Martini et al. Chapter 9

Study of muscular tissue (mus = mouse, -cle = little) What are the Muscular Tissues like? Excitability (irritability) Contractility Extensibility Elasticity

Skeletal* muscle tissue striated & voluntary studied as the muscular system Cardiac muscle tissue striated & autorhythmic Smooth muscle tissue nonstriated & involuntary

Motion body parts (or substances in body) Stability body parts (or substances in body) Heat production basal metabolic rate & shivering

Skeletal muscles are organs Muscle cells are called “fibers” Nervous tissue -> sensory & motor neurons Blood vessels (lined by epithelia) Connective tissues wrappers

Each cell/fiber is covered by C.T. endomysium bundles of cells are “fascicles” Fascicles are surrounded by perimysium Whole muscles are held together by epimysium Tendons or aponeuroses extend from muscles direct or indirect attachments usu. to bone Deep fascia fills in between muscles Superficial fascia fills in between muscle & skin

Organmuscle Tissue fascicle Cell myofiber Organelle myofibril Chemical myofilament(s) myosin & actin

Muscle cells are “excited” by nervous tissue A motor neuron stimulates multiple cells Small units are for precise movements Large units are for powerful movements Muscles have many dif. sized motor units Point of excitement = neuromuscular junction Distal tips of motor neuron = axon terminals neurotransmitter (ACh) crosses synaptic cleft acetylcholine binds to motor end plates of cell

A very long slender cylindrical cell Cell membrane = sarcolemma Cytoplasm = sarcoplasm containing lots of mitochondria & glycogen multiple* peripheral nuclei myofibrils: contractile organelles striated & made of sarcomeres sarcoplasmic reticulum: SER filled w/Ca transverse tubules: connect sl to sr

Sarcomere: a section of a myofibril Striations = pattern of myofilaments thick “myosin” & thin “actin” Z discs A & I bands H zone M line

Calcium “frees-up” the myosin heads they repeatedly “pull actin” toward M-line Z discs also move toward M-line I bands & H zone disappear A band length remains constant Lack of Ca = relaxed muscle antagonist can extend sarcomeres

Red/Slow twitch (posture) aerobic: needs oxygen & glucose to make ATP lots of blood, myoglobin & mitochondria White/Fast Twitch (power) anaerobic: works briefly from stored supplies less blood, glycogen inclusions Intermediate Fast Twitch (lower limbs) All muscle have combination of types

Heart Shorter branched cells branched myofibrils = harder to see striations Intercalated discs Long refractory period, no tetanus

No parallel myofilaments intermediate filaments maintain cell shape Single-unit vs. multiunit types sheet all contracts due to gap junctions (stomach) groups of cells are innervated (arrector pili muscles)

Muscle changes throughout life Development Diseases