1) The document discusses skeletal muscle anatomy and physiology, describing the different types of skeletal muscle fibers and their classifications based on architecture and function. 2) It also covers motor units, nerve supply, and applied concepts like muscle paralysis, spasm, atrophy, hypertrophy, and regeneration. 3) Key points include the structures of skeletal muscle like tendons and fascicles, fiber types, and how muscles are classified based on their prime mover, antagonist, fixator, or synergist actions.

1. www.slideshare.net 1
Maj Rishi Pokhrel
Anatomy
NAIHS

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
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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?
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4. MUSCLE
(Latin – Mus = Mouse)
(Gk = Mys)
• Myositis, myopathy, myology
• Resemble mouse - tapering
ends (tendons) - tail
• Contractile tissue - brings
about movement
• Motors of body
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5. Properties
• Excitability – nerve impulse stimulates contraction
• Contractility – Long cells shorten & generate pulling force
• Elasticity – Can recoil after being stretched
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6. Muscle tissue: types
 Skeletal
 Striated & voluntary
 Cardiac
 Striated & involuntary
 Smooth
 Nonstriated & involuntary
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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
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8. Skeletal muscles: microscopy
Connective tissue coverings:
 Epimysium – entire muscle
 Perimysium – fascicles
 Endomysium – muscle fibre
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9. Skeletal muscles: microscopy
• Multinucleated cylindrical cell, nucleus at periphery
• Exhibit cross striations
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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
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11. 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
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13. Raphe
• Fibrous band; interdigitating
fibres of aponeurosis
• Stretchable
• E.g. Mylohyoid raphe
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MR

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
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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
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16. MOTOR UNIT
• 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
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17. Classification of skeletal muscle
• Based on
– Architecture of fasciculi
– Action
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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
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19. FASCICULAR ARCHITECTUREParallel 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
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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
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Oblique fasciculi

21. Spiral / twisted fasciculi
– Trapezius
– Lattisimus dorsi
– Pectoralis major
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22. CRUCIATE FASCICULI
• Fasciculi are crossed
– Sternocleidomastoid (SCM)
– Masseter
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SCM
Masseter

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

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
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Deltoid

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
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Flexor tendon

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

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• 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
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