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Maj Rishi PokhrelAnatomy

NAIHS

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

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

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

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

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

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

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

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

• 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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