So, I recently got interested in neuroscience and decided to learn more. Having had no formal training in neurobiology before, I just registered for this course on Coursera.
https://www.coursera.org/learn/neurobiology/
Let's see how it goes.
There's only one type of neurons that leaves the central nervous system (CNS) and goes directly to muscles, and that's the motor neuron.
There are a hundred thousand out of 200B neurons in the CNS.
The motor neurons are contained either in the brain stem or in the spinal chord. But, there are no motor neurons in the forebrain.
Perception -- the conscious perception of sensory inputs, the conscious appreciation of sensory inputs -- depends entirely on the forebrain.
The conscious appreciation of sensory inputs depends on the cerebral cortex.
Homeostasis is a distributed process, which depends on forebrain, brain stem and spinal chord.
The contribution of forebrain to homeostasis is hormonal. The contribution of brain stem is through autonomic changes (changes we are not consciously in control of) as well as through consciously made movements.
Same is true for spinal chord.
Higher Abstract Functions depend entirely on forebrain.
Neurons have four parts. The first is the cell body, also called the Soma. And this is the part that all cells have, this is cell central.
The cell body has coming out it from a number of dendrites, and these dendrites branch. And they continue to branch. And so, that makes a tree which we call the dendritic arbor or the dendritic tree.
And these dendrites are responsible for gathering in information. They're the sentries. They are the ears of the cell, of the neuron. They're taking in all information. So information is going in to the dendrites.
Axon carries the information along the length of it.
Neurons talk to neurons. But neurons also, go talk to muscles. And neurons talk to glands. And neurons talk to the cardiac, to the heart, to the cardiac muscle and so on.
Source of image: https://courses.lumenlearning.com/boundless-psychology/chapter/neurons/
This is the axon and you can see that it gives off these little terminals, and it also has places where there's just simply a swelling on root. So these are all synaptic, these swellings are synaptic terminals. The long slender projection of the nerve cell is an axon.
Image source: screenshot at 5:44 from https://www.coursera.org/learn/neurobiology/lecture/oGT73/neuronal-uniqueness-stars-of-the-sky
And the anatomy of the neurons is different in appearance. But, it's also different in the sense of what is a neuron connected to, what neurons are talking to it, and what neurons is it talking to. So the inputs and the outputs of each neuron are going to be different.
In addition to the anatomy, the other differences include excitability -- and this is essentially how talkative is the neuron; how much do you have to goad it to get it to say something.
Some neurons are talking all the time; and some neurons are very laconic, very unlikely to speak.
And finally, there's how do they speak? And what we're talking about is the neurotransmitter. What is the neurotransmitter -- or what's the chemical, the substance -- that the neuron uses?
There is also a difference in both speed -- whether is something fast or slow -- or also whether it's affirmative or or negative -- 'yes' or 'no', and how fast does it take you to get to 'yes' or 'no'.
**Glial Cells**
The human brain contains 86B neurons and 85B Glia.
**Different types of Glia:**
🔸 Astrocytes: Astrocytes are really important type of Glia. They're essentially responsible for keeping the environment clean, they're the sanitation worker of the brain. So they are picking up all the refuse that the neurons have let loose including excess ions, excess #neurotransmitters and their metabolites.
They also are very important during development. They allow neurons to get to where they have to go during development. #Neurons are born in one place and they have to go some place else, and what highway did they take? They hitch on a progenitor cell that is going to become an #Astrocyte.
And, in addition when synapses are formed, the synapses are not maintained without some effort, and part of that is that the synapses are enveloped in the processes of #Astrocytes. So, there's a lot of structural and metabolic support that the Astrocytes are providing for neurons.
🔸 Oligodendrocytes and Schwann Cells: The #oligodendrocytes make myelin in the CNS and the #SchwannCells make it in the Peripheral Nervous System. So all these demyelinating diseases will affect either central myelin or peripheral #myelin. They will not affect both -- central or peripheral.
Because they are made by two different types. The Oligodendrocytes in the central nervous system and a Schwann cells in the peripheral nervous system.
🔸 Microglia: #Microglia are the one exception to the rule that
nervous system, that the cells of the nervous system come from Ectoderm. These are actually essentially immune cells coming from the blood lineage. These are immune cells that have invaded into the central nervous system and their job is to be quiet. And if we're healthy and everything goes well, they are quiet. But when there is a problem these microglia react, they try to rectify things, they try and bring some attention to areas of damage and what is emerging is that sometimes they go overboard and they start to participate in making the problem as well as solving the problem.
@crackurbones and NG2 glia hang around too and contribute to scar formation and immune signaling when they don’t feel like making oligos!
