Summary with Muscles & Nerve Supply

Pelvic Wall (Lectures 20 & 21) – Summary with Muscles & Nerve Supply What is the Pelvis? • A strong, ring-shaped bony structure at the bottom of the trunk. • Connects the spine to lower limbs. • Functions: o Transfers body weight to legs o Provides attachment to muscles & ligaments o Protects pelvic organs (bladder, rectum, uterus) Bones of Pelvis (Mnemonic: Hi-Sac-Coc) 1. Hip bones (ilium, ischium, pubis) – 2 2. Sacrum – fused vertebrae (5) 3. Coccyx – tailbone (4 fused bones) Pelvic Joints • Sacroiliac joints (2) – sacrum with ilium • Pubic symphysis – between pubic bones • Sacrococcygeal symphysis – between sacrum and coccyx Parts of Pelvis Greater (False) Pelvis • Upper part • Supports intestines • Helps hold uterus during pregnancy Lesser (True) Pelvis • Lower part • Contains bladder, uterus, rectum • Passage for baby during childbirth Pelvic Inlet Boundaries (Mnemonic: SAP): • Sacral promontory (posterior) • Arcuate line (lateral) • Pubic symphysis (anterior) Pelvic Outlet Boundaries: • Posterior: Tip of coccyx • Lateral: Ischial tuberosities, sacrotuberous ligament • Anterior: Pubic arch Subpubic angle is wider in females Pelvic Muscles & Nerve Supply Piriformis Muscle • Origin: Anterior sacrum • Insertion: Greater trochanter of femur • Action: Lateral rotation of hip • Nerve: Nerve to piriformis (from sacral plexus) Obturator Internus • Origin: Obturator membrane and surrounding bone • Insertion: Greater trochanter • Action: Lateral rotation of thigh • Nerve: Nerve to obturator internus (sacral plexus) Pelvic Floor (Pelvic Diaphragm) • Supports pelvic organs & maintains continence • Made of: o Levator ani (3 parts): 1. Pubococcygeus 2. Puborectalis 3. Iliococcygeus o Coccygeus Actions: • Supports pelvic organs • Helps during urination, defecation, coughing, childbirth • Acts as sphincter for rectum and vagina Nerve Supply: • Levator ani: Pudendal nerve (S2–S4) & branch of S4 • Coccygeus: Branches from S4 & S5 Important Pelvic Ligaments • Sacrotuberous ligament: Sacrum → ischial tuberosity • Sacrospinous ligament: Sacrum → ischial spine → Together form greater and lesser sciatic foramina Hip Bone Components (Mnemonic: I-P-I) 1. Ilium: Upper flat part (with iliac crest) 2. Pubis: Front part, joins at pubic symphysis 3. Ischium: Lower back part, has ischial tuberosity → Together form the acetabulum (hip socket) Pelvic Cavity (Lecture 22) – Summary with Muscles & Nerves Pelvic Cavity • Space between the pelvic inlet and outlet • Contains pelvic organs: ureters, bladder, uterus, rectum Ureters • Tubes that carry urine from kidneys to bladder • Length: ~25 cm • Path: o From renal pelvis → along psoas major → crosses pelvic brim → reaches bladder wall obliquely (prevents backflow) 3 narrow parts of ureter (Mnemonic: PBP) 1. Pelvic-ureteric junction 2. Brim of pelvis 3. Passage into bladder wall 🫙 Urinary Bladder • Muscular sac for storing urine (~500 ml capacity) • Located behind pubic symphysis • Covered partly by peritoneum • Shape: Pyramidal when empty, becomes ovoid when full Parts of the Bladder: • Apex: Points forward; attached to umbilicus (via median umbilical ligament) • Base (posterior surface): Has trigone • Neck: Lowest part; connects to urethra (rests on prostate in males) Trigone of Bladder • Smooth triangular area between: o 2 ureter openings (above) o Urethral opening (below) • Interureteric ridge connects both ureters • Uvula vesicae = small bump near urethra (from prostate) Bladder Muscles • Detrusor muscle: Smooth muscle wall (3 layers) o • Function: Contracts to empty bladder Sphincter vesicae: Circular muscle at bladder neck o Function: Prevents urine leakage Bladder Nerve Supply (Mnemonic: SPeCS) 1. Sympathetic (T12–L2 via hypogastric plexus) o Relaxes bladder wall (stores urine) 2. Parasympathetic (S2–S4 via pelvic nerve) o Contracts bladder wall (voids urine) 3. Somatic (S2–S4 via pudendal nerve) o Controls external urethral sphincter (voluntary) 4. Central sensory (afferents): Send signals to brain when bladder is full