musculo

• skeletal muscle is long and cylindrical with multinucleated cells
• skeletal muscle produces movements at joints, is stimulated by the nervous system, contracts and relaxes rapidly, produces heat through aerobic energy and assists in blood return to the heart
• skeletal muscle makes up 40% of body weight
• cardiac muscle has striated cells with a single nucleus and branching network
• cardiac muscle is self-excitatory but is influenced by nervous system and hormones
• myocardium is located in the middle of the heart
• smooth muscle cells are tapered at each end, are single-nucleated and nonstriated with dense bodies
• smooth muscle actiosn include: peristalsis, sphincters, and contraction, and help maintain blood pressure by regulating size of arteries
• muscle fibers are muscle cells and are wrapped in endomysium and form a fascicle
• fasicles are wrapped in perimysium and form a muscle wrapped in epimysium
• excitation contraction coupling starts with action potential travelling along motor neuron and reach neuromuscular junction
• ach release is triggered at the neuromuscular junction
• ach binds to receptors in the muscle fibers to cause depolarization and generation of an action potential on the sarcolemma of the muscle
• action potential generated by ach release travels into T tubules deep into muscle fiber
• t tubules open voltage-gated calcium channels in the SR so that Ca can flow into the muscle fiber
• ca in muscle fiber binds to troponin and changes the troponin-myosin comples
• myosin is exposed after Ca binding, and can bind to actin binding sites to form cross-bridges
• ATP causes myosin heads to move and actin filaments to slide past myosin filaments to induce a muscle contraction
• after a contraction, Ca2+ pumps use ATP hydrolysis to help actively transport Ca back from the muscle fiber cytoplasm to the SR to be ready for the next contraction
• thin filaments are made up of troponin, actin and tropomyosin
• thick filaments contains myosin heads bind to actin binding sites on the thin filament
• extrafusal muscle fibers are skeletal muscle alpha fibers that generate tension by contraction
• intrafusal muscle fibers are sensory fibers that provide feedback to the brain to relay information concerning the state of the contraction of muscle
• golgi tendon organs are where muscle attaches to the bone and detects overstretching of muscle
• muscle tone is affected by inactivity: muscles become atonic (weak) and may atrophy (waste away)
• isotonic contractions are short and thicken the muscle to cause movement such as lifting a weight continuously , squatting, push-ups
• isometric contractions do not shorten the length of the muscle but do increase the muscle tension such as holding up a weight or holding a plank
• slow twitch is characterized by type i fibers and is used for endurance, it uses aerobic metabolism because it has more myoglobin and mitochondria i.e soleus in standing
• fast twitch fibers are type ii and have a light stain with 2x more power than slow twitch i.e gastrocnemius in jumping
• type iia fast twitch fibers can be aerobic or anaerobic
• type iib fast twitch fibers are anaerobic
• myostatin (GDF8) is a GF produced in mucle cells that has autocrine function to limit muscle growth and its suppression can lead to overproduction of muscle mass with cardiovascular problems
• smooth muscle contraction involves Ca ion binding to enzyme complex calmoudin-myosin light chain kinase in myosin
• calmousin-myosin light chain kinase complex breaks up ATP into ADP and transfers inorganic phosphate directly to mysoin to activate it
• in smooth muscle relaxation, Ca is pumped out of the cell and inorganic phosphate is removed from myosin to inactivate it
• multi unit smooth muscle includes each cell contracting individually for fine control and gradual responses for respiratory pathways and large arteries (requires high neuron supply)
• single unit smooth muscle cells contract together because of gap junctions which allows it to act as a synctium and need fewer neurons, found in GI tract and uterus
• spontaneous depolarization = pacemaker potential = automaticity
• spontaneous depolarization does not require external stimuli to depolarize the cell membrane towards membrane potential
• spontaneous depolarization uses channels and ion gradients of intracellular Na or Ca or extracellular K to induce a change in membrane potential and this lead to AP generation