Muscular System

Muscles Three types of muscle tissue Cardiac – found only in the heart. Non-voluntary Smooth/visceral – found in all internal organs. Non-voluntary Skeletal – associated with the skeletal system. Voluntary

Cardiac Muscle Cells are cylindrical and striated Single large, centrally located nucleus Branched and connected to each other via intercalated discs

Smooth Muscle Cells are spindle shaped, non-striated Single large, centrally located nucleus Gap junctions are found between cells

Skeletal Muscle Cells are very long, cylindrical and striated Multinucleated, found towards periphery

Functions of Skeletal Muscle Body Movement Maintenance of posture Production of body heat Communication Characteristic Properties of Muscle Contractibility Excitability Extensibility Elasticity

General Terms Origin [head] – end of muscle attached to the bone that is stationary Insertion – end of muscle attached to the bone that moves Belly – largest portion between origin and insertion Agonist – muscle causing an action when it contracts Antagonist – muscle that works in opposition to agonist – move structure in opposite direction Synergists – muscles that work together to move a structure

Types of Muscle Contractions Isometric – length of muscle doesn't change, but tension increases. Isotonic – length of muscle changes Concentric – tension in muscle is great enough to overcome opposing resistance and muscle shortens. Eccentric – tension in muscle stays constant, but opposing resistance is great enough to cause muscle to increase in length.

Muscle Anatomy Skeletal muscle fibers = muscle cells Each fiber has a connective tissue covering = external lamina  endomysium

Muscle Anatomy Every muscle has an extensive blood supply Specialized nerve cells called motor neurons are associated with muscles – every muscle fiber receives innervation from a muscle fiber

Muscle Shapes Grouped according to fasciculi [bundle of muscle fibers- bound by connective tissue] Pennate – fasciculi arranged like barbs of feather Unipennate, Bipennate, Multipennate Parallel – fasciculi arranged parallel to long axis of muscle Convergent- base is much wider than insertion triangular shape Circular –fasciculi arranged in circle around an opening sphincters

Muscles of Facial Expression The skeletal muscles of the face are attached to the skin [cutaneous muscles] Orbicularis oculi Occipitofronatalis Levator palpebrae Corrugator supercilii

Levator palpebrae

Muscles of Facial Expression Orbicularis oris Buccinator Zygomaticus – major / minor Levator anguli oris Risorius Levator labii superioris Depressor anguli oris Depressor labii inferioris mentalis

1.Platysma 2.M. risorius 3.M. levator anguli oris 4.M. zytomaticus (major et minor) 5.M. levator labii superioris 6.M. angularis 7.M. buccimator 8.M. robicularis oris 9.M. mentalis 10.M. depressor labii inferioris 11.M. depressor anguli oris

Muscles of Mastication Temporalis Masseter Pterygoids – lateral/medial Suprahyoid Muscles Infrahyoid Muscles

Proteins found in Muscle Tissue Myofibrils bind muscle fibers. Composed of two myofilaments actin [thin/light/I] myosin [thick/dark/A] Organized in sarcomeres – which join end to end to form myofibrils

Actin Myofilament Primary protein = actin Seconday proteins = tropomyosin– covers active sites on actin troponin – binds to actin, tropomyosin and calcium

Myosin Myofilaments made of many molecules of myosin protein. Shaped like hockey stick/golf club: rod - head head wants to bind to actin binding site - form crossbridges Heads contain ATPase - capable of breaking down ATP - energy release

Muscle Fiber Physiology Input from nervous system starts contraction. Neurotransmitter is acetylcholine [Ach] Calcium ions released due to action potential [stimulus that causes change of membrane permeability] Calcium causes release of Ach from synaptic vesicles - which causes release of sodium, enhancing cell permeability and action potential. Ach is rapidly broken down by acetylcholinesterace - and choline /acetic acid is recycled. Action potential causes muscle contraction = excitation/contraction coupling

Excitation - Contraction Coupling Sarcoplasmic reticulum are specialized cell organelles that concentrate Calcium ions [2000x] Channels between the sarcoplasmic reticulum are called T- tubules - carry action potential to sarcoplasmic reticulum [sr] SR releases calcium into sarcoplasm of fibers, surrounding the myofibrils Calcium binds to troponin. Causes the troponin / tropomyosin complex to swivel off actin’s bind site Myosin heads seize opportunity and bind with actin = Cross Bridge

Cross bridging consists of myosin binding to actin To release this binding, ATP is broken by ATPase [stored in myosin’s head]. Energy allows release of myosin from actin, and the ADP + P are stored in myosin head for future use. When myosin releases from an actin and then binds with next actin on myofibril = Power Stroke When myosin releases form cross bridge and returns to ‘resting’ position = Recovery Stroke Full rest/recovery of muscle requires the active transport of calcium back to sarcoplasmic reticulum. Requires Achase, ATP When calcium leaves troponin - then troponin/tropomyosin complex returns to actin’s binding site.