Endocrine Lab Report Essay

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Earthworm Smooth Muscle

In this experiment, contractions of the earthworm gut are measured in an organ bath with a force transducer. The effect of neurotransmitters and ionic concentrations on contraction strength and rate will be investigated.

Written by staff of ADInstruments
With acknowledgement to: Dr. Stuart I. Cromarty, Department of Natural Sciences, Assumption College, Worcester, MA, USA.


Smooth muscle is one of three muscle fiber types found in animals. Unlike skeletal and cardiac muscle cells, smooth muscle cells are not striated, and have single nuclei. Smooth muscles are typically under control of the autonomic nervous system, and do not contract voluntarily. Smooth muscle contracts slowly,
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Dissection: exposing the gut

1. Remove the earthworm from the ethanol and place it on a dissection tray.

2. Pin the earthworm to the tray using one pin on either end of the worm.

3. Moisten the earthworm with room temperature earthworm saline. You must keep the worm moist at all times during the dissection.

4. Locate the clitellum (copulatory organ); this structure is closest to the anterior of the earthworm.

5. Using fine pointed scissors, carefully make a shallow incision in the clitellum. Make this incision to the side of the midline; this techniques will prevent you from cutting into the gut. NOTE: It is essential not to cut deeply during the dissection; you will damage the gut tissue. If you tear the gut, obtain another earthworm and start over.

6. Continue cutting the skin of the earthworm towards the anterior end. It is best to use an upward-pointing direction with the scissors. As you cut the skin, pin back the skin to expose the gut.

7. When you have successfully opened the earthworm, inspect the gut and moisten the worm with earthworm saline. If the gut is not damaged, continue with the next step.

Dissection: removing the gut

1. With the gut exposed, use a blunt probe to dissect away the septa that connect the underside of the gut to the body wall. You only need to expose 3-5 cm of the anterior gut.

2. When the gut is loosened from the body wall, again
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