Chapter 9: Muscle physiology

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Presentation transcript:

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

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

Fig. 09.02 09.02.jpg Myofilaments

dArk band and lIght band Fig. 09.03 09.03.jpg

Fig. 09.05 09.05.jpg

Fig. 09.09 09.09.jpg

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 09.15.jpg Neuromuscular junction myoneural junction

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

Fig. 09.11b 09.11b.jpg

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

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

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.

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