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Saturday, May 12, 2012

Apologia General Science, Module 16, The Human Nervous System

Interactive Study Links
►The Nervous System: 
(In these games, the motor nervous system and the sensory nervous system are collectively called the Somatic Nervous System.)
• Nervous System Game #1 - click and match
• Nervous System Game #2 - click and match
• Neuron Game - click and match
• Label the Neuron - drag and drop
• Label the Eye - drag and drop
• Label the Brain - drag and drop
• Label the Ear - drag and drop (The eardrum is also the tympanic membrane.  The ossicles - the hammer, anvil, and stirrup - are referred to by their scientific names.  See if you can find these names online or in a book.)

Other Study Links
diagram of a neuron and a synapse (source - Great simplified article!)
diagram of a human brain
diagram of a human eye (source)
diagram of the human ear (source)

(1) p. 387-392, Introduction; Neurons: The Basic Unit of the Nervous System

►Another video with Khan Academy, if you want it.

Neurotransmitters take the signal across the synapse (a gap between the axon of one neuron, and the dendrite of the next neuron).

Neurons are composed of cell bodies, dendrites, and axons.
Nerves are made of the dendrites and axons, but not the cell bodies of neurons.

The cell bodies of neurons tend to cluster together in groups, called ganglia.  Several ganglia clustered together is called a plexus (nerve center).


(2)  p. 393-396, The Basic Layout of the Human Nervous System

White matter vs. gray matter
See image (source)


(3) p. 397-399, Our "Split" Brains

Right-brain vs. Left-brain.
This lady is hilarious! =D

This video seems to indicate that people who are left-brain dominant tend to take things literally.  I bet you probably  know someone like that!  And it's not always men.  But we are all different; no one is totally left- or right-brained only.  There are combinations.
And of course, the corpus callosum connects the right and left hemispheres of our brain.

►But here is another funny for your enjoyment.
A wife asks her husband, "Could you please go shopping for me and buy one gallon of milk, and if they have eggs, get 6."
A short time later the husband returns home with 6 cartons of milk.
The wife asked him, "Why did you buy 6 gallons of milk?"
He replied, "They had eggs." =D

What would happen if the corpus callosum didn't connect the two sides of your brain?


(4) p. 400-401, The Brain and Blood

The Blood-Brain Barrier
Brain capillaries are different than other capillaries in the body.
Other capillaries are more permeable (penetrable) than brain capillaries, and have gaps between the blood cells in them.  They allow more substances to get in and out.
The capillaries in the brain have a barrier.  There are no gaps between the blood cells in these capillaries.  They are sealed with "gaskets."
Certain things, such as water, oxygen, and glucose are transported through the cells in the brain's capillaries, but there is no "leaking" (on purpose) as there is with other capillaries in the body.
Some things that are bad are able to break through the blood-brain barrier, such as drugs or alcohol.  When these get into the Central Nervous System, it can cause major problems!
"More than 100 years ago, it was discovered that if blue dye was injected into the bloodstream of an animal, that tissues of the whole body EXCEPT the brain and spinal cord would turn blue..."
►Read the rest of this simple explanation of the blood-brain barrier.


(5) p. 402-405a, The Peripheral Nervous System (PNS)

The PNS is divided into three main divisions:
  1. sensory nervous system - your 5 senses
  2. motor nervous system - your skeletal muscles
  3. autonomic nervous system - smooth muscles, cardiac muscle, and glands

The first two are controlled by voluntary muscles.
Watch this short video about the PNS, and that all the spinal nerves have both a sensory route and a motor route.

The autonomic nervous system is as the name sounds - automatic - and is controlled by involuntary muscles.
The autonomic nervous system is divided into two more divisions:
-sympathetic division - fight or flight
-parasympathetic division - rest and digest


(6) p. 405-407, The Human Sense of Taste

One more video, if you'd like to watch it.


(7) p. 408-409, The Human Sense of Smell


(8) p. 410-415a, The Human Sense of Vision
At 1:15, he mentions muscles that change the shape of the lens.
These are the ciliary muscles.  They change the shape of the lens so that you can change focus instantly between objects that are close or far away.

I have one eye that focuses slightly slower than the other.  In my "good" eye, I don't notice any change when I am looking down at a book, then glance up at the news playing on the television in the next room.  However, in my slow eye, it takes maybe half a second.  About as long as a medium-slow blink.
Years ago, I went to the eye doctor because of this, and because my pupils are different sizes.  I was told a long name for it, and that it wouldn't affect my vision.  I don't recall when I noticed my pupil being this way.  I do remember that I knew about it when I was a young teen, but I don't ever remember "discovering" this anomaly.  ;)


(9) p. 415-417a, The Human Sense of Touch

I could find no suitable videos for this section.


(10) p. 417-419, The Human Sense of Hearing
The small bones in your ear, the malleus, incus, and stapes, are sometimes called the hammer, anvil, and stirrup because of their shape.
Together these tiny bones are referred to as ossicles.
The cochlea is filled with fluid, which helps in transmitting signals to the brain.

Why we get dizzy when we spin:

This video is just so that you can get a better idea of the 3 dimensions of the semicircular canals.  (You do not need to learn this terminology that indicates positioning in the body.)
You can see that one is horizontal, and two are vertical, but in different directions.

When you are riding in a car then stop suddenly, your body keeps moving forward.
After you stop spinning, the fluid in your ear is still moving and makes you feel off balance.


  1. I must compliment you for this very interesting blog.

    Thank you so much for your efforts.
    Linda translator from Nice France.

  2. Thank you, and you're welcome. =)


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