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April 7th, 2006

Muscle Anatomy and Physiology Lab.

Peter Brodfuehrer and Will Franklin, Biology Dept. Bryn Mawr College

Introduction to Skeletal Muscles

Skeletal muscle is the type of muscle that we can see and feel. When a body builder works out to increase muscle mass, skeletal muscle is what is being exercised. Skeletal muscles attach to the skeleton and come in pairs -- one muscle to move the bone in one direction and another to move it back the other way. These muscles usually contract voluntarily, meaning that you think about contracting them and your nervous system tells them to do so. They can do a short, single contraction (twitch) or a long, sustained contraction (tetanus).

Parts of a Skeletal Muscle

The basic action of any muscle is contraction. For example, when you think about moving your arm using your biceps muscle, your brain sends a signal down a nerve cell telling your biceps muscle to contract. The amount of force that the muscle creates varies -- the muscle can contract a little or a lot depending on the signal that the nerve sends. All that any muscle can do is create contraction force.

A muscle is a bundle of many cells called fibers. You can think of muscle fibers as long cylinders, and compared to other cells in your body, muscle fibers are quite big. They are from about 1 to 40 microns long and 10 to 100 microns in diameter. For comparison, a strand of hair is about 100 microns in diameter, and a typical cell in your body is about 10 microns in diameter.

A muscle fiber contains many myofibrils, which are cylinders of muscle proteins. These proteins allow a muscle cell to contract. Myofibrils contain two types of filaments that run along the long axis of the fiber, and these filaments are arranged in hexagonal patterns. There are thick and thin filaments. Each thick filament is surrounded by six thin filaments.

Thick and thin filaments are attached to another structure called the Z-disk or Z-line, which runs perpendicular to the long axis of the fiber (the myofibril that runs from one Z-line to another is called a sarcomere). Running vertically down the Z-line is a small tube called the transverse or T-tubule, which is actually part of the cell membrane that extends deep inside the fiber. Inside the fiber, stretching along the long axis between T-tubules, is a membrane system called the sarcoplasmic reticulum, which stores and releases the calcium ions that trigger muscle contraction.

Energy for Muscle Contraction

Muscles use energy in the form of ATP. The energy from ATP is used to reset the myosin crossbridge head and release the actin filament. To make ATP, the muscle does the following:

1 Breaks down creatine phosphate, adding the phosphate to ADP to create ATP

2 Carries out anaerobic respiration, by which glucose is broken down to lactic acid and ATP is formed

3 Carries out aerobic respiration, by which glucose, glycogen, fats and amino acids are broken down in the presence of oxygen to produce ATP (see How Exercise Works for details).

Muscles have a mixture of two basic types of fibers: fast twitch and slow twitch. Fast-twitch fibers are capable of developing greater forces, contracting faster and have greater anaerobic capacity. In contrast, slow-twitch fibers develop force slowly, can maintain contractions longer and have higher aerobic capacity. Training can increase muscle mass, probably by changing the size and number of muscle fibers rather than the types of fibers.

Article from How Stuff Works


Muscle Anatomy and Physiology Lab

Peter Brodfuehere and Will Franklin

Web site describing different muscle types. What Gives Meat it's Color?




  • Prepare slides with PAP pen - draw a rectangle about the size of a coverslip on the slide.
  • Cut at least 3-4 separate thin slices of muscle tissue from the exposed end of the muscle with a scalpel. Lay each slice on your slide with the scalpel.
  • Let the sections thaw for 30 minutes. This will let water leaving the sections evaporate, so the sections will adhere better to the slide.
  • Stain sections: pipet the prepared SDH staining solution over the sections. Each bench will have one or 2 vials containing the solution.
  • Incubate slides for 15 minutes on you lab bench. Observe any changes in overall color during this time.
  • Stop the reaction as follows: wash the solution off the slide with several gentle rinses of water provided in squeeze bottles.
  • Pipet glycerol solution over all sections. Put a coverslip on top of the sections, and dry off the bottom of the slide very well.
  • Examine your slide under the compound light microscope and make the observations and measurements described in the next section.


  • Classify 60 adjacent muscle fibers by differences in STAINING INTENSITY of the cells. Do you have 3 categories? More? Less?
  • Convert your raw numbers into the percentage of cells in each staining intensity category. This is the number you will record in the group table.
  • Measure the cross-sectional diameter of 20 cells in each staining intensity category, using the widest point to measure each fiber. Make these measurements using ocular reticle measurement units.
  • Calculate the mean of your 20 measurements in each staining category. This is the number you will record in the group table.

Fatigue Experimental Protocol:

  • Open “Muscle Fatigue Lab” on the desktop or Bio 102 folder. One channel is the EMG muscle activity from the forearm. Another channel is labeled “grip” and is the trace of the force produced when the hand dynamometer is squeezed. The final channel is a calculated/transformed trace that reflects the overall activity of the raw EMG signal and gives a simpler view of the muscle’s electrical activity.
  • Connect EMG electrodes to your inner right forearm muscles 1/3 distal to your elbow and the ground electrode (green) to your wrist. You will also be using a hand dynamometer which is connected to Channel 2 input on the PowerLab unit.


  • The volunteer should hold the Grip Force Transducer in the same hand with the EMG electrodes and sit quietly.


  • Using only your index finger, squeeze the dynamometer 10 times for 1 s, each time with varying force. Practice before you record your data.


  • Squeeze as hard as possible to produce maximum tension again using you’re your index fingers and hold it for 10 secs. DO NOT LOOK AT THE SCREEN.


  • Rest for 1 minute and repeat maximum squeeze for 20 secs, 40 secs, 1 min, 2 min and 3 min (or until your arm muscles become fatigued). What would happen if you watched the traces while squeezing? Try it!


  • Repeat steps 3-6 with your pinky finger.

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