Nerves and Neurotransmission

00:01 Nerves, neuroglia and neurotransmission.

00:06 Nerves and various neural communication networks are so important with our ability to communicate within the body.

00:14 The brain has to be able to control the various limbs to undergo movement, has to be able to control things like organs, so you get blood flow and so you get digestion to occur.

00:25 And how you do that is all via nerves.

00:29 Any individual nerve has a number of structural components, and although this is not an anatomy class, we're going to go through a couple of those now because we need to use them in physiology to better understand how this communication works.

00:43 So if we start off with the soma or cell body, this is where we're going to have the nerve- packets of neurotransmitters are going to be produced.

00:55 You notice there are some small dendrites usually around the nerve body or the soma.

01:00 These can be part of the communication network to be able to receive signals.

01:06 Then you notice that we go down to the axon, and there's a specialized region of the axon known as the axon hillock.

01:13 Here we then have some glial cells that are wrapping around our axon.

01:19 You'll see these various nodes of Ranvier.

01:21 And finally we get to the synapses themselves.

01:25 And these are little terminal buttons, sometimes called boutons.

01:32 If we go all the way to those axon terminals to start off our process, because this is where communication is actually happening, you need to electrically provide information down the axon.

01:47 But once we get to the axon terminal, we still need to communicate past a synapse.

01:52 You notice there's a little gap there.

01:54 We can't pass electricity across that gap.

01:57 We are going to have to put a substance out into the synaptic cleft, have it diffuse across and bind to a postsynaptic receptor.

02:07 How do we get the neurotransmitter to be released? First, we need to get the neurotransmitter to the axon terminal.

02:15 Those are transported down the axon because usually there's not the production capacity in these axon terminals.

02:22 So those are traveling down as vesicles.

02:26 The vesicles then are stored within the axon terminal.

02:31 Here we need to now have some way to activate them, to get them to want to go to the synaptic cleft to dump out their substance.

02:40 The signal is electrical.

02:43 It is an electrical signal that's coming down the axon, which then stimulates voltage -gated calcium channels.

02:51 These voltage-gated calcium channels allow calcium influx into the axon terminal. Why does calcium want to travel into the cell? Because of the concentration gradient.

03:03 So there is more calcium on the outside of the cell than inside the cell, and that allows this concentration gradient to work.

03:11 Once calcium is in the axon terminal, it causes a reaction with the vesicle to want to migrate towards the synaptic cleft, dock and fuze and spill its quanta of neurotransmitter into the synaptic cleft. It then diffuses across to a postsynaptic receptor.

03:34 It binds that receptor and has an action.

03:38 Usually, it's some sort of allowing for ions to travel through, or maybe causing a cascade response within that postsynaptic cell.

03:47 So this whole process is done simply to get across that little gap that we can't pass electricity across.

03:56 The quanta of neurotransmitter that's released can be classified into a number of different classification schemes.

04:04 Small molecules such as amino acids, and good examples of these would be glutamate, Gaba, glycine all fit in this amino acid classification.

04:15 Cholinergic classification- that's acetylcholine.

04:19 Catecholamines are things like dopamine, norepinephrine, and epinephrine.

04:25 And finally, our monoamines are things like serotonin and histamine.

04:30 Those are our small molecule classifications for our neurotransmitters.

04:35 But we also have some peptide.

04:37 Peptide transporters are things like opioids.

04:41 We also have other ones that serve various functions such as in the enteric nervous system.

04:48 So these peptide hormones, neurotransmitters are important in the process of getting information across.

04:55 We may not use them quite as much as we do some of the small molecule ones, but they are very important in specific areas of the body.