GROSS ANATOMY SKELETAL MUSCLES

BY TAHIR AMIN SULEHRIAGRADUATE STUDENT(FIRST YEAR 2014)

MYOLOGYSTUDY OF MUSCLES THE TERM “MUSCLE” IS DERIVED FROM LATIN WORD “MUSCULUS” DIMINUTIVE OF “MUS” MEANING MOUSE. THEY WERE NAMED SO BECAUSE THEIR BELLY RESEMBLES BODY OF THE MOUSE AND THEIR TENDONS RESEMBLE MOUSE’S TAIL. MUSCLES ARE CONTRACTILE TISSUES THAT BRING ABOUT MOVEMENTS OF DIFFERENT BODY PARTS. THEY CAN BE REGARDED AS MOTORS OF HUMAN BODY BECAUSE THEY PROVIDE ALL THE FORCE NECESSARY TO PERFORM DIFFERENT TYPES OF MOVEMENTS. WHETHER IT IS THE LOCOMOTION OF BODY AS A WHOLE OR JUST MOTION OF ITS PARTS, ITS ALL BECAUSE OF MUSCLES.

TYPES OF MUSCLES

MUSCLES ARE OF THREE TYPES; SKELETAL, SMOOTH AND CARDIAC.

SKELETAL MUSCLES

•THEY ARE ALSO KNOWN AS STRIPED, STRIATED, SOMATIC AND VOLUNTARY MUSCLES

•THEY ARE THE MOST ABUNDANT TYPE AND ARE FOUND ATTACHED TO THE SKELETON. FOR THIS REASON THEY ARE CALLED SKELETAL MUSCLES.

•THEY ARE INNERVATED BY SOMATIC NERVOUS SYSTEM AND ARE THEREFORE UNDER VOLUNTARY CONTROL. THEY OBEY THE WILL OF HUMAN BEINGS.

•THEY RESPOND QUICKLY TO STIMULI AND ARE CAPABLE OF RAPID CONTRACTIONS. THEY GET FATIGUED EASILY BECAUSE OF THEIR RAPIDITY.

PARTS OF A TYPICAL SKELETAL MUSCLE

A TYPICAL SKELETAL MUSCLE CONSISTS OF TWO ENDS AND TWO PARTS

ENDS:A TYPICAL SKELETAL MUSCLE CONSISTS OF TWO ENDS. THESE ARE;1.ORIGIN IS ONE END OF THE MUSCLE WHICH REMAINS FIXED DURING ITS CONTRACTION.2.INSERTION IS THE OTHER END WHICH MOVES DURING ITS CONTRACTION. IN THE LIMB MUSCLES, THE ORIGIN IS USUALLY PROXIMAL TO INSERTION.

PARTS:A TYPICAL SKELETAL MUSCLE CONSISTS OF TWO PARTS. THESE ARE;3.FLESHY PART IS CONTRACTILE, AND IS CALLED THE ‘BELLY’.4.FIBROUS PART IS NON-CONTRACTILE AND INELASTIC. WHEN CORD-LIKE OR ROPE-LIKE, IT IS CALLED TENDON; WHEN FLATTENED, IT IS CALLED APONEUROSIS.

FASCICULAR ARCHITECTURE OF MUSCLES THE ARRANGEMENT OF MUSCLE FIBERS VARIES ACCORDING TO THE DIRECTION, FORCE AND RANGE OF HABITUAL MOVEMENT AT A PARTICULAR JOINT. THE FORCE OF MOVEMENT IS DIRECTLY PROPORTIONAL TO THE NUMBER AND SIZE OF MUSCLE FIBERS, AND THE RANGE OF MOVEMENT IS PROPORTIONAL TO THE LENGTH OF FIBERS. THE MUSCLES CAN BE CLASSIFIED ACCORDING TO THE ARRANGEMENT OF THEIR FASCICULI INTO THE FOLLOWING GROUPS.

FASCICULAR ARCHITECTURE OF MUSCLES

MUSCLE WITH PARALLEL FASCICULI

THESE ARE MUSCLES IN WHICH THE FASCICULI ARE PARALLEL TO THE LINE OF PULL. THESE MUSCLES MAY BE:

1.QUADRILATERAL, FOR EXAMPLE THYROHYOID,

2.STRAP-LIKE, FOR EXAMPLE STERNOHYOID AND SARTORIUS.

3.STRAP-LIKE WITH TENDINOUS INTERSECTIONS, FOR EXAMPLE RECTUS ABDOMINIS.

4.FUSIFORM, FOR EXAMPLE BICEPS BRACHII, DIGASTRIC.

THE RANGE OF MOVEMENT IN SUCH MUSCLES IS MAXIMUM.

MUSCLES WITH OBLIQUE FASCICULI WHEN THE FASCICULI ARC OBLIQUE TO THE LINE OF PULL, THE MUSCLE MAY BE TRIANGULAR, OR PENNATE (FEATHCR-LIKE) IN THE CONSTRUCTION. THIS ARRANGEMENT MAKES THE MUSCLE MORE POWERFUL, ALTHOUGH THE RANGE OF MOVEMENT IS REDUCED. OBLIQUE ARRANGEMENTS ARE OF THE FOLLOWING TYPES:

1.TRIANGULAR, E.G. TEMPORALIS, ADDUCTOR LONGUS.

2.UNIPENNATE, E.G. FLEXOR POLLICIS LONGUS, EXTENSOR DIGITORUM LONGUS, PCRONCUS TCRTIUS, PALMAR INTCROSSCI.

3.BIPENNATE, E.G. RECTUS FEMORIS, DORSAL INTEROSSEI, PCRONCUS LONGUS, FLEXOR HALLUCIS LONGUS.

4.MULTIPENNATE, E.G. SUBSCAPULARIS, DELTOID (ACROMIAL FIBERS].

5.CIRCUMPENNATE, E.G. TIBIALIS ANTERIOR.

MUSCLES WITH SPIRAL OR TWISTED FASCICULI

SPIRAL OR TWISTED FIBERS ARE FOUND IN TRAPEZIUS, PECTORALIS MAJOR, LATISSIMUS DORSI, SUPINATOR, ETC. IN CERTAIN MUSCLES THE FASCICULI ARE CROSSED. THESE ARE CALLED CRUCIATE MUSCLES, E.G. STERNOCLEIDOMASTOID, MASSETER AND ADDUCTOR MAGNUS.

NOMENCLATURE OF MUSCLES1.ACCORDING TO THEIR SHAPE, E.G. TRAPEZIUS, RHOMBOIDEUS, SERRATUS ANTERIOR, LATISSIMUS DORSI, ETC.

2.ACCORDING TO THE NUMBER OF HEADS OF ORIGIN, E.G. BICEPS, TRICEPS, QUADRICEPS, DIGASTRIC, ETC.

3.ACCORDING TO THEIR GROSS STRUCTURE, E.G. SEMITENDINOSUS, SEMIMEMBRANOSUS, ETC.

4.ACCORDING TO THEIR LOCATION, E.G. TEMPORALIS, SUPRA-SPINATUS, INTERCOSTALES.

5.ACCORDING TO THEIR ATTACHMENTS, E.G. STYLOHYOID, CRICOTHYROID, ETC.

6.ACCORDING TO THEIR ACTION, E.G. ADDUCTOR LONGUS, FLEXOR CARPI ULNARIS, ABDUCTOR POLLICIS LONGUS, ETC.

7.ACCORDING TO DIRECTION OF THEIR FIBERS, E.G. RECTUS ABDOMINIS, TRANSVERSUS ABDOMINIS, ORBICULARIS OCULI.

8.A MUSCLE WITH TWO BELLIES WITH AN INTERVENING TENDON IS CALLED DIGASTRIC MUSCLE. MUSCLE WITH NUMBER OF INTERVENING TENDONS OR INTERSECTIONS IS THE RECTUS ABDOMINIS.

9.THE MUSCLES THAT EXTEND OVER TWO OR MORE JOINTS ARE CALLED DIARTHRIC OR POLYARTHRIC MUSCLES, E.G. FLEXOR CARPI RADIALIS AND FLEXOR DIGITORUM PROFUNDUS.