THE NERVOUS SYSTEM HISTOLOGY AND DISSECTION LAB

PERIPHERAL NERVE HISTOLOGY.

Longitudinal Section of Peripheral Nerve

• The prefixes epi-,peri-, and endo- are Latin for “above, around, and within.”
• The bundling of the nervous tissue compared to the muscle tissue.  Muscle tissue is covered with many fibers by connective tissue, nervous tissue has different structure because they are composed by neurons, not myocytes like muscle tissue. 
• What type of connective tissue is represented in the dark purplish-blue area? Perineurium connective tissue is represented in the dark purplish-blue area.  

Longitudinal Section of Peripheral Nerve

Find each of these structures in Slide 2, describe their structure, not function, in detail (two or more “things”) to distinguish them from other the other structures on the list.

a. Node of Ranvier-  Node of Ranvier are located between the Schwann cells of the Myelin shealth and the Neuron axon and are just considered “short gaps” that are uninsulated in the nervous system. 

b. Axon- Axon is long and slender.  It has a tube-like structure. 

c. Myelin sheath- Myelin sheath, unlike the others, are fatty and insulated cells.

d. Endoneurium-  Endoneurium cells are made up of collagen and are darker and thicker than the other nerve cells. 

Cross-section Through Peripheral Nerve

• To diagnose a nerve disease, what could the lipids tell you?  By the amount of lipids and the current physical stature of the lipids could determine if the patient has any lysosomal storage diseases, for example.

Slides 4 and 5 are peripheral nerves stained with Verhoeff's van Giesson stain showing fasicles, epineurium, perineurium, endoneurium, and axons and myelin. 

Cross-section Through Peripheral Nerve.

Longitudinal Section Through Peripheral Nerve

Practice your skills. Find each of these structures describe their structure, not function, in detail (two or more “things”) to distinguish them from other the other structures on the list.

a. Fascicles-  Nerve fascicles are small bundles of nerve fibers that are enclosed by Perinerurium and Endoneurium cells. 

b. Perineurium- The Perineurium is cell with an almost transparent, tube-like shaped layer that is made up of three other layers relating to protecting the individual nerve fibers in the peripheral nervous system.

c. Endoneurium- Endoneurium cells are made up of collagen and are darker and thicker than the other nerve cells. 

d. Axon-  Axon is long and slender.  It has a tube-like structure. 

e. Myelin- Myelin sheath, unlike the others, are fatty and insulated cells.

VIEWING SHEEP BRAIN DISSECTION

The sheep brain is quite similar to the human brain except for proportion.

Open this link. http://www.biologycorner.com/anatomy/sheepbrain/sheep_dissection.html, and based on the photos, answer these questions.

1. How is the orientation of the sheep brain in the sheep’s body different from how our brains are oriented in our bodies?  There are a few differences of orientation between a human brain and that of a sheep.  One of the first most distinctive; the size.  The human brain is larger and heavier than a sheep’s brain.  Also, the human brain has more contours and ridges than the sheep’s brain.  The brain of a sheep is placed horizontal off the backbone region whereas the human brain is placed vertically. 
2. Describe the appearance of the dura mater. What is its function?  The dura mater appears to be a white, strong, fascia -like tissue covering the outer layer of the brain.  The function of the dura mater is to protect, surround and support the spinal cord. 
3. The convolutions of the brain are also visible as bumps (gyri) and grooves (sulci). Why might an organ include bumps and grooves?  These bumps and grooves (Gyri and Sulci) allow the cortex of the brain flexibility and separates the four lobes.
4. Dark spider-webby structures are visible. What are these?   The dark spider-webby structures are blood vessels. 
5. The pineal gland is one we may not know about or think about very much. Its function in humans is lesser but as important as in other animals. Contrast the human pineal gland function with that of a reptile or other mammal.   The pineal gland controls the reproduction and circadian rhythms and relates to the instinct debate amongst scientists and philosophers as to whether or not humans even have instincts.  The pineal gland is larger in mammals and reptiles. 
6. Ventricles in the brain are similar in function to ventricles in the heart. What is a ventricle?  The cerebral ventricles are a communicating network of interconnected, cerebrospinal fluid (CSF) filled spaces that lie below the brainstem and forebrain. 
7. The cerebellum only loosely connects to the rest of the brain when the dura is removed. It looks almost like a separate structure. What nervous system functions does it perform? What happens when one drinks too much alcohol in terms of the cerebellum?  The cerebellum regulates motor movements.  When one drinks too much alcohol, the cerebellum  slows down the motor receptors and allows for less balance control. 
8. Compare and contrast the functions of the thalamus and the hypothalamus.   The thalamus is a small olive shaped structure that  serves as a communicator for impulses  in the brain.   It directs sensory input to the cerebral cortex.  The Hypothalamus is located below the thalamus and acts  as a water and hormone monitor as well as a temperature regulator. 
9. Compare and contrast gray matter and white matter. White matter is made of axons connecting difference parts of grey matter to each other.  Grey matter has a pinkish-grey color and contains cell bodies, dendrites and axon terminals of neurons.  This is where the synapses are located.
10. State one thing that surprised you about the structures of the brain you saw at this link.  I am surprised that the sheep brain literally appears to be identical to that of a human brain.  

BRAIN TRICKS

1. Visit this site, http://braintricks.org/index.php. 
2. Choose five of the brain tricks, observe the phenomena. 
1. Color Blindness Test.    This test seemed pretty simple.  I received a score of 100/100 so I’m assuming there wasn’t too many tricks to this game.
2. Hidden Face.   This was also pretty self explanatory to me.  Once you see the face, it’s definitely there, not an illusion. 
3. Color Perception.  This trick was great.  It definitely allowed my eyes to experience this illusion and was surreal almost that this is not what was really there (a green dot circling the “x”, independently). 
4. Black Dot Illusion.  Very similar to the color perception.  The “black blobs” in between the black squares indicate an illusion. 
5. Motion  blindness.  I shared this experience with my four year old son and witnessed that the yellow dots were definitely still present when he was focusing but not when I was.  I became a part of the illusion. 
6. Spinning Image.  This was crazy.  I had to check with friends and family to see if indeed this image was not truly moving.  Once again, just an illusion.
3. For each of the five, describe your experience in a few sentences. CHECK
4. Form a hypothesis about why you perceive the images the way you do? In other words, why would one “see” something that isn’t “there”? (Review hypotheses in Chapter 1.)   Because of  nerve cells in the brain that  correlate with the optima when visualizing an image, sometimes it’s possible that the perception does not communicate with the physical movement of the stimulus source creating an optical illusion.  
5. How would you test the hypothesis?   I would test this hypothesis by evaluating individuals while they experience similar brain tricks just as I just did. 
6. Do you now think differently about how you perceive the world? In other words, can you trust what is there even if you “see it with your own eyes”? Explain in a few sentences.   I’ve always been curious in philosophy with the question “If a tree falls in the middle of the forest and nobody is around to witness, does it make a sound.”  And the answer is, if you want it to make a sound then it did.   And I think it relates to perception as well.  If you want to see something that truly may not be there, then you are choosing to see this image. Close your eyes otherwise.