1. The document describes skeletal muscle, including its classification, structure, properties, innervation and applied anatomy. 2. Key points include that skeletal muscle is striated, voluntary muscle attached to bones that acts as the motors of the body. It describes the fascicular architecture of muscles and how they are classified based on this. 3. Laws of innervation and the concept of motor units are also explained. Applied anatomy discusses muscle paralysis, spasm, atrophy, hypertrophy and regeneration.

1. 1

2. At the end of this class, you should be able to ..
• Describe skeletal muscle
• Classify skeletal muscles
• Understand concepts: motor point, motor unit
• Describe Laws of innervation
• Appreciate importance of skeletal muscles in
clinical practice

3. • A male child born to healthy parents with
normal pregnancy
– Walking was delayed … 4 years
– Calf muscles grew unusually large
– Couldnot walk after 11 years
– Died at the age of 20 – respiratory failure
– His elder brother was fine
• What went wrong?

4. MUSCLE
(Latin – Mus = Mouse)
(Gk = Mys)
•
•
Myositis, myopathy, myology
Resemble mouse - tapering
ends (tendons) - tail
Contractile tissue - brings
about movement
Motors of body
•
•

5. Properties
• Excitability – nerve impulse stimulates contraction
• Contractility – Long cells shorten & generate pulling force
• Elasticity – Can recoil after being stretched

6. Muscle tissue: types
▪ Skeletal
▪ Striated & voluntary
▪ Cardiac
▪ Striated & involuntary
▪ Smooth
▪ Nonstriated & involuntary

7. Skeletal muscle: features
•
•
•
•
Striped / Striated / Somatic / Voluntary
Most abundant
Attached to skeleton
Supplied by somatic nerves; voluntary control
Responds quickly to stimuli
Capable of rapid contraction; easily fatigued
Help in adjusting to external environment
•
•
•
• Under highest nervous control of cerebral cortex

8. Skeletal muscles: microscopy
Connective tissue coverings:
▪ Epimysium – entire muscle
▪ Perimysium – fascicles
▪ Endomysium – muscle fibre

9. Skeletal muscles: microscopy
•
•
Multinucleated cylindrical cell, nucleus at periphery
Exhibit cross striations

10. SKELETAL MUSCLE: PARTS
•
•
Fleshy, Contractile - Belly
Fibrous, Non contractile
– Tendon (cord like)
– Aponeurosis (flattened sheet)
Origin: relatively fixed during
contraction
Insertion: moves during
contraction
Origin & insertion / attachments
•
•
•

11. Tendon
• Fibrous, cord like, non-contractile
• Composed of bundles of
collagen fibres
• Surrounded by epi-tendineum
• Supplied by sensory nerve
• Vascular needs- minimal
• Tendon transfer & transplantation
• Heals very slowly

12. Aponeurosis
• Attachment of muscle by thin,
broad sheet
Composed of parallel bundles of
collagen fibres
E.g. External oblique
aponeurosis
•
•

13. Raphe
• Fibrous band; interdigitating
fibres of aponeurosis
Stretchable
E.g. Mylohyoid raphe
•
•

14. Nomenclature of skeletal muscles
•
•
•
•
•
•
•
•
Shape: Trapezius, Rhomboideus, Deltoid
Number of heads: Biceps, Triceps, Quadriceps
Structure: Semimembranosus, Semitendinosus
Location: Temporalis, Supraspinatus
Attachments: Stylohyoid, Cricothyroid
Action: Adductor longus, Flexor carpi ulnaris
Direction of fibres: Rectus abdominis, Transversus abdominis
Relative position: Medial & lateral pterygoids

15. Nerve supply
•
•
Nerve supplying a muscle - motor nerve
Motor point
– Site where motor nerve enters muscle
– May be one or more
– Electrical stimulation at this point is more effective
Sensory supply: proprioception
•

16. •
•
Motor unit - motor neuron & all muscle fibres it supplies
Fine movements (fingers, eyes) - small motor units: 5-10
fibres
Large weight-bearing muscles (thighs, hips) - large motor
units :100-200 fibres
Hybrid muscles
•
•

17. Classification of skeletal muscle
• Based on
– Architecture of fasciculi
– Action

18. Fascicular architecture
• Force - directly proportional to number & size of
muscle fibres
• Range - directly proportional to length of fibres
• Classified: According to arrangement of fasciculi
– Parallel
– Oblique
– Spiral
– Cruciate

19. Parallel fasciculi
•Fasciculi are parallel to line of pull
•Range of movements is maximum
•Subtypes
– Quadrilateral -Thyrohyoid
– Strap like - Sartorius
– Strap like with tendinous intersections - Rectus abdominis
– Fusiform - Biceps brachii

20. • Fasciculi oblique to line of pull
• Power increased, range decreased
• Subtypes
– Triangular - Temporalis
– Unipennate - Flexor pollicis longus
– Bipennate - Rectus femoris
– Multipennate – Deltoid (middle fibres)
– Circumpennate - Tibialis anterior
Oblique fasciculi

21. Spiral / twisted fasciculi
– Trapezius
– Lattisimus dorsi
– Pectoralis major

22. CRUCIATE FASCICULI
• Fasciculi are crossed
– Sternocleidomastoid (SCM)
– Masseter

23. Classification :action of muscle
• Prime mover
• Antagonist
• Fixator
• Synergist

24. Prime mover
• Muscle or group of muscles
that bring about a desired
movement
Gravity may also assist
E.g. Brachialis as flexor at
elbow joint
•
•

25. Antagonist (opponent)
• Muscle or group of muscles that directly oppose movement
under consideration
Relax & control movement to make it smooth, jerk free &
precise.
Prime mover & antagonist cooperate
E.g. Triceps in elbow flexion
•
•
•

26. Fixators (fixation muscles)
• Stabilize parts & thereby
maintain position while
prime movers act
E.g.: Muscles holding
scapula steady are acting as
fixator while deltoid moves
humerus
•

27. Synergists
•
•
•
Special fixation muscles
Partial antagonist to prime mover
When a prime mover crosses two or more joints, synergists
prevent undesired actions at intermediate joints

28. Laws of innervation
• Hilton’s law: “the nerve supplying the muscles
extending directly across and acting at a given joint
also innervate the joint & skin overlying the joint
“Only actions are represented in cortex”
“Spinal segments supplying the antagonists are in a
sequence”
“Spinal segments supplying immediately distal group of
muscles are in sequence”
•
•
•

29. Applied anatomy
Paralysis / paresis
• Loss of power of movement
• Muscles are unable to contract
• Damage to motor neural pathways
– Upper motor neuron (UMN)
– Lower motor neuron (LMN)

30. • Muscular spasm – spontaneous / involuntary
contraction
• May be
– Localized – commonly caused by a “muscle pull”
– Generalized – seen in Tetanus & Epilepsy
Applied anatomy

31. • Disuse atrophy
– Muscles not used for long time, become thin & weak
– Reduction in size (muscular wasting)
– Seen in paralysis & generalized debility
• Hypertrophy
– Excessive use of a particular muscle results in better
development or hypertrophy (Body builders & Athletes)
Applied anatomy

32. • Regeneration
– Capable of limited regeneration
– Large regions damaged- regeneration does
not occur & replaced by CT
• Muscular dystrophy
– Inherent defect in cell membrane of muscle
– Rupture of muscle fibers
– X- linked recessive
– Duchene’s & Baker’s