Reflexes Lab

A sensory neuron carries the message from the receptor to the central nervous system (the spinal cord and brain). A motor neuron carries the message from the central nervous system to the effector. For instance, in the knee-jerk reflex arc the sensory

neuron directly connects to the motor neuron in the spinal cord.

Reflexes tested:

The photopupillary reflex is a reflex that adjusts the size of the upil in order to adjust for the varying degree of light in the area. To test this, we had a classmate cover his eye and cover it. After 5 minutes he uncovered his eye and the results are as follows:

The reason the response occurred was because the eye detected the intensity of the light and corrected for it, allowing less light into the eye. This ultimately reduced the stress on the eye.

The knee jerk reflex is a sudden involuntary forward movement of the lower leg that can be produced by a firm tap to the tendon located just below the kneecap. The term is loosely applied to any muscular response or belief that is automatic rather than thought. To test this we tapped our classmates knee. The results are as follows:

The reason this response occured was due to the pressure on the tendon. Remember that the knee is like a lever, and once the tendon is pressed in, it shortens, pulling up the knee.

The blink reflex is an involuntary blinking of the eyelids elicited by stimulation of the cornea (such as by touching or by a foreign body), though could result from any peripheral stimulus. To test this reflex we had our classmate hold surran wrap up by his face and stare at us throwing cotton balls at him, the results were as follows.

The results were due to speed and direction of the objects we were throwing at him. If we were to throw the cotton balls at his chest, he would likely not blink.

The plantar reflex is a superficial reflex obtained by stroking the skin on the lateral edge of the sole of the foot, starting at the heel advancing to the ball of the foot then continuing medially to the base of the great toe. The normal response is flexion of all the toes. On our test subject, she did not flex her toes. The reason she did not flex was likely due to the absence of the nerve responsible for the action in her foot

Finally, we tested our somatic nervous system by trying to catch a ruler as it fell

Our response times were as follows:

As shown in the graph, when asked to text while trying to grab the ruler, reaction times were more than doubled. This was because we cannot physically do two things at once, instead, we can only switch off from one task to another very rapidly.

Brain Dissection Analysis

In this lab, we dissected a sheep brain. As we dissected the brain, we followed certain guidelines. As a part of these guidelines, we had to answer questions as we completed each step. The following are the guideline questions and my appropriate responses:

Question 1:  Take a picture with your pins in place.  Draw a detailed sketch of the brain and label each of the structures you just identified on that paper.   

Question 2:  What is the function of each of these structures?  Make a table that describes each of these parts and their functions.

Cerebrum-  Allows for a higher level of thinking, such as emotions and thought and action.

Cerebellum- receives information from the sensory systems, the spinal cord, and other parts of the brain and then regulates motor movements

Brainstem-  functions include regulation of heart rate, breathing, sleeping, and eating

Question 3:  What is the function of myelin in a neuron?

Myelin helps the neuron conduct its electrical signal faster by decreasing the channels the action potential has to cross. Imagine taking a piece of paper (representing an axon) and folding it into thirds. The middle portion is the ‘myelin’. Take the the two ends that are not the myelin and connect them. This is essentially the space that the electrochemical signal now has to travel due to the myelin.

Question 4: Take a picture with your pins in place.  Draw a detailed sketch of the cross-section and label each of the structures from the table above.

(picture taken after longitudinal cut of the corpus callosum)  

Question 5: What is the function of each of the structures you pinned in Step 8?  Make a table with the structure name and the function (written in your own words).

Thalamus (Yellow) - works to correlate several important processes, including consciousness, sleep, and sensory interpretation

Optic nerve (Green) - to transfer visual information from the retina to the appropriate vision centers of the brain via electrical impulses (right eye to left brain and vise versa)

Medulla Oblongata (Pink) - regulates breathing, heart and blood vessel function, digestion, sneezing, and swallowing

Pons (Purple) - control center for important nerves in the body

Midbrain (Blue) -  the portion of the central nervous system associated with vision, hearing, motor control, sleep/wake, arousal (alertness), and temperature regulation

Corpus Callosum (Red) -  to hold both hemispheres together

Hypothalamus (Brown) - the portion of the brain that regulates hormones

Question 6:  Make a detailed drawing of your cross section (of the cerebrum), and also take a picture.  Shade the gray matter and white matter to distinguish between them in your drawing.  Label the gray matter and white matter in your drawing.

And now time for the fun part, my personal perspective on the lab:

During this lab, I was the one who actually performed the cuts. First we cut through the corpus callosum, the tissue that holds the hemispheres together. I then proceeded to cut the brainstem in half. After doing so, we identified and labeled the structures in question # 5. After identifying the structures, we removed the pins and cut the brain once more across the hemispheres to reveal the grey and white matter.

I really enjoyed this dissection as we got to relate it back to our previous notes. For example, we had recently learned about myelinated vs unmyelinated nervous cells and their roles in the brain. Another example is the the identification of the different portions of the brain. To be honest, this was one of the more gratifying things about the dissection as the group as a whole was able to use anatomical terms we learned from first semester (such as anterior and posterior) and apply them in the dissection. Although the material may not have been taught in correlation to the specific dissection or what have you, we were still able to connect the major themes from the lectures. Due to the relatively short nature of the dissection, there is little more to connect with. However, the lab was still very interesting as we got to dissect a friggin brain!