How does striated muscle contract?

Answer 1

Striated muscles, like all other muscles, including cardiac and smooth, use a method called the sliding filament theory. This is the current model of how muscles contract and was developed by Hugh Huxley in the 1960's.

Answer 2

Acetyl choline will have diffused through the synaptic cleft at a neuromuscular junction and will have binded to receptors of sodium ion channels on the postsynaptic neurone, which in this case is the myofirbil. This cause the sodium ion channels to open, this cause an influx of sodium ions into the myofibril, producing an action potential. This action potential travels through t-tubules in the sarcoplasm of the myofibril. Calcium ions are absorbed by the sarcoplasmic reticulum. This causes the calcium ion channels in the reticulum to open, causing an influx of calcium ions into the sarcoplasm. These ca2+ ions remove tropomyosin molecules away from the actin filaments, exposing their binding sites. This allows bulbous myosin heads, which have a molecule of ADP attached, to form cross-bridges with the binding site. The myosin head then changes it's angle causing the ADP molecule to remove itself. An ATP molecule then binds to the myosin head, allowing it to move away from the actin filament. Ca2+ ions activate ATPase, this enzyme hydrolyses ATP to ADP producing energy which allows myosin to form another cross bridge with actin, further along the filament. This is called the sliding filament mechanism.

Answer 3

Back in the 1600's three rock bands were emerging. The A-Band the I-band and H-zone where the most popular. They all competed to win the Battle of the Zone Overlap.But sadly they were stopped by the Z-lines of Black Friday shoppers. So in short The muscle only only contract when a great deal is found.

Answer 4

The brain sends electrical impulses to the muscles telling them to pull. Muscles extend and relax when the brain tells them not to pull or contract. The nervous system is the electrical highway of the human body. If a nerve is severed or the spinal cord is severed certain muscles will not receive messages from the brain. They will not have feeling either.

Answer 5

An action potential (AP) propagates on the somatic nervous system from the brain to the muscle. The somatic neuron branches many times at the muscle and extends to different muscle fibers; this is called a motor unit. The AP triggers voltage-gated Ca++ channels on the synaptic end bulb. The inflow of Ca++ triggers exocytosis of synaptic vesicles filled with ACh into the synaptic cleft. ACh move across the synaptic cleft to receptors on ligand-gated Na+ channels in the motor end plate. Ach opens the Na+ channels, when the Na+ flows into the sarcolemma it depolarizes forming a muscle AP. T-tubules invaginating the sarcolemma allow the AP to travel down to the Ca++ releasing channels on the sarcoplasmic reticulum (SR) triggering them to open. The Ca++ floods the sarcoplasm and attach to troponin in the thin filaments of the sacromeres. The bond alters the conformation of the troponin releasing it from holding the tropomyosin. The tropomyosin rotates off the actins' myosin binging site. ATP binding sites on the myosin heads of the think filaments use ATPase to hydrolyze ATP to ADP and a phosphate. When the actin's myosin-binding site is exposed, the energized myosin head attaches to the site forming a crossbridge and releasing the phosphate. The ATP site on the myosin head releases the ADP. As a result, the myosin head rotates toward the center or M-line, sliding the thin filaments past the thick filaments this is called the powerstroke. The powerstroke contracts the sacromeres, and the muscle contracts to do the work requested by the brain. The crossbridge breaks when a new ATP attaches to the myosin-head binding site. ATPase hydrolyses the ATP and the myosin-head repeats the crossbridge - powerstroke - release cycle again up to 5x a second. The cycle stops when the sacromere is fully contracted or the muscle AP dies. When the AP stops a protein called calsequestrin in the sarcoplasm binds to the Ca++ releasing it from the troponin. The Ca++ release channels close and Ca++ is sequestered to the SR to be stored. The troponin rotates and holds the tropomyosin over the actin's myosin-binding sites. Crossbridges stop forming causing the sacromere to relax and the muscle to relax.