The Muscular System
The muscular system is responsible for the movement of the human body. Attached to the bones of the skeletal system are about 700 named muscles that make up roughly half of a person’s body weight. Each of these muscles is a discrete organ constructed of skeletal muscle tissue, blood vessels, tendons, and nerves. Muscle tissue is also found inside of the heart, digestive organs, and blood vessels. In these organs, muscles serve to move substances throughout the body. There are three types of muscle tissue: visceral, cardiac, and skeletal.
Visceral Muscle is found inside of organs like the stomach, intestines, and blood vessels. The weakest of all muscle tissues, visceral muscle makes organs contract to move substances through the organ. Because visceral muscle is controlled by the unconscious part of the brain, it is known as involuntary muscle—it cannot be directly controlled by the conscious mind. The term “smooth muscle” is often used to describe visceral muscle because it has a very smooth, uniform appearance when viewed under a microscope. This smooth appearance starkly contrasts with the banded or striated appearance of cardiac and skeletal muscles.
Cardiac Muscle is found only in the heart, cardiac muscle is responsible for pumping blood throughout the body. Cardiac muscle tissue cannot be controlled consciously, so it is an involuntary muscle. While hormones and signals from the brain adjust the rate of contraction, cardiac muscle stimulates itself to contract.
The cells of cardiac muscle tissue are striated—that is, they appear to have light and dark stripes when viewed under a light microscope. The arrangement of protein fibers inside of the cells causes these light and dark bands. Striations indicate that a muscle cell is very strong, unlike visceral muscles.
Skeletal Muscle is the only voluntary muscle tissue in the human body—it is controlled consciously. Every physical action that a person consciously performs (e.g. speaking, walking, or writing) requires skeletal muscle. The function of skeletal muscle is to contract to move parts of the body closer to the bone to which the muscle is attached. Most skeletal muscles are attached to two bones across a joint, so the muscle serves to move parts of those bones closer to each other.
Skeletal muscle cells form when many smaller progenitor cells lump themselves together to form long, straight, multi-nucleated fibers. Striated just like cardiac muscle, these skeletal muscle fibers are very strong. Skeletal muscle derives its name from the fact that these muscles always connect to the skeleton in at least one place.
The kids had a lot of fun with this activity – I hadn’t expected that they would enjoy it so much. In groups of three, students took turns to do a few lifts I first demonstrated. I chose to do bicep curls, bench press, and squats – but any weight lifting exercise will work.
Students should choose weights which are comfortable to use, but heavy enough to do 15-20 reps. Students rotate three times (each time a new exercise is demonstrated) so students have the opportunity to do each task.
- The lifter of each group will slowly lift the weight up and down in a “bicep curl” with their dominant arm.
- The other group members will observe all muscle groups working/moving while the lifter is doing the bicep curls. One member can use a skin-safe marker to circle the muscles that are being used.
- All students should then write down exactly what type of movements the group observed while the bicep curls were happening.
Students should then switch group roles, and then repeat the steps listed while performing a “bench press” exercise with the weights and finally the “squats”.
Encourage students to make a sketch of what they believe the circled muscles should look like after recording their observations and circling the muscle groups that are moving on the arms of the lifters. Students will need to consider where each muscle connects to the bones in order for them to be activated during each different exercise movement.
Muscle Fatigue Lab – How does fatigue affect performance?
I then led the group through a lab activity that is perfect for integrating math skills – graphing, finding mean and range, and finding percent of decrease and increase. I was the timer for the whole group and I trusted each student to count
Each student places their right forearm flat on a table so the back of the fingertips are flat on the tabletop. He/she closes and opens the right hand as fast as possible until the timer says stop, being sure the fingertips touch the palm when closed and the fingertips touch the table when open.
The timer times each trial for 30 seconds and upon calling stop, students record their count on a data table or chart in their notebook. This process is repeated for six 30-second intervals with one 30-second rest interval between the 3rd and 4th trial. After the activity has been completed for the right hand, repeat the steps for the left hand.
Using the data collected students are then instructed to create a graph. The data and graph can then be used to discuss the results of the activity.
Bring it Home
- Calculate your horsepower. Weigh yourself on a bathroom scale (pounds). Measure the vertical height of a flight of stairs (meters). Use a stopwatch to record the time it takes you to walk up the stairs (one step at a time). Calculate your weight in newtons (your weight in pounds multiplied by 4.45). [A newton is a unit of force – in this case, the force of gravity that you must overcome to climb the stairs.] Calculate the work you did climbing the stars in joules (your weight in newtons multiplied by the distance or height of the stairs). Calculate the power in units called watts (work in joules divided by the amount of time it took). Lastly, calculate the horsepower used by dividing the watts by 746 [one unit of horsepower (hp) is equal to 746 watts] .
- Gluteus maximus, soleus, sartorius – why do we call muscles by Latin names?
- Keep an exercise chart for one week. At the end of the week, evaluate your effort. How well are you exercising? Write a good health goal to improve. List three steps you can take to reach your goal.
- Are you an athlete? A swimmer, runner, or basketball player for example. Research the muscle groups that are most used by athletes in your sport of choice and write a 5-paragraph essay describing how these muscles are used and what one can do to strengthen these muscles. This activity choice will count for two points.
- What is muscular dystrophy?
- Present a simple exercise routine done to your favorite music.
- Interview a coach and ask about sports-related injuries to the muscular system. Share what you learned with the class.
- Take a poll. Ask your friends and family how much time they spend on daily exercise. Create a graph to share the results.
- Learn how to control the muscles in your face. Find a diagram online or in a reference book of the facial muscles. What muscles do you use to: a) open / shut nostrils, b) pull scalp back / down, c) pull ears back, d) raise ears, e) open mouth wide, f) wink with one eye, then the other, g) pull top lip down, and h) pull mouth corners up / down.
- Cut apart a chicken leg (drumstick and thigh still attached) and carefully observe how they are attached to the bone. Also look at the joint. Sketch and label in your notebook
- If you and your child think of other activities, go for it!!
My kiddos wanted to create a skit to share what they had learned about the importance of dynamic stretching before exercise as well as what to do in case of a sports related injury. Here is their video that I originally posted to Facebook:
Next week in STEM Club, we will explore the Digestive System.