X-bridges (a-m\ 3 Contributions WA Passive (yam) Resistance 3-5 Developed(I-P=D) Characteristics Tth⊥ Mechanisms Hills Eqn(pg7) Recruit >fibers Force (15 Limitations Sarcomeres 50-60 Fused tetanus, Building a muscle Fining Strategy Control CC. SE PE Speed: Fast Active: CC=T, nonlin dashpot Properties 0 Conceptual Model/ Size Principle thermal Posture: mG Coordination Extensors Space Flig untermeasures Mass Duration Questions/ Activation YUILe
Outline Review of muscle contraction From aP generation to contraction of fibers Muscle proprioceptors(spindles and golgi tendons) Afferent and efferent axons
Outline • Review of Muscle Contraction – From AP generation to contraction of fibers – Muscle proprioceptors (spindles and Golgi tendons) – Afferent and efferent axons
Muscle Strength Loss in Spaceflight Start with Earth-normal muscle magnitudes and directions for mid-stance (Cheal et al., 19921 Mag(BW X(med-lat) Y(post-ant)Z (dist-prox) Gluteus medius 0.80 -0.67 0.18 0.72 Gluteus minimus 0.30 -0.78 0.21 0.59 lliopsoas 1.30 -0.10 0.73 0.68 Reduce muscle strength with duration of weightlessness 40% lower at 6 months. 60% lower at 12 months based on lit 21%o lower peak activated force 17 day flight [Widrick et al., 1999 120 days of HDT bed rest (Koryak, 1999: 44%/33%(M/F)decline in isometric max voluntary contraction(MVC) 36%/11%(M/F) decline in isometric twitch contraction(Pt) 34%/24%(M/F)decline in tetanic contraction force(Po) Maximal explosive power(MEP)reduced to 67% after 31 days, and to 45%after 180 days of space flight (Antonutto et al., 1999]
Muscle Strength Loss in Spaceflight • Start with Earth-normal muscle magnitudes and directions: for mid-stance [Cheal et al.,1992] : Mag (BW) X (med-lat) Y (post-ant) Z (dist-prox) Gluteus medi us 0.80 -0.67 0.18 0.72 Gluteus minim us 0.30 -0.78 0.21 0.59 Iliopso as 1.30 -0.10 0.73 0.68 • Reduce muscle strength with duration of weightlessness: – 40% lower at 6 month s, 6 0 % lower at 1 2 months, based on lit. • 21% lo w er pe a k activated force 17 day flight [Widrick et al., 1999] • 120 days of H D T bed rest [Kory ak, 1999] : – 44% / 33% (M/F) decline i n isometric max. voluntary contraction (MVC) – 36% / 11% (M/F) decline i n isometric t witc h contraction (Pt) – 34% / 24% (M/F) decline in tetanic contraction force (Po) • Maximal e xplo sive po w er (MEP) reduced to 67% after 31 d a ys, and to 45% after 180 days of space flight [Anto n utto et al., 1999]
Muscles: Effectors of the Motor System The major output of the elaborate information processing that takes place in our brain is the generation of a contractile force in our skeletal muscles · Muscle fasciculus Muscle fiber · Myofibril Sarcomere each motor neuron innervates a number of muscle fibers s although Each muscle fiber is innervated by only one motor neuron The motor neuron and all the fibers it innervates is called a motor unit ( the smallest functional unit controlled by the motor system)
Muscles: Effectors of the Motor System • The major output of the elaborate information processing that takes place in our brain is the generation of a contractile force in our skeletal muscles. • Muscle fasciculus – Muscle fiber • Myofibril – Sarcomere • Each muscle fiber is innervated by only one motor neuron, although each motor neuron innervates a number of muscle fibers • The motor neuron and all the fibers it innervates is called a motor unit (the smallest functional unit controlled by the motor system)
Muscles: Effectors of the Motor System The number of muscle fibers innervated by one motor neuron is called the innervation ratio. The innervation ratio can vary between 10 and 2000 a low innervation ratio indicates a greater capacity for finely grading the muscle total force
Muscles: Effectors of the Motor System • The number of muscle fibers innervated by one motor neuron is called the innervation ratio. The innervation ratio can vary between 10 and 2000 • A low innervation ratio indicates a greater capacity for finely grading the muscle total force