Internal structure of skeletal muscle cell<br />Nucleus: Contain the genetic material of the cell<br />Sarcolemma: Plasma membrane of muscle cell<br />Sarcoplasmic Reticulum: The endoplasmic reticulum of the muscle cell<br />T Tubule: Invagination of the Sarcolemma project deep into Muscle cells interior<br />Terminal cisternae: Serve as specialized reservoirs for Ca ions<br />Triad: Consist of one T-Tubule laying between two terminal cisternae <br />Mitochondria: The site of ATP synthesis<br />Myofibril: Bundle of contractile filaments<br />
Myofibrils Structure<br />Myofibrils -cylindrical structures within muscle fiber<br />Are bundles of protein filaments <br />Two types of myofilaments<br />Actin filaments (thin filaments)<br />Myosin filaments (thick filaments)<br />At each end of the fiber, myofibrils are anchored to the inner surface of the sarcolemma<br />When myofibril shortens, muscle shortens (contracts)<br />
Myofibrils Structure<br />MYOFIBRILS ACCOUNT<br /> FOR ABOUT <br />80% OF THE CELLULAR<br /> VOLUME OF<br />A SKELETAL MUSCLE<br /> FIBER. THEY ARE THE<br /> CONTRACTILE ORGANELLE<br /> OF SKELETAL MUSCLE FIBERS.<br />
Myofibrils Structure<br />WITHIN THE MYOFIBRIL,<br /> ARE THICK AND THIN<br />MYOFILAMENTS.<br />THESE MYOLFILAMENTS<br /> ARE ARRANGED IN A<br /> REGULAR PATTERN, A<br /> SARCOMERE,WHICH<br /> PRODUCES A REPEATING<br />SERIES OF DARK AND LIGHT BANDS.<br />
The Thick Filament (Myosin)<br />Consists of the protein called myosin.<br />A myosin molecule is shaped a bit like a golf club, but with 2 heads.<br />The heads stick out to form the cross bridge<br />Many of these myosin molecules stick together to form a thick filament<br />Each head contains two binding sites, one for actin and one for ATP. <br />
Thin Filament (Actin)<br />The thin filament consists of a protein called actin. It compose of actin subunit twisted into double helical chain. Actin has specific binding site to which the myosin head binds<br />The thin filament also contains tropomyosin. The position of tropomyosin cover the binding sites on the actin during unstimulated muscle<br />The third component is troponin. Attached along the tropomyosin strand.Which expose the binding site of actin to myosin <br />
Arrangement of Myofilament<br />The arrangement of thick and thin myofilaments forms light and dark alternating bands (striation). <br />A band: Dark region, correspond to the length of thick filament<br />I band: light region, only thin filaments, correspond to distance between adjacent thick filaments<br />In the middle of the light band is the Z-line: Protein disc anchor the thin filaments<br />The repeating unit from one Z-line to the next is called the sarcomere<br />H zone: Light stripe in the center of the dark (A) band, region between thin filaments<br />M line: Line in the center of H zone, Protein connect myosin filaments<br />Sarcomere: Contractile unit, extends from one Z line to the next, include the entire A band and half I band on each side of A band<br />
MOTOR UNIT<br /><ul><li>A MOTOR UNIT IS A MOTOR NEURON AND ALL OF THE MUSCULE CELLS IT INNERVATES.
THE NUMBER OF MUSCLE FIBERS PER MOTOR UNIT MAY BE AS HIGH AS SEVERAL HUNDRED OR A FEW AS FOUR.</li></li></ul><li>MOTOR UNIT<br />STIMULATION OF A <br />SINGLE MOTOR UNIT CAUSES A WEAK<br />CONTRACTION OF THE <br />ENTIRE MUSCLE, OR A NUMBER OF MOTOR UNITS MAY CAUSE A STRONG CONTRACTION OF THE ENTIRE MUSCLE.<br />
NEUROMUSCULAR JUNCTION<br />CONSISTS OF:<br />1. THE AXON TERMINAL: The distal end of an axon, contains neurotransmitter substance within synaptic vesicles<br />2. SYNAPTIC CLEFT: The space between the axon terminal and the folded region of the muscle cell membrane<br />3. THE MOTOR END PLATE: The folded portion of the sarcolemma<br />
Excitation contraction coupling<br />Transmission of action potential along transverse tubules (T tubules)<br />T tubules action potentials caused release of Ca ions inside the muscle fiber.<br />Ca ions caused contraction<br />Overall process called Excitation Contraction Coupling <br />
Neuromuscular transmission<br />Action Potential through motor nerve fiber<br />Axon Terminal<br />Opening of Voltage gated Calcium channels<br /><br />Entry of Calcium ions from Extracellular fluid<br /><br />Opening of vesicles & release of Ach<br /><ul><li>The function of neuromuscular junction is to transmit the impulses from the nerve to the muscle.
When the impulses are transmitted from nerve to the muscle, a series of events occur in the neuromuscular junction:</li></ul>Release of acetylcholine <br />Action of acetylcholine <br />Binding with receptors <br />Miniature end plate potential <br />Destruction of acetylcholine <br />Synaptic cleft<br />Passage of Ach<br />Postsynaptic membrane<br />Binding of Ach with Receptor and formation of <br />Ach-Receptor complex<br /><br />Opening of the ligand gated sodium channels <br />& entry of sodium ions from ECF<br /><br />Development of end plate potential<br />Muscle Fiber<br />Generation of Action Potential<br /><br />Excitation contracting coupling<br /><br />Muscular contraction<br />