Biol 224.3 - Animal Body Systems Lecture 13: Animal Locomotion: Skeletal Muscles PDF

Biol 224.3 – Animal Body Systems Lecture 13: Animal Locomotion: Skeletal Muscles Dr Joan Forder Supplementary Reading: Textbook (5th Edition, Chapter 43, pages 1181-1189) 1 Where we are going...

Biol 224.3 – Animal Body Systems Lecture 13: Animal Locomotion: Skeletal Muscles Dr Joan Forder Supplementary Reading: Textbook (5th Edition, Chapter 43, pages 1181-1189) 1 Where we are going The Neuromuscular Junction Action Potential Conduction Calcium Release Cross Bridge Binding Function of ATP Cross Bridge Cycling Generating Force & Movement Neural Regulation of Skeletal Muscle Contraction Stretch Activation 2  The Neuromuscular Junction (NMJ) motoron From Drosophila larva 3 The Neuromuscular Junction (NMJ) Motor neuron axon terminal Acetylcholine (presynaptic) causes a muscle fibre SYNAPSE - depolarization 7 neurotrans- Depolarization - mitters channels results in muscle action potential (AP) Muscle fibre (postsynaptic) Nicotinic Fig 43.6 receptor 4 Muscle AP is conducted to interior of muscle fiber Along membrane of t-tubules similar to endoplasmic reticulum what used to = sarcolemma (be plasma membrane continuous with sarcolemma SR - stores Ca++ (keeps cytoplasmic [Ca++] low, SR [Ca++] high) uses Ca-ATPase to pump Ca++ from cytoplasm Fig 43.4 (sarcoplasm) 5 Muscle AP is conducted to interior of muscle fiber Along membrane of t-tubules Ryanodine receptor (RyR) - Ca++ channel in sarcolemma whename Dihydropyridine receptor (DHPR) - voltage gated channel in t-tubule membrane - at rest plugs RyR MAP produces conformational change in DHPR - Unblocks RyR - Ca++ diffuses out of sacroplasmic reticulum into sarcoplasm along large concentration gradient Fig 43.4 6 MAP from NMJ causes Ca++ release into sarcoplasm What happens next? Sliding filament theory of muscle contraction Fig 43.6 7 Filaments slide past each other to shorten a sarcomere myosinstasea the : move H zone I band A band shorter shorter same width Fig 43.5 8 Filaments slide past each other to shorten a sarcomere 9  Cross Bridge Binding losingaa Sliding due to cross bridge anothe rest. /actions e binding between filaments Actin and Myosin - deratinS Protein polymers Have respective binding sites Change in myosin shape after cross bridge formation moves filaments past each other Fig 43.6 10  ATP Required for Detachment In presence of high sarcoplasmic Ca++, cycle of binding and unbinding continues movein ATP required to detach actin/myosin at t a chea myosin No ATP (e.g. death) then filaments remain bound - rigor mortis ATP also needed for Ca++ pump workingt on sarcolemma used Fig 43.6 11 Sliding due to cross bridge binding between filaments Fig 43.6 12  Crossbridge Cycling Overall muscle contraction due to H zone I band A band continual crossbridge shorter shorter same width cycling PLUS the formation of many, many crossbridges per sarcomere 13 Fig 43.5 Generating Force & Movement Small molecular movements translate into overall muscle shortening sarcomere length ~2.5 µm micrometres Muscle shortening & lever action generate distance shortened per force & movement sarcomere ~0.25 µm ~ 40,000 sarcomeres shorten a muscle by 1.0 cm Assuming 200,000 sarcomeres: 200,000 x 0.25 = 50,000 µm = 50 mm = 5 cm Fig 43.17 14 Neural Regulation of Skeletal Muscles Reflex Arc Motor unit recruitment & tetanus Stretch Activation Reflex Arcs Stretch receptors & motor neurons connect in CNS Reflex arcs operate “automatically” Important in posture, coordinating limb movements Integrated with conscious motor control by CNS will study this in lab #4 Neural stimulation always shortens skeletal muscles Muscles usually found in antagonistic pairs 16 Motor Unit Recruitment & Tetanus Recruitment of small Whole-muscle contraction motor units Relative strength of adjusts muscle force 0 1 2 3 4 5 Number of motor units recruited Motor unit = one neuron plus all muscle Recruitment of large Whole-muscle contraction motor units Relative strength of fibers it contacts units more motor movement. = larger 0 1 2 3 4 5 Fig 43.9 Number of motor units17 recruited  Tetanus : constant contraction of a muscle. Multiple action potentials will lead to tetanus (a form of summation) contracts &State Produces much more force than a twitch Fig 43.8 18  Some muscles are stretch-activated Asynchronous flight muscle Smaller SR – more sarcomeres Indirectly attached to wing Mn AP:contraction < 1 Max wbf > 1000 Hz Mechanical coupling more efficient use of ATP see Fig 43.10 19 WEDS. = review