Download - Muscle
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Maj Rishi PokhrelAnatomy
NAIHS
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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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• 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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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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Properties• Excitability – nerve impulse stimulates contraction
• Contractility – Long cells shorten & generate pulling force
• Elasticity – Can recoil after being stretched
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Muscle tissue: types
Skeletal Striated & voluntary
Cardiac Striated & involuntary
Smooth Nonstriated & involuntary
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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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Skeletal muscles: microscopyConnective tissue coverings:
Epimysium – entire muscle Perimysium – fascicles Endomysium – muscle fibre
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Skeletal muscles: microscopy• Multinucleated cylindrical cell, nucleus at periphery
• Exhibit cross striations
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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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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
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Aponeurosis
• Attachment of muscle by thin, broad sheet
• Composed of parallel bundles of collagen fibres
• E.g. External oblique aponeurosis
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Raphe
• Fibrous band; interdigitating fibres of aponeurosis
• Stretchable
• E.g. Mylohyoid raphe
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MR
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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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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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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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Classification of skeletal muscle
• Based on– Architecture of fasciculi– Action
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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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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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• 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
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Spiral / twisted fasciculi
– Trapezius
– Lattisimus dorsi
– Pectoralis major
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CRUCIATE FASCICULI
• Fasciculi are crossed – Sternocleidomastoid (SCM)– Masseter
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SCM
Masseter
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Classification : action of muscle
• Prime mover• Antagonist• Fixator• Synergist
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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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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
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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
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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
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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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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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• 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
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• 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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