Thursday, October 18, 2012

Brain Anatomy and Functions

Let's talk about the most amazing organ in the most complex organism on the planet, shall we? :)

Here is a basic orientation:

Brain Stem
The most ancient ("primitive") part of the brain is the brain stem.  This part of your brain is responsible for basic functions to keep you alive.  Includes the Medulla oblongata, Pons, and Midbrain.  First a look at the parts:


Here is a view of a frontal slice through the human brain stem:
1- Cerebrum, 2- thalamus, 3-midbrain, 4- pons, 5- medulla oblongata, 6- spinal cord (Source)

Now a look at each part and the centers each contains that help keep you alive in-the-moment.  Things that could kill you in a matter of seconds or minutes if they don't work properly are controlled here.  We'll start with the most inferior part and move up.

Medulla Oblongota

Control centers of Medulla:
  • Vasomotor- regulate blood pressure
  • Cardiac center - controls heart rate, strength of contraction
  • Respiratory center - controls respiratory muscles, is sensitive to pH (so it can respond by increasing or decreasing respiratory rate which will bring the body back into homeostasis as far as pH)
  • Respiratory reflexes - vomiting, swallowing, coughing, sneezing

Mnemonic from Physiology student - "programming your VCR makes you vomit"

Another cool thing that happens in the medulla:

  • Decussation of fiber tracts - decussation is a fancy scientific word for swapping.  As you all know, the right side of the brain controls the left side of the body, and vice verse.  The medulla is where the nerve fibers cross over.  (Also referred to as "decussation of pyramids".)
  • Pathway between spinal cord and brain
  • Fine control of respiration
Inferior view (looking up at bottom of brain) showing the Pons (Wikipedia)

Mesencephalon (midbrain)
  • Conduction pathway between cerebral hemispheres
  • Reflexes based on visual stimuli (moves head and eyes to protect them from being hit or poked)

That is the brain stem.  Next we will continue superiorly.

Paired organ at top of brain stem, see picture below
Thalamus is the purple part.  Detailed anatomy of brain stem if you want that info. (Source)
  •  General sensations of pain, heat, cold, pressure (can't pinpoint location or intensity)
  • Sensory Gatekeeper - pathway between cerebral cortex and sensory/somatic systems.  Shuts out some sensory info to allow for greater focus on important things.  So it takes in all that general info and filters out what's not important (such as the sensation of your clothes touching your skin so stuff like that doesn't become distracting)

Reticular Activating System
Housed in the brainstem and thalamus is the Reticular Activating System, shown below in red.
This system controls your waking state and alertness, sending signals to the cerebral cortex to keep you awake and alert.  This allows you to direct your attention to specific events.  It also holds back sensory info at other times to allow you to sleep, and controls your circadian rhythms (sleep-wake transition).  In fact, if I understand correctly, the RAS has an inhibatory affect on the part of the brain that contributes to sleepiness - the Preoptic Area (POA) of the Hypothalamus.  Likewise, the POA can inhibit the RAS when it's time to sleep.  Pretty cool.
An even more cool fact - this alertness center is very active when awake, and is suppressed during deep sleep, but during REM sleep when you are dreaming, the RAS is just as active as when you are awake! :)

The inferior part (floor) of the thalamus.  See picture above, the purple front section on left picture.  Also, the picture below gives a more general orientation.  Here are its functions.

  •  Manager of the Autonomic Nervous System
    • Rage & aggression
    • Hunger & satiety
    • Fluid osmolarity
      • Thirst center
      • Anti-diuretic hormone (ADH)
    • Body temp
  • Regulates the Anterior Pituitary Gland, which affects:
    • Growth
    • Sexual Function
    • Lactation (breast feeding), regulated by oxytocin
    • Thyroid function
    • Stress, regulated by cortisol
Here's a more detailed diagram of the hypothalamus:


The motor integrating center - makes last-minute fine tuning adjustments to motor activities, controlling coordination.
Tells "how far, how fast, and when to put the brakes on"
Sobriety tests are really testing the functionality of the cerebellum.  Depends on sight and proprioception (info on what your body position actually is right now) input.  Prevents dysmetria and past-pointing.  (Dysmetria = missing the mark; past-pointing = moving beyond the mark.)

The cerebellum processes input from other areas of the brain, spinal cord and sensory receptors to provide precise timing for coordinated, smooth movements of the skeletal muscular system. A stroke affecting the cerebellum may cause dizziness, nausea, balance and coordination problems.



Basal Ganglia/ Basal Nuclei
Trains the brain to do fine motor activities
Suppresses unwanted movement
Initiates trained complex movement patterns
Lesion in this area causes Parkinson's disease


Limbic System
Includes parts surrounding the brain stem: cerebral cortex, basal nuclei, thalamus, and hypothalamus
Responsible for "fight or flight" type of survival, and species survival instincts:
  • aggression
  • fear
  • feeding
  • sexual behavior
  • motivation

Cortices of the Brain

Primary Motor Cortex
Voluntary contraction of skeletal muscle

Premotor Cortex
Stereotyped movements - "computer programmer" for repeatedly used actions
*Broca's Area
Controls muscles responsible for speech - only on the left side of the brain

Somatosensory Cortex
Pinpoints location and intensity of temperature, touch, pressure, and pain (general sensations of these come from thalamus, then are passed on here to get more details)

Primary Visual Cortex
Primary Auditory Cortex
Olfactory Cortex
Gustatory Cortex

Parietal-Temporal-Occipital Association Cortex
Interprets primary sensations from somatic, auditory, and visual areas
*Wernicke's area
Allows for interpretation/ understanding of language (both written and spoken)

Prefrontal Association Cortex
Planning for voluntary activities
Perceiving consequences of future actions
Responsible for personality traits 
Teen drinking impairs the development in this area

For additional information related to the brain, see these other posts:

Action Potentials

Action Potentials Up Close



 Brain Food: Nutrition for Learning & Memory

Nervous System


  1. I was wondering if you could discuss the pina.

  2. The detailed drawings are very useful. Nice job!

    1. I didn't make the drawings, there is a website source listed below each picture. But thank you!

  3. Thanks for this info. It’s really helpful because you were able to simplify each of the function of the parts of the human brain. The illustrations were great help in pinpointing each part because of its detail and clarity.

    Brooke Arredondo

    1. Thanks Brooke, I appreciate the feedback. It was a fun post to make. Hope to go into more detail soon with the other parts.

  4. Can you describe what the brain stems function is and examples of use in everyday life. Also there is a foreign object during a surgery that had protruded from one end of the brain stem to the other and I am trying to see how much damage this is going to cause. The object was a shunt catheter.

    1. Sounds like a good homework critical thinking problem, and is beyond the scope of what I'm trying to do on this blog in giving an overview of all the parts. I did describe the brain stem and its functions. The parts included are the Medulla, Pons, and Midbrain. If a part of the brain is impaired, basically whatever functions it has in that area will be impaired. Best of luck with your studies!

  5. How does an Arnold Chiari II affect the brain and the cerebellum?

    1. I am not familiar with this, I may look into what it is in the future. Thanks for your interest. However, I am not a good source for question-answer type of detailed information as I am not an exert in neuroscience.

  6. that"s were it travel too?

    1. Since this is not a grammatically coherent sentence I do not know what you are attempting to ask me, sorry.

  7. thanks for the useful overview!

  8. What part makes us perceive the way we do? Is consciousness just an illusion created by all the different parts working at once, or is a specific area of the brain that provides us with conscious thought?

    1. Pretty much the entire brain is involved in perception. A lot of conscious thought that goes on when you are simply thinking about things is in the prefrontal cortex, but it really would involve many parts of the brain, as they all work together. I do not think you can pinpoint any area of the brain as the location of consciousness.