13 October 2008
description
Transcript of 13 October 2008
13 October 2008
Chapter 9: Muscle physiologyLab this week: Sensory Physiology and HearingAll instructions provided during lab (no advance prep)Short preferable for testing cutaneous receptors of calf.
Test # 2 Monday 20 October
Fig. 09.01
Striated (with sarcomeres)
Cylindrical/polygonal
branched fusiformFusion of myoblasts produce multinucleated skeletal myofibers
Fig. 09.02
Myofilaments
Fig. 09.03
dArk band and lIght band
Fig. 09.05
Fig. 09.09
Fig. 09.15
1 AP in motor axon leads to 1 AP in myofiber because end plate potential (EPP) is always suprathreshold
Neuromuscular junctionmyoneural junction
Fig. 09.11aAction potentials are conducted into T-tubles
Fig. 09.11b
Fig. 09.12Ca++ 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
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
a) Isometricb) Isotonic
i) Concentricii) Eccentric
Examples: lifting a barbell