Reflex Lab

One of the greatest things about scientific education is the ability to conduct experiments in order to gain a deeper understanding of the material. To further our understanding of the nervous system, our class recently conducted a lab experiment to measure reflexes that occurred after nerve stimulus. This lab measured two main types of reactions: voluntary and involuntary. Voluntary reactions occur after conscious thought while involuntary reactions occur after subconscious signals are received. To measure these reactions, we had a test subject undergo a series of six tests, four that measured involuntary reactions, and two that measured voluntary reactions. To gain a more accurate understanding of the differences between the two types of reactions, we measured not only the amount of nerve activity after each stimulus, but also the time lapsed between the stimulus and the reaction itself.


To set up the lab, we attached three electrode tabs to the subject;  a black tab (ground) was placed on the calf area, while both the green (positive) and red (negative) electrode tabs were attached to the quadriceps, with the red tab more proximal to the hips than the green tab.

                                        

                                         

The first test administered measured a voluntary response; the test subject sat on a desk with their eyes closed, and a hammer was struck against the desk, generating a loud sound. After hearing this sound, the test subject's leg rapidly lifted into the air. The nerve activity was measured on the computer system, and the time between the hammer striking the desk and the reaction itself was measured to demonstrate a specific reaction time of .23 seconds.

                         

During the second test, the involuntary reflexes of the patellar tendon were measured. To collect this data, the test subject became relaxed, again with closed eyes, and was tapped with a small mallet on a contact point of the tendon. The nerve activity of the patellar tendon in the quadriceps was measured, as well as the time that lapsed between the initial contact and the reflex that occurred, .07 seconds.

                         

The third test administered measured not only reflexes, but also reinforced reflexes. For this test, the subject sat with eyes closed, as in the other tests, but also hooked their hands together at chest level (like one would in a traditional choir). As in Test 2, the patellar tendon was struck with a small mallet, however, every time a reflex occurred, the subject was asked to pull their hands away without actually breaking the connection between their hands. This movement reinforced the reflex that was visible in the legs. Again, both nerve activity and time between the stimulus and reaction were recorded, this time being .04 seconds. 

                          

Test 4 was a repetition of Test 1, again measuring voluntary reaction, however, this test used a larger hammer to generate the sound. The reaction time in this test was equal to .22 seconds.

                         

Test 5 was also a repetition of Test 2, the difference being the use of a larger mallet to administer the strike to the patellar tendon. The reaction time from this test was .04 seconds.

                         

The same procedure was followed for Test 6 as was followed during Test 3, the difference being the size of the mallet used during the test. For Test 6, a larger mallet was used to strike the patellar tendon than the smaller mallet used during Test 3. The reaction time for this test was .04 seconds.

                          

To visualize and more closely compare the reaction times as well as the nerve activity, the data from each test was organized into the following graphs:

It is very likely that the reaction time was slower during the voluntary tests due to the fact that there was no direct stimulus to the nerves, only voluntary instinct. The subject had to process the sound and think about moving their leg before any type of reaction ever occurred, while the involuntary tests interacted with the nerves directly, forcing the subject to move before they even had a chance to voluntarily process the idea that a stimulus had occurred.  

It was very interesting to visually picture the electrical activity of nerves, as well as analyze why reaction times differ depending on the type of reaction caused through nerve stimulus. 

Sheep Brain Dissection

As the class began to learn more about nerves and the nervous system, we had the opportunity to look at a sheep's brain, and through the dissection process, we were able to understand its basic anatomy. To maximize this learning opportunity, we dissected three brains and cut them on three different planes: saggital, frontal, and transverse.  During this dissection lab, we were asked to label pictures of the brain, which can be seen below.

The Effects of Heroin on the Brain

As we dig farther into neurons and their physiology, we are beginning to look at how they function in the brain. While doing this, our class was assigned to select a research topic that would enhance our understanding of neuron functionality. For this assignment, I chose to research how heroin affects the brain. My presentation on this topic can be found here; I hope you enjoy it!

Neurophysiology

Neurophysiology is a very interesting subject that works with three main components: neurons, nervous systems, and nerves. Today, we are going to look at how they function, beginning with the anatomy of the neuron.

https://upload.wikimedia.org/wikipedia/commons/6/6d/GolgiStainedPyramidalCell.jpg

The neuron is a cell, and so it has many common components such as a nucleus, cell membrane, cell body, and different channels that ions can travel through. The neuron works to communicate signals to other neurons, muscles, and even glands. When they communicate, the signal they send causes the muscle to contact, the gland to secrete, or the next neuron to continue passing the signal through the nervous system. Neurons come in many shapes and sizes, however, all neurons have dendrites and one axon that extends from the cell body, a receptive portion, and a signaling portion.

The axon acts as the conducting or transmitting portion of the neuron, passing the signal along to the next neuron through the axon terminal and synapse. The axon connects to the cell body through the axon hillock. Axons can be from 1-2 inches to longer than a meter.

The cell body acts as a communicator between the dendrites and the axon. As the signal is received through the dendrites, the cell body passes it along to the axon. The cell body is also the main nutritional and metabolic portion of the cell.

The dendrites act as the cell receptors, receiving signals from other neurons and passing those signals through the cell. The flow of energy is directional in neurons, flowing from the dendrites, through the cell body and axon, into the next cell.

Some axons are covered in insulation bodies called myelin sheaths. These sheathes are made when Schwann cells wrap around the axon, releasing cytoplasm as it compresses in a spiral-like structure. The spaces between these sheaths are known as nodes of Ranvier. These nodes occur between every sheath, and allow ions to flow across the membrane.

There are four main channel types within the nervous system: the Sodium leak, Voltage Gated Na+, K+ Potassium Leak, and Voltage-Gated K+ channels. These ion channels are embedded in the neuron membrane, and work to control the movement of ions across the membrane. They are selective, regionally located, functionally unique, and either passive or active. Without these channels, there would be no possibility of neuron excitability. 

Ions channels are selective, in that the ions they permit to cross the membrane must fit a certain criteria. The ion must have a certain size, charge, and must attract and hold a certain level of water. These standards vary between the different channel types. 

There are also active and passive channel types. Active channels open and close, while passive channels are always open and allow ions to flow freely across the membrane. 

Some active channels have gates that are controlled by voltage; membranes with more positively concentrated ions on the outside and more negatively concentrated on the inside create membrane potential, or resting potential, producing a voltage that opens the channel. Channels can also be opened by chemical processes. Neurotransmitters can bind to certain active channels and force them open, allowing ions to travel through. 

Different ion channel types can be found on different parts of the neuron. Passive channels can be found on the dendrites, cell body, and axon; chemically gated channels can be found on the dendrites and cell body; voltage gated channels can be found on the axon hillock, unmyelinated axons, and the nodes of Ranvier. 

The Sodium/Potassium pump works to keep a balance of sodium and potassium inside and outside of the cell. The pump works with an active process involving ATP hydrolysis, transforming ATP into ADP+P, which allows potassium to enter the cell and forces sodium out. 

Resting potential, or RP, occurs when the inside of a neuron is more negative (-70mV) than outside of the neuron membrane. No change in voltage will occur over time, and the sodium and potassium will not reach equilibrium, as the outside of the neuron will have more sodium and the inside will have more potassium. 

Synaptic potentials occur at -55mV, when a receptor on the dendrite receives a signal sent by the axon terminal. Such signals are referred to as neurotransmitters. When neurotransmitters are received, other molecules are permitted to pass through, such as Na+. mV will increase for a short time, while this potential is active, and then return to normal when it is no longer needed.

Action potentials occur during a brief reversal of membrane polarization, in which mV increases  suddenly and greatly (-70mV to 30mV). In this type of situation, Na+ is allowed to travel into the membrane, and K+ is forced out. This potential only occurs in the axon, and is commonly known as a nerve impulse.

Thanks to nerves and their amazing communications, thoughts like this:

http://41.media.tumblr.com/tumblr_mbv4c62Wgu1rhx82io1_500.jpg

can turn into actions, like this:

https://s-media-cache-ak0.pinimg.com/236x/8d/8f/8f/8d8f8fc158f257f1ed778f915f579d33.jpg

EMG Chewing Lab

Today, we are going to explore a lab that was conducted in class this week. The goal of this lab was to monitor the electrical activity of the masseter muscle as different foods were eaten, and discover which foods require the most electrical activity. To accomplish this, a group member attached monitors to their cheek and forearm, and ate four different foods. For a constant variable, we also tracked the electrical activity of the jaw when it was at rest and when it was clenched. 

As the monitor collected data, it recorded it in a chart where wavelengths were visible and could be measured. These charts can be seen below.

Penut Butter and Jelly Sandwich Chart

 Cookie Chart

Ruffles Potato Chips Chart 

Oreo Ball Chart

 Compiled mV Data 

Relaxed Jaw/Clenched Jaw Chart

 To find the delta mV, we measured the Maximum mV of a given wave and subtracted the Minimum mV from it. The resulting number was then graphed. We repeated this process for the constant variables and the other foods.

The graph below illustrates the compiled data from the experiment.

As you can see from the graph, the peanut butter and jelly sandwich required the most electrical muscle activity, 0.538 mV, while the chips required the least amount of electrical activity, 0.38 mV.  I believe this was the case as a result of the textures of the foods. The Oreo ball and PB&J were much "gooey-er" than the other foods, which were light and crunchy. More effort was required to break down the softer, stickier substances than the cookie and chips, resulting in more electrical use.

The results from this lab were very different than my hypothesis- the complete opposite, in fact. I thought that the chips would require more electrical activity, as the initial bite is more difficult than the initial bite of the PB&J. I did not take into account, however, the following bites. The chip became easier to chew the longer it was in the subject's mouth, while the PB&J only varied slightly. It is also more difficult to complete the bite through a sticky substance than it is to take a quick, sharp bite from a chip, which I had not thought about, either. It would be very interesting to repeat this lab with different, more diverse foods, such as steak and raw carrots. This would show more varying results than those reflected in the original experiment.

Thanks for joining in the exploration of electrical muscle activity!

Muscle Anatomy and Physiology Model Building

Hello everyone! Today we are going to discuss muscle anatomy as well as the anatomy and physiology of the neuromuscular junction. 

First up is the skeletal muscle anatomy, as can be seen in the illustrations below. The first picture shows the muscle in its entirety while the second depicts a zoomed-in view of the myofibril. 

As you can see, each part of the muscle anatomy is composed of bundles of fibers that work together. This is a very general description, however, it can be broken down to the parts labeled above.

Next is the anatomy and physiology of the neuromuscular junction. In basic understanding, the neuromuscular junction is where a motor neuron can transmit a signal to the muscle fiber, which then causes the muscle to contract. Just like in the muscle, there are multiple components to this junction. 

To begin with, calcium enters the neuron through the voltage-gated calcium channel. This begins a process that results in the secretion of a neurotransmitter, acetylcholine, from the axon terminal. The acetylcholine travels across the synapse until it is intercepted by the acetylcholine receptors within the muscle cell membrane. The acetylcholine causes sodium ions to passe through the neurotransmitter-gated channel in the acetylcholine receptors, and into the muscle cell. Once it has done its job, the acetylcholine is broken down by an enzyme called acetylcholinesterase. This prevents the muscle from overcontracting. As the sodium ion passes through the neurotransmitter-gated channel, it depolarizes and excites the muscle cell membrane upon entrance. The muscle then contracts due to this impulse, and the neuromuscular junction has served its purpose, for the time being.

To make this model, I used styrofoam, a funnel, and "I Love Lucy"'s Vitameatavegamin candies.

Check out a video of the neuromuscular junction model here: http://youtu.be/Vt8lekZoBUI.

Thanks for joining me in this lesson about muscle anatomy and physiology!

Bone Growth, Development, and Remodeling

Bones are very interesting in both their growth and function, as well as their recovery after damage has occurred. We are going to explore this further, beginning with bone growth and development.

Bone Growth and Development Overview
When babies are born, their skeletal system contains 300 components. These components are actually pieces of cartilage, which undergo a process called ossification, that allows them to become bone. The bony skeletal structure begins to develop at 8 weeks, endochondral ossification begins at the second month, and bone growth continues even after birth.

Bony skeleton development: 

http://images.agoramedia.com/wte3.0/gcms/fetal-development-skeletal-system-article.jpg

Cartilage contains no blood vessels or nerves, and are surrounded by perichondrium, which prevents outward growth. Some of the cartilage remains, however, such as that found in the nose and ear. Cartilage can be classified as hyaline, elastic, or fibrocartilage. Matrix is secreted both inside and against the outside of the bone, through appositional and interstitial processes. This calcifies, or hardens the bone. Cartilage calcifies during normal bone growth, as well as during old age, which causes arthritis.

The pieces that do ossify often fuse together, creating a skeletal system of 206 bones by the end of development. Bones can be classified into two categories: axial skeleton and appendicular skeleton. The axial skeleton contains the bones of the skull, vertebral column, and rib cage. The appendicular skeleton contains the bones of the upper and lower limbs, as well as the shoulders and hips. Bones can also be classified as long bones, short bones, flat bones, and irregular bones. Long bone growth generally stops around the end of puberty, which prevents you from getting taller.

Fetal skull before fusion:

http://bio.sunyorange.edu/updated2/embry.html/2.The%20Skeletal%20System_files/45%20FRONTAL.jpg

Skull after fusion:

https://shortnotesinplasticsurgery.files.wordpress.com/2012/04/1289-and-1290.jpg

The Ossification Process 

There are two types of ossification: intramembranous ossification, which replaces the thin connective tissue membrane with bone, and endochondral ossification, which replaces fetal cartilage with bone. Both types, however, rely on the thyroid hormone calcitonin for the regulation of calcium metabolism.

In bone production, there are three really important cells to consider: osteoblasts, osteoclasts, and osteocytes. Since your bones are always either growing or adapting to support your body, there are cells that will actually destroy bone, and others that will repair the bone to support its new requirements. Osteoclasts originate in bone marrow, and move to the bone surface where they will eat away old bone or protuberances that are out of place. Osteoblasts also come from the marrow and make their way to the surface to fill in cavities and restore bone. After their job is done, they flatten and line the surface of the bone. They then work to regulate calcium, as well as activate osteoclasts through the production of special proteins. Osteocytes come from osteoblasts and can be found inside the bone. As the osteoblasts build the bone, some surround themselves with new material while extending "arms", called dendrites, to other osteocytes. Osteocytes sense pressures and cracks, and help direct osteoclasts to where the bone needs to be dissolved.

The process of ossification:

http://skeletalsystemdev.weebly.com/uploads/7/0/4/3/7043675/5513674_orig.jpg?467

Diagram of osteoclasts, osteoblasts, and osteocytes in action:

http://www.nature.com/bonekey/knowledgeenvironment/2012/120229/bonekey201236/images_article/bonekey201236-f1.jpg

Diagram depicting bone growth and remodeling:

http://classes.midlandstech.edu/carterp/Courses/bio210/chap06/Slide17.JPG

And there you have it: the background of bone growth, development, and remodeling!