The Muscles (Myology) By Dr.Pardeep Kumar

The General Description of Muscles

Muscular System The Muscular System Muscles are responsible for all types of body movement – they contract or shorten and are the machine of the body. Skeletal is a voluntary muscle Skeletal muscles share 40% of body weight.

Muscular System Characteristics of Muscles Muscle cells are elongated (muscle cell = muscle fiber) Contraction of muscles is due to the movement of microfilaments

Muscular System Skeletal Muscle Characteristics Most are attached by tendons to bones Cells are multinucleate Striated – have visible banding Voluntary – subject to conscious control Cells are surrounded and bundled by connective tissue = great force, but tires easily

Muscular System Skeletal Muscles (striated or voluntary muscles) are those which attach to bones and have the main function of contracting to facilitate movement of our skeletons.

Structure of skeletal muscle Structure of skeletal muscle Muscular System Structure of skeletal muscle Structure of skeletal muscle

Structure of skeletal muscle Structure of skeletal muscle Muscular System Structure of skeletal muscle Structure of skeletal muscle Epimysium: This is the connective tissue wrap just under the deep fascia that surrounds the entire muscle Perimysium: This connective tissue surrounds each individual fascicle (bundle of muscle fibers). Endomysium: This is the connective tissue wrapped around each individual muscle cell (fiber). Myofibrils: threadlike fibrils that make up the contractile part of a striated muscle fiber. Fascia – on the outside of the epimysium   skeletal muscle structure

Structure of skeletal muscle Structure of skeletal muscle Muscular System Structure of skeletal muscle Structure of skeletal muscle Muscle fibers are made up of a group of myofibrils. Myofibrils contain myofilaments. The myofibrils have distinct, repeating microanatomical units, termed sarcomeres, which represent the basic contractile units of the muscle fiber/cell (myocyte). Myofilaments (actin & myosin) are responsible for muscle movement.

Structure of skeletal muscle Muscular System Structure of skeletal muscle Myofilaments: (Thick and Thin) Myosin: thick filaments Actin: thin filaments A unit of thick and thin filaments is known as a Sarcomere. These structures hold the key to muscle contraction. The staggered thin and thick filaments has the effect as one might pull a rope towards oneself hand over hand.

Structure of skeletal muscle Muscular System Structure of skeletal muscle

Structure of skeletal muscle Muscular System Structure of skeletal muscle

Muscular System Skeletal Muscle Attachments Epimysium blends into a connective tissue attachment Tendon – cord-like structure Aponeuroses – sheet-like structure Sites of muscle attachment Bones Cartilages Connective tissue coverings

Origin and insertion of muscles Muscular System Origin and insertion of muscles Muscles are attached to at least two points Origin: the point where the tendon attaches to the bone which does not move during muscle action. Insertion: the point where the tendon attaches to the bone which moves during an action. e.g. Action of biceps muscle: Scapula is origin (Proximal point) and radius is the insertion. (distal point)

Muscular System Action of skeletal Muscles Prime mover – muscle with the major responsibility for a certain movement Antagonist – muscle that opposes or reverses a prime mover Synergist – muscle that aids a prime mover in a movement and helps prevent rotation

Muscular System Naming of Skeletal Muscles Direction of muscle fibers Example: rectus (straight) Relative size of the muscle Example: maximus (largest)

Muscular System Naming of Skeletal Muscles Location of the muscle Example: many muscles are named for bones (e.g., temporalis) Number of origins Example: triceps (three heads)

Muscular System Naming of Skeletal Muscles Location of the muscles origin and insertion Example: sterno (on the sternum) Shape of the muscle Example: deltoid (triangular) Action of the muscle Example: flexor and extensor (flexes or extends a bone)

Muscles of Trunk Muscular System It includes:- Muscles of Back Muscles of thorax Diaphragm Muscles of abdomen

The muscles of back Superficial group Trapezius Latissimus dorsi Levator scapulae Rhomboideus Major Rhomboideus Minor

2.Levator scapular 1.Trapezium Deltoid Triangle of ausculation 3.Rhomboideus 4.Latissimus dorsi Thoracolumbar fascia

Trapezius Origin – medial 3rd of superior nuchal line of occipital bone External occipital protuberance Ligamentum nuchae Spine of 7th cervicle vertebrae T1 – T12 spines Corresponding supraspinatous ligaments Insertion – Lateral 3rd of clavicle Acromion & upper lip of crest of spine Medial end of spine of Scapula Action – Rotate the scapula during abduction of the arm beyond 90 Weakness of this muscle leads to dropping shoulder

Muscular System Base of skull (occipital protuberance)

Latissimus Dorsi Origin posterior part of iliac crest Spines of lower 6 Thoracic vertebrae lower 3 or 4 ribs Lumbar Fascia Inferior angel of scapula Insertion floor of the inter tubercular sulcus Nerve Supply – Thoracodorsal nerve Action It extends, adducts & medailly rotates the arm

Levator Scapulae Origin Transverse process of upper 4 cervical vertebrae Insertion Superior angle & Medial border of scapula Nerve Supply Dorsal scapular nerve 3rd & 4th cervical nerve Action – Elevation of scapula

Rhomboideus Major Origin – 2nd – 5th thoracic spine I – Medial border of scapula Nerve Supply – Dorsal scapular nerve Action – Elevates the medial border & of scapula & pulls it medially

Rhomboideus Minor Origin Lower part of ligamentum nuchae Spines of lower 7th cervicle & 1st thoracic vertebrae Insertion Medial border of scapula Nerve Supply – Dorsal scapular nerve Action – Elevates the medial border of scapula & pulls it medially

Triangle of auscultation Small triangular gap at the back Boundary Superiorly - Lateral border of Trapezius Laterally - Medial border of scapula Inferiorly - Upper border of latissimus dorsi. Floor is by seventh rib, 6th & 7th intercostal spaces & rhomboideus major.

Clinical Importance of auscultation Only part not covered by the muscle. Used to hear the respiratory sounds are better heard with stethoscope On the Right side – Breadth sound is auscultated On the Left side – Any kind of Esophageal obstructions can be by auscultation

Muscles of Thorax

The muscles of thorax Extrinsic muscles Intrinsic muscles Pectoralis major Pectoralis minor Serratus anterior Intrinsic muscles Intercostales externi Intercostales interni

Pectoralis major Origin Insertion Action Anterior surface of medial half of clavicle Anterior surface of sternum 6th costal cartilage Insertion Crest of great tubercle of Humerus Action Adduction Flexion Medical rotation

Pectoralis minor (lies deep to pectoralis major) Origin Anterior external surface of 3rd to 5th ribs. Insertion Coracoid process of scapula Action Forward and downward movement of scapula

Serratus anterior Origin Insertion External surface of upper 8~9 ribs. Oblique externus abdominis Insertion Anterior surface of medical border of scapula

Origin: lower border of each rib Insertion: upper border of each rib Intercostales externi Origin: lower border of each rib Insertion: upper border of each rib Action: elevate the rib (muscles of inspiration) Replaced anteriorly by external intercostals membrane. Intercostales interni Origin: upper border of rib Insertion: lower border of rib Action: depress ribs (muscles of expiration) Replaced posteriorly by internal intercostals membrane.

Diaphragm Shape and position: Origin dome-shaped between thorax and abdomen, consists of a peripheral muscular part and a central tendon Origin Sternal part: xiphoid process Costal part: lower six ribs and costal cartilages Lumbar part: arises by two crura from upper 2~3 lumbar vertebrae Insertion: central tendon Weak areas: triangular spaces without muscular tissue Lumbocostal triangle: between costal and lumbar parts. Sternocostal triangle: between costal and sternal parts.

Openings in the diaphragm Aortic hiatus－lies anterior to the body of the 12th thoracic vertebra between the crura. It transmits the aorta, thoracic duct Esophageal hiatus －for esophagus and vagus nerves at level of T10. Vena cava foramen －for inferior vena cava, through central tendon at T8 level T8 T10 T12

Action: Contraction: the dome moving downward, increases the volume of thoracic cavity which results in inspiration, at the same time the intra-abdominal pressure is increased assists in defecation, vomiting or child birth. Relaxation: the dome returns to the former position, reduces the volume to the thoracic cavity, resulting in expiration.

Muscles of abdomen Anterolateral group Obliquus externus absominis Oblequus enternus abdominis Transversus abdominis Rectus abdominis

Posterior group Quadiatus lumborum Psoas major

Obliquus externus abdominis Origin : external surface of lower 8 ribs. downward, forward and medially (run down and inward) Insertion : iliac crest The lower part of aponeurosis of this muscles forms Inguinal ligament Lacunar ligament Superficial inguinal ring －triangular-shaped defect in aponeurosis of obliquus externus abdominis above pubic tubercle

Obliquus internus abdominis Deep to obliquus externus abdominis General direction of fibres: upwards, forwards and medially Origin: thoracolumbar fascia Anterior 2/3rd of iliac crest Lateral 2/3 of inguinal ligament Insertion: Cartilage of 7th to 10th ribs

Transversels abdominis Deep to obliquus internus Origin Inner surface of costal cartilage of lower 6 Ribs. Thoracolumbar fascia Iliac crest Lateral 1/3rd of inguinal ligament Insertion Sheath of rectus abdominis Inguinal falx with aponeurosis of obliquus internus abdominis

Inguinal falx : arch over spermatic cord, inserted with transverses abdominis fiber into medial part of pecten of pubis Cremaster: around the spermatic cord and testis

Rectus abdominis Position: lie on to either side of midline Origin: pubic crest and symphysis Insertion: xiphoid process and 5th-7th costal cartilages Has 3-4 tendinous intersections

Similar functions for above four pairs of muscles Support and compress the abdominal viscera Increase intra-abdominal pressure, aid in expulsive efforts-vomiting, coughing, sneezing, defecation, urination and childbirth. Depress ribs, assist in (the act of force(4)expiration. Flex, lateral flex, and rotate vertebral column

Sheath of rectus abdominis Ant layer－formed by fusion of aponeurosis of obliquus externus abdominis and anterior leaf of aponeurosis of obliquus internus abdominis Post layer Formed by fusion of posterion leaf of aponeurosis of obliquus internus abdominis and aponeurosis of transverses abdominis Absent in about 4-5cm below the umbilicus, where aponeuroses of all three muscles form anterior layer the lower free border named arcuate line Below this line rectus abdominis in contact with transverse fascia

Linea alba －tendinous raphe between right and left recti from xiphoid to pubic symphysis.

Inguinal region Boundaries Inguinal ligament Lateral margin of rectus abdominis A horizontal line stretching from anterior iliac spine to lateral margin of rectus abdominis

Descent of testes Seven-week embryo showing the testis before its descent from the dorsal abdominal wall

Fetus at 28 week the testis passing through the inguinal canal

Newborn

Inguinal canal Position: oblique passage, 4cm long, located 1.5cm above medial half of inguinal lig.

Boundaries Ant wall Aponeurosis of obliquus externus abdominis Obliquus internus abdominis (lateral third of wall)

Post wall Transverse fascia Inguinal flax medially Roof－arched lower fibers of obliquus internus and transversua abdominis Floor－inguinal lig．

Two openings Superficial inguinal ring Deep inguinal ring －defect in transverse fascia 1.5cm above midpoint of inguinal ligament

Structures passing through the inguinal canal Spermatic cord and ilioinguinal nerve in males Round ligament of uterus and ilioinguinal nerve in females

Inguinal Triangle (of Hesselbach) Boundaries Inguinal ligament inferiorly Lateral border of rectus abdominis medially Inferior epigastric artery laterally

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