Differences between synapses and neuromuscular junctions

So for one of the differences, it says 'NMJ are always excitatory, synapses can be inhibitory or excitatory', but I don't understand exactly what this means?

Thanks

So for one of the differences, it says 'NMJ are always excitatory, synapses can be inhibitory or excitatory', but I don't understand exactly what this means?

Thanks

Well basically, a neuromuscular junction can't really inhibit skeletal muscle because skeletal muscle's natural state is to be relaxed. So if you were to have an inhibitory neuromuscular junction then it wouldn't do anything because all you'd be doing is inhibiting something that is already not doing anything. So neuromuscular junctions can only be excitatory because activation of the NMJ stimulates muscle to contract.

Synapses on the other hand can be stimulatory or inhibitory. This is important because most neurones are active all of the time, for example some neurones in the sympathetic nervous system are constantly being activated to stimulate some blood vessels to constrict, however if for some reason the body needs to widen those blood vessels, then you need to inhibit the sympathetic neurones that are causing them to constrict. This is done by a inhibitory synapse in the brain, which inhibits the sympathetic neurone from firing as frequently.

^ This was pretty poorly explained, someone else might be able to have a better crack at it

Synapses are between two neurones. Releasing neurotransmitters, the pre-synaptic neurone (the one that fires first) tells the post-synaptic neurone whether it needs to be switched on or off. So depending on the type of synapse, it can inhibit or excite the post-synaptic neurone that comes after.

At the neuromuscular junction, you have a connection between a neurone and an effector muscle. For skeletal muscle you have Acetylcholine released; this always excites the muscle cell. So if you excite the neurone at the neuromuscular junction, the result will always be muscle contraction. Same at cardiac muscle and smooth muscle, although there the neurotransmitter is nor-adrenaline I believe.

Well. First let me explain the difference in meaning between synapse and NMJ. Synapses are connections between nerve cells, while NMJ is quasi the entrance to a muscle cell. To transmit a stimulus in form of an action potential from a nerve cell to another ones and to a muscle cell after that, the neurotransmitter receptors on the NMJ has to be opnened by acethylcholine. This happens when a stimulus in form of an action potential has arrived a synapse.

A stimulus is excitatory when the stimulus threshold is overrun. This leads to a transmission of the stimulus from a nerve cell to another one and thus to a certain muscle cell. A stimulus is inhibitory when the stimulus threshold is underrun, that is to say the stimulus is too weak for a transmission from nerve cell to nerve cell.

Based on this explanation, NMJ has always to be excitatory, otherwise stimuluses are not able to arrive muscle cells and so to use body parts which are commected with those muscle cells. Apart from the main function of the synapses, namely to transmit stimuluses from nerve cell to nerve cell, some of them are inhibitory to prevent that it comes to an overstimulation. Imagine you have 100 thoughts in your brain at the same time, because 100 stimuluses are transmitting in so many different nerve cells! you would get insane, wouldn't you? that is why synapses are also inhibitory to guarantee that just the important stimuluses are transmitting for our perception.

Thank you!



Got it, thank you

It has been explained pretty well already. One other difference between NMJ's and synapses is that NMJ's always contain acetylcholine as the neurotransmitter in vertebrates, whereas synapses can use this and a variety of other neurotransmitters.