Exercise 14 Microscopic Anatomy, Organization, and Classification of Skeletal Muscle

SKELETAL MUSCLE Voluntary or involuntary? Striated or not? Multinucleate or uninucleate?

Terminology “Myo-” or “-Mys-” = muscle “Sarco-” = flesh

Figure 12.1a Microscopic anatomy of skeletal muscle. Muscle Fiber Nuclei Dark A band Light I band Nuclei Fiber 5

Figure 12.1b Microscopic anatomy of skeletal muscle. Muscle Fiber Anatomy Sarcolemma Sarcoplasm Sarcolemma Mitochondrion Myofibril Dark A band Light I band Nucleus 6

Figure 12.1c Microscopic anatomy of skeletal muscle. Myofibrils Composed of myofilaments Actin (thin filaments) & myosin (thick filaments) Z disc H zone Z disc Thin (actin) filament Thick (myosin) filament I band A band I band M line 7

Sarcoplasmic Reticulum (SR) Transverse tubules Sarcoplasmic Reticulum (SR) Smooth ER Terminal cisternae: enlarged portion of SR on either side of T tubule Triad = T tubule + 2 terminal cisternae Fig. 10-3

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Nuclei of muscle fibers Figure 12.3 Photomicrograph of muscle fibers, longitudinal and cross sections (800). Nuclei of muscle fibers Muscle fibers, longitudinal view Muscle fibers, cross-sectional view 10

Figure 12.1d Microscopic anatomy of skeletal muscle. Sarcomeres Organized group of myofilaments Contractile units, smallest functional unit of muscle fiber Z-line to Z-line M line Z disc Z disc Thin (actin) filament Elastic (titin) filaments Thick (myosin) filament I band: LIGHT midline is Z line/disc Thin only A band: DARK Thick and thin M line in middle 11

Myofilaments Thick filaments: myosin “cross-bridges” Contraction: myosin head changes shape & will grab onto actin…and pull it toward M-line Fig. 10-7

Myofilaments Thin filaments: 3 types of protein molecules actin Tropomyosin Troponin

Connective Tissue Wrappings: 3 Layers Epimysium = outer Perimysium = central Endomysium = inner

Connective Tissue Wrappings Epimysium Epi = on (outside layer) Surrounds entire muscle

Connective Tissue Wrappings Perimysium Peri = around (central layer) Divides muscle into compartments: Fascicle = bundle of muscle fibers (cells) Connective Tissue Wrappings Fig. 10-1

Connective Tissue Wrappings Endomysium Endo = inside (inner layer) Surrounds individual skeletal muscle cells (fibers) Fig. 10-1

Connective Tissues, cont. Layers continuous & interwoven – blend into one another Muscle’s ends: layers unite to form Bundle: TENDON Attach skeletal muscles to bones Contraction pulls the bone(s) Broad sheet: APONEUROSIS Attach skeletal muscles to bones or other muscles

Muscle—covered by epimysium Fascicles—covered by perimysium Connective tissue layers! Muscle—covered by epimysium Fascicles—covered by perimysium Fiber (cell)—covered by endomysium Myofibril—covered by sarcoplasmic reticulum Sarcomere—contains thick and thin filaments

Figure 12.4 Connective tissue coverings of skeletal muscle. Epimysium Perimysium Epimysium Bone Endomysium Tendon Muscle fiber within a fascicle Blood vessel Perimysium wrapping a fascicle Endomysium (between individual muscle fibers) Muscle fiber Fascicle Perimysium 20

Blood & Nerve Supply Muscles need lots of energy, lots of oxygen Blood vessels supply these Each fiber (cell) has capillary blood supply Contraction stimulated by nerve impulses Axons (nerve fibers) penetrate connective tissue layers, & innervate individual muscle fibers (cells)

How Muscles Contract: DVD

Neuromuscular Junction Junction of motor neuron & a muscle fiber MOTOR Neuron —elongated portion = axon synaptic terminals synaptic cleft

Neuromuscular Junction Synaptic terminals synaptic vesicles Filled with acetylcholine (ACh) Neurotransmitter Release triggers muscle contraction motor end plate Sarcolemma, has receptors to bind ACh

Neuromuscular Junction “Action Potential” Fig. 10-10

Neuromuscular Junction Motor unit = A single motor neuron & ALL the muscle fibers it controls Fig. 10-17

Figure 12.5 The neuromuscular junction. Synaptic vesicle containing ACh Sarcolemma Mitochondrion Synaptic cleft Axon terminal of motor neuron Fusing synaptic vesicles ACh Sarcoplasm of muscle fiber ACh receptors Junctional folds of sarcolemma 31

Figure 12.6 Photomicrograph of neuromuscular junctions (750). Terminal branch of an axon Axon terminal at neuromuscular junction Muscle fibers 32

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Figure 12.6 Photomicrograph of neuromuscular junctions (750). Terminal branch of an axon Axon terminal at neuromuscular junction Muscle fibers 36

Review Figure 12.1 37

Review Figure 12.2 38

Action potential Nucleus Junctional folds of the sarcolemma Part of a Review Figure 12.3 Action potential Nucleus Junctional folds of the sarcolemma Part of a myofibril 39