NOTICE: Posting schedule is irregular. I hope to get back to a regular schedule as the day-job allows.

Sunday, February 20, 2011

Back to Basics

The LabRats are back in the lab and we can return to the discussion of parts of the brain.

For the next few weeks, this blog will work through the essential sections of The Lab Rat's Guide to the Brain which deal with the functions of the brain, and which of the various regions, cortices (plural of cortex, if the term is unfamiliar), ganglia and /or nuclei  are responsible for those functions.  Before going in depth into the sections, I prefer to specify the *types* of functions first.

I will describe brain function in terms of:

(A) Input
(B) Output
(C) Processing
(D) Control

Clearly "Output" and "Control" could be thought of as the same thing, but I will clarify that in my classification scheme, "Output" results in an action of the body, while "Control" results in a change to the body's internal workings.

Now, what are the "Inputs"?  Vision, Hearing, Smell, Taste and Touch.  Those are the five basic senses.  In addition, there are special cases:  "Proprioception," the sense of body and limb position is a special case of "Touch," although the receptors are in the joints and muscles and not the skin.  Balance is tightly associated with the sense of hearing, but is controlled mostly by proprioceptors, pressure sensors on the feet, and the proprioceptor-like neurons of the semicircular canals.  Smell and Taste are essentially the same sense - what we sometimes call "Chemoreception" - and there are special instances of chemoreception through skin receptors.  This brings us to pain.  The sense of Pain is closely intermingled with all of the senses, each can signal a painful stimulus, but for the most part it is organized with, and associated with the sense of touch.

Outputs:  The commonly considered outputs of the brain are speech and muscle movement.  In truth there are many more outputs, but most of them fall into regulating the various physiological systems fo the body, and are more appropriately considered "Control" functions.  In addition, muscle movement is not just moving the limbs, but also includes eye blinks, pupil dilation and constriction, "scanning" movements, adjustments of the ear drum, swallowing, breathing, and piloerection (goosebumps).

Processing is the function that involves the largest percentage of the brain.  Once a sensory neuron reports to the appropriate part of the brain, that information is *represented* then *associate*.  Smell gets associated with taste, and we decide which foods we like.  Sound and vision are associated, and we can track a moving car, bird, airplane, or that baseball flying toward us at 75-80 mph.  Vision, touch (vibration) and proprioception are associated, and we are certain we've *hit* that baseball out of the park.  Vision, hearing, and proprioception are associated to give us the power of speech and reading. 

Memory is processing; as is "executive function" or decision-making. 

Control functions take two forms - what we call the "autonomic" - and you can substitute the word "automatic" - functions, and coordination.  Taking the latter type first, coordination usually involves association between the Input and Output functions.  Vision plus eye movement (and pupil dilation) provides tracking.  There is a brain area that performs precisely those functions.  Proprioception plus muscle movement plus vision plus the sense of touch  is necessary to coordinate the smooth muscle movements necessary to reach out - *find* the object we are reaching for, stop the hand, grasp the object, and move it to another position.  Autonomic functions include resting heart rate, breathing rate, body temperature, blood pressure, hunger, fear, excitement, and even mating.

To reiterate from a previous blog, the diagram of the various "lobes" of the brain at right also serve to divide up functions as well.  If one were to draw a line directly downward from the point marked "Central Sulcus," most Input functions would be to the right and Output to the left.  Red (Frontal), Orange (Cerebellum), and light Blue (Brainstem) are Control areas.  Blue (Parietal) and Yellow (Temporal) are Processing areas, although there are also some processing in the Frontal lobe. 

Over the next several blogs, we will work from back (Occipital) to front (Frontal) regions and describe a bit of the organization, roles, and specialization of each brain area.  We will then work "downward" into subcortical areas and the brain stem, with a brief discussion of the spinal cord.  Along the way I'll introduce some of the mnemonics we learned in Medical School for keeping all of this straight long enough to pass exams, the LabRats will probably make an appearance, and I'll collect questions for the mailbag.

To paraphrase Joe Bastardi's weather wisdom (  "Protect your brain, it's the only brain you've got!"

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