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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 MuscleCells 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 MuscleBody Movement
Maintenance of posture
Production of body heat
Communication
Characteristic Properties of MuscleContractibility
Excitability
Extensibility
Elasticity
General TermsOrigin [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 changesConcentric – 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 ShapesGrouped 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 MasticationTemporalis
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 PhysiologyInput 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 CouplingSarcoplasmic 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.
