A&P Lab Practical

• The skeletal system is the framework that supports, protects, and allows movement.
• Smooth muscle is in the walls of hollow organs. It is involuntary and not striated.
• The following prefixes refer to muscle: myo, mys, and sarco
• Cardiac muscle is involuntary. It has its own intrinsic contraction rhythm which is altered by nervous control to meet the body's need for circulation
• Skeletal muscle makes up about 40% of the cell mass of the body
• Loss of muscle function as a consequence of strokes damaging neurons in the brain are called upper motor neuron lesions
• Muscles use chemical energy such as ATP to produce mechanical energy in directed movements
• Skeletal muscle is voluntary. It is relatively powerful and can rapidly contract but tire rapidly
• Excitability relates to the electric charge differential which can be changed upon stimulation to ultimately produce an intracellular muscle response. Present in all cell membranes
• Contractibility relates to muscles shortening when stimulated
• Extensibility relates to muscle cells stretching, sometimes past their resting length
• Elasticity relates to the muscle's ability to recoil to the resting cell length after being stretched
• Muscles are highly energetically active which allows them to generate a lot of heat that contributes to maintaining body temperature
• Tendons connect muscles to bones and are made of collagen fibers (connective tissue). Can pass around friction points like boney projections or joints due to rigidity and size of the tendon
• Direct attachment is when the periosteum or perichondrium is fused with the muscle's epimysium
• Indirect attachments are more durable, small, and more common. Tendons or aponeurosis is an example.
• Joints act as pivot points for motion when skeletal muscle contracts
• Myosin molecule is made up of 4 light and 2 heavy polypeptide chains; 2 globular heads (each is the 2 light chains) hinged to rod like tail which consists of a helix of two polypeptide chains
• Cross bridges form when the myosin heads link the thick and thin filaments together. Happens when the muscle contracts.
• Globular actin polymerized together is termed filamentous actin
• Z line is made of the protein alpha actinin
• sarcolemma is the plasma membrane of a muscle fiber
• sarcoplasm is the cytoplasm
• myoglobin stores oxygen
• glycosides are granules of glycogen that can be broken down to supply ATP from glucose for energy. Present in the muscle cells
• Myofibrils are repeating units of sarcomeres. They are connected together at Z lines by desmin filaments.
• Sarcomeres are the functional contracting unit of muscle and are made of myofilaments. Runs from Z line to Z line
• Dark A bands and light I bands are next to each other. Each A band has a middle region termed the H zone which is bisected by myomesin to produce the M line. The midline region of the I band is the Z line
• The thick filaments contain myosin and run the length of the A band. The thin filaments contain actin, tropomyosin and troponin
• Tropomyosin spirals around actin to reinforce it. When the muscle is relaxed, it blocks actin's myosin-binding sites
• Troponin has three polypeptides:

  1. inhibitory and blocks actin
  2. bind tropomyosin so that it can bind with actin
• Myofilaments are anchored to the sarcolemma at Z lines and M lines
• Elastic filaments are made of titan. It runs from Z line to the thick filaments to hold them in place and provide flexible recoil to the sarcomere.
• Dystrophin links thin filaments to the sarcolemma. Can lead to muscle dystrophy is abnormally expressed
• The sarcoplasmic reticulum forms terminal cisterns or cross channels at the A and I band junctions. This controls the calcium levels by storing or releasing calcium to control muscle fiber contraction
• T tubule and terminal cisterns make the triad
• All cell plasma membranes carry a polarization or resting charge. This means that the inside of the cell is more negative relative to the outside
• Prior to contraction, concentration of sodium is greater outside the membrane so more sodium goes into the cell than potassium diffuses out. This makes the inner surface of the sarcolemma less negative through depolarization. Begins at the end plate and can also be called end plate potential
• Voltage gated sodium channels on the surrounding sarcolemma respond to the charge by opening to allow sodium to enter down electrochemical gradient. Once the threshold potential (-85mV) is achieved, more channels open to form the depolarization wave along the sarcolemma or the muscle action potential
• After a certain charge is reached, the voltage gated sodium channels close and the voltage gated potassium channels open immediately. Allows for membrane to be more negative through repolarization. The cell cannot be simulated again until the membrane is sufficiently negative, this is the refractory period