As it contracts it -causes movement -maintains posture -stabilizes joints -and generates heat.

 Skeletal muscle (voluntary)  muscle attached to the skeleton  cells are long, striated, and multinucleate  Connective tissue coverings (endomysium, perimysium, and epimysium) enclose and protect the muscle fibers and increase the strength of skeletal muscles.  Smooth muscle (involuntary)  cells are uninucleate, spindle-shaped, and arranged in opposing layers in the walls of hollow organs.  Cardiac muscle (involuntary)  cells are striated, branching and fit closely together arranged in spiral bundles in the heart.

Connective Tissue Wrappings *endomysium: forms a sheath around a fiber *perimysium: coarse membrane that surrounds several sheathed fibers *fascicle: bundle of fibers covered in perimysium *epimysium: tough overcoat that surrounds several fascicles that make a muscle

 Skeletal muscles attach to bone using tendons or aponeuroses.  Tendons: stong, cord-like structures ▪ Can cross bony projections ▪ Used to stabilize joints  Aponeuroses: sheet-like structures that attach muscle indirectly

Microscopic Anatomy sarcolema- plasma membrane that serves as the “muscle husk” myofibrils- long ribbon- like organelles which nearly fill the cytoplasm. Alternating light (I) and dark (A) bands give the striped appearance. Midsection of the light band is the Z disc Midsection of the dark band is the H zone

Microscopic Anatomy, Cont. sarcomere- unit of a myofibrile that stretches from one Z to the next Z. Myofilaments- threadlike protein structures within the sarcomere Myosin- thick fibers that split ATP to generate power. Heads or cross bridges link filaments during contraction. Actin- thin fibers that are anchored to the Z disc

 During contraction:  Myosin heads pull on actin filaments.  Actin filaments slide toward the center of the sarcomere.  Light zones disappear.

 Irritability  Ability to receive and respond to stimuli  Contractility  Ability to forcibly shorten

 Motor unit: one neuron and all muscle it stimulates.  Neuromuscular junction: where nerve fiber ends (axon terminals) at skeletal muscle.  Synaptic cleft: gap between axon terminals and sarcolema.

 Nerve impulse to axon  Chemical release of neurotransmitter.  ACh crosses synaptic cleft and attaches to receptors.  Muscle becomes permeable to Na+.  Inward rush of Na generates electrical impulse, Action Potential.  AP travels over muscle causing contraction.

 Direct phosphorolation of ADP by creatine phosphate.  ATP transfer of phosphate group from CP to ADP ATP  Lasts about 20 seconds. (makes 1 ATP)  Aerobic Respiration  C 6 H 12 O 6 CO 2 + H 2 O + energy (ATP)  Yields 36 ATP.  Requires oxygen.

 Anaerobic Glycolysis and lactic acid formation.  Glucose pyruvic acid + 2 ATP  Without oxygen, pyruvic acid converts to lactic acid.  Fast process. Good for seconds of energy.  Lactic acid accumulation causes muscle fatigue and soreness.

Types and Names

 Origin  Attachment to the immovable or less movable bone  Insertion  attachment to the movable bone **When a muscle contracts, the insertion moves toward the origin.

Example: During contraction of the biceps, the insertion moves toward the origin.

 Flexion  Movement that decreases the angle of a joint.  Bringing two bones closer together  Extension  Increases the distance or angle between two bones.  If extension is >180 degrees, it is called hyperextension.

 Rotation  Movement of a bone around its longitudinal axis. ▪ Lateral: away from midline ▪ Medial: toward midline

 Abduction  away from central axis of the body  Adduction  closer to central axis of the body

 Circumduction  Common in ball and socket joints  Proximal end of limb is stationary while distal end moves in a circle.

SPECIAL MOVEMENTS OF THE FOOT. UP AND DOWN MOVEMENTS AT THE ANKLE.

MOVEMENTS OF THE RADIUS AROUND THE ULNA. MOVEMENT OF THE THUMB.

 Prime mover  Muscle that has the major responsibility for causing a movement.  Antagonist  Muscles that oppose or reverse a movement  Synergyst  Help prime movers  Fixator  Special synergists  Stabilize the origin of the prime mover

Homeostatic Imbalance

 In the fetus, muscles are laid down in segments and then segments are invaded by nerves.  Occurs very early in the pregnancy.

 Muscular Dystrophy  Congenital muscle-destroying disease  Duchenne: usually diagnosed between age 2-6 ▪ Normal child begins to fall, lose coordination. ▪ Wheel chair by age 12 ▪ Generally do not live beyond teens  Myastenia gravis  Happens in adults  Shortage of acetylcholine receptors at neuromuscular junctions results in generalized muscle weakness.

 Nerve Damage  Destruction of nerve supply to muscle causes the muscle to lose tone and become paralyzed.  Over time, the muscle with become soft and atrophy.