Lecture 13, 04 Oct 2005 Chapter 16 & 17 Navigation & Muscle Function Vertebrate Physiology ECOL 437 (aka MCB 437, VetSci 437) University of Arizona Fall 2005 Vertebrate Physiology 437 Chapter 16 1. Navigation Chapter 17 2. Muscle instr: Kevin Bonine t.a.: Kristen Potter -Paper Topics -Short Seminar Write-Up due 10 Nov 1 2 Navigation (Chapter 16) 1 2 3 4 5 3 Hill et al. 2004 4 Hill et al. 2004 Fig 16.3 Example: Movements and Orientation Dead Reckoning Sea Turtles Thousands of kilometers Feeding areas to nesting beaches Chelonia mydas Leatherbacks travel farthest 5 Site Fidelity - Feed together - Nest at original beach - Males similar? 6 10-8, Pough et al. 2001 1
Movements and Orientation Leatherback Orientation 1. Local 1. Local - Visual and chemical cues Salamanders? Lizards? - Audio cues e.g. breeding pond - use multiple cues Zug et al. 2001 7 start 8 10-13, Pough et al. 2001 Movements and Orientation Orientation 1. Local 1. Local Some local cues reliable even in new environment Zug et al. 2001 - Downhill orientation (newts toward water) - Orientation toward bright blue and purple light (hatchling sea turtles moving toward ocean) 9 10 Movements and Orientation Orientation 1. Local Ability to orient w/o local cues -Y-axisorientation Movements and Orientation Orientation 1. Local - Sun position changes daily and seasonally 10-17, Pough et al. 2001 - Sun ~ Moon, star 10-16, Pough et al. 2001 11 Many vertebrates tend to be less oriented if sky overcast 12 2
Movements and Orientation Orientation 1. Local - Sun pineal organ ( third eye ) in many reptiles Important for: - photoperiod entrainment - circadian rhythms - internal clock In some lizards: more advanced parietal eye (with retina, lens, cornea) 10-18, Pough et al. 2001 13 Movements and Orientation Orientation 1. Local - Sun polarized light - atmosphere scatters light - e-vector perpendicular to sun s rays - related to position of sun - overcast interferes Some detect with extraoptic photoreceptors (usually pineal body) Hill et al. 2004 Fig 16.6 10-20, Pough et al. 2001 14 Movements and Orientation Orientation 1. Local 3. Magnetic Orientation and Navigation True Navigation : 1. Compass Sense Many vertebrates can 2. Map Sense - detect earth s magnetic field - relate to gravitational field (e.g., sea turtles) -magnetic receptors not well understood - amphibs, alligators, box turtles, sea turtles - probably use with chemical and visual cues Hill et al. 2004 Fig 16.8 15 16 Navigation via Magnetic Fields Pigeon Orientation - Pelagic Whales - Homing Pigeons - Cave salamanders - Bacteria etc. Helmholtz Coil -often aredundant system - Magnetite particles (Fe 3 O 4 ) orient with magnetic field - Receptors detect -> processed in CNS 17 Hill et al. 2004 Fig 16.9 18 3
Hatchling Loggerhead SeaTurtles North Atlantic Subtropical Gyre Hill et al. 2004 Fig 16.11 19 Angel Shark 20 Vertebrate Physiology 437 1. Muscle A. Sarcomere B. Cross-bridge cycling C. Length-tension relationship D. Excitation-contraction coupling E. Force-Velocity curves, Power F. Fiber Types G. Fatigue 21 Muscle Uses: - most observable animal behavior - most visceral function - generally act by shortening Classification: - striated skeletal or cardiac - smooth walls of hollow organs All muscle movement based on myofilaments (actin and myosin) sliding past each other Utilize: ATP, Ca 2+, ~APs (Myo-, Sarco- = muscle related ) 22 Skeletal Muscle Structure: - muscle attached to bone (skeleton) via tendons - muscle comprises elongate, multinucleate, muscle fibers - multinucleate muscle fibers derived from combination of many myoblasts (embryonic muscle cells) - within each muscle fiber are many parallel myofibrils - each myofibril contains sarcomeres arranged in series (end-to-end) - sarcomere is functional unit of muscle 23 Sarcomere Sarcomeres in adjacent myofibrils are aligned leading to striated appearance Z-disk at each end of sarcomere Actin thin myofilaments attached to each Z-disk Myosin thick myofilaments in between actins (6,3) Actin and Myosin overlap is what allows muscle contraction (6,3) 24 4
Sarcomere Areas within sarcomere given names: Z-disk (actin attaches) I-band (actin only) A-band (myosin length) M-line (midpoint of myosin) H-zone (myosin only) Which regions change length and which remain the same as the sarcomere shortens? Z-disk (actin attaches) I-band (actin only) A-band (myosin length) M-line (midpoint of myosin) H-zone (myosin only) During muscle contraction, myosin thick filaments slide past actin thin filaments During muscle contraction, myosin thick filaments slide past actin thin filaments toward Z-lines 25 toward Z-lines 26 Sarcomere Composition Actin composed of: individual molecules of G-actin (globular) united into chains called F-actin (filamentous) which form a two-stranded helix In the groove of the two F-actin strands is tropomyosin, which also has globular troponin molecules attached to it Sarcomere Composition Myosin composed of: 2 heavy chains with globular heads 2 essential light chains 2 regulatory light chains The light chains are involved in the speed of contraction (important for different muscle fiber-types) 27 Myosin molecules spontaneously aggregate into complexes with the heads at the ends and the tails toward the middle 28 Sarcomere Function Actin and Myosin molecules slide past each other, but don t themselves change length Cross Bridges and Force Production Myosin head binds to actin (actomyosin), then pulls myosin toward z-line thereby shortening sarcomere (= contraction) Sliding Filament Theory Vander et al., 2001 Cross-bridges form transiently between myosin head and actin filament (actomyosin) Sarcomere shortens during contraction 29 Cross-bridge forces are additive. Same force all along myofibril. 30 5
Sarcomere Function Number of Crossbridges (and therefore contraction magnitude) increased with appropriate overlap of actin with myosin heads 31 Length-Tension Relationship Normal muscle function at or near the plateau (1.8-2.2) 32 Length-Tension Relationship Length-Tension Relationship Why lose force production at short end? What constrains muscle length in the body? 33 Hill et al. 2004, Fig 17.12 34 Vander et al., 2001 Myosin head has to be able to detach and bind again to actin further along in order to continue to generate force Detachment requires ATP bind to Cross Bridges and Force Production ATP required for the (3) dissociation of actin and myosin (else rigor mortis) Myosin acts as an ATPase, hydrolyzing ATP to ADP + P i (4) (Energy of ATP hydrolysis cocks the myosin head) Actomyosin complex forms (= crossbridge) (1) Myosin releases ADP and P i (very slowly (2) unless bound to actin) Vander et al., 2001 ATP binds to myosin Cross bridge stronger when Pi released, then myosin head rotates Movement about 10-12 nm myosin head 35 Cycle repeats until Ca++ resequestered or run out of energy 36 ATP hydrolysis 6
San Diego State University College of Sciences Biology 590 - Human Physiology Actin Myosin Crossbridge 3D Animation* Hill et al. 2004, Fig 17.5 37 38 Regulation of Contraction CALCIUM and the cross bridge Need free Ca 2+ in cytosol to get contraction Dipsosaurus dorsalis Calcium binds troponin which is attached to tropomyosin on actin Callisaurus draconoides This causes conformational change in tropomyosin exposing actin binding sites for myosin heads (not shown) Phrynosoma platyrhinos Without calcium, contraction is inhibited Vander et al., 2001 39 Thanks to Duncan Irschick and Steve Reilly 40 Excitation-Contraction Coupling: How an AP in muscle plasma membrane leads ultimately to changes in intracellular [Ca 2+ ], and therefore contraction Excitation-Contraction Coupling, from the beginning 1. AP from CNS arrives at neuromuscular junction. Artificially change membrane potential. In reality, most AP s lead to all-or-none 2. ACh released into synapse. 3. ACh binds to nicotinic receptors on motor endplate. 4. Ion channels for K+ and Na+ open; greater Na+ influx leads to depolarization and AP in muscle plasma membrane EPP = Endplate Potential (~Excitatory Post-Synaptic Potential or EPSP) response of muscle (-90mV -> +50mV) 41 42 7
Excitation-Contraction Coupling, the middle I 5. Change in membrane potential (AP) reaches deep into the muscle cell via transverse tubules (T-tubules; one per Z-disk) Excitation-Contraction Coupling, the middle II 6. T-tubules have voltage sensitive proteins called dihydropyridine receptors 7. Dihydropyridine receptors in the T-tubules are mechanically linked with ryanodine receptors (RR) on the sarcoplasmic reticulum (SR) The ends of the SR adjacent to the T-tubule are called terminal cisternae (w/ calsequestrin) 43 8. Calcium stored in the SR. Released into the cytosol via the ryanodine receptor channel when the RR is mechanically triggered by the voltage sensitive dihydropyridine receptor. 44 Excitation-Contraction Coupling, the last bit Time course of excitation-contraction events 9. Calcium triggers release of more calcium from some ryanodine receptors that are not linked to dihydropyridine receptors Called calcium-induced calcium release 10. Calcium binds to troponin leading to actomyosin complex Latent period about 2ms 11. After repolarization, calcium actively (requires ATP) moved back into SR where much of it is bound to calsequestrin 12. Muscle relaxes as long as ATP is present to allow actomyosin complex to dissociate 45 46 Review of EC Coupling and Muscle Contraction Thanks to Randi Weinstein Force-Velocity Curve Sherwood, 1997 (Also, see your text) 47 Randall et al., 2002 Greatest force during isometric contraction Greatest velocity when muscle is unloaded 48 8
Muscles can produce power Different Muscle Fiber-Types Randall et al., 2002 Muscle fiber types vary in their mechanical properties Power = force * velocity Randall et al., 2002 Maximum power output is found at intermediate force and velocity (~40%) 49 50 Histochemistry The electric eel - Electrophorus electricus Serial sections stained for: matpase (fast-twitch) SDH (oxidative) FOG (fast-twitch oxidative glycolytic; dark matpase and dark SDH) SO (slow-oxidative; light matpase, dark SDH) FG (fast-twitch glycolytic; dark matpase, light SDH) 51 The eel generates electric charge in a battery of biological electrochemical cells, each cell providing about 0.15 V and an overall potential difference of ~ 700 V. Note that the eel's head is the cathode(+) and its tail the anode(-). The cells extend over the length of the eel. Thanks to Professor Don Stevens, Zoology, for the picture and expert advice. 52 Dipsosaurus dorsalis Control of Muscle Force Callisaurus draconoides Phrynosoma platyrhinos Two primary factors can be adjusted to increase whole-muscle force: the force developed by each contracting fiber (summation) the number of muscle fibers contracting within a muscle (recruitment) Thanks to Duncan Irschick and Steve Reilly 53 54 9
Summation It s all about CALCIUM Control of Muscle Force Two primary factors can be adjusted to increase whole-muscle force: the force developed by each contracting fiber (summation) the number of muscle fibers contracting within a muscle (recruitment) Increase force by decreasing time between individual action potentials (increase rate of stimulation) 55 56 Motor Unit Motor unit = motor neuron and all of the muscle fibers it innervates Each muscle consists of many intermingled motor units Motor Neurons Recruitment Muscle fibers AP in motor neuron causes all innervated fibers to contract simultaneously 57 Increase force by adding more motor units 58 Bone Parallel Elastic Muscle Component & (sarcolemma, Tendon connective tissue within muscle) Bone Muscle Model Randall et al., 2002 Contractile Unit (sarcomeres) Series Elastic Component (tendon, connective tissue linking muscle fibers to tendon, titin, Z-line material, crossbridge links) 59 Hill et al. 2004, Fig 17.8 60 10
Isometric Contraction Isotonic Contraction iso = same metric = length iso = same tonic = tension Purely isotonic contraction Randall et al., 2002 61 Randall et al., 2002 62 Cellular Energetics Myosin ATPase Actin + Myosin crossbridge movement 75% ATP ADP + P Immediate energy source i PCr + ADP Cr + ATP Ca 2+ pumped Ca 2+ ATPase back into SR Non-oxidative energy source 25% Glucose 2 Lactate + 2 ATP Oxidative energy source Glucose + O 2 CO 2 + H 2 O + 36 ATP Energy systems differ in their rate of and capacity for producing ATP 63 Fatigue Fatigue can result from many factors including; -decreased motivation -failure of neuromuscular transmission -accumulation of metabolic end-products -dehydration Cause of fatigue depends on intensity & duration of exercise 64 Fatigue Continuous exercise at moderate speeds results in net accumulation of P i PCr + ADP + H + Cr + ATP ATP + H 2 O ADP + P i + H + + energy P i accumulation is correlated with development of fatigue, as is lactic acid accumulation (drop in ph) Exercise also produces net accumulation of lactic acid Correlation vs. Causation 65 Wilson et al., 1988 66 11
Muscle Biopsy prepare homogenate & perform enzymatic analysis of homogenate (e.g., creatine phosphate, ATP, P i, lactate, glucose, glycogen) Pros: low cost per assay Cons: many samples required for time course 31 P-Magnetic Resonance Spectroscopy Intact muscle (e.g., creatine phosphate, ATP, P i, ph) Pros: multiple time points for each preparation Cons: high cost per preparation 67 ph can be determined from position of P i peak 68 31 P-Magnetic Resonance Spectroscopy PCr Rat muscle P i ATP Time Kushmerick & Meyer, 1985 rest recovery 69 Postulated Mechanisms of P i Effect on Force Reduced cross-bridge force development Reduced Ca 2+ release from sarcoplasmic reticulum Reduced Ca 2+ sensitivity of myofilaments Decreased ph (e.g., lactic acid) does not seem to have much effect on contractility - but may cause pain! Cooke & Pate, 1985; Allen & Westerblad, 2001; Westerblad et al. 2002 70 12