LAB 6 SMOOTH MUSCLE; AUTOMATIC ACTION

• Procedure

  1. Pith a frog, sit open the abdomen and expose the stomach

  2. Place the frog on a frog board, and secure the limbs by means of pins or pieces of string

  3. Attach the hook of the muscle lever to the cardia of the stomach taking care that the muscle lever is in a horizontal position and that the stomach is not stretched too much

  4. With a very slow drum, take at least normal tracings

  5. After obtaining normal tracings, drop about 5-8 drops of acetylcholine or acetecholine solution on the surface of the stomach and note the appearance of the tracings as well as the appearance of the stomach

  6. At the height of the tracings, drop the same amount of adrenaline solution on the surface of the stomach and again note any change in the tracing and in the appearance of the stomach

  7. Remove the smoked paper from the drum and label the tracings
• Types of smooth muscle

  • Visceral smooth muscle
  • Multi-unit smooth muscle
• Automaticity in visceral smooth muscle is due to its unstable membrane potential
• Smooth muscle is differentiated histologically from skeletal muscles in that it lacks visible cross-striations
• Visceral smooth muscles react more to chemical or neurohormonal forms of stimuli rather than electrical stimuli
• Visceral smooth muscle is characterized by having an unstable membrane potential
• In enervated preparations, the membrane potential averages -50 mV
• Smooth muscles in general possess plasticity not shown in this experiment
• Preparation


  Differentiate between smooth and skeletal muscles histologically and physiologically
• Materials and equipment

  • Stimulating and recording apparatus
  • Muscle lever
  • Adrenaline 2:10,000 solution
  • Acetylcholine or acecholine solution
• Visceral smooth muscles may possess activity in the absence of nervous stimulation
• Experiment 6

  1. To find out some of the properties of smooth muscles that tend to distinguish them from the other types of muscles

  2. To find out how smooth muscles are able to maintain a certain degree of tone