Anatomy LC6 Muscles of the Trunk PDF

UNIVERSITY OF NORTHERN PHILIPPINES ANATOMY LC6- MUSCULAR SYSTEM: TRUNK COLLEGE OF MEDICINE, BATCH 2028 DR. VILLANUEVA-DE GRANO...

UNIVERSITY OF NORTHERN PHILIPPINES ANATOMY LC6- MUSCULAR SYSTEM: TRUNK COLLEGE OF MEDICINE, BATCH 2028 DR. VILLANUEVA-DE GRANO | 09/16/2024 - COURSE OUTLINE I. MUSCLES OF THE BACK I. MUSCLES OF THE BACK Muscles of the back are organized into superficial, A. Superficial Group intermediate, and deep groups B. Intermediate Group Extrinsic Muscles – originates embryologically C. Deep (Intrinsic) Group from locations other than the back (e.g. Superficial D. Thoracolumbar Fascia and Intermediate groups) II. SPINOTRANSVERSALES MUSCLES A. Erector spinae Superficial Extrinsic Anterior Related to Upper B. Transversospinales Rami of Limb Movements C. Segmental Muscles Spinal (Appendicular III. SUBOCCIPITAL MUSCLES Nerves groups) IV. SPRAIN, STRAIN, SPASM Intermediate Extrinsic Anterior Respiratory V. MUSCLES OF THE THORAX Rami of Function A. Scalene Muscles Spinal B. Pectoral Region Nerves C. Thoracic Wall VI. MUSCLES OF THE ABDOMEN Deep Intrinsic Posterior Directly related to A. Diaphragm Rami of head and B. Functions and Actions Spinal vertebral column C. Rectus sheath, Linea alba, and Nerves movements Umbilical Ring Table 1. Muscles of the Back: Superficial, Intermediate, Deep D. Posterior Abdominal Wall VII. PELVIS VIII. PERINEUM A. Deep B. Superficial Perineal Pouch C. Injury to the Pelvic Floor A. SUPERFICIAL GROUP Innervation: Anterior rami of spinal nerves Function: Related more on movements of the appendicular group particularly the upper limb MUSCLE ORIGIN INSERTION INNERVATION FUNCTION Trapezius Superior nuchal line, Lateral ⅓ of MOTOR - accessory Assists in rotating the (Superficial) External occipital clavicle, Acromion, nerve (XI) scapula during protuberance, spine of Scapula abduction of humerus Ligamentum nuchae, PROPRIOCEPTION above horizontal ; Spinous process of C7 - C3 and C4 upper fibers elevate, to T12 Middle fibers adduct, and lower fibers depress scapula Latissimus dorsi Spinous processes of Floor of Thoracodorsal nerve Extends, adducts and T7 to L5 and sacrum, intertubercular (C6-C8) medially rotates iliac crest, ribs 10-12 sulcus of humerus humerus Levator scapulae Transverse process Upper portion C3-C4 and dorsal Elevates scapula from C1 to C4 medial border of scapular nerve scapula (C4,C5) Rhomboid major Spinous process from Medial border of Dorsal scapular Retracts (adducts) , (Bigger) T2-T5 scapula between nerve (C4, C5) and elevates scapula spine and inferior angle Rhomboid minor Lower portion of Medial border of Dorsal Scapular Retracts (adducts) and (On top of ligament um nuchae, scapula at spine of nerve (C4, C5) elevates scapula rhomboid major) spinous process of C7 scapula to T1 Table 2. Superficial group of back muscle BATCH 2028 1A 1 ANATOMY LC 6: MUSCULAR SYSTEM - TRUNK Dr. DE GRANO 09/16/2024 Figure 1. Muscles of the Back B. INTERMEDIATE GROUP AKA: Respiratory Group of Back Muscles Extrinsic Innervation: Anterior Rami of spinal nerves Function: provides respiratory function because it is the only one attached to the ribs MUSCLE ORIGIN INERTION INNERVATION FUNCTION Serratus posterior Lower portion of Upper border of Anterior rami of upper Elevates ribs 2 to 5 superior Ligament um nuchae, ribs II to V just thoracic nerve spinous processes of C7 lateral to their (T2-T5) to T2 and supraspin ous angles ligament Serratus posterior Spinous process of T11 Lower border of Anterior rami of lower Depress ribs 9-12 inferior to L3 and supraspin ous ribs 9-12 just thoracic nerve and may prevent ligaments lateral to their (T9-T12) lower ribs from being angles elevated when the diaphragm contracts Table 3. Intermediate group of back muscles C. DEEP (INTRINSIC) GROUP D. THORACOLUMBAR FASCIA They usually surround and more related to spine Surrounds, covers and lend stability and strength to Innervation: Posterior rami of Spinal Nerves the back muscles Function: Directly related to head, neck and Covers the deep muscles of the back & the trunk vertebral column movements Critical to the overall organization and integrity of The deep or intrinsic muscles of the back extend the deep group of back muscles from the pelvis to the skull. Superiorly will pass anterior to the Serratus ○ Splenius capitis & cervicis (spinotransversales posterior and it is continuous with the deep fascia in muscles) - capitis = head, cervicis = back the neck ○ The extensors and rotators of the head & neck In the Thoracic Region, it covers the deep muscles ○ Erector spinae and transversospinalis - the and separates them from the muscles in superficial extensors and rotators of the vertebral column and intermediate groups. ○ Interspinales and intertransversarii - the short Medially, it will attach to the spinous process of the segmental muscles thoracic vertebrae Laterally, to the angles of the ribs BATCH 2028 1A 2 ANATOMY LC 6: MUSCULAR SYSTEM - TRUNK Dr. DE GRANO 09/16/2024 Figure 2. Thoracolumbar fascia and the deep back muscles (transverse section) II. SPINOTRANSVERSALES MUSCLES Together, they draw the head backward, extending the neck. Individually, each muscle rotates the head to one side - the same side as the contracting muscle MUSCLE ORIGIN INSERTON INNERVATION FUNCTION Splenius Lower half of Mastoid process, skull Posterior rami of Together: draw head capitis Ligamentum below lateral one third middle cervical backward extending neck; nuchae, spinous of superior nuchal line nerves Individually: draw and rotate processes of C7 to head to one side (turn face to T4 same side) Splenius Spinous processes Transverse processes Posterior rami of Together: extend neck; cervicis of T3 to T6 of C1 to C3 middle cervical Individually: draw and rotate nerves head to one side (turn face to same side) Table 4. Spinotransversales Muscles. A. ERECTOR SPINAE Largest group of intrinsic back muscles. Lie posterolaterally to the vertebral column between the spinous processes medially and the angles of the ribs laterally. MNEMONIC The names that are attached signifies the area From lateral to medial: like: I = Ilocostalis muscle ○ Lumborum- lumbar area Like = Longissimus muscles ○ Thoracic - thoracic area Standing = Spinalis muscle (nearest to the actual spine) ○ Spinalis - spine MUSCLE ORIGIN INSERTION Iliocostalis lumborum Sacrum, spinous processes of lumbar and lower Angles of the lower 6 or 7 ribs two thoracic vertebrae and their supraspinous ligaments, and the iliac crest Iliocostalis thoracis Angles of the lower six ribs Angles of the upper six ribs and the transverse process of C7 Iliocostalis cervicis Angles of ribs 3 to 6 Transverse processes of C4 to C6 Longissimus thoracis Blends with iliocostalis in lumbar region and is Transverse processes of all thoracic attached to transverse processes of lumbar vertebrae and just lateral to the vertebrae tubercles of the lower nine or ten ribs Longissimus cervicis Transverse processes of upper 4 or 5 thoracic Transverse process of C1 to C6 vertebrae Longissimus capitis Transverse processes of upper four or five Posterior margin of the mastoid thoracic vertebrae and articular processes of process lower three or four cervical vertebrae Spinalis thoracis Spinous processes of T10 or T11 to L2 Spinous processes of T1 to T8 (varies) Spinalis cervicis Lower part of ligamentum nuchae and spinous Spinous process of C2 (axis) process of C7 (sometimes T1 to T2) Spinalis capitis Usually blends with semispinalis capitis With semispinalis capitis Table 5. Erector Spinae Group of Back Muscles BATCH 2028 1A 3 ANATOMY LC 6: MUSCULAR SYSTEM - TRUNK Dr. DE GRANO 09/16/2024 Figure 3.1. Deep layers back muscles Figure 3.2. Deep group of back muscles – transversospinalis and segmental muscles. BATCH 2028 1A 4 ANATOMY LC 6: MUSCULAR SYSTEM - TRUNK Dr. DE GRANO 09/16/2024 B. TRANSVERSOSPINALES Found deep to the erector spinae and consist of 3 major subgroups - the semispinalis, multifidus and rotatores muscles Bilateral contraction: Extension of the vertebral column Unilateral contraction: Trunk turns/rotates in the opposite direction SEMISPINALIS CAPITIS Muscles that support the thoracic area, the surfaces area and the capitis area Bilateral contraction: pulls the head posteriorly Unilateral contraction: pulls the head posteriorly and turns it, causing the chin to move superiorly and turn towards the side of the contracting muscle MUSCLE ORIGIN INSERTION Semispinalis thoracis Transverse processes from T6 to T10 Spinous processes of upper four thoracic and lower two cervical vertebrae Semispinalis cervicis Transverse processes of upper T5 or T6 Spinous processes of C2 (axis) to C5 Semispinalis capitis Transverse processes of T1 to T6 (or T7) Medial area between the superior and and C7 & articular processes of C4 to C6 inferior nuchal lines of occipital bone Multifidus Sacrum, origin of erectum spinae, posterior Base of spinous processes of all superior iliac spine, mammillary processes vertebrae from L5 to C2 (axis) of lumbar vertebrae, transverse processes of thoracic vertebrae, and articular processes of lower four cervical vertebrae Rotatores lumborum Transverse processes of lumbar vertebrae Spinous processes of lumbar vertebrae Rotatores thoracis Transverse processes of thoracic vertebrae Spinous processes of thoracic vertebrae Rotatores cervicis Articular processes of cervical vertebrae Spinous processes of cervical vertebrae Table 6. Transversospinales group of back muscles C. SEGMENTAL MUSCLES Two groups innervated by posterior rami of spinal nerves. First group: Levatores costarum muscles Second group - true segmental muscles of the back: ○ Interspinales - between adjacent spinous processes; and ○ Intertransversarii - between adjacent transverse processes Vertebral column stabilizer - allows more effective action of the large muscle group MUSCLE ORIGIN INSERTION FUNCTION Levatores Short paired muscles arising Small muscles between Contraction elevates rib costarum from transverse processes of the transverse processes C7 to T11 of contiguous vertebrae Interspinales Short paired muscles attached Postural muscles that stabilize to the spinous processes of adjoining vertebrae during contiguous vertebrae, one on movements of vertebral each side of the interspinous column ligament lntertransversarii Small muscles between the Postural muscles that stabilize transverse processes of adjoining vertebrae during contiguous vertebrae movements of vertebral column Table 7. Segmental Back Muscles. III. SUBOCCIPITAL MUSCLES Last group of muscles of the back Group of deep muscles that move the head Connect vertebra CI (the atlas) to vertebra CII (the axis) and connect both vertebrae to the base of the skull Form the boundaries of the suboccipital triangle: Medial: rectus capitis posterior major Lateral: obliquus capitis superior Inferior: obliquus capitis inferior Note: Rectus capitis posterior minor does not form the border of the suboccipital triangle. Superficial extrinsic back muscles are axio-appendicular muscles, that's the third upper limb except for the trapezius, innervated by cranial nerve XI (accessory nerve) BATCH 2028 1A 5 ANATOMY LC 6: MUSCULAR SYSTEM - TRUNK Dr. DE GRANO 09/16/2024 MUSCLE ORIGIN INSERTION INNERVATION FUNCTION Rectus capitis Spinous process of Lateral portion of Posterior ramus of C1 Extension of head, posterior major axis (C2) occipital bone below rotation of head same inferior nuchal line side of muscle Rectus capitis Posterior tubercle of Medial portion of Posterior ramus of C1 Extension of head posterior minor atlas (C1) occipital bone below inferior nuchal line Oblique capitis Transverse process Occipital bone between Posterior ramus of C1 Extension of head superior of atlas (C1) superior and inferior and bends it on same nuchal line side Oblique capitis Spinous process of Transverse process of Posterior ramus of C1 Rotation of face on inferior axis (C2) atlas (C1) the same side Table 8. Suboccipital Group of Back Muscles Figure 4. Suboccipital Muscles of the Deep Group of Back Muscles IV. SPRAIN, STRAIN, SPASM Back sprain - only ligamentous tissue is involved, without dislocation or fracture; excessively strong contractions related to movements of the vertebral column Back strain - common sports injury; overly strong muscular contraction; involves some degree of stretching or microscopic tearing of muscle fibers; if a weight is not properly balanced on the vertebral column, strain is exerted on the muscles Spasm - protective mechanism after an injury or in response of inflammation; sudden involuntary contraction of one or more muscle groups V. MUSCLES OF THE THORAX Axio-appendicular muscles - extend from the thoracic cage (axial skeleton) to bones of the upper limb (appendicular skeleton); act primarily on the upper limbs Muscles that may also function as accessory muscle of respiration, helping to elevate the ribs to expand the thoracic cavity during deep and forceful respiration (e.g., after a long run): pectoralis major and pectoralis minor muscles A. SCALENE MUSCLES Scalene muscles - act primarily on the vertebral column; also serve as accessory respiratory muscle by fixing the ribs and enabling the muscles connecting the ribs to be more effective in elevating the lower ribs during forced inspiration B. PECTORAL REGION Figure 5. Pectoralis Muscles. BATCH 2028 1A 6 ANATOMY LC 6: MUSCULAR SYSTEM - TRUNK Dr. DE GRANO 09/16/2024 MUSCLES OF THE PECTORALIS REGION MUSCLE ORIGIN INSERTION INNERVATION FUNCTION Pectoralis Medial half of clavicle and Lateral lip of Medial & lateral adduction, medial rotation, major anterior surface of sternum, intertubercular pectoral nerves and flexion of the humerus first seven costal cartilages, sulcus of humerus at the shoulder joint aponeurosis of external oblique Subclavius Rib 1 at junction between rib Groove on the Nerve to Pulls clavicle medially to and costal cartilage inferior surface of subclavius stabilize sternoclavicular middle third joint; depresses tip of clavicle shoulder Pectoralis Anterior surfaces of the third, Coracoid process Medial pectoral Depresses tip of shoulder; minor fourth, & fifth ribs, and deep of scapula nerves protracts scapula fascia overlying the related intercostal spaces C. THORACIC WALL After the position of the ribs and sternum and so change the thoracic volume during breathing reinforce the thoracic wall Figure 12. Muscles of the thoracic wall. MUSCLES OF THE THORACIC WALL Muscle Superior attachment Inferior attachment Innervation Function External intercostal Inferior margin of rib superior margin of rib Intercostal nerves Most active during above below (T1-T11) inspiration; supports intercostal space; moves rib superiorly Internal intercostal Lateral edge of costal superior margin of rib Intercostal nerves Most active during groove of rib above below deep to the (T1-T11) expiration; supports attachment of the intercostal space; related external moves ribs inferiorly intercostal Innermost Medial edge of costal internal aspect of Intercostal nerves Acts with internal intercostal groove of rib above superior margin of rib (T1-T11) intercostal muscles below Subcostales Internal surface (near internal surface of Related intercostal May depress ribs angle) of lower rib second or third rib nerves below Transversus inferior margins and Internal aspect of Related intercostal Depresses costal thoracis internal surfaces of deep surface of the nerves cartilages costal cartilages of body of sternum, ribs II-VI xiphoid process, and costal cartilages of ribs IV-VII BATCH 2028 1A 7 ANATOMY LC 6: MUSCULAR SYSTEM - TRUNK Dr. DE GRANO 09/16/2024 VI. MUSCLES OF THE ABDOMEN A. DIAPHRAGM Double-domed, musculotendinous partition separating the thoracic and abdominal cavities. Chief muscle of inspiration Descends during inspiration Muscular part is situated at the peripherally with fibers that converge radially on the trifoliate central aponeurotic part, the central tendon: ○ Sternal part ○ costal part - forms the right and left domes ○ Lumbar part - forms right and left muscular crura that ascend to the central tendon Has right and left domes ○ Right dome - higher; during expiration, it reaches as high as the 5th rib ○ Left dome - lower; ascends to 5th intercostal space The right dome is higher than the left dome owing to the presence of the liver Origin: Inferior of the ribs, sternum, and lumbar vertebra Insertion: Central tendon Nerve supply: Phrenic nerve Action: Inspiration, Depresses the floor of the thorax Apertures of the Structures Level diaphragm passing through Caval T8 Inferior vena cava, right phrenic nerve Oesophageal T10 Oesophagus, right and left vagus nerves, oesophageal branches of left gastric vessels, lymphatics Aortic T12 Aorta, thoracic duct azygos vein Table 8. Apertures of the diaphragm. Figure 11. The Diaphragm Crura: Musculotendinous bands Right crus - Larger and longer than left crus, arise from the first three or four lumbar vertebrae Left crus - Arises from the first two or three lumbar vertebrae ARCUATE LIGAMENTS Median arcuate ligament: A median tendinous arch connecting the right and left crura Medial arcuate ligament: On each side, connecting each crus with the tip of transverse process of L1 Lateral arcuate ligament: On each side, connecting the tip of transverse process of L1 with the last rib B1. FUNCTIONS AND ACTIONS ABDOMINAL WALL ANTEROLATERAL MUSCLES (5) Three flat muscles: Two vertical muscles: External oblique Rectus abdominis Internal oblique Pyramidalis muscles Transversus abdominis muscles BATCH 2028 1A 8 ANATOMY LC 6: MUSCULAR SYSTEM - TRUNK Dr. DE GRANO 09/16/2024 Figure 12. Anterolateral abdominal wall BATCH 2028 1A 9 ANATOMY LC 6: MUSCULAR SYSTEM - TRUNK Dr. DE GRANO 09/16/2024 B2. FUNCTIONS AND ACTIONS Together the muscles are critical for the maintenance of many normal physiological functions Formation of a firm but flexible wall - keeps the abdominal viscera intact and protects it from injury, and helps maintain the anatomical position of the viscera against gravity Contraction of these muscles assists both quiet and forced expiration by pushing the viscera upward and in coughing and vomiting Involved in any action that increases intra abdominal pressure-parturition, micturition and Figure 13. Organization of the rectus sheath. defecation (A) Transverse section through the upper three-quarters of the Move the trunk and help to maintain posture rectus sheath (B) Transverse section through the lower one-quarter of the rectus sheath C. RECTUS SHEATH, LINEA ALBA, AND UMBILICAL RING D. POSTERIOR ABDOMINAL WALL Rectus Sheath (encloses the muscle) Anterolateral walls are distensible, although the ○ Strong, incomplete fibrous compartment of the posterior abdominal wall functions for rectus abdominis and pyramidalis muscles weight-bearing and it is reinforced by the vertebral ○ Formed by the decussation and interweaving of column and muscles that act on it, that is why it is the aponeuroses of the flat abdominal muscles flexible but not really distensible. This is because ○ They are also found in your rectus sheath in it acts a weight bearing unit reinforce by vertebral superior and inferior epigastric arteries and column veins together with your lymphatic vessels and Formed in the midline by the five lumbar some of your abdominal nerves vertebrae and their intervertebral discs and ○ The anterior wall: is formed by the laterally by the 12th ribs, the upper part of the aponeuroses of the external oblique, and of half bony pelvis, the psoas muscles, the quadratus of the internal oblique. lumborum muscles, and the aponeuroses of origin ○ The posterior wall: is formed by the of the transversus abdominis muscles. aponeuroses of half the internal oblique and of Psoas - Greek word meaning “muscles of the loin” the transversus abdominis. Iliacus - Iliopsoas (psoas minor will merge with ○ 1/3 of the distance between the umbilicus and psoas inferiorly) the pubic symphysis- only an anterior wall exists; the rectus abdominis is in direct contact with the transversalis fascia. ○ The demarcation point where the posterior wall ends is called the arcuate line. Fibers of the anterior and posterior layers of the sheath interlace in the anterior median line to form the complex linea alba Middle of rectus abdominis is Linea alba The posterior layer of the rectus sheath is also deficient superior to the costal margin At its middle, underlying the umbilicus, the Linea alba contains the umbilical ring (this is where fecal umbilical vessels pass through from umbilical cord and placenta) ○ Defects in the linea alba through which the fetal umbilical vessels passed to and from the umbilical cord and placenta ○ All layers of the anterolateral abdominal wall fuse at the umbilicus. Linea Semilunaris: a vertical, curved structure that Figure 13. Inferior View and Transverse Section of Abdominal Muscles runs along the lateral edges of the rectus abdominis muscle in the anterior abdominal wall Conjoint Tendon: is a sheath of connective tissue formed from the lower part of the common aponeurosis of the abdominal internal oblique muscle and the transversus abdominis muscle,joining the muscle to the pelvis. ○ Confluence of the internal oblique and transverse abdominis fibers, which strengthen the medial half of the posterior wall of the inguinal canal Figure 14. Posterolateral view of abdominal muscles. BATCH 2028 1A 10 ANATOMY LC 6: MUSCULAR SYSTEM - TRUNK Dr. DE GRANO 09/16/2024 MUSCLE ORIGIN INSERTION INNERVATION FUNCTION Psoas Transverse processes, With iliacus into Lumbar plexus Flexes thigh on trunk; if bodies, and intervertebral lesser trochanter of thigh is fixed, it flexes trunk discs of 12th thoracic and femur on thigh, as in sitting up five lumbar vertebrae from lying position Quadratus lliolumbar ligament, iliac 12th rib Lumbar plexus Fixes 12th rib during lumborum crest, tips of transverse inspiration; depresses 12th processes of lower lumbar rib during forced expiration; vertebrae laterally flexes vertebral column of the same Iliacus Iliac fossa With psoas into Femoral nerve Flexes thigh on trunk; if lesser trochanter of thigh is fixed, it flexes the femur trunk on the thigh, as in sitting up from lying position Table 9. Muscles of the Posterior Abdominal Wall. VII. PELVIS (L. basin) Area of transition between trunk & lower limbs Muscles of the pelvic floor ○ The pelvic floor is formed by the bowl or funnel-shaped pelvic diaphragm (composed of coccygeus and levator ani muscles + fascias) ○ The pelvic diaphragm lies within the lesser pelvis, separating the pelvic cavity from the perineum, for which it forms the roof. ○ Your levator ani muscles include your pubococcygeus, iliococcygeus, puborectalis (pubocorsaticus, puboperinealis, puboanalis) muscles Functions: ○ Support the organs of the pelvic cavity ○ Flex the sacrum and coccyx ○ Control the movement of materials through the urethra and anus Figure 15. Muscles of pelvic walls and floor (a, b) The obturator internus and piriformis are muscles that act on the lower limb but are also components of the pelvic walls. (c) The muscles of the levator ani and the coccygeus comprise the pelvic diaphragm that forms the floor of the pelvic cavity. BATCH 2028 1A 11 ANATOMY LC 6: MUSCULAR SYSTEM - TRUNK Dr. DE GRANO 09/16/2024 MUSCLES OF THE PELVIS Boundary Muscle Proximal attachment Distal Innervation Action Attachment Lateral Obturator Pelvic surfaces of the Greater Nerve to obturator Rotates thigh wall internus ilium and ischium; trochanter of intern us laterally; assists in obturator membrane femur (L5,S1,S2) from holding head of femur sacral plexus in acetabulum Posterior Piriformis Pelvic surface of S2 - Greater Anterior rami of Rotates thigh wall S4 segments; superior trochanter of S1 and S2 laterally; abducts margin of greater sciatic femur thigh; assists in notch & sacrotuberous holding head of femur ligament in acetabulum Floor Coccygeus Ischial spine Interior end of Branches of S4 Forms small part of (ischiococcygeus) sacrum and and S5 spinal pelvic diaphragm that coccyx nerves supports pelvic viscera; flexes coccyx Levator ani Body of pubis; Perineal body; Nerve to levator Forms most of pelvic (puborectalis, tendinous arch of coccyx; ani (branches of diaphragm that helps pubococcygeus, & obturator fascia; ischial anococcygeal S4), inferior anal support pelvic viscera iliococcygeus) spine ligament ; walls (rectal ) nerve, and resists increases of prostate or and coccygeal in intra-abdominal vagina, rectum, plexus pressure and anal canal Pubocorsaticus, pubovaginalis, and puboanalis - the subdivisions of your pubococcygeus muscles depending on the muscle that they support. Puborectalis - a muscular strain that maintains an angle or flexure called your perineal flexure at the anal-rectal junction. It is this junction that forms a part in the mechanism that keeps your fecal continence. liococcygeus muscle - joins the same muscle on the other thigh to form a ligament that extends to the renal aperture to the coccyx. Levator ani muscles - help support your pelvic viscera and to maintain the closure of your rectum and vagina. VIII. PERINEUM Lies below the pelvic diaphragm “Diamond-shaped” structure between the external Between the genitalia and the anus BOUNDARIES: Anterior – pubic symphysis Posterior – tip of coccyx Lateral – inferior pubic rami and inferior ischial rami, and sacrotuberous ligament Roof – pelvic floor Base – skin and fascia SURFACE BORDERS: ○ Anterior: mons pubis in females, base of penis in males ○ Lateral: medial surfaces of the thighs ○ Posterior: superior end of the intergluteal cleft Figure 16. Surface borders of the perineum There is an imaginary line between ischial tuberosities which divide perineum to triangular regions. BATCH 2028 1A 12 ANATOMY LC 6: MUSCULAR SYSTEM - TRUNK Dr. DE GRANO 09/16/2024 (Anterior) urogenital triangle - contains the roots of external genitalia, and in women, the openings of the urethra and the vagina. In men, the distal part of the urethra is enclosed by erectile tissues and opens at the end of the penis. ○ Divides into superficial and deep perineal space (both sexes), by Perineal Membrane (Posterior) Anal triangle - contains anus and external anal sphincter No difference in the female and male deep perineal musculature. Figure 17. Perineum in women Figure 18. Perineum in men EXTERNAL ANAL SPHINCTER Muscles Origin Insertion Innervation Function Deep part Surrounds superior Pudendal nerve (S2 Closes anal canal aspect of anal canal and S3) and branches directly from S4 Superficial part Surrounds lower part Anchored to perineal of the anal canal body and anococcygeal body Subcutaneous Surrounds part anal aperture Table 10. Muscles of the Anal Triangle A. DEEP PERINEAL POUCH Is open above and is not separated from more superior structures by a distinct layer of fascia. The parts of the perineal membrane and structures in the deep perineal space are enclosed by the urogenital hiatus above therefore they contributed to the pelvic floor and is part of the urogenital system in the pelvic cavity even though the perineal membrane and the deep perineal pouch are usually considered parts of the perineum. Figure 19. Muscles of the perineal pouch (A) female (B) male BATCH 2028 1A 13 ANATOMY LC 6: MUSCULAR SYSTEM - TRUNK Dr. DE GRANO 09/16/2024 Perineal Membrane & Adjacent Pubic Arch Provide attachment for the roots of the external genitalia and the muscles associated with them. Figure 20. Perineal Membrane and Deep Perineal Pouch (Medial View) MUSCLES OF THE DEEP PERINEAL POUCH Muscle Origin Insertion Innervation Function External urethral From the inferior ramus of Surrounds Perineal branches Compresses the sphincter the pubis on each side membranous part of of the pudendal membranous urethra; and adjacent walls of the urethra nerve (S2 to S4) relaxes during micturition deep perineal pouch Deep transverse Medial aspect of ischial Perineal body Perineal branches Stabilizes the position of perineal of the pudendal the perineal body nerve (S2 to S4) Compressor Ischiopubic ramus on Blends with partner Perineal branches Functions as an urethrae each side on other side anterior of the pudendal accessory sphincter of the (in women only) to the urethra nerve (S2 to S4) urethra Sphincter Perineal body Passes forward Perineal branches Functions as an urethrovaginalis lateral to the vagina of the pudendal accessory sphincter of the (in women only) to blend with partner nerve (S2 to S4) urethra (also may facilitate on other side anterior closing the vagina to the urethra B. SUPERFICIAL PERINEAL POUCH Contains the space that lies beneath the skin of the perineum. It contains erectile structures that join together to form penis in men and the clitoris in women. Skeletal muscles are associated mainly with the rectal structures attached to the perineal membrane and adjacent bones Figure 21. Muscle in the superficial perineal pouch (A) in Women (B) in Men BATCH 2028 1A 14  ANATOMY LC 6: MUSCULAR SYSTEM - TRUNK Dr. DE GRANO 09/16/2024 Muscles Origin Insertion Innervation Function Ischiocavernosus Ischial tuberosity Crus of penis and clitoris Pudendal nerve Move blood from crura into and ramus (S2 to 54) the body of the erect penis and clitoris Bulbospongiosus In women: In women: bulb of Pudendal nerve Move blood from attached perineal body vestibule, perineal (S2 to 54) parts of the clitoris and In men: membrane, body of clitoris, penis into the glans In men: perineal body, and corpus cavernosum removal of residual urine midline raphe In men: bulbospongiosus, from urethra after urination; perineal membrane, corpus pulsatile emission of cavernosum semen during ejaculation Superficial transverse Ischial tuberosity Perineal Pudendal nerve Stabilize the perineal body perineal and ramus (S2 to 54) Table1Table 1. Muscle of the superficial perineal pouch An important landmark of the urogenital triangle = perineal body ○ The perineal body is an ill-defined fibromuscular mass located in the middle of the inter-ischial line between the two triangles: the urogenital triangle and the anal triangle. It is important because many muscles attach to the perineal body, such as the superficial transverse perineal. It has posterior communication with your external anal sphincter and anterior relations with the bulbospongiosus and with the deep and superficial transverse perineal. The perineal body extends superiorly into the rectovaginal septum of the pelvis. For the pelvis, it is important to remember that the ability of your muscular fascia pelvic floor to relax and descend is critical to the functions and definitions in parturition. C. INJURY TO THE PELVIC FLOOR During childbirth, the pelvic floor supports the fetal head while the cervix of the uterus is dilating to permit the delivery of the fetus. Perineum, levator ani, and ligaments of the pelvic fascia may be injured during childbirth Most often torn muscles (Supports urethra, vagina and anal canal): pubococcygeus and puborectalis Weakening of the levator ani and pelvic fascia may decrease support for the vagina, bladder, uterus, or rectum or alter the position of the neck of the bladder and the urethra May cause urinary stress incontinence or lead to the prolapse of one or more pelvic organs. Tearing of the puborectalis→ leads to fecal incontinence. It is important to repair it anatomically to prevent fistula formation. Figure 22. (A) Tear of perineum and (B) Tear of pubococcygeus during childbirth Reference(s): Moore, K. L., Dalley, A. F., & Agur, A. M. R. (2014). Clinically Oriented Anatomy (7th ed.). Philadelphia, PA: Wolters Kluwer Health/Lippincott Williams & Wilkins. Dra. Ana Patricia Villanueva-de Grano lecture and PowerPoint presentation (9/16/2024) BATCH 2028 1A 15