Microscopic Anatomy Of Skeletal Muscle Worksheet – I. Skeletal muscle fibers (as cells) A. Sarcolemma – cell membrane B. Sarcoplasm – cytoplasm 1. Contains many nuclei and mitochondria. contraction 2. Consists of two main protein filaments a) Actin b) Myosin 3. Sarcoplasmic reticulum a) Membrane channel network b) Helps regulate intracellular Ca2+ levels c) Stores and releases Ca2+ stores. (a) The sarcolemma extends inward (b) increases the surface area of the muscle cell (c) is connected by a parallel terminal forming triangles surrounding each sarcomere.
Rod-like contractile elements occupy most of the muscle cells. Finally, there are sarcomeres which appear striated and adjacent myofibril strips are aligned.
Microscopic Anatomy Of Skeletal Muscle Worksheet
Two types: thick and thin. Thick filaments contain myosin molecules bound together, and filaments contain actin molecules (other proteins). Along with thick fibers, fine fibers shorten the muscle. Elastic fibers maintain the organization of the A-band and are elastic at the end of muscle contraction
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III. Sarcomere A. General 1. Sarcomere -> functional (contractile) muscle contraction unit 2. Actin -> thin filament; includes troponin and tropomyosin; forms bridges with myosin 3. Myosin -> thick filament; forms bridges with actin 4. Z-disc -> zone where thin filaments are attached; A line separating two adjacent sarcomeres B. Part of sarcomere 1. M-line -> middle part of sarcomere a) bound by protein titin (elastic filament) 2. H-zone -> bright zone within A band. a) Contains only thick (myosin) filaments b) Shortens during muscle contraction c) No myosin heads 3. I-band -> Light zone of sarcomas a) Contains only thin filaments (movement) b) Located in the middle. Z line c) shortens during muscle contraction 4. A-Band -> dark zone of sarcomas a) covered area of thick and thin filaments b) remains the same size during muscle contraction 5. Titin -> Large protein Z disc with thick filaments (myosin ) a) Attach thick filaments to the M-line b) Elasticity allows muscle cells to spring back into shape (spring back) when stretched during contraction Muscles are responsible for all body functions. There are three main muscles in the body Skeletal muscles Cardiac muscles Smooth muscles © 2015 Pearson Education, Inc.
Skeletal and smooth muscle cells are long (muscle cell muscle fiber) Muscle contraction and shortening depends on the movement of the microfilaments. Inc.
Most are attached to bones by ligaments Cells are multilayered Striated – visible stripes Free – under conscious control © 2015 Pearson Education, Inc.
Cells are surrounded and connected by connective tissue Endomysium – covers a single muscle fiber Perimysium – wrapped around a fascicle (wrap) of muscle fibers Epimysium – covers all skeletal muscle fascia outside the epimysium © 2015 Pearson Education, Inc.
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Muscle fibers (cells) Blood vessels Perimysium Epimysium (wrapped by muscle) Fascicles (wrapped by perimysium) Endomysium (between fibers) Tendons
Epimysium becomes a bundle of connective tissue Tendon-fibrous structure Primarily collagen fibers Strong and small, often crossing joints Aponeurosis-like structure binds muscle to bone, cartilage, and connective tissue © 2015 Pearson Education, Inc.
Sarcolemma is a specialized plasma membrane Myofibrils are long organelles inside muscle cells Light (I) bands and dark (A) bands give muscles a complex appearance © 2015 Pearson Education, Inc.
Group I pattern light band Z disk contains only thin filaments.
Exercise 14 Microscopic Anatomy And Organization Of Skeletal Muscle
Z disc H zone Z disc Thin (actin) myofilament Thick (myosin) myofilament Group I Group I M line Sarcomeres (b) Myofibril or fibril (a complex organelle composed of bundles of myofilaments)
Sarcomere is the contractile unit of a muscle fiber Sarcomere Organization Myofilaments form a band Thick filaments myosin filaments Thin filaments actin filaments © 2015 Pearson Education, Inc.
Thick filaments myosin filaments Contains ATPase enzyme made from myosin protein Myosin head Heads are called bridges that connect thick and thin filaments during contraction © 2015 Pearson Education, Inc.
Filaments actin filaments Actin is composed of contractile proteins. Actin is anchored to the Z disc. At rest, there is a zone in the A band called the H zone that does not contain actin filaments © 2015 Pearson Education, Inc.
Identify The Skeletal Muscles And Give Their Origins, Insertions, Actions And Innervations
Sarcomere M line Z disc Z disc Thin (actin) myofilament Thick (myosin) myofilament (c) Sarcomere (myofibril segment)
Sarcoplasmic Reticulum (SR) specialized Endoplasmic Reticulum surrounds myofibril stores and releases calcium © 2015 Pearson Education, Inc.
Excitability (also called Responsiveness) – the ability to perceive and respond to a stimulus Contractility – the ability to shorten when receiving an appropriate stimulus – the ability of muscle cells to stretch Elasticity – the ability to return after a stretch and continue to rest . © 2015 Pearson Education, Inc.
Skeletal muscles must be stimulated by motor neurons (nerve cells). A motor unit or single motor neuron and all skeletal muscle cells stimulated by that neuron © 2015 Pearson Education, Inc.
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Figure 6.4a Motor units. Axon terminals in the neuromuscular junction Spinal cord Motor unit 1 Motor unit 2 Motor neurons Nerve Axon Motor cell organ Muscle Muscle fibers (a)
Neuromuscular Connection Motor neuron axon terminal and muscle sarcolemma Neurotransmitter Acetylcholine (ACh), a chemical released by the nerve when a nerve impulse arrives at the axon terminal, is a neurotransmitter that stimulates skeletal muscle © 2015 Pearson Education, Inc.
Synapse cleft Gap between nerve and muscle Nerve and muscle are not in contact. Filled with interstitial fluid © 2015 Pearson Education, Inc.
When a nerve impulse reaches the axon terminal of a motor neuron, calcium channels open and calcium ions enter the axon terminal. Calcium ions release acetylcholine (ACh) in certain synaptic vesicles, where ACh diffuses across the synaptic cleft and binds to receptors on the sarcolemma. muscle cells © 2015 Pearson Education, Inc.
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If enough ACh is released, the sarcolemma becomes transiently permeable to sodium (Na), allowing sodium to enter the cell and potassium to leave the cell. Depolarization allows sodium ions to enter the cell. stopped, contraction occurs © 2015 Pearson Education, Inc.
Acetylcholinesterase (AChE) breaks down acetylcholine into ketoacids, ACHE choline stops muscle contraction © 2015 Pearson Education, Inc.
The cell returns to its resting state: Potassium ions move out of the cell The sodium-potassium pump returns sodium and potassium ions to their original state © 2015 Pearson Education, Inc.
Slide 2 Motor neuron Myelinated axon Nerve impulse Neuromuscular connection Axon terminal Muscle fiber Sarcolemma Nuclear action potential reaches motor neuron axon terminal. 1 Axon Terminal with Synaptic Vesicle Motor Neurons Mitochondrion Ca2 + Ca2 + Synapse Cell Sarcolemma Associated Synaptic Vesicle ACh Receptor ACh Muscle Fiber Sarcoplasm Sarcolemma Layer
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Slide 3 An action potential reaches the end of a motor neuron axon. 1 ACh synaptic vesicles containing calcium (Ca2+) are open and Ca2+ enters the axon terminal. 2 Motochondrion Ca2 + Ca2 + axon terminal
Slide 4 An action potential reaches the end of a motor neuron axon. 1 ACh synaptic vesicles containing calcium (Ca2+) are open and Ca2+ enters the axon terminal. 2 Mitochondrion Ca2 + Ca2 + Ca2 + Enter the axon terminal of motor neurons, some synaptic vesicles release their contents (the neurotransmitter acetylcholine) by exocytosis. 3 Synapse cleft Sarcolemma Fuse Synaptic Vesicle ACh Receptor ACh Muscle fiber Sarcoplasm Sarcolemma layer
Slide 5 An action potential reaches the end of a motor neuron axon. 1 ACh synaptic vesicles containing calcium (Ca2+) are open and Ca2+ enters the axon terminal. 2 Mitochondrion Ca2 + Ca2 + Ca2 + Enter the axon terminal of motor neurons, some synaptic vesicles release their contents (the neurotransmitter acetylcholine) by exocytosis. 3 Synapse cleft Sarcolemma Synaptic vesicle ACh receptor ACh meets muscle fiber sarcoplasm Acetylcholine diffuses across the synaptic cleft and binds to sarcolemma receptors. Sarcolemma 4 layers
Slide 6 ACh-coupled channels are open, allowing Na+ to enter the muscle fiber and K+ to pass through the muscle fiber simultaneously. As more Na+ ions enter than K+ ions leave, local changes (depolarization) occur in the electrical state of the membrane. This ultimately leads to work potential. 5 Na + K + ion channels are open in the sarcolemma; ions pass through.
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Slide 7 ACh degenerates ACh Na+ The ion channel is closed; ions cannot pass through. The enzyme acetylcholinesterase breaks down AC at the synaptic cleft and completes the process. 6 Acetylcholinesterase K+
Figure 6.6 Comparison of action potential with a dry brush fire. Small twig match flame Light the twigs. 1 The fire spreads quickly along the branches. 2 (a) Neuromuscular junction A muscle cell or fiber Na+ moves along a nerve fiber line to the cell. 1 Work potential
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