Muscle tissue is composed of contractile cells called muscle fibers. There are three main types of muscle tissue: skeletal, cardiac, and smooth muscle. Skeletal muscle is striated and voluntary. Cardiac muscle is also striated and involuntary. Smooth muscle lacks striations and is involuntary. Muscle fibers contract when stimulated by motor neurons, shortening through a sliding filament mechanism utilizing actin and myosin fibers.

1. Muscle Histology
Assoc. Prof Dr. karim Al-Jashamy IMS 2009

2. Muscular Tissue
 Muscle tissue is composed of cells which have the
ability to contract (shorten) and relax (lengthen).
 Muscle tissue is highly vascular zed and dense
tissue.
 Muscle tissue can not regenerate itself once it has
been destroyed.
 Muscle cells are called muscle fibers.
 There are three types of muscle tissues:
a. Striated or skeletal muscle
b. Cardiac muscle or myocardial tissue
c. Smooth or visceral muscle

3. Muscular Tissue Types
 Striated or skeletal muscle: This muscle is composed of
long, cylindrical, parallel fibers.
 There are bands or striations present which run across the
width of the fiber. These fibers are multinucleated (more
than one nucleus present per cell).
 This type of muscle tissue is under conscious or voluntary
control.
 This muscle has the greatest strength of contraction but
tires most rapidly. It functions are locomotion and facial
expressions.

4. Muscular Tissue Types
 Cardiac muscle: Cardiac muscle fibers are branched at the end
with striations present, usually only one nucleus is present per
cell.
 The branches of each fiber come into contact at specialized
junctions called intercalated discs.
 It is involuntarily controlled by the autonomic nervous system
and hormones. Its contractions are short, but the muscle fibers
are constantly contracting.
 Its function is to create the pump which propels the blood
throughout the body.

5. Muscular Tissue Types
 Smooth or visceral muscle: These cells are spindle-shaped
(tapered on the ends) and lack striations.
 They have one nucleus present. They produce weaker
contractions, however they contract for extended periods of
time.
 They are involuntarily controlled by the autonomic nervous
system or hormones.
 They are found in the digestive organs, arteries and veins,
the trachea and bronchiole tubes, and the urogenital tract.
Their contractions propels or moves substances or objects
from one location to another.

6. Functions of muscle tissue
 Movement
 Maintenance of
posture
 Joint stabilization
 Heat generation

7. Special functional characteristics of muscle
 Contractility
 Only one action: to shorten
 Shortening generates pulling force
 Excitability
 Nerve fibers cause electrical impulse to travel
 Extensibility
 Stretch with contraction of an opposing muscle
 Elasticity
 Recoils passively after being stretched

8. Types of Muscle Tissue
Skeletal
•Attach to and move skeleton
•40% of body weight
•Fibers = multinucleate cells (embryonic cells fuse)
•Cells with obvious striations
•Contractions are voluntary
Cardiac: only in the wall of
the heart
•Cells are striated
•Contractions are
involuntary (not
voluntary)
Smooth: walls of hollow organs
•Lack striations
•Contractions are involuntary (not voluntary)

9. Similarities…
 Their cells are called fibers because they are elongated
 Contraction depends on myofilaments
 Actin
 Myosin
 Plasma membrane is called sarcolemma
 Sarcos = flesh
 Lemma = sheath

10. Skeletal muscle
Epimysium:
surrounds
whole muscle
Perimysium
Endomysium is around each
is around
muscle fiber
fascicle

11.  Each muscle: one nerve, one artery,
one vein Skeletal Muscle
 Branch repeatedly
 Attachments
 One bone to another
 Cross at least one movable joint
 Origin: the less movable attachment
 Insertion: is pulled toward the origin
 Usually one bone moves while the
other remains fixed
 In muscles of the limb, origin lies
proximal to the insertion (by
convention)
 Note: origin and insertion may switch
depending on body position and
movement produced

12. Attachments continued
 Many muscles span two or more joints
 Called biarticular or multijoint muscles
 Cause movements at two joints
 Direct or “fleshy” attachments
 Attachments so short that muscle appears to attach directly
to bone
 Indirect: connective tissue extends well beyond the
muscle (more common)
 Tendon: cordlike (most muscles have tendons)
 Aponeurosis: flat sheet
 Raised bone markings where tendons meet bones
 Tubercles, trochanters, crests, etc.

13. Some sites showing animations
of muscle contraction
 http://entochem.tamu.edu/MuscleStrucContractswf/i
ndex.html
 http://www.brookscole.com/chemistry_d/templates/s
tudent_resources/shared_resources/animations/musc
les/muscles.html

14. Skeletal muscle
 Fibers (each is one
cell) have striations
 Myofibrils are
organelles of the cell: This big
these are made up of cylinder is a
-an organelle
fiber: 1 cell
filaments
 Sarcomere
 Basic unit of contraction
 Myofibrils are long
rows of repeating
sarcomeres
 Boundaries: Z discs (or
lines)

15. Myofibrils
 Made of three types of filaments (or myofilaments):
 Thick (myosin)
 Thin (actin)
 Elastic (titin)
______actin
_____________myosin
titin_____

16. Sliding Filament Model
__relaxed sarcomere__ _partly contracted_
fully contracted
Sarcomere “A” band constant
shortens because because it is
actin pulled caused by
towards its middle myosin, which
by myosin cross doesn’t change
bridges length
Titin resists overstretching

18. EM (electron microscope): parts of 2 myofibrils

19.  Sarcoplasmic reticulum is smooth ER
 Tubules surround myofibrils
 Cross-channels called “terminal cisternae”
 Store Ca++ and release when muscle stimulated to contract
 To thin filaments triggering sliding filament mechanism of
contraction
 T tubules are continuous with sarcolemma, therefore whole
muscle (deep parts as well) contracts simultaneously

20. Neuromuscular Junction
Motor neurons innervate muscle
fibers
Motor end plate is where they
meet
Neurotransmitters are released
by nerve signal: this initiates
calcium ion release and muscle
contraction
Motor Unit: a motor neuron and all the muscle fibers it innervates (these all
contract together)
•Average is 150, but range is four to several hundred muscle fibers in a motor
unit
•The finer movement, the fewer muscle fibers /motor unit
•The fibers are spread throughout the muscle, so stimulation of a single motor
unit causes a weak contraction of the entire muscle

23. Types of skeletal muscle fibers
 Fast, slow and intermediate
 Whether or not they predominantly use oxygen to produce
ATP (the energy molecule used in muscle contraction)
 Oxidative – aerobic (use oxygen)
 Glycolytic – make ATP by glycolysis (break down of sugars without
oxygen=anaerobic)
 Fast fibers: “white fibers” – large, predominantly anaerobic,
fatigue rapidly (rely on glycogen reserves); most of the skeletal
muscle fibers are fast
 Slow fibers: “red fibers” – half the diameter, 3X slower, but can
continue contracting; aerobic, more mitochondria, myoglobin
 Intermediate: in between

24.  A skeletal muscle contracts when its motor
units are stimulated
 Amount of tension depends on
1. the frequency of stimulation
2. the number of motor units involved
 Single, momentary contraction is called a muscle
twitch
 All or none principle: each muscle fiber either
contracts completely or not at all
 Amount of force: depends on how many motor
units are activated
 Muscle tone
 Even at rest, some motor units are active: tense the
muscle even though not causing movement: “resting
tone”

25.  Muscle hypertrophy
 Weight training (repeated intense workouts): increases
diameter and strength of “fast” muscle fibers by increasing
production of
 Mitochondria
 Actin and myosin protein
 Myofilaments containing these contractile proteins
 The myofibril organelles these myofilaments form
 Fibers enlarge (hypertrophy) as number and size of
myofibrils increase
[Muscle fibers (=muscle cells) don’t increase in number but
increase in diameter producing large muscles]
 Endurance training (aerobic): doesn’t produce hypertrophy
 Muscle atrophy: loss of tone and mass from lack of stimulation
 Muscle becomes smaller and weaker
Note on terminology: in general, increased size is hypertrophy; increased number of
cells is hyperplasia

26. Tendon Anatomy
 Very strong, stronger than muscle for size
 As strong as bone with a failing point similar to steel!
 Can transmit force through ability to glide
 Passive component of the musculotendinous unit in
light of their incredible influence on the foot.
Tendon Histology
 30% Collagen, 2% Elastin,
68% Water
 Bulk is supplied by reticulin
 70% Type I collagen

27. Ligament Histology
 33% Composition: 90% Type I
collagen,
Elastin, Glycosaminoglycans.
67% Water

28. Anatomy of the Tendon
 Tropocollagen – the most basic molecular unit of
tendon
 3 Coverings:
 Endotenon- fascicles are surrounded by this areolar
CT, contains BV, L, N, and FB.
 Epitenon- Fascicles bound together by this 1-2 cell
fibroblastic & synovial layer
 Paratenon- loose areolar layer continuous with the
epitenon & perimysium, straight.

29. Anatomy of the Tendon
 Tendon/Synovial Sheath: acts like a pulley when
tendon has an angled course.
 Peritenon- term applied collectively to all CT
structures associated with a tendon incl para-, meso-
, epi-, and endotenon.

30. Tendon Anatomy

31. Tendon Anatomy

32. Tendon Circulation
 3 Sources:
a) Small amount from the central blood vessels
originating in the muscle.
b) Some from vessels of the bone and periosteum
near the tendon’s insertion.
c) Majority comes from small vessels in the
paratenon or through the mesotenon. If absent
then carried thru the vincula. Synovial fluid also
nourishes the tendon.

33. Tendon Sheath Anatomy

34. Tendon Innervation
 Afferent supply only
 Source in musculotendinous
junction and external local
nerves.
 Golgi tendon organs: monitor
increases in tension rather than
length.

35. Tendon Attachment to Bone
 Attach at 90° angles to bone
in 4 layers:
1. Tendon collagen fibers
2. Fibrocartilage
3. Bone
4. Sharpey’s fibers – originate
in bone and end in
perisoteum.