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Chapter 9: Muscle physiology

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1 Chapter 9: Muscle physiology
13 October 2008 Chapter 9: Muscle physiology Lab this week: Sensory Physiology and Hearing All instructions provided during lab (no advance prep) Short preferable for testing cutaneous receptors of calf. Test # 2 Monday 20 October

2 Cylindrical/polygonal
Striated (with sarcomeres) Fig 09.01.jpg Cylindrical/polygonal branched fusiform Fusion of myoblasts produce multinucleated skeletal myofibers

3 Fig 09.02.jpg Myofilaments

4 dArk band and lIght band
Fig 09.03.jpg

5 Fig 09.05.jpg

6 Fig 09.09.jpg

7 Neuromuscular junction myoneural junction
1 AP in motor axon leads to 1 AP in myofiber because end plate potential (EPP) is always suprathreshold Fig 09.15.jpg Neuromuscular junction myoneural junction

8 Action potentials are conducted into T-tubles
Fig a 09.11a.jpg

9 Fig b 09.11b.jpg

10 Fig. 09.12 Ca++ sequestration is slower than Ca++ release from SR
3 Roles of ATP Preview: one mechanism of fatigue is AP conduction failure in t-tubules at high fAP 09.12.jpg

11 Sequence of Events Leading to Contraction of Skeletal Muscle
Action potential in motor axon Release of Acetylcholine into synaptic cleft of NMJ ACh binds to nAChRs in sarcolemma Increase permeability to Na+ and K+ via nAChR (inotropic) Sarcolemma depolarizes (End Plate Potential =EPP) Threshold exceeded....AP generated and conducted across the sarcolemma AP conducted into Transverse tubules Depolarization detected by DHP (dihydropyridine) receptors in T-tubules Conformational change in DHP receptors leads to opening of Ca++ channels in sarcoplasmic reticulum

12 Diffusion of Ca++ out of SR into cytoplasm
Ca++ constantly pumped back into SR by primary active transport pumps in the SR membrane Ca++ in SR stored in combination with Calsequestrin Ca++ binds to troponin Tropomyosin shifts to expose binding sites of F-actin Myosin heads (which have already hydrolyzed ATP) bind to sites on F-actin Powerstroke of myosin crossbridge IF Ca++ AND ATP REMAIN AVAILABLE CROSSBRIDGE RELEASES ADP AND FRESH ATP BINDS, PERMITTING RELEASE AND RE-FORMATION OF NEW CROSSBRIDGE IF Ca++ unavailable (returned to sarcoplasmic reticulum) tropomyosin covers F-actin binding sites myosin head units unable to attach to actin......end of contraction.

13 Types of contractions Examples: lifting a barbell a) Isometric
b) Isotonic i) Concentric ii) Eccentric

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