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2. Muscles Sarcomere: functional unit of muscle contraction Z line: region where actin and myosin filaments interweave I band: actin filaments of two adjacent sarcomeres. A band: region where actin and myosin filaments overlap H zone: a light area within the A band consisting entirely of myosin filaments.

3. Actin/Myosin Actin filaments are associated with tropomyosin molecules, which block myosin from interactin with actin’s active sites. Tropomyosin is held in place by troponin molecules.

4. Muscle Contraction Acetylcholine signal received by muscle in synaptic cleft, causes depolarization of the muscle fiber and an action potential. The action potential travels along the T-tubule membranes. Calcium channels in the sarcoplasmic reticulum open, allowing stored calcium ions to be released. Calcium ions bind to troponin, moving tropomyosin away from the actin active sites and allowing myosin to bind. Myosin heads bind to actin, and the energy of ATP is converted into the mechanical energy of sliding filaments.

5. lol immune Immunity has three levels: barriers, generalized immune responses, and specific immune responses. Barriers include such physical barriers as skin, as well as chemical agents such as saliva, mucous, and vaginal secretions.

6. General responses General, or non-specific immune responses involve inflammation and white blood cells known as phagocytes. Toll-like receptors, surface receptors on phagocytes, recognize PAMPs (pathogen- associated molecular patterns) and trigger nonspecific immune responses. Phagocytes and natural killer cells destroy invading or infected cells.

7. Inflammatory response (yay allergies!) =( The inflammatory response is triggered by the release of histamine by macrophages and mast cells. Inflammation involves vasodilation: blood vessels expand, bringing more blood and macrophages to the area of infection. This is aided by increased capillary permeability. Phagocytosis increases, a main function of inflammation.

8. Specific immunity Specific immune responses have two components: cell- mediated and antibody-mediated immunity. Helper T cells are activated by antigen-presenting cells, or APCs, which display foreign antigens on their own cell surface. Helper T cells activate B cells, which mature into plasma cells and produce antibodies. Helper T cells also activate cytotoxic, or killer T cells, which destroy pathogens in cell-mediated immunity. Memory B and T cells serve to provide immune protection after the initial infection has passed.