - tells nerve terminal that they’re close to a muscle and tells the muscle that there’s a nerve terminal close by - communicating with each other.
- Occurs early in development.
What is a synaptic vesicle?
- Cannot move around freely - the nerve terminal is filled with other things.
- Vesicular associated proteins push them towards the release point.
- They are pulled towards the central part (active zone - where transmission actually happens).
- They are primed - conditioned so that they’re ready to go when an action potential comes down - very close to being released.
- All it takes is a little bit of calcium to come in when an action potential comes down and the vesicle releases its contents.
- These proteins and filaments inside the neuron are bringing the vesicles to the appropriate place, where they’re going to be released effectively and quickly. This is why synaptic transmission is very fast.
What are voltage gated Na2+ channels?
- Calcium channels can also be blocked.
- Animals living in cone shell has a barb containing conotoxins.
- Conotoxins block calcium channels very effectively -> block neurotransmission -> you die very quickly.
- Omega-conotoxin - used as pain killer.
What is a transmitter-gated channel?
- Post synaptic receptors are highly concentrated in this area - 10,000 times more concentrated than elsewhere.
- This is so that when the transmitter comes out, the first (second) thing that it sees is the receptors and hits it.
- The receptors open up, allowing sodium to flow in - local depolarization.
- The first thing that the transmitter sees is a hostile environment - acetylcholinesterase is found all over the place (enzyme that breaks down acetyle choline). As soon as acetyle choline comes out at the neuromuscular junction, the first round of acetyle choline will never see the receptors - gets broken down by the enzyme and occupies it. The remainder of acetyle choline passes through and hits the receptors -> receptors open and local depolarization happens. Then the acetyle choline comes off and immediately, acetylecholinestrase breaks that down -> Terminal goes back to a ready state again and receptors reactivate themselves, getting ready for a second stimulus.
- If acetyle choline is not broken down fast enough, you get a depolarising block. They block acetylecholinestrase -> you get excessive amount of acetyle choline hitting receptors -> receptors become inactivated -> you become paralysed -> your lungs stop working -> death
- The system is very well balanced - it relies on acetyle choline, cholinesterase, amount of transmitter, amount of receptors being in balance
- Any imbalance will cause a disease.
- Some diseases are known to affect this.
- E.g. Myasthenia gravis - immune system attacks acetyle choline receptors -> end up with weakness in contractions.
- E.g. Multiple sclerosis - immune system attacks myelin sheaths -> signals become more confused -> slower signals -> paralysis.
Post synaptic receptors are ______ (highly/lowly) concentrated in this area - 10,000 times more concentrated than elsewhere. Why?
highly
- This is so that when the transmitter comes out, the first (second) thing that it sees is the receptors and hits it.
- The receptors open up, allowing sodium to flow in - local depolarization.
The first thing that the transmitter sees is a _____ environment - acetylcholinesterase is found all over the place (enzyme that breaks down acetylcholine). As soon as acetylcholine comes out at the _______, the first round of acetyle choline will never see the receptors - gets broken down by the enzyme and occupies it. The remainder of acetylcholine passes through and hits the receptors -> receptors open and local ______ happens. Then the acetylcholine comes off and immediately, acetylecholinestrase breaks that down -> Terminal goes back to a ready state again and receptors ______ themselves, getting ready for a second stimulus.
hostile; neuromuscular junction; depolarization; reactivate
If acetylcholine is not broken down fast enough, you get a _____ block. They block acetylecholinestrase -> you get ____ amount of acetylcholine hitting receptors -> receptors become _______ -> you become _____ -> your lungs stop working -> death
depolarising; excessive; inactivated; paralysed