muscle anatomy

1. Section 1, Chapter 9
Muscular System

2. Muscle is derived from Musculus, for “Mouse”
Imagine a mouse running beneath the skin.
Functions of Muscles:
1. Body movement
2. Maintain posture
3. Produces heat
4. Propel substances
through body
5. Heartbeat
Types of muscles include:
1. Smooth muscle
2. Cardiac muscle
3. Skeletal muscle

3. Smooth Muscle
Characteristics of smooth muscles
• Involuntary control
• Tapered cells with a single, central
nucleus
• Lack striations

4. Smooth Muscle
There are two types of smooth muscles
• Multi-unit Smooth Muscle
• unorganized cells that contract
as individual cells
•Located within the iris of eye
and the walls of blood vessels
• Visceral (single-unit) Smooth Muscle
• Form sheets of muscle
• Cells are connected by gap junctions
• Muscle fibers contract as a group
• Rhythmic contractions
• Within walls of most hollow organs
(viscera)

5. Cardiac Muscle
•Located only in the heart
•Striated cells
•Intercalated discs
• Muscle fibers branch
•Muscle fibers contract
as a unit
• Self-exciting and rhythmic

6. Skeletal Muscle
• Usually attached to bone
• Voluntary control
• Striated (light & dark bands)
• Muscle fibers form bundles
• Several peripheral nuclei

7. Coverings of Skeletal Muscle
Fascia
• Dense connective tissue surrounding skeletal muscles
Tendons
• Dense connective tissue that attaches muscle to bones
• Continuation of muscle fascia and bone periosteum
Aponeurosis
• Broad sheet of connective tissue attaching muscles to
bone, or to other muscles.

9. Coverings of Skeletal Muscle
Epimysium
• Connective tissue that covers the
entire muscle
• Lies deep to fascia
Perimysium
• Surrounds organized bundles of
muscle fibers, called fascicles
Endomysium
• Connective tissue that covers
individual muscle fibers (cells)

10. Figure 9.3 Scanning electron micrograph of a fascicle
surrounded by its perimysium. Muscle fibers within the
fascicle are surrounded by endomysium.

11. Organization of Skeletal Muscle
Fascicle
Organized bundle of muscle fibers
Muscle Fiber
Single muscle cell
Collection of myofibrils
Myofibrils
Collection of myofilaments
Myofilaments
Actin filament
Myosin filament
Figure 9.2
Skeletal muscle
organization

13. Skeletal Muscle Fibers
Sarcolemma
• Cell membrane of muscle fibers
Sarcoplasm
• Cytoplasm of muscle fibers
Sarcoplasmic Reticulum
• Modified Endoplasmic Reticulum
• Stores large deposits of Calcium
sarcolemma

14. Skeletal Muscle Fibers
(Transverse)T-tubules:
• invaginations of sarcolemma,
extending into the sarcoplasm.
Cisternae:
• enlarged region of sarcoplasmic
reticulum, adjacent to the t-tubules
Triad
• T-tubule + adjacent cisternae
Openings into t-tubules

15. Myofibrils
Myofibrils are bundles of
actin and myosin filaments.
• Actin – thin filament
• Myosin – thick filament
Striations appear from the
organization of actin and
myosin filaments
Figure 9.4 Organization of actin and myosin filaments

16. Sarcomere
A sarcomere is the functional unit of
skeletal muscle
• A sarcomere is the area between
adjacent Z-lines.
•During a muscle contraction the z-lines
move together and the sarcomere shortens.

17. Sarcomere

18. Striations appear from alternate light and dark
banding patterns.
Z Line is the attachment site of actin
filaments (center of I bands)
I Bands (light band): consists of only
actin filaments
A Bands (dark band) : consists of
myosin filaments and the overlapping
portion of actin filaments
Figure 9.5 thin and thick filaments in a
sarcomere.

19. filaments
Thin filaments
composed of actin proteins
Thin filaments are
associated with troponin
and tropomyosin proteins
Thick filaments
composed of myosin proteins
During muscle contraction the
heads on myosin filaments
bind to actin filaments forming
a Cross-bridge

20. Cross-Bridges
When a muscle is at rest, myosin heads are extended in the “cocked” position.
During a contraction, myosin heads bind to actin, forming a cross-bridge and the
myosin head pivot forward (Power Stroke) and back (Recovery stroke)

21. Troponin-Tropomyosin Complex
The troponin-tropomyosin complex prevents crossbridge formation when the muscle is at rest.
Tropomyosin
Blocks binding sites on
actin when a muscle is
at rest
Troponin
Ca2+ binds to troponin
during a muscle contraction.
Troponin moves repositions the
tropomyosin filaments, so the
myosin and actin filaments can
interact.