Bio 449 Lecture 16 Muscle II Excitationcontraction coupling

Bio 449 Lecture 16 - Muscle II Excitation-contraction coupling Excitation Contraction Tropomyosin and troponin Cross-bridge cycling Mechanics of muscle contraction Twitch contractions Isometric Isotonic Tetanic contractions Isometric Terms to Know Motor neuron Neuromuscular junction (aka endplate) Sarcolemma Lectures 15 -17: Oct. 6, 2010 Terms to Know Transverse tubules (T-tubules) Sarcoplasm (aka myoplasm) T (Transverse) tubules Dihydropyridine receptors Ryanodine receptors (or channels) Tropomyosin Troponin Isometric contraction Isotonic contraction Twitch contraction Tetanic contraction (tetanus) Summation Latent period Contraction time 50% relaxation time Force-velocity curve Readings Chapter 11, pages 396 -401 Chapter 12

Length-tension curve Fig. 12 -16

Excitation-contraction coupling

Neuromuscular junction Schwann cell sheath Somatic motor neuron The neuromuscular junction Axon terminal Mitochondria Muscle fiber Terminal bouton Motor end plate Synaptic vesicle (ACh) Presynaptic membrane Synaptic cleft Nicotinic ACh receptors Fig. 11 -12 Postsynaptic membrane

Neuromuscular junction Somatic motor neuron Axon terminal Ca 2+ ACh Voltage-gated Ca 2+ channel Skeletal muscle fiber Action potential Acetyl + choline ACh. E Nicotinic receptor Fig. 11 -13 Ca 2+ Motor end plate Closed channel Na+ ACh K+ Open channel K+ Na+

T-tubules and SR T-tubule brings action potentials into interior of muscle fiber. Thin filament Sarcolemma Sarcoplasmic reticulum stores Ca 2+ Fig. 12 -4 Thick filament

Excitation-contraction coupling Axon terminal of somatic motor neuron Muscle fiber ACh Na+ Ry. R Motor end plate T-tubule Sarcoplasmic reticulum Ca 2+ DHP Z disk Actin Ca 2+ released Troponin Tropomyosin M line Myosin head Myosin thick filament Fig. 12 -11 Myosin thick filament

Troponin and tropomyosin Thin filaments Troponin Tropomyosin Fig. 12 -3 Actin chain Nebulin G-actin molecule

Cross-bridge cycle 1 Troponin G-Actin 3 Tropomyosin shifts, exposing binding site on actin 2 TN TN Tropomyosin blocks binding site on actin Cytosolic Ca 2+ Myosin head Pi ADP Power stroke ADP 4 Pi Relaxed state. Myosin head cocked. Fig. 12 -9 Initiation of contraction 5 Actin moves

Mechanics of muscle contraction

Twitch contractions

Isometric twitch

Isotonic twitch

Tetanic contractions

Exam 1 results Mean: 80. 2 SD: 12. 8 Max: 98. 5