4 2. Smooth Spindle-shaped Cell Single nucleus in each cell No StriationsInvoluntarySlow, sustained contractionsIn hollow visceral organs (stomach, bladder, respiratory passages)Cross SectionNucleus is in center of cell. Cells much smaller.
8 Muscle Functions Produce movement Maintain posture Stabilize joints locomotion & manipulationHelp blood move through veins & food thru small intestinesMaintain postureStabilize jointsBody temp homeostasisShivering: movement produces heat energy
9 Muscle Requirements Demands continuous oxygen/nutrient supply. Axon of neuronMotor end plate (terminus)Demands continuous oxygen/nutrient supply.Lots of arteries/capillaries to muscle.Each muscle cell w/ its own nerve ending controlling its activity.Produce much metabolic waste due to constant activity.
10 Muscle Attachments Most muscles span joints Attaches to bone in two places: (video)1. Insertion: the moveable boneBicep insertion is the radius2. Origin: the stationary bonebicep originates in two different places in scapulaAttachment typesDirect: attaches right onto bone- ex. intercostal muscles of ribsIndirect: via tendon or aponeurosis (sheet-like tendon) to connect to bone- leaves bone markings such as tubercle
11 Muscle OrganizationMuscles are complex bundled structures: fibers within fibers
13 Muscle Fibers A Muscle Fiber = Muscle Cell HUGE cell: m in diametercan be hundreds of centimeters long (created by cytoplasmic fusion of multiple embryonic cells)extends the length of the muscleMain content: bundles of proteins (actin and myosin)Multinucleatedto maintain high rate of protein synthesis.Muscle fiber nucleus = myonucleus
14 Insulation of MusclesMuscle cells must be insulated from one another by specialized membranesMuscle cells work electricallyif not insulated, nerves cannot control individual muscles.
15 Epimysium surrounds entire muscle Dense CT that merges with tendonEpi = outerMys = musclePerimysium surrounds muscle fasciclesPeri = aroundWithin a muscle fascicle are many muscle fibersEndomysium surrounds muscle fiberEndo = within
16 Structural Terminology Associated with Muscle Fibers Prefixes: myo, mys, and sarco all refer to muscleSacroplasmic Reticulum = Smooth ER of muscle (regulates calcium levels for muscle contraction)Sarcoplasm = CytoplasmTo maintain ATP production during cellular respiration, contains high amounts of:mitochondriaglycosomes that store sugaroxygen binding protein called myoglobinSarcolemma = Plasma MembraneT tubules - The sarcolemma of muscle cells are not just on the outside, rather forms tubes that dive into the muscle cellsMyosin and Actin= muscle proteins that create muscle cytoskeletal filaments for contraction
17 myofibrilSarcoplasmic ReticulumMyosin (red) and Actin (blue)T-tubulesarcolemma
18 MicrostructuresEach muscle fiber (muscle cell), is composed of many myofibrils.Organized system of cytoskeleton filaments of actin and myosin proteins that do the actual contractingMyofibrils are NOT CELLSA sarcomere is one segment of a myofibril (muscle segments).The series of sarcomeres produce the striated appearance of muscles
21 Sarcomere organization Myofibril composed of repeating series of sarcomeres with dark A and light I bands.I bands intersected by Z discs mark the outer edges of each sarcomere.Contraction happens within one sarcomere.