The muscular system contains three types of muscle tissue - cardiac, smooth, and skeletal. Skeletal muscle is voluntary and found associated with bones, containing striated, multinucleated cells. Skeletal muscle functions include body movement, posture, and heat production. Muscles have properties of contractibility, excitability, and elasticity. Contractions can be isometric or isotonic, with isotonic contractions being either concentric to shorten a muscle or eccentric to lengthen it against resistance. Muscle fibers are bundled and innervated by motor neurons. Calcium release triggers cross-bridging between actin and myosin filaments, causing muscle contraction through an energy-requiring cycle.

1. Muscular System

2. 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

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

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

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

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

8. 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

9. 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.

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

13. 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

14. 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

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

18. Levator palpebrae

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

20. 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

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

26. 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

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

29. 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

30. 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

31. 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

34. 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.