Lab Project #3: Build a Movable Limb

What causes a limb to move? The movement of bodily parts can be attributed to the bones, joints, muscles, and tendons. And, the occurrence of shifting limbs is also linked to the microscopic processes of neurons carrying action potential to muscle cells and the sliding filaments of actin and myosin units in muscle cells. But, looking at our body from an external perspective and trying to understand these actions can be a little hard to grasp. So, why not break it down into simplest terms with a three dimensional model made out of household materials.
Picture 1: All of the materials I used for this project.

This is a model of a movable limb using the materials: rigid wrap, sticks, Styrofoam ball, red pipe cleaners, and white clay. Starting with the exterior of the movable limb, I decided to work with the arm and I made a mold of my arm with the material, rigid wrap. Next, which is the joint and bones of the arm, I used a Styrofoam ball to represent the joint and sticks from my backyard to stand for the bones. The joint and bones of the arm are very vital to limb movement. Bones support and protect the body, allow
Picture 2: Materials rigid wrap, sticks, styrofoam ball, & red pipe cleaners used as arm form, bones, joint, and muscles.
for flexibility inside the body, store calcium, phosphate, and fat, and produce blood cells. They also perform several processes such as, bone growth and development, renewal of bone, and repair of a fracture. Then, bones are joined at joints, particularly in the arm, at a synovial joint. A synovial joint is filled with lubricant that provides free movement for the bone and muscles attached. As I continued building my model, I inserted the muscle and tendons into my mold. I used red pipe cleaners to represent the bicep and tricep muscle of the arm. And, I used white clay to stand for the tendons. The importance of muscle allows for the body to maintain posture, protect internal organs, and provide heat and
Picture 3: Materials white and yellow clay used for tendon and neuron.
movement. Inside the arm, there are two major muscles that are located within the upper region of it, which are the bicep and tricep. When the arm is straight, the bicep is relaxed and the tricep is contracted, which is displayed in the example of the model. And, when the arm is bent, the bicep is contracted and the tricep is relaxed, also displayed in model. The tendons aid in the attachment of muscle fibers to the skeleton. Along with the model that I created of the interior of the arm, there are also several smaller models that display the different microscopic processes
Picture 4: Model of arm mold, bones, and joint of the movable limb.
that happen inside the muscle cells.

Picture 5: Model of arm mold, bones, joint, muscle, and tendon. The arm is straight, meaning the bicep muscle is relaxed and the tricep muscle is contracted.

This is a model of a neuron using the materials: yellow clay, red and gold pipe cleaners, and blue tube beads. Starting with the neuron, I used yellow clay to represent the cell body and dendrites, which is the center of the neuron and the tiny branches that extend from the neuron. Then, I used gold pipe cleaners to represent the neuron’s axon and blue tube beads to stand for the Schwann cells that cover the axon. Neurons are cells that transmit nerve impulses to parts of the nervous system. And, the structure of the neuron consists of a cell body, which contains the nucleus,
Picture 6: Model of arm when it is bent, where the bicep muscle is contracted and the tricep muscle is relaxed.
dendrites, which receive signals from sensory receptors and other neurons, and an axon, which conducts the nerve impulse. The axon also has Schwann cells that wrap around it, which help protect the axon and carry out the process of action potential, which will be discussed later. In this particular model, there are three different neurons being shown that demonstrate the
Picture 7: Materials white, yellow, & green clay, gold pipecleaners, blue tube beads, and dowels used for potassium ions & gates, neuron & axon background, sodium ions & gates, axon, Schwann cells, and axon's direction of impulse.
direction of nerve conduction, beginning from the sensory receptors within the body’s senses, the sensory neuron (takes information to the nervous system), the interneron (receives information from sensory neuron), the motor neuron (takes information away from the nervous system), and ending with the
Picture 8: Model of neurons and how a nerve impulse is carried.
axon of a motor neuron. As the direction of impulse continues to the axon, this is where action potential occurs.

This is a model of action potential using the materials: yellow, green, and white clay, and a dowel. Starting with the axon of the neuron, I used a dowel to represent the direction of the impulse that was occurring. Then, I used yellow clay for the close-up of the
Picture 9 & 10: Model of action potential as the sodium gates open & close and the potassium gates open & close, changing voltage.
axon. Next, I used the green clay to represent the sodium ions and the sodium gates and white clay to represent the potassium ions and the potassium gates that are within the axonal membrane. Action
potential is the swift change in polarity of the membrane of an axon. The progression of action potential begins with the opening of the sodium gates, where sodium flows into the axon and depolarizes the membrane, creating a voltage change from -65 mV to +40 mV (these numbers signify the electrode inside the axon). Then, ending with the sodium gates closing and the potassium gates opening, allowing for potassium ions to flow out of the axon. This repolarizes the membrane of the axon by changing the voltage from +40 mV back to -65 mV. Action potential can also occur with the assistance of the Schwann cells.

Picture 11: Model of the propagation of action potential across the axon.

This is a model of the propagation of action potential using the materials: gold pipe cleaners and blue tube beads. Starting with the gold pipe cleaners, I used this to stand for the axon of a neuron. Then, I placed the blue tube beads onto the gold pipe cleaners to signify the location of the Schwann cells. In the action of propagation of action potential, the Schwann cells allow for action potential to jump across each one by the created gaps between them (saltatory conduction) in order to continue the process at a rapid pace. The process of action potential also occurs within muscle cells.


This is a model of a muscle cell using the materials: saran wrap, yellow clay, green and red pipe cleaners, and straws. Starting with the sarcolemma, I used saran wrap to represent the muscle cell membrane. Then, I used straws to represent the myofibril. And, I used the green pipe
Picture 12 & 13: Materials saran wrap, yellow & rust clay, green pipecleaners, & straws used for the sarcolemma, sacroplasmic reticulum, myosin unit, t-tubule membrane tubes, & bundle of muscle fibers.
cleaners to represent the t-tubule membrane tubes and yellow clay to represent the sacroplasmic reticulum. Lastly, I used red pipe cleaners to signify the muscle that the muscle cell was going in to. In a muscle cell, the sarcolemma is the plasma membrane of the muscle fiber, the myofibril is a bundle of small muscular filaments that aid in contraction of the
Picture 14: Model of muscle cell.
muscle, the t-tubule membrane is an extension of the plasma membrane that communicates nerve impulses to free calcium ions from the sacroplasmic reticulum, and the sacroplasmic reticulum stores calcium until action potential (conveyed by the t-tubules) causes the release. The muscle fiber goes into the muscle in order to carry action potential throughout the cells, which are stimulated by the axons of motor neurons.

Picture 15 & 16: Materials small red beads, large red beads, and blue pony beads used for actin filaments, actin unit, troponin, and calcium.
The release of calcium from the sacroplasmic reticulum can be displayed from this model using the materials: yellow clay, blue pony
Picture 17: Model of calcium release from the sacroplasmic reticulum.
beads, and a straw. Starting with the yellow clay, I used this to represent the sacroplasmic reticulum. Then, I used the blue pony beads to represent the calcium ions; and, I used the straw to represent the t-tubule. In the action of calcium release, the motor neuron nerve impulses travel to the axon and create a connection to the muscle cell (by way of synapse). The message that is communicated within the t-tubeles of the cell causes the calcium to release from the sacroplasmic reticulum. The calcium is then utilized in the actin-myosin units that cause them to shorten.


Picture 18: Model of single actin-myosin unit.
This is a model of a single actin-myosin unit using the materials: strands of red beads and rust clay. Starting with the red beads, I used this to represent the actin unit and I used the red clay to represent the myosin unit. Actin and myosin are the two major proteins that make up the filaments in myofibrils that make muscle. These units occur together to carry out several processes.

One process is the use of calcium (that is released by action potential in the sacroplasmic reticulum) as it binds to myosin. This is displayed in the following model using the materials: red beads,
Picture 18: Model of calcium binding to myosin.
green pipe cleaners, and different colored, blue pony beads. Starting with the red beads, I used this to represent the actin filament that also has black coloring that represents the myosin binding sites. Then, I used green pipe cleaners to represent the tropomyosin. And, I used the dark blue pony beads to represent the troponin and the light blue pony beads to represent the calcium. The actin protein unit also has sub-protein units called tropomyosin and troponin. The tropomyosin is threaded along the actin unit and the troponin is located amongst the threads at different sections. As calcium is released, it connects to the troponin, which causes the tropomyosin to move across the actin unit, exposing myosin-binding sites. Then, the process of muscle contraction can occur.

This is a model of myosin cross-bridges bringing actin filaments together using the materials:
Picture 19: Model of myosin cross-bridges bringing actin filaments together and shortening the muscle.
green pipe cleaners, small red beads, and rust clay. Starting with the green pipe cleaners, I used this to represent a section of the actin-myosin unit of one myofibril. Then, I used strung, small red beads to represent the actin units and rust clay to represent the myosin units. After the myosin binding sites are exposed on the actin units, the myosin units breakdown energy (ATP) to attach to the sites on the actin, forming cross-bridges. Then, energy is released from the myosin unit that allows for the cross-bridges to change their positions on the actin unit. This pulls the actin filaments to the center of the actin-myosin unit, causing the shortening of the muscle.

The movement of bodily parts can be attributed to the bones, joints, muscles, and tendons. And, the occurrence of shifting limbs is also linked to the microscopic processes of neurons carrying action potential to muscle cells and the sliding filaments of actin and myosin units in muscle cells. In order to understand the movement of the body, I made models of the arm and its basic internal parts, the neuron, the process of action potential, and the muscle cell, and the process of muscle contraction out of household materials. This project was very helpful for my learning style. It gave me a hands-on experience to understanding how the arm was structured and how movement occurred. I was able to finally grasp the processes of action potential and muscle contraction.