Muscle Overview Three types of muscle tissue are skeletal, cardiac and smooth Muscle contraction depends on two types of myofilaments – actin and Myocin
TYPES OF MUSCLE
SKELETAL MUSCLE ORGAN A WHOLE MUSCLE CONSISTS OF A LARGE NUMBER OF MUSCLE FIBERS (CELLS) , PLUS CONNECTIVE TISSUE WRAPPINGS, BLOOD VESSELS, AND NERVE FIBERS.
SKELETAL MUSCLE ORGAN THE OUTERMOST LAYER, WHICH ENCIRCLES THE WHOLE MUSCLE ORGAN, IS THE EPIMYSIUM. IT IS COMPOSED OF CONNTECTIVE TISSUE.
SKELETAL MUSCLE ORGAN THE NEXT LAYER IS THE PERIMYSIUM. IT SURROUNDS GROUPS OF 10 TO 200 MUSCLE FIBERS, SEPARATING THEM INTO BUNDLES CALLED FASCICLES.
SKELETAL MUSCLE ORGAN THE DEEPEST LAYER IS THE ENDOMYSIUM. IT SURROUNDS EACH MUSCLE FIBER SEPARATING ONE FROM ANOTHER. IT IS COMPOSED OF LOOSE CONNECTIVE TISSUE.
SKELETAL MUSCLE ANATOMY A MUSCLE FIBER OR CELL IS ELONGATED, MULTINUCLEATED, AND IS STRIATED.
Parts of a Muscle
SKELETAL MUSCLE ANATOMY
SKELETAL MUSCLE CELL ANATOMY
Internal structure of skeletal muscle cell Nucleus: Contain the genetic material of the cell Sarcolemma: Plasma membrane of muscle cell Sarcoplasmic Reticulum: The endoplasmic reticulum of the muscle cell T Tubule: Invagination of the Sarcolemma project deep into Muscle cells interior Terminal cisternae: Serve as specialized reservoirs for Ca ions Triad: Consist of one T-Tubule laying between two terminal cisternae Mitochondria: The site of ATP synthesis Myofibril: Bundle of contractile filaments
Myofibrils Structure Myofibrils -cylindrical structures within muscle fiber Are bundles of protein filaments Two types of myofilaments Actin filaments (thin filaments) Myosin filaments (thick filaments) At each end of the fiber, myofibrils are anchored to the inner surface of the sarcolemma When myofibril shortens, muscle shortens (contracts)
Myofibrils Structure MYOFIBRILS ACCOUNT FOR ABOUT 80% OF THE CELLULAR VOLUME OF A SKELETAL MUSCLE FIBER. THEY ARE THE CONTRACTILE ORGANELLE OF SKELETAL MUSCLE FIBERS.
Myofibrils Structure WITHIN THE MYOFIBRIL, ARE THICK AND THIN MYOFILAMENTS. THESE MYOLFILAMENTS ARE ARRANGED IN A REGULAR PATTERN, A SARCOMERE,WHICH PRODUCES A REPEATING SERIES OF DARK AND LIGHT BANDS.
The Thick Filament (Myosin) Consists of the protein called myosin. A myosin molecule is shaped a bit like a golf club, but with 2 heads. The heads stick out to form the cross bridge Many of these myosin molecules stick together to form a thick filament Each head contains two binding sites, one for actin and one for ATP.
Thin Filament (Actin) 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 The thin filament also contains tropomyosin. The position of tropomyosin cover the binding sites on the actin during unstimulated muscle The third component is troponin. Attached along the tropomyosin strand.Which expose the binding site of actin to myosin
Arrangement of Myofilament The arrangement of thick and thin myofilaments forms light and dark alternating bands (striation). A band: Dark region, correspond to the length of thick filament I band: light region, only thin filaments, correspond to distance between adjacent thick filaments In the middle of the light band is the Z-line: Protein disc anchor the thin filaments The repeating unit from one Z-line to the next is called the sarcomere H zone: Light stripe in the center of the dark (A) band, region between thin filaments M line: Line in the center of H zone, Protein connect myosin filaments 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
ACTIN, TROPOMYSOIN, TROPONIN
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.
MOTOR UNIT STIMULATION OF A SINGLE MOTOR UNIT CAUSES A WEAK CONTRACTION OF THE ENTIRE MUSCLE, OR A NUMBER OF MOTOR UNITS MAY CAUSE A STRONG CONTRACTION OF THE ENTIRE MUSCLE.
NEUROMUSCULAR JUNCTION CONSISTS OF: 1. THE AXON TERMINAL: The distal end of an axon, contains neurotransmitter substance within synaptic vesicles 2. SYNAPTIC CLEFT: The space between the axon terminal and the folded region of the muscle cell membrane 3. THE MOTOR END PLATE: The folded portion of the sarcolemma
Excitation contraction coupling Transmission of action potential along transverse tubules (T tubules) T tubules action potentials caused release of Ca ions inside the muscle fiber. Ca ions caused contraction Overall process called Excitation Contraction Coupling
Neuromuscular transmission Action Potential through motor nerve fiber Axon Terminal Opening of Voltage gated Calcium channels Entry of Calcium ions from Extracellular fluid Opening of vesicles & release of Ach
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:
Release of acetylcholine Action of acetylcholine Binding with receptors Miniature end plate potential Destruction of acetylcholine Synaptic cleft Passage of Ach Postsynaptic membrane Binding of Ach with Receptor and formation of Ach-Receptor complex Opening of the ligand gated sodium channels & entry of sodium ions from ECF Development of end plate potential Muscle Fiber Generation of Action Potential Excitation contracting coupling Muscular contraction