Prof. Enyin Lai laienyin@zju

1. Skeletal muscle contraction and sciatic nerve Prof. Enyin Lai laienyin@zju.edu.cn

2. Muscle Types of muscle: • Skeletal muscle骨骼肌 • Cardiac muscle 心肌 • Smooth muscle平滑肌

3. Muscle contraction • The sliding filament mechanism（肌丝滑行机制）, in which myosin（肌凝蛋白） filaments bind to and move actin （肌纤蛋白）filaments, is the basis for shortening of stimulated skeletal, smooth, and cardiac muscles. • In all three types of muscle, myosin and actin interactions are regulated by the availability of calcium ions. • Changes in the membrane potential of muscles are linked to internal changes in calcium release and contraction.

4. Muscle contraction • Neuronal influences on the contraction of muscles is affected when neural activity causes changes in themembrane potential of muscles. • Smooth muscles operate in a wide variety of involuntaryfunctions such as regulation of blood pressure andmovement of materials in the gut.

5. Structure of skeletal muscle

6. Skeletal muscles are attached to the skeleton by tendons. Skeletal muscles typically contain many, many muscle fibers.

7. The latent period between excitation and development of tension in a skeletal muscle includes the time needed to release Ca++ from sarcoplasmic reticulum, move tropomyosin, and cycle the cross-bridges.

8. General process of excitation and contraction in skeletal muscle • Neuromuscular transmission • Excitation-contraction coupling • Muscle contraction

9. A single motor unit（运动单位） consists of a motor neuron and all of the muscle fibers it controls.

10. The neuromuscular junction（神经肌接头）is the point of synaptic contact between the axon terminal of a motor neuron and the muscle fiber it controls. Action potentials in the motor neuron cause Acetylcholine（乙酰胆碱） release into the neuromuscular junction. Muscle contraction follows the delivery of acetylcholine to the muscle fiber.

11. Twitch contraction 单收缩 • The mechanical response of a single muscle fiber to a single action potential is know as a TWITCH

12. Frequency-tension relation频率-张力关系 Complete dissipation of elastic tension between subsequent stimuli. S3 occurred prior to the complete dissipation of elastic tension from S2. S3 occurred prior tothe dissipation of ANY elastic tension from S2. T e m p o r a l s u m m a t i o n.

13. Unfused tetanus非融合性强直收缩: partial dissipation of elastic tension between subsequent stimuli. Fused tetanus融合性强直收缩: no time for dissipation of elastic tension between rapidly recurring stimuli. Frequency-tension relation

15. Objectives • To make a sciatic nerve & gastrocnemius (SNG) (坐骨神经和腓肠肌) preparation • To measure the effects of different stimulus intensities and frequences on the muscle response • To measure a single twitch, incomplete tetanus and complete tetanus

16. Parotid glands • Experimental animal: Toad

17. Ringer`s solution is a solution of recently boiled distilled water containing NaCl 6.5g, KCl 0.14g, CaCl2 0.12g, NaHCO3 0.20g, NaH2PO4 0.01g per liter To keep moist and the activity of preparation

18. Equipment Required • RM6240 biological signal collecting system • Force transducer

19. Intact Nerve-Muscle Prep • Pith the toad with a probe, resulting in the toad not feeling pain • As soon as the brain and spinal cord destroyed, the toad should become flaccid foramen magnum

20. Peel the skin of one leg • Fix the toad on the frog board with the dorsal surface uppermost

21. Gastrocnemius • Identify the gastrocnemius muscle • Tie a knot around the achilles tendon using suture thread • Cut the achilles tendon as close to the bottom of the foot as possible Shank muscles

22. Locate the sciatic nerve in the thigh region • Use the glass hooks to separate the sciatic nerve • Pass a piece of thread beneath the sciatic nerve

23. thread gastrocnemius sciatic nerve electrode • Hold knee in place by pushing down two T-pins • Tie the free end of the thread to the hole on the end of the tongue of the force transducer • Place the stimulating electrode on the sciatic nerve

24. Attention 1: Do not touch the nerve with any object that is made of metal; this will render the nerve useless • Attention 2: Avoid stretching or otherwise damaging the nerve. Keep the tissue moist with frog ringer’s solution

25. transducer

26. Start the software • Switch the RM6240 Data Acquisition System on • Click on the “RM6240USB2.0q(I)(English)” icon on the Desktop of computer

27. Exercise 1: effect of stimulus intensity on twitch amplitude • Set record parameters

28. loose • The recording trace should be set to zero

29. Apply a light load to the muscle by raising the force transducer with the tension adjuster until the trace moves approximately 2 g above the baseline • Make sure to lift the muscle vertically to an angle that is perpendicular to the rest of the toad leg

30. Display the stimulation mark

31. Begin the recording • Change the stimulus intensityto 0.2V • Determine the threshold intensityby increasing the stimulus intensityin 0.1V increments • Stop and save the recording trace

32. maximal stimulus threshold stimulus Data analysis • Observe the grape showing the relationship between the stimulus intensity and contraction amplitude, record the following values: • Threshold stimulus: (volts) • Maximal stimulus: (volts) 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 0.5 1.9

33. Cancel scribe line Zoom width maximal stimulus Regional measurement threshold stimulus • Observe a single twitch induced by maximal stimulus • Zoom in the image

34. amplitude latent period Contraction period Relaxation period Cancel scribe line Regional measurement • Record the following values in a single twitch induced by maximal stimulus : • Latent period: (ms) • Contraction Period: (ms) • Relaxation period: (ms) • Contraction amplitude: (g)

35. Exercise 2: effect of stimulus frequency on twitch amplitude • Set record parameters

36. Display the stimulation mark • Begin the recording

37. 6 • Set the stimulus intensity to the lowest value that will give strong contraction in the exercise 1 • Stop and save the recording trace

38. complete tetanus incomplete tetanus twitch Data analysis • Determine the following values: • A single twitch:≤ Hz, Contraction amplitude :g • Incomplete tetanus:― Hz, Contraction amplitude :― g • Complete tetanus: ≥ Hz, Contraction amplitude: ≥ g

39. Requirement for Experimental Report • Title • Aim • Results • Observe the grape showing the relationship between the stimulus intensity and contraction amplitude, record the following values: • Threshold stimulus: (volts) • Maximal stimulus: (volts)

40. Record the following values in a single twitch induced by maximal stimulus : • Latent period: (ms) • Contraction Period: (ms) • Relaxation period: (ms) • Contraction amplitude: (g) • Determine the following values: • A single twitch:≤ Hz, Contraction amplitude :g • Incomplete tetanus:― Hz, Contraction amplitude :― g • Complete tetanus: ≥ Hz, Contraction amplitude: ≥ g