LAB 7 NERVE FUNCTION AND FACTORS AFFECTING NERVE CONDUCTION

• Experiment 7

  Nerve function and factors affecting nerve conduction
• Chemical stimulation

  Cut off the portions previously stimulated. Apply NaCl crystals on the end of the nerve and note the results. Apply 1% HCl on another preparation and note the result
• Electrical stimulation

  Apply mild faradic and galvanic shocks on the nerve and compare the results
• Materials and equipment

  • Stimulating and recording apparatus
  • Two frogs
  • Ether
  • 2% novocaine
  • NaCl crystals
  • 1% HCl solution
• Mechanical stimulation


  Pinch the free end of the nerve with forceps and note the results
• Effect of cold on nerve conduction

  Lay the nerve over a vial containing water and ice and test for conduction
• Procedure


  1. Different forms of stimuli

  2. Mechanical stimulation

  3. Thermal stimulation

  4. Chemical stimulation

  5. Electrical stimulation

  6. The influence of chemicals on nerve conduction

  7. Effect of cold on nerve conduction
• Thermal stimulation


  Apply a hot glass rod to the nerve and note the results
• The influence of chemicals on nerve conduction

  Apply ether and novocaine on the nerve and test for conduction
• Preparation


  Enumerate the different physiological properties of nerves
• The sciatic nerve is a mixed nerve with motor and sensory fibers. Motor fibers belong to nerve fiber type A, least susceptible to anesthetics like ether and novocaine. Sensory fibers belong to nerve fiber type C, most susceptible to anesthetic agents
• Conduction of an impulse in a nerve may be affected by certain chemical substances. The degree of effect depends on the type of nerve fiber involved
• Nerve stimulation - Mechanical

  Pinching the nerve causes localized tissue destruction at the point of stimulation
• Cold temperature has very little effect on myelinated nerves. The sciatic nerve, being myelinated, is less susceptible to cold temperatures due to myelin acting as a good insulator protecting against temperature variations
• Nerve stimulation - Chemical with 1% HCl solution


  Dipping the nerve fiber in a solution of 1% HCl causes more pronounced and longer-lasting fibrillar twitching
• The response of the sciatic nerve varies depending on which effect predominates between motor and sensory fibers
• Nerve stimulation - Chemical with NaCl crystals


  Application of NaCl crystals on the surface of a nerve fiber causes slight fibrillar twitching of the muscle, lasting longer than mechanical and thermal stimuli. Disadvantage: variable results due to unfixed chemical amount
• Effect of cold on nerve conduction
• The influence of chemicals on nerve conduction
• Nerve stimulation - Electrical with mild faradic and galvanic shocks


  Mild faradic and galvanic shocks produce strong contractions of the muscle. Faradic current response occurs or is stronger when the circuit is "broken," while galvanic current response occurs or is stronger when the circuit is "made"
• Nerve stimulation - Thermal


  Application of a hot glass rod on the surface of a nerve fiber causes a slight contraction of the muscle, transient due to local coagulation of proteins interfering with membrane permeability