Lecture 12: How is skeletal muscle tiss. organized? • Hierarchical organization of Muscle – Key concept • Connective Tissue Elasticity • Elasticity of connective tissues • Passive tension when stretched • Muscle cell formation • SA/V challenges • Muscle cell (myocyte) organelles • Sarcomeres within a myofibril • Sarcomere shortening  contraction • Active tension during contraction (sarcomere overlap) • Neuromuscular junction (details later with neurons) • T-tubules, sarcoplasmic reticulum & calcium roles • Thick & thin filaments, ATP, sliding filaments….

Dr. Casey Self, Biology 118, Autumn 2015 (pollev.com/cjself) 10/13/2016 1 Describe the hierarchical organization of a skeletal muscle.

http://entochem.tamu.edu/MuscleStrucContractswf/index.html 10/13/2016 http://faculty.pnc.edu/pwilkin/saladinch10.html 2 How do such long muscle cells form?

blast =

Myoblasts

Can we form many new myofibers (mature muscle cells) after birth?

10/13/2016 3 What are the functions of organelles in a skeletal muscle cell?

1 muscle fiber = 1 muscle cell 1 cell = many myofibrils http://www.brookscole.com/chemistry_d/templates/student_resources/ 1 myofibril = many sarcomeres 10/13/2016shared_resources/animations/muscles/muscles.html 1 sarcomere = many filaments 4 Describe the design & function of a sarcomere

Muscle Fiber

Thick filament (Myosin proteins) 1 Sarcomere Or Z-line

Thin filament (Actin proteins)

http://droualb.faculty.mjc.edu/Course%20Materials/Elementary%20Anatomy%20and%20Phy 10/13/2016 siology%2050/Lecture%20outlines/skeletal_muscle_physiology.htm 5 Why is the muscle cell membrane highly folded at a neuromuscular junction?

Ach receptors in motor end plate

10/13/2016 6 WhatHow does is calcium’s the excitation role of the in T -atubules skeletal muscle contraction? Topen-tubule the calcium channelsThin filament in the SR? Sarcolemma &Thick

Sarcoplasmic Reticulum stores Ca2+ Calcium Channels

https://www.youtube.com/watch?v=8wa04qYsaps http://droualb.faculty.mjc.edu/Course%20Materials/Physiology%20101/Chapter 10/13/2016 %20Notes/Fall%202007/chapter_12%20Fall%202007%20Phy%20101.htm 7 Explain the actions of myosin, effect of ATP & change in sarcomere length

10/13/2016 https://www.youtube.com/watch?v=gJ309LfHQ3M 8 Explain the actions of myosin, effect of ATP & change in sarcomere length

10/13/2016 9 Explain why active tension varies with sarcomere length

10/13/2016 http://droualb.faculty.mjc.edu/Course%20Materials/Physiology%20101/Chapter%20Notes/Fall%202007/chapter_12%20Fall%202007%20Phy%20101.htm 10 Describe the elastic

properties of the organ.

Extensors Flexors

10/13/2016 11 Review Questions from Skeletal Muscle Lecture 1. What tissues form part of a muscle (organ)? List 3 broad functions of skeletal muscle. Describe the anatomical hierarchy of a muscle organ using these: organ, fascicle, 1 cell or myocyte = 1 muscle fiber, sarcomere, myofilaments. 2. Describe the roles of the connectives in a muscle (organ). What produces passive tension when a muscle is stretched? Predict what might affect the elasticity of different skeletal muscles or elasticity between different individuals. 3. Describe the development of muscle fibers from myoblast stem cells. Graph the proliferation of myofibers & myoblasts on the Y-axis with age on the X-axis. Describe the organization or location of the nuclei, myofibrils, sarcoplasmic reticulum and mitochondria within a myocyte (1 muscle cell). 4. Draw a sarcomere showing thick and thin filaments, & the z-line. How does a sarcomere shorten during a contraction? What limits sarcomere shortening? Graph the active tension curve of a muscle with resting length on the X-axis; explain why active tension varies at different sarcomere lengths. 5. What neurotransmitter is released by excited motor neurons at a neuromuscular junction for skeletal muscle? What role do T-tubules play in the excitation of the sarcoplasmic reticulum in a muscle cell? 6. Explain the importance of both channel-mediated diffusion out of the SR (into cytoplasm) & active transport of Ca2+ back into the sarcoplasmic reticulum. 7. Describe the major steps involved in a muscle contraction with regards to actin, 2+ 10/13/2016myosin, activation sites, Ca and energy (ATP ADP). 12 1. Bentzinger CF & Rudnicki MA. (2014) Rejuvenating aged muscle stem cells. Nature Medicine 20: 234–235.

2. Korhonen MT, Cristea A, Alen M. 2006. Aging, muscle fiber type, and contractile function in sprint-trained athletes. J Appl Physiol. 101: 906–917.

3. Lee SSM, & Piazza SJ. 2009. Built for speed: musculoskeletal structure and sprinting ability. J Exp Biol. 212:3700-3707.

4. Schrauwen-Hinderling VB, et al. 2006. Intramyocellular lipid content in Human skeletal muscle. Obesity 14:357–367.

5. Shefer B, et al. 2010. Reduced satellite cell numbers and myogenic capacity in aging can be alleviated by endurance exercise. PLoS ONE 5(10): e13307. doi:10.1371/journal.pone.0013307

1. Timmons JA, et al. 2010. Using molecular classification to predict gains in maximal aerobic capacity following endurance exercise training in humans. J Appl Physiol 108: 1487–1496.

2. Verdijk LB, et al. 2007. Satellite cell content is specifically reduced in type II skeletal muscle fibers in the elderly. Am J Physiol Endocrinol Metab. 292(1):E151-157.

3. Verdijk LB, et al. 2009. Skeletal muscle hypertrophy following resistance training Is accompanied by a fiber type–specific increase in satellite cell content in elderly men. J Gerontol A Biol Sci Med Sci. 64A(3): 332–339.

4. Weppler CH & Magnusson SP (2010) Increasing muscle extensibility: a matter of increasing length or modifying sensation? Physical Therapy 90(3): 438-449.

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