Muscles

1. Muscle
Dr. Rohin Garg
Associate Professor,
Department of Anatomy,
AIIMS, Rajkot, Gujarat, India.

2. Muscle tissue vs. Muscle as an organ
One of the 4
primary tissue
types
How many
subtypes?
Made up of _____
tissue types.
> 700 skeletal
muscles
Word roots:
sarco
mys

3. There are four characteristics associated with
muscle tissue:
 Excitability
 Contractility
 Extensibility
 Elasticity
- Tissue can receive & respond to stimulation
- Tissue can shorten & thicken
- Tissue can lengthen
- After contracting or lengthening, tissue always
wants to return to its resting state

4. Function of Skeletal Muscles
1. Skeletal movement
2. Posture and body position
3. Support of soft tissues
4. Guarding of entrances & exits
5. Maintenance of body temperature

5. Gross Anatomy
Each skeletal muscle is wrapped by 3 concentric
layers of connective tissue.

6. Three types of muscle
Skeletal Cardiac
Smooth

7. Skeletal muscle tissue
• Associated with & attached to the skeleton
• Under our conscious (voluntary) control
• Microscopically the tissue appears striated
• Cells are long, cylindrical & multinucleate

8. Smooth (visceral) muscle tissue
• Makes up walls of organs & blood vessels
• Tissue is non-striated & involuntary
• Cells are short, spindle-shaped & have a single nucleus
• Tissue is extremely extensible, while still retaining ability
to contract

9. Cardiac muscle tissue
• Makes up myocardium of heart
• Unconsciously (involuntarily) controlled
• Microscopically appears striated
• Cells are short, branching & have a single nucleus
• Cells connect to each other at intercalated discs

10. Differentiation
 Location
 Voluntary/Involuntary
 Histology
 Shape, branching, Nuclei
 Striations (Light & Dark Bands)
 Intercalated Disc
 Nerve Supply
 Blood Supply
 Speed of Contraction
 Fatigue

11. 1) Slow (or Red) Fibers [Type I]
Slower but continuous contraction for
extended periods
Smaller diameter (~ half)
contain myoglobin
more capillaries
more mitochondria
More oxidative enz
Less phosphorylases
Do not fatigue as fast due to ?
Three Types of Muscle Fibers

12. Fast contraction after nervous stimulation
Large diameter
large glycogen reserve
More phosphorylases
few mitochondria
Less oxidative enz
Less myoglobin
densely packed myofibrils
Fatigue fast due to mainly anaerobic respiration
2) Fast (or White) Fibers [Type II]

13. 3) Intermediate Fibers
Have attributes inbetween fast and slow
types
Most skeletal muscles contain mixture of
fiber types. Proportion of fast to slow depends
on ___________?
One motor unit only contains one fiber type
Eye, hand: ____ fibers dominate
Back, calf: ____ fibers dominate

14. Microanatomy of Skeletal Muscle Fibers
Some vocabulary:
Skeletal muscle fiber or
myofiber
Sarcolemma
Sarcoplasm
Sarcoplasmic reticulum
Myofilaments
Contractile Unit=
Sarcomere

15. Thin Filament: Actin

16. Thick Filament: Myosin

17. Anatomy of
Skeletal Muscles
Origin—
– stationary end of a
muscle when contracts
Belly--
– thicker, middle region of
muscle
Insertion—
– mobile end of muscle

18. Organization of Skeletal Muscle Fibers
Effect of individual muscle contraction
determined by:
1. arrangement of muscle fibers
2. way of attachment to skeletal system
Bundles of muscle fibers =
Muscle fibers within 1 fascicle are parallel
4 types of fascicle organization

19. Muscle types based on fascicle direction
10-19

20. 10-20
Skeletal Muscle types —based
on fascicle direction
1. Fusiform muscles
– Features:
– biceps brachii m., gastrocnemius of the calf
2. Parallel muscles; long, uniform width, having
parallel fascicles
– rectus abdominis m., sartorius of the thigh, zygomaticus
major
3. Convergent muscle; fan-shaped, broad at origin
and tapering to a narrower insertion
– pectoralis major of the chest

21. 10-21
Skeletal Muscle Type
4. Pennate muscles (feather-shaped)
– fascicles insert obliquely on a tendon, like the shaft of the
feather
– Unipennate—fascicles approach the tendon from one side;
palmar interosseus (hand) (Fig.)
– Bipennate—fascicles approach the tendon from both sides;
rectus femoris (thigh) (Fig.)
– Multipennate--like feathers with their quills on a single
point; deltoid (shoulder) (Fig.)
5. Circular muscles (sphincters)
– Features:
– orbicularis oculi (eyelids), orbicularis oris, urethral and
anal sphincters

22. Circular Muscles
= Sphincters
Concentric fibers
adjust opening
Examples: orbicularis
occuli and oris

23. Types of Actions
 flexion, extension
 adduction, abduction
 elevation, depression
 circumduction
 pronation, supination
etc. . . . .

24. Muscles based on actions
 Action— movement produced by a muscle
Prime mover or agonist
– produces . . .
– Example: in flexing the elbow, the prime mover is the
brachialis
Antagonist is a muscle that . . .
– opposes the _____________
– Moderates the speed or range of the agonist;
preventing excessive movement and injury
– Example: Triceps brachii
Action of Paradox

25. Muscles based on actions
Fixator is a muscle that . . .
– Stablize proximal joint
– Elbow flexion– the rhomboids holds the
scapula in place.
Synergist aids the prime mover
– May stabilize the nearby joint
– Or modify the direction of movement
– Example: works with brachialis, biceps brachii as a
synergist to flex the elbow

26. Naming of skeletal Muscles
Orientation of fibers
Size & shape
Location
Action
Attachments
Gross Structure (no. of Heads, depth)
Use muscle name to help identify its location,
appearance and function!

27. Motor Point
Motor Unit
Hybrid/Composite Muscle
Types of action
Isometric
Isotonic: 1-Concentric; 2- Eccentric

28. Few Definitions
Paralysis: Anaesthesia
Spasm
Atrophy/Hypertrophy/Hyperplasia
Myasthenia gravis
Ischaemia
Angina

29. Any Vestigial Muscle?
Longest?
Smallest?
Largest?
Intramuscular Injections?