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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 Muscle. Cells are cylindrical and striated

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Muscular System

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  • 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
Cardiac Muscle

Cells are cylindrical and striated

Single large, centrally located nucleus

Branched and connected to each other via intercalated discs

smooth muscle
Smooth Muscle

Cells are spindle shaped, non-striated

Single large, centrally located nucleus

Gap junctions are found between cells

skeletal muscle
Skeletal Muscle

Cells are very long, cylindrical and striated

Multinucleated, found towards periphery

functions of skeletal muscle
Functions of Skeletal Muscle

Body Movement

Maintenance of posture

Production of body heat


Characteristic Properties of Muscle





general terms
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
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
Muscle Anatomy
  • Skeletal muscle fibers = muscle cells
  • Each fiber has a connective tissue covering = external lamina endomysium
muscle anatomy13
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
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



Muscles of Facial Expression

The skeletal muscles of the face are attached to the skin [cutaneous muscles]

Orbicularis oculi


Levator palpebrae

Corrugator supercilii


Muscles of Facial Expression

Orbicularis oris


Zygomaticus – major / minor

Levator anguli oris


Levator labii superioris

Depressor anguli oris

Depressor labii inferioris




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
Muscles of Mastication



Pterygoids – lateral/medial

Suprahyoid Muscles

Infrahyoid Muscles

proteins found in muscle tissue
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
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
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
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.