Anatomy and Physiology series: The Central Nervous System part I (aka Braaaiinns!...for any zombie lovers out there)

(Note:  The central nervous system does also comprise of the spine as well as the brain, but for the sake of brevity, I'm going to just focus on the brain and, more specifically, on the areas most involved in speech and communication.)

I wrote a bit about the central nervous system before in this post, so I might repeat some of what I said there here, but I will hopefully go into more detail than that previous post.  Topics we'll go over are the regions of the brain and their associated functions, including lobes of the brain, and the Wernicke-Geschwind model.  Let's build our brain from the "bottom up," or from the lower-level functions to the higher ones.  Conveniently for us, this is the way our brain is organized already, so...yay!

If you travel up a spinal column on a skeleton up to the skull, you'd see a big hole there, the foramen magnum (which conveniently translates to "great hole").  This is the point where the spinal cord enters to connect to the brain, and if you're looking at a spinal column above this hole, it traditionally becomes the brain stem at this point.  The brain stem is the most primitive, or oldest (evolutionarily-speaking), part of our brain, and it includes our medulla and pons.  It's in charge of our heart beat, breathing rate, maintaining conscious awareness, transmission of sensory and motor information from our brain to body and vice versa, and regulating our sleep cycle.  It's got a lot going on, but all of these functions are essential functions for our survival.  This is why damage to the brain stem often results in death (heart beat and breathing stops), and why if our brain is severely damaged but our brain stem is intact, we would still be breathing and have a beating heart.

The hypothalamus is right above the brain stem, and is involved in a whole lot of functions that I'm not going to get into too much here.  Among other things, it links the endocrine system with the nervous system, controls hunger, thirst, sleep cycles, and all kinds of other things.

The thalamus is located right above the hypothalamus and it is considered a major relying-station, if you will.  It receives and transmits sensation and motor signals to our cerebral cortex, and newer research has shown that it is actually selective (on an non-conscious level) of what signals it sends on (but we don't know how or why it acts this way).

The cerebellum, or "little brain," is important for fine motor control.  Now, it's important to say that the cerebellum does not initiate any motor control, it just fine-tunes it to allow for precision and smoothness to our movements.

The rest of what we're going to talk about are areas in the cerebral cortex.  The cerebral cortex is a layer of neural tissue that lies on top of our cerebrum.  This cortex has five layers of neural tissue that vary in thickness based on function.  (So if you're looking at the cerebral cortex from the motor area of the brain, you'd see that the layer of neural tissue for motor function (the fifth layer...containing mostly pyramidal cells) is much thicker than the other five layers.)  Now, because the cerebral cortex is involved in so many, many functions that our brain does, we've isolated certain areas by function just to make it easier to talk about the dang thing.  So the first way it's classified is by lobe.

The lobes of the brain correspond to the bones of the skull with the same name.  And here they are!:

There are two temporal lobes, one on each side of the head

A super-brief summary of function goes like this:  The Occipital lobe takes all the incoming visual information, puts it together, and sends it to the frontal lobe.  The Parietal lobe takes in all the sensory information and also does some spatial processing (like with objects) and sends that info off to the frontal lobe for processing.  The Temporal lobes take in all the auditory info and olfactory (sense of smell) info, associates it (sorta like making a nice summary of the important stuff) and, you guessed it, sends it off to the frontal cortex for processing.  So the Frontal lobe is a bit like the manager of the whole thing.  It is where you consciously analyze all this information you're taking in, and there are some analyzing going on in the back of your conscious thought in this lobe as well.  The prefrontal cortex, which is like a sub-set of the frontal cortex, is the seat of your personality and your own personal perception of the world (or your qualia, if you read the "Neuroscience, I Think I Love You" post.)

At this point, I've noticed this is going to be a bit longer than I anticipated, so I'm going to split this post up into two different ones.  So part II will get into the communication and speech systems going on in our brain, and then, in following posts, I'm going to finally put it all together into the physiology of the articulatory system.  Whew.

*Seikel, J. A., King, D. W., & Drumright, D. G. (2010). Anatomy and physiology for speech, language, and hearing. Clifton Park, NY: Delmar.