Monday, July 7, 2008

Unit 3 Lab Project: Build a Movable Limb


The purpose of this lab was to
1. Create a movable limb
2. To demonstrate how muscle action is initiated
3. To demonstrate the process by which the muscle actually contracts

These 3 items were to be built using regular household items. I ended up using 4 models to demonstrate all of the details that were required.

Limb parts listed with materials that represent each.

Movable Limb
Biceps brachii - artificial evergreen branch
Humerus - cinnamon stick
Radius - cinnamon stick
Ulna - cinnamon stick
Capitulum - small, sparkly gold ball covered with masking tape
Trochlea - small gold bell covered with masking tape


Building the limb:

A movable limb - as the biceps brachii contracts, the radius (along with the ulna) moves toward the humerus:

Muscle fiber with axon
Sarcolemma - purple plastic wrap
T tubule - thin green paper-coated wire
Myofibrils - glue sticks
Axons - brown pipe cleaners
Schwann cells - oval wooden beads


Building the muscle fiber and axon:

The muscle fiber with axons:

Note: After uploading this image, I realized I made a mistake on this one. I should have had one axon with several axon terminals reaching to the 2 muscle fibers.

Lastly, a basic image of one myofibril showing how the individual sarcomeres line up along the length of it:

Myosin - artificial evergreen limb with masking tape around the center
Myosin head - artificial evergreen needle
Actin - natural jute rope
Troponin - cloth rose
Tropomyosin - gold bead rope
Sarcoplasmic reticulum - green jute rope
Calcium ions - red hearts


Building the sarcomere:

The sarcomere:

The sarcoplasmic reticulum in close vicinity to the sarcomere. In the photo on the left, calcium is stored in the sarcoplasmic reticulum. The photo on the right shows the release of the calcium ions from the sarcoplasmic reticulum:

Calcium ions combine with troponin on actin:

Myosin heads attach to actin in the photo on the left. In the photo on the right, the power stroke of the myosin heads moves the actin filaments past the myosin filaments. In this way, the actin filaments approach one another and the sarcomere shortens. As the sarcomeres of a myofibril shorten, the myofibril shortens. This is how a muscle contracts:

Action potential
Axonal membrane - wooden blocks
Sodium ions - white textured balls
Potassium ions - wooden balls
Gated sodium ion channel - green lettered wooden blocks
Gated potassium ion channel - red lettered wooden blocks


Resting potential:

Action potential begins as gated sodium ion channels open, sodium ions move from outside of the axon to the inside. The action potential propagates along the axon as the sodium channels open from left to right, sodium move inside the cell, and the inside of the cell changes from -65mV to +40mV. This voltage change also moves from left to right, which is the propagation of the action potential:

Action potential ends as the voltage changes back from +40mV to -65mV. This change happens as the gated potassium ion channels open to allow potassium ions to move from the inside to the outside of the axon. This voltage change also occurs from left to right along the axon:

The four models provide above detail several important functions of our body. First, the movable limb model shows how the contraction of a muscle can move a limb around a joint. Second, the model of the muscle fiber shows the basic structures that are involved with muscle contraction. It also lays the groundwork to understand how sliding of the filaments of the sarcomere result in contraction of the muscle fiber. The third model details the structures of the sarcomere and shows how calcium ions are released from the sarcoplasmic reticulum and then combine with troponin on the actin filaments. It also shows how the myosin power stroke slides the actin filaments towards each other to shorten the sarcomere. And the last model illustrates the movement of sodium and potassium ions across the axonal membrane. The movement of these ions contributes to the action potential.

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