Exercise 28 - Muscle and Skeletal Systems

STUDENT OBJECTIVE

Students study muscle at the microscopic, gross, and physiological levels. They also study bone at the microscopic and gross levels, and compare endoskeletons with other types of skeletal systems.

EQUIPMENT AMOUNT (Class of 24 with 8 groups)
Compound microscope 1/student
Stimulator and electrode 1/group or lab
Kymograph or recorder, stylus or transducer 1/group or lab


MATERIALS

Earthworms, live 1/group
Frogs, live 1/group or lab
Cheesecloth, 10 cm ´ 10 cm squares 1/group or lab
Femur clamps for frog 1/group or lab
Kymograph accessories 1/group or lab
Ring stands 1/group or lab
Fetal pigs from previous exercise 1/student
Dissecting trays 1/student
Dissecting instruments set/student
Fresh beef bones cut longitudinally Demonstration
Dry mammalian long bones 1/group
Exoskeleton examples (insects, millipedes, crabs, spiders) several/lab
Endoskeleton examples (human, frog, bird) 2/lab
Prepared slides (can be shared to reduce costs)
  Skeletal muscle, longitudinal section (CBS#H1310)* 1/student
  Smooth muscle, longitudinal section (CBS#H1260)* 1/student
  Earthworm, cross section (CBS#Z1250)* 1/student
  Bone (CBS# 780)* 1/student
  Cartilage, hyaline (CBS#680)* 1/student
  Grasshopper, cross section (CBS#Z2045)* 1/student

SOLUTIONS

Amphibian Ringer's solution

PREPARATION

Four Weeks before Lab

Order frogs so that they arrive the week prior to the lab. Paper and ink for the kymograph should also be ordered as needed.

Week before Lab

  1. A medium-sized container is needed for holding the frogs when they arrive. A lid for the container can be fashioned out of screening. Place container in a cool part of the lab. Do not use frogs with red-leg infections (those with red skin on the ventral surfaces of thighs). Change water daily.

  2. The setup for studying muscle contraction should be checked for malfunctions and a trial demonstration made at this time. If students do the muscle experiments, additional setups will be needed.

  3. Amphibian Ringer's solution preparation:

    0.14 g KCL
    6.50 g NaCl
    0.12 g CaCl2
    0.20 g NaHCO3

    Dissolve salts in 750 ml water and dilute to final volume of 1 liter. Store in several small (200 ml) containers with caps.

One Hour before Lab

Frogs should be pithed just prior to using. Throughout the entire procedure, keep the specimens moist by covering with a cheesecloth soaked in Ringer's solution.

ANSWERS TO CRITICAL THINKING QUESTIONS

  1. Neuromuscular excitability is extremely sensitive to calcium. Hypercalcemia would lead to increased heart (cardiac muscle) irritability and may cause life-threatening cardiac arrhythmias. Hypocalcemia would depress the heart. Also very low Ca++ levels would increase excitability of the neurons (due to increased Na+ permeability). Peripheral nerves may discharge impulses spontaneously, leading to tetanic muscle contraction.

  2. Weight. Flight requires a light skeleton. The bones of birds are incredibly light and delicate. They are hollow with an internal framework of bars giving structural support. The spaces are filled with air rather than marrow.

  3. By closely studying the bones to determine possible function (i.e., weight bearing, etc.), analyzing bone ends to determine joint structure and range of movement, and analyzing sites of muscle attachment, scientists can deduce a theoretical body shape. Computer mirror-imaging can help fill in gaps and computer-assisted sterolithography can guide a laser to sculpt a model from resin.

SUPPLEMENTAL MATERIALS

Bio Sci II, videodisc has many useful images of muscles and bones. Dubuque, IA: Wm. C. Brown Publishers. See appendix.

Muscle: Dynamics of Contraction, 21-minute film. Chicago, IL: Encyclopaedia Britannica Educational Corp.

The Skeletal System and Its Function, slide set. West Los Angeles, CA: Science Software Systems, Inc. #200-0360

The Skeleton, 12 minute film. Chicago, IL: Encyclopaedia Britannica Educational Corp.

What Is a Muscle, 15 minute video filmstrip. Burlington, NC: Carolina Biological Supply. #49-8349

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