Muscle Tissue PDF

Muscle Tissue Graduate Histology and Cell Biology September 19, 2023 Marli Crabtree Objectives 1. Recognize skeletal, cardiac and smooth muscle tissue at the light and electron microscopic level 2. List key characteristics of each muscle type 3. Recognize components of a sarcomere in skeletal and...

Muscle Tissue Graduate Histology and Cell Biology September 19, 2023 Marli Crabtree Objectives 1. Recognize skeletal, cardiac and smooth muscle tissue at the light and electron microscopic level 2. List key characteristics of each muscle type 3. Recognize components of a sarcomere in skeletal and cardiac muscle and analogous structures in smooth muscle 4. Describe the steps of contraction for each muscle type 5. Describe the function of the neuromuscular junction and conditions that can disrupt it 6. Describe the function of muscle spindles and Golgi tendon organs Lecture Overview Basics: Skeletal: Cardiac: Smooth: • Types of muscle tissue • Classifications • Vocabulary • Sarcomeres • Structural organization • Characteristics • Contraction • Mechanism • Disruptions • Sensory • Characteristics • Organization • Contraction • Mechanism • Conduction structures • • • • Characteristics Structures Organization Contraction • Mechanism Main function of muscle tissue? Contraction! Three types of muscle tissue: Can be classified based on type, morphology, or function Striated Skeletal Smooth Cardiac Longitudinal cuts! Involuntary Note on vocabulary: Sarcoplasm - cytoplasm of muscle cells Sarcoplasmic reticulum – smooth endoplasmic reticulum of muscle cells Sarcolemma - muscle cell membrane & its external lamina Sarcomere Z A Z Contractile/functional unit of all striated muscle fibers • Cardiac • Skeletal sarcomere Extends from Z-line to Zline Z-line anchors the actin filaments of two sarcomeres sarcoplasm Z Z Sarcomere Z A-band: • Stain dark • Contains both thick filaments (myosin) and thin filaments (actin) • Contains H-band and M-line I-band H-band M-line H-band: contains only myosin • M-line: anchors myosin • MIDLINE I-band: • Stains light • Contains only thin filaments (actin) • Encapsulates z-line • Stitches! Z A-band M Z Z H Sarcomere: Molecular Assembly Z-line anchors the actin at each end of the sarcomere Titin: large protein with elastic properties • One end connects to z-line and other attaches to myosin filament Nebulin: supports and ensures uniform length in the actin filaments Quiz yourself! Muscle Contraction Elevation of Ca++ is the trigger for ALL muscle contraction For muscle contraction to occur: Ca++ must be available • Binding between actin and myosin After contraction, Ca++ must be quickly removed Lecture Overview Basics: Skeletal: Cardiac: Smooth: • Types of muscle tissue • Classifications • Vocabulary • Sarcomeres • Contraction • Structural organization • Characteristics • Contraction • Mechanism • Disruptions • Sensory • Characteristics • Organization • Contraction • Mechanism • Conduction structures • • • • Characteristics Structures Organization Contraction • Mechanism Skeletal muscle Organization Muscle fiber surrounded by endomysium : myofibril, contractile thread C: capillaries N: nucleus • Note that it is peripherally located m: mitochondria Characteristics Longitudinal section Muscle fiber = muscle cell • Cylindrical, striated fibers • Multi-nucleated • Elongated nuclei • Peripherally located Rapid, voluntary movements Cross section Structures Sarcoplasmic reticulum: • Source of INTERNAL (intracellular) Ca++ • Contains many Ca++ pumps (voltage gated channels) • Extend into terminal cisternae around myofibrils (store Ca++) Transverse (T) tubules: • Deep fingerlike invaginations of the cell membrane that surround the myofibrils Triad Triad: Terminal cisternae and T-tubules are organized into triads along the A- and I-band boundaries This is important for uniform and rapid contraction of myofibrils Actin and Myosin Filaments Actin: • Thin filaments • Contains binding site for myosin • At rest, this binding site is blocked by the troponintropomyosin complex • Contains tropomyosin & troponin • Troponin – contains binding site for Ca++ Myosin: • Thick filaments • Heads bind actin & ATP Neuromuscular Junction (NMJ) Motor neurons give rise to axon branches that synapse with muscle fibers Each axonal branch forms a dilated termination situated at the muscle cell surface • This synaptic surface is called the motor end plate or neuromuscular junction (NMJ) NMJ Motor endplate Mechanism of Contraction Nerve impulses come from motor neurons 1. ACh released at NMJ binds to receptors on sarcolemma. 2. AP is generated & travels down Ttubule. 3. Ca++ is released from the sarcoplasmic reticulum in response to the change in voltage. 4. Ca++ binds troponin; cross-bridges form between actin and myosin. 5 2 3 6 5. Acetylcholinesterase removes ACh from synaptic cleft. 6. Ca++ is transported back into the sarcoplasmic reticulum. 7. Tropomyosin binds active sites on actin causing the cross-bridge to detach. 4 7 Disruptions to the NMJ Myasthenia gravis: autoimmune disease; antibody is produced against ACh Curare: muscle relaxant; antagonist on ACh receptors Botulinum toxin: potent neurotoxin from Clostridium botulinum, inhibits vesicle fusion and release of ACh (BOTOX) Muscle Spindles & Golgi Tendon Organs Striated muscles and myotendinous junctions contain sensory receptors that send feedback to CNS Act as proprioceptors • Proprioception: perception of the position and movement of the body in space Muscle Spindles & Golgi Tendon Organs The sensory innervation of muscle arises from two sources: 1. Spiral nerve endings in muscle spindles • Sense stretch and rate of stretch 2. Golgi tendon organs, nerve endings in the tendons • Sense tension Lecture Overview Basics: Skeletal: Cardiac: Smooth: • Types of muscle tissue • Classifications • Vocabulary • Sarcomeres • Structural organization • Characteristics • Contraction • Mechanism • Disruptions • Sensory • Characteristics • Organization • Contraction • Mechanism • Conduction structures • • • • Characteristics Structures Organization Contraction • Mechanism Cardiac muscle Characteristics Longitudinal section Intercalated discs Striated, short fibers Nuclei: - One or two nuclei per cell - Ovoid or box-shaped - Centrally located Cells boundaries = intercalated discs Contract and relax spontaneously • Numerous gap junctions provide continuity between cells • Serve as "electrical synapses" Cross section Organization Actin and myosin arranged in sarcomeres with Z lines, and H, I, and A bands Difference: branching connected by intercalated discs I Ba Z Line nd AB and HB and Organization Intercalated discs are formed by: • Desmosomes • Fascia adherens • Gap junctions Intercalated Disc Desmosomes and fascia adherens provide connective forces between cells Gap junctions allow for electrical synchronized cont raction Gap Junctions Intercalated discs CELL 1 Ad Des Ad Des CELL 2 Gap Junctions UMC-093 Cross & Mercer Organization: Triad vs Dyad Triad: • At junction of I and A bands • One T-tubule and two adjacent terminal cisternae Diad: • T-tubule is found on the Z-line • One adjacent terminal cisterna Mechanism of Contraction 1. Nerve impulse comes from pacemaker cells and triggers muscle impulse which travels down the Ttubule. 2. Muscle impulse triggers Ca++ from the sarcoplasmic reticulum and T-tubule. 3. Ca++ binds to troponin and triggers conformational change to tropomyosin which exposes active binding site and allows myosin head to bind actin. 4. Myosin head utilize ATP and perform a “power stroke” to pull actin filaments toward the M line of the sarcomere. Unique to cardiac muscle Same as skeletal muscle Mechanism of Contraction Slow leakage of Ca++ responsible for rhythmic contraction/relaxation Rhythmic contraction of cardiac muscle is controlled by the sinoatrial node (SA node) • Influenced by autonomic (sympathetic/parasympathetic) control and hormonal control Purkinje fibers (in ventricles of the heart) Myocardium UMC_122 ardium Endoc Working fibers Large, modified cardiac muscle cells Part of heart conducting system Lecture Overview Basics: Skeletal: Cardiac: Smooth: • Types of muscle tissue • Classifications • Vocabulary • Sarcomeres • Structural organization • Characteristics • Contraction • Mechanism • Disruptions • Sensory • Characteristics • Organization • Contraction • Mechanism • Conduction structures • • • • Characteristics Structures Organization Contraction • Mechanism Smooth muscle Characteristics Specialized for slow, steady contraction • Non-striated Found in blood vessels, respiratory tract, digestive tract, uterus, bladder, and more Nucleus: • One per cell • Centrally located • "Hot-dog" shape (relaxed) • "Corkscrew" shape (contracted Cells are fusiform in shape and often arranged in sheets Characteristics Usually looks like a "sheet" of smooth muscle cells Individual cells are joined together by various junctional complexes: • Mechanical junctions: transmit force • Gap junctions: transmit excitations SM cells are active in synthesizing and depositing extracellular matrix components (elastic, collagen, reticular fibers) Structures Caveolae Lack T-tubules Caveolae: • Short membrane invaginations • Contain several pumps and ion channels • Entry point of extracellular calcium SER: smooth endoplasmic reticulum • Site of intracellular calcium storage Ca2+ Smooth ER Organization Contraction is still achieved my myosin and actin Actin: inserted into dense bodies and dense plaques (analogous to Z-lines in striated muscle) Myosin: myofilaments are suspended between two or more actin filaments Organization Thick and thin myofilaments crisscross obliquely through the cell, using the dense bodies and plaques for support Less regular arrangement compared to striated muscle Red lines indicate possible routes for contractile filaments to travel, connecting to dense bodies and plaques Organization We also have cell-to-cell connections that utilize the dense bodies and plaques • Intermediate filaments (desmin) and Factin filaments • Helps transmit contractile forces through adjacent cells Contraction Contraction is triggered by increase in free extracellular Ca++ Smooth muscle does NOT use troponin or tropomyosin, instead calmodulin and myosin light-chain kinase (MLCK) • Calcium binds to calmodulin Innervated by post-ganglionic autonomic nerves Myosin Actin - Mechanism 1. Autonomic neurotransmitters/stretch/ hormones can trigger Ca++ channels to open 2. Ca++ binds calmodulin 3. Ca++/calmodulin complex activates myosin light chain kinase (MLCK) which phosphorylates myosin light chain (MLC) (makes up the myosin head) 4. Phosphorylated MLC allows myosin to bind actin and contraction occurs 5. Myosin head releases actin when myosin light chain phosphatase (MLCP) dephosphorylates the myosin light chain Lecture Overview Basics: Skeletal: Cardiac: Smooth: • Types of muscle tissue • Classifications • Vocabulary • Sarcomeres • Structural organization • Characteristics • Contraction • Mechanism • Disruptions • Sensory • Characteristics • Organization • Contraction • Mechanism • Conduction structures • • • • Characteristics Structures Organization Contraction • Mechanism Questions? Email me: [email protected] Characteristics of Muscle Tissue Classes Skeletal Cardiac Smooth Characteristics Striated Striated Non-striated Type of movement Voluntary Involuntary Involuntary # of nuclei (N) Multi-nucleated Uni- OR multi-nucleated Uni-nucleated N location Peripheral Central Central N shape "Plate" Ovoid or rectangular "Hot-dog" or "corkscrew" Innervation Somatic motor Autonomic NS Autonomic NS Contraction Fast, transient Fast, rhythmic Slow, persistent Unique characteristics • Discrete myofibrils • ACh at NMJ • Intercalated discs • Pacemaker cells • Fusiform cell shape • Dense bodies, plaques Slide adapted from Dr. Kanyicska Muscle Fibers in Cross Section Skeletal Cardiac Smooth Muscle Fibers in Longitudinal Section Skeletal Cardiac Smooth Compare smooth muscle to dense CT! Sources Junquiera’s Basic Histology Text and Atlas, 13th edition Lecture: Muscle Tissue, Dr. Casey Boothe, Graduate Histology, Fall 2022 Lecture: Muscle Tissue, Dr. Audra Schaefer, Medical Histology, Summer 2022 Lecture: Muscle Tissue, Shannon Curran, Graduate Histology, Fall 2021