1.
BIOMECHANICS &
ERGONOMICS-I
SHS.213.Lec-07
RESOURCE PERSON:
DR SANIA MAQBOOL
REFERENCE TEXT:
BASIC BIOMECHANICS – SUSAN J. HALL

2.
The Biomechanics of Human
Skeletal Muscle

3.
INTRODUCTION
► Types of muscle
► Skeletal muscle
► Structure and organization of skeletal muscle
► Structure of sarcomere
► Excitation contraction coupling

4.
Types of muscles
► Cardiac muscle: composes the
heart
► Smooth muscle: lines hollow
internal organs
► Skeletal (striated or voluntary)
muscle: attached to skeleton
via tendon

5.
FUNCTIONS of Skeletal Muscles
► Strength and Protection to skeleton by
distributing loads and absorbing shock
► Enable the joints to move
► Maintain body posture against force by
group action of muscles

6.
SKELETAL MUSCLE WORK
► Dynamic work – permits the locomotion and positioning of body
segments in space
► Static work – maintains body posture or position

7.
STRUCTURE AND
ORGANIZATION OF MUSCLE

8.
ORGANIZATIONAL HIERARCHY
► MUSCLE
► MUSCLE FASCICLE
► MUSCLE FIBER
► MYOFIBRIL
► SARCOMERE

9.
1. Muscle Fibers
► A single muscle cell is
termed a muscle fiber
► It is the structural unit of
skeletal muscle.
► It consist of many
myofibrils
► The plasma membrane
surrounding the muscle
fiber is called the
sarcolemma.
► The specialized
cytoplasm is termed
sarcoplasm

10.
1. Muscle Fibers 11
Structure & organization
o Several layers of connective tissue provide
the superstructure for muscle fiber
organization
o Each muscle fibre, is surrounded by a thin
connective tissue called the endomysium

11.
1. Muscle Fibers 13
Structure & organization
o Fibers are bundled into fascicles by connective
tissue sheaths referred to as the perimysium.
o Groups of fascicles forming the whole muscles are
then surrounded by the epimysium, which is
continuous with the muscle tendons

12.
MYOFIBRIL
► Each muscle fiber is composed of large numbers of delicate strands
► Myofibrils are contractile elements of muscle
► Almost 1µm in diameter

13.
MYOFIBRIL
► Myofibrils lie parallel to each other in sarcoplasm
► Extends throughout its length
► Vary in number depending on the size of muscle

14.
SARCOMERE
► Basic structural unit of the muscle fibre
► Transverse banding pattern in striated muscle
► Repeats itself along the length of muscle

15.
SARCOMERE
► It contains
► Actin – thin filaments
► Myosin – thick filaments
► Titin – elastic filaments
► Nebulin – inelastic filaments

16.
► The sarcoplasm of a muscle fiber contains
parallel, threadlike myofibrils, each
composed of myosin and actin filaments

17.
ACTIN
► Chief component of thin filaments
► Double helical structure
► Strands of beads spiral around each other

18.
ACTIN
► Two additional proteins – troponin, tropomyosin
► They are responsible for making and breaking contacts between
actin and myosin

19.
ACTIN
► TROPOMYOSIN – long polypeptide chain lies in between helices of
actin. Blocks myosin binding when muscle is relaxed.
► TROPONIN – globular molecule attached at regular intervals to
tropomyosin

20.
MYOSIN
► Thicker filament
► Resembles a lollipop
► Globular head projecting from a long shaft

21.
TITIN
► Third set of myofibril
filaments
► 1µm long
► Largest polypeptide
spans from Z – line to
M- line

22.
TITIN
► Connects the thick
filaments with Z-line
► Maintains central
position of A band
throughout
contraction and
relaxation

23.
NEBULIN
► Inelastic part
► Span from Z – line to actin filament
► Act as a template for thin filament assembly

24.
Sarcomere
•The alternating dark and
light bands give muscle its
striated appearance
•The A bands contain thick,
rough myosin filaments
•surrounded by thin,
smooth actin filaments
•The I bands contain only
thin actin filaments.
SARCOMERE STRUCTURE

25.
SARCOMERE STRUCTURE
► H – Zone (band containing only thick filament)
► A – band (dark band of myosin, overlap between actin and myosin)
► I – band (light band, contains portion of thin filaments not
overlapped with thick filaments)

26.
SARCOMERE STRUCTURE
► M – line ( narrow dark area in center of H zone)
► Z – line ( Thin filaments are attached at either end of sarcomere)

27.
► A network of membranous channels known as the sarcoplasmic
reticulum is associated with each fiber externally(with repeating
pattern of sarcomere).Regulate levels of calcium.
► Internally, the fibers are transected by tiny tunnels called
transverse tubules that open only externally. Help signals each
region of muscle cell

28.
MOLECULAR BASIS OF MUSCLE
CONTRACTION
► Sliding filament theory
► “Active shortening of sarcomere and hence the muscle results from
the relative movement of actin and myosin filaments past one
another while each retains its original length”

29.
► Sliding filament theory: relative movement of actin &
myosin filaments yields active sarcomere shortening
► Myosin heads or cross-bridges generate contraction
force
► Sliding of actin filaments toward center of
sarcomere: decrease in I band and decrease in H
zone as Z lines move closer
36
1. Muscle Fibers

30.
EXCITATION – CONTRACTION
COUPLING

31.
https://www.youtube.com/watch?v=MmZQ
RJZNIvA

32.
“I wish everyone could become
rich and famous so that they
can realize its not the answer.”
Jim Carrey

33.
SUMMARY
► Types of muscle
► Skeletal muscle
► Structure and organization of skeletal muscle
► Structure of sarcomere
► Excitation contraction coupling

34.
References
► Hall, S. J. Basic Biomechanics, (5th ed.), (Chinese, Korean, and
Portuguese editions also published) (2006). Dubuque: McGraw-Hill.

35.
QUIZ
► Draw structure of sarcomere

36.
QUIZ
► Enlist all events of excitation contraction coupling