Speedmen’s Anatomy Atlas

Head & Neck — Layer-by-Layer Anatomy

Explore the anatomical planes from the external surface to the cranial cavity. Select a layer to study its components, relationships and clinical significance.

Layer explorer

Essential anatomical orientation

Anterior: toward the front; posterior: toward the back.
Superior / inferior: above / below.
Medial / lateral: toward / away from the midline.
Superficial / deep: nearer to / farther from the body surface.
Ipsilateral / contralateral: same side / opposite side.

Study method: identify the layer, name the structure, describe its function, then trace its arterial supply, venous drainage and nerve supply.

Scalp: the five anatomical layers — S.C.A.L.P.

Layer	Medical term	Key features	Clinical relevance
S	Skin	Hair follicles, sebaceous glands, sweat glands; dense hair-bearing skin.	Scalp lacerations may bleed profusely because vessels are held open by dense connective tissue.
C	Connective tissue	Dense, fibrofatty superficial fascia containing cutaneous nerves and vessels.	Fibrous septa tether vessels, limiting vasoconstrictive retraction after injury.
A	Aponeurosis — galea aponeurotica	Tendinous sheet connecting frontalis and occipitalis muscles; part of the epicranius.	Full-thickness wounds crossing the galea may gape due to muscle pull.
L	Loose areolar connective tissue	Mobile plane between galea and pericranium; contains emissary veins.	Potential “danger area” because infection can spread via emissary veins to intracranial venous sinuses.
P	Pericranium	Periosteum covering the external surface of cranial bones.	Subperiosteal bleeding is limited by suture lines where periosteum is firmly attached.

Scalp S.C.A.L.P. layers and dural venous drainage — Study diagram — S.C.A.L.P. layers, emissary veins to superior sagittal sinus, then transverse → sigmoid → internal jugular vein; subdural space is between dura and arachnoid (not a scalp layer). Tap image to enlarge.

Facial muscles — muscles of expression

Innervation: Facial nerve (CN VII).

Orbicularis oculi: closes eyelids; palpebral and orbital parts.
Orbicularis oris: closes and protrudes lips.
Buccinator: compresses cheek; keeps food between occlusal surfaces.
Zygomaticus major/minor: elevates upper lip and mouth angle.
Frontalis: elevates eyebrows and wrinkles forehead.
Platysma: tenses skin of anterior neck and depresses mandible/lower lip.

Muscles of mastication

1108 Muscle that Move the Lower Jaw — OpenStax, CC BY 4.0

Innervation: Mandibular division of trigeminal nerve (CN V3).

Masseter: elevates mandible; powerful jaw closure.
Temporalis: elevates and retracts mandible.
Medial pterygoid: elevates and assists protrusion.
Lateral pterygoid: protrudes and assists depression; contributes to side-to-side movement.

Major cranial bones

Neurocranium: frontal, parietal (paired), temporal (paired), occipital, sphenoid and ethmoid bones.
Viscerocranium: maxillae, zygomatic, nasal, lacrimal, palatine, inferior nasal concha, vomer and mandible.
Landmarks: bregma, lambda, pterion, asterion, supraorbital margin, mastoid process and foramen magnum.

Meninges & intracranial spaces

Dura mater: periosteal and meningeal layers; forms dural venous sinuses.
Arachnoid mater: avascular membrane; CSF circulates in the subarachnoid space.
Pia mater: delicate vascular membrane closely adherent to brain surface.
Epidural space: potential space in cranium; middle meningeal artery injury may cause epidural haematoma.
Subdural space: potential space; tearing of bridging veins may cause subdural haematoma.

Neurovascular anatomy of the head

Arterial supply

Gray513 — Henry Vandyke Carter, Public domain

Internal carotid artery (ICA): contributes to anterior cerebral circulation via anterior cerebral artery (ACA) and middle cerebral artery (MCA).
Vertebral arteries: unite to form basilar artery; supply posterior circulation through posterior cerebral arteries (PCA) and branches.
External carotid artery (ECA): supplies much of the face and scalp; branches include superficial temporal, maxillary, facial and occipital arteries.
Circle of Willis: arterial anastomotic ring at the base of the brain.

Venous drainage

Dural venous sinuses: superior sagittal, straight, transverse, sigmoid and cavernous sinuses.
Internal jugular vein (IJV): major venous outflow from cranial cavity.
Emissary veins: connect extracranial veins with dural venous sinuses.

Cranial nerves — high-yield overview

CN I Olfactory: smell.
CN II Optic: vision.
CN III, IV, VI: most extraocular movements.
CN V Trigeminal: facial sensation; mastication (V3).
CN VII Facial: facial expression; taste anterior 2/3 tongue.
CN VIII Vestibulocochlear: hearing and balance.
CN IX, X: swallowing, phonation and visceral functions.
CN XI Accessory: sternocleidomastoid and trapezius.
CN XII Hypoglossal: tongue movement.

Clinical correlation — stroke: MCA territory infarction commonly produces contralateral face/arm-predominant weakness or sensory loss; dominant-hemisphere involvement may cause aphasia, while non-dominant involvement may cause neglect. Clinical presentation depends on the exact vascular territory and collateral circulation.

Integumentary System

The integument comprises the skin and its appendages: hair, nails, sebaceous glands and sweat glands.

Epidermis

Keratinized stratified squamous epithelium; avascular. Layers (deep to superficial): stratum basale, spinosum, granulosum, lucidum (thick skin only), corneum.

Cells: keratinocytes, melanocytes, Langerhans (epidermal dendritic) cells and Merkel cells.

Dermis

Connective tissue containing vessels, sensory receptors, nerves, hair follicles and glands. Papillary layer = loose areolar CT; reticular layer = dense irregular CT.

Hypodermis / subcutaneous tissue

501 Structure of the skin — OpenStax College : J. Gordon Betts, Peter Desaix, Eddie Johnson., CC BY 3.0

Adipose tissue and loose connective tissue; anchors skin, stores energy, provides insulation and permits skin mobility.

Skin functions

Barrier protection, thermoregulation, sensation, immune defence, vitamin D synthesis and prevention of fluid loss.

Clinical assessment terms

ErythemaMacerationExcoriationLichenificationNon-blanchable erythemaTurgorPressure injury

Pressure injury assessment requires inspection of skin colour, temperature, moisture, tissue consistency, pain and blanchability, with attention to darker skin tones where colour change may be less visible.

Muscular System

Skeletal muscle

1007 Muscle Fibes (large) — OpenStax, CC BY 4.0

Striated, voluntary muscle composed of multinucleated fibres. Sarcomeres contain actin and myosin; contraction follows excitation–contraction coupling and calcium release from sarcoplasmic reticulum.

1105 Anterior and Posterior Views of Muscles — OpenStax, CC BY 4.0. Tap image to enlarge.

Cardiac muscle

Striated, involuntary myocardium; branching cells joined by intercalated discs containing desmosomes and gap junctions.

Smooth muscle

Non-striated, involuntary muscle in vessel walls and hollow organs; regulated by autonomic, hormonal and local signals.

Ageing & sarcopenia

Progressive loss of skeletal muscle strength and mass. Assess strength, physical performance and muscle quantity; consider nutrition, resistance exercise, illness burden and falls risk.

Skeletal System

Axial skeleton

Skull, auditory ossicles, hyoid bone, vertebral column, ribs and sternum. Provides central support and protects brain, spinal cord and thoracic organs.

Appendicular skeleton

Pectoral girdles, upper limbs, pelvic girdle and lower limbs. Supports locomotion and manipulation.

Bone tissue

605 Compact Bone — OpenStax Anatomy and Physiology, CC BY 4.0

Cortical (compact) bone provides structural strength; trabecular (cancellous) bone distributes load and houses marrow. Osteoblasts form bone; osteoclasts resorb bone; osteocytes maintain matrix.

Joint classification

909 Types of Synovial Joints — OpenStax College, CC BY 3.0

Fibrous, cartilaginous and synovial joints. Synovial joints include articular cartilage, joint cavity, capsule and synovial membrane.

Clinical correlation: osteoporosis reduces bone strength and increases fragility-fracture risk, particularly at the hip, vertebrae and distal radius. Falls prevention and fracture liaison pathways are important components of care.

Nervous System

Central nervous system (CNS)

1306 Lobes of Cerebral CortexN — OpenStax, CC BY 4.0

Brain and spinal cord. The cerebrum supports cognition, language, sensation and voluntary movement; cerebellum coordinates movement and balance; brainstem regulates vital functions and contains cranial nerve nuclei.

Peripheral nervous system (PNS)

1201 Overview of Nervous System — OpenStax, CC BY 4.0

Cranial nerves, spinal nerves, ganglia and peripheral receptors. Carries sensory input to CNS and motor output to effectors.

Autonomic nervous system

Sympathetic (“fight or flight”), parasympathetic (“rest and digest”) and enteric divisions regulate visceral function.

Neuron & synapse

Dendrites receive signals; soma integrates; axon conducts action potentials; synapse transmits signals via neurotransmitters or electrical coupling.

Cardiovascular & Vascular Anatomy

Heart chambers

2008 Internal Anatomy of the HeartN — OpenStax College, CC BY 3.0

Right atrium → right ventricle → pulmonary circulation; left atrium → left ventricle → systemic circulation. Valves: tricuspid, pulmonary, mitral and aortic.

2120 Major Systemic Artery — OpenStax College, CC BY 3.0. Tap image to enlarge.

Vessel wall

2102 Comparison of Artery and Vein — OpenStax College, CC BY 3.0

Tunica intima (endothelium), tunica media (smooth muscle and elastic tissue), tunica adventitia (connective tissue). Arteries carry blood away from heart; veins return blood; capillaries enable exchange.

Microcirculation

2105 Capillary Bed — OpenStax College, CC BY 3.0

Arterioles regulate resistance and tissue perfusion; capillaries enable gas/nutrient exchange; venules collect blood and participate in inflammation.

Haemodynamics

2109 Systemic Blood Pressure — OpenStax College, CC BY 3.0

Cardiac output = heart rate × stroke volume. Blood pressure reflects cardiac output and systemic vascular resistance. Perfusion depends on pressure gradient and vascular resistance.

Thorax — Thoracic Wall, Pleura, Lungs & Mediastinum

Study the thoracic cage, respiratory passages, pleural cavities, heart and great vessels in their anatomical relationships.

Thoracic cage & intercostal spaces

Gray112 — Henry Vandyke Carter, Public domain

Boundaries: sternum anteriorly, 12 thoracic vertebrae posteriorly, 12 pairs of ribs and costal cartilages laterally. The thoracic inlet communicates with the root of the neck; the thoracic outlet is closed by the diaphragm.

Intercostal muscles: external intercostals assist inspiration; internal intercostals (interosseous part) assist forced expiration; innermost intercostals form the deepest layer. The main neurovascular bundle runs in the costal groove in the order VAN — Vein, Artery, Nerve.

Diaphragm

Principal muscle of inspiration. Attachments include xiphoid process, lower six ribs/costal cartilages and lumbar crura/arcuate ligaments; inserts into the central tendon. Motor supply: phrenic nerves (C3–C5). Caval opening T8, oesophageal hiatus T10, aortic hiatus T12 (approximate vertebral levels).

Pleura & pleural recesses

2313 The Lung Pleurea — OpenStax College, CC BY 3.0

Visceral pleura covers lung surface; parietal pleura lines thoracic wall, diaphragm and mediastinum. The pleural cavity is a potential space with a thin lubricating fluid layer. Costodiaphragmatic recess is a dependent pleural recess; pleural effusion may collect here.

Lung anatomy

2312 Gross Anatomy of the Lungs — OpenStax College, CC BY 3.0

Right lung: superior, middle and inferior lobes; horizontal and oblique fissures. Left lung: superior and inferior lobes; oblique fissure, cardiac notch and lingula. Each bronchopulmonary segment is supplied by a segmental (tertiary) bronchus and a branch of the pulmonary artery.

Tracheobronchial tree

Gray961 — Henry Vandyke Carter, Public domain

Trachea → main bronchi → lobar bronchi → segmental bronchi → bronchioles → terminal bronchioles → respiratory bronchioles → alveolar ducts → alveolar sacs/alveoli. The right main bronchus is generally wider, shorter and more vertical than the left.

Mediastinum

Superior mediastinum contains thymus (prominent in childhood), great vessels, trachea, oesophagus, thoracic duct and major nerves. Inferior mediastinum is divided into anterior, middle (heart/pericardium) and posterior compartments.

Pericardium & heart

Fibrous pericardium surrounds serous pericardium (parietal and visceral layers; visceral layer = epicardium). Heart wall: epicardium, myocardium and endocardium. Chambers: right/left atria and ventricles. Valves: tricuspid, pulmonary, mitral and aortic.

Coronary circulation

Gray497 — Henry Vandyke Carter, Public domain

Right coronary artery (RCA) and left coronary artery (LCA) arise from aortic sinuses. LCA commonly divides into anterior interventricular artery (LAD) and circumflex artery (LCx). Coronary dominance is defined by the artery giving rise to the posterior interventricular branch.

Clinical correlation: Pneumothorax introduces air into the pleural cavity and may impair lung expansion. Tension pneumothorax causes progressive intrathoracic pressure, mediastinal shift and obstructive shock; it is a clinical emergency.

Abdomen — Abdominal Wall, Peritoneum & Viscera

Understand the abdominal wall layers, peritoneal spaces, organ positions, vascular territories and autonomic innervation.

2401 Components of the Digestive System — OpenStax College, CC BY 3.0. Tap image to enlarge.

Anterolateral abdominal wall

1112 Muscles of the Abdomen — OpenStax, CC BY 4.0

Layers: skin → superficial fascia (Camper fatty layer and Scarpa membranous layer) → external oblique → internal oblique → transversus abdominis → transversalis fascia → extraperitoneal fat → parietal peritoneum. Rectus abdominis lies within the rectus sheath.

Inguinal canal

Gray1146 — Henry Vandyke Carter, Public domain

Oblique passage through lower anterior abdominal wall. Deep ring is an opening in transversalis fascia; superficial ring is an opening in external oblique aponeurosis. Transmits spermatic cord in males and round ligament of uterus in females. Inguinal hernias may be indirect (lateral to inferior epigastric vessels) or direct (medial).

Peritoneum & mesenteries

2403 The PeritoneumN — OpenStax College, CC BY 3.0

Parietal peritoneum lines the body wall; visceral peritoneum covers organs. Greater omentum hangs from greater curvature of stomach; lesser omentum connects liver to lesser curvature/duodenum. Mesentery suspends bowel and carries neurovascular structures.

Stomach & small intestine

2415 Histology of StomachN — OpenStax College, CC BY 3.0

Stomach regions: cardia, fundus, body, pyloric antrum and pyloric canal. Small intestine: duodenum (four parts), jejunum and ileum. Jejunum generally has thicker wall, more prominent plicae circulares and fewer arterial arcades than ileum.

Large intestine

Caecum and vermiform appendix → ascending colon → transverse colon → descending colon → sigmoid colon → rectum → anal canal. Characteristic features: taeniae coli, haustra and appendices epiploicae.

Liver, gallbladder & biliary tree

2425 Gallbladder — OpenStax College, CC BY 3.0

Liver has right and left anatomical lobes; functional division follows portal and hepatic venous anatomy. Hepatocytes perform metabolism, synthesis and detoxification. Right/left hepatic ducts form common hepatic duct; cystic duct joins to form common bile duct.

Pancreas & spleen

Gray1100 — Henry Vandyke Carter, Public domain

Pancreas: head, uncinate process, neck, body and tail; mostly retroperitoneal. Exocrine acini secrete digestive enzymes; islets of Langerhans have endocrine function. Spleen lies in left upper quadrant, is intraperitoneal and filters blood.

Abdominal aorta & portal system

Gray531 — Henry Vandyke Carter, Public domain

Gray533 — Henry Vandyke Carter, Public domain

Major unpaired branches: coeliac trunk, superior mesenteric artery (SMA), inferior mesenteric artery (IMA). Portal vein usually forms from superior mesenteric and splenic veins; it carries nutrient-rich blood to liver sinusoids.

Clinical correlation: Referred pain can arise because visceral and somatic afferents converge in spinal segments. For example, early appendicitis may cause poorly localised periumbilical pain before irritation of parietal peritoneum produces right lower quadrant pain.

Back & Vertebral Column

Vertebral column

7 cervical, 12 thoracic, 5 lumbar, 5 fused sacral and usually 4 fused coccygeal vertebrae. Typical vertebra has body, vertebral arch (pedicles and laminae), vertebral foramen and processes. Intervertebral foramina transmit spinal nerves.

Intervertebral disc

Fibrocartilaginous symphysis comprising outer annulus fibrosus and gelatinous nucleus pulposus. Discs permit movement and absorb load; posterolateral disc herniation may compress a spinal nerve root.

Deep back muscles

Erector spinae: iliocostalis, longissimus and spinalis; bilateral contraction extends spine, unilateral contraction laterally flexes. Transversospinales: semispinalis, multifidus and rotatores; stabilise and rotate vertebral column.

Spinal cord & spinal nerves

Gray675 — Henry Vandyke Carter, Public domain

Spinal cord typically ends at L1–L2 in adults as conus medullaris; lumbar and sacral roots descend as cauda equina. Dorsal root carries sensory afferents; ventral root carries motor efferents; roots unite to form mixed spinal nerve.

Dermatomes & myotomes

Grant 1962 663 — Grant, John Charles Boileau, Public domain

A dermatome is an area of skin supplied mainly by one spinal nerve root. A myotome is a group of muscles receiving motor innervation from a spinal segment. Key screening examples: C5 shoulder abduction, C6 wrist extension, C7 elbow extension, L4 ankle dorsiflexion, L5 great toe extension, S1 plantarflexion.

Spinal meninges

Gray770 — Henry Vandyke Carter, Public domain

Dura, arachnoid and pia mater surround spinal cord. The epidural space is a real space containing fat and venous plexus; it is the target for epidural anaesthesia. Lumbar puncture is commonly performed below the conus medullaris, typically L3–L4 or L4–L5.

Clinical correlation: Cauda equina syndrome may present with saddle sensory loss, bladder/bowel dysfunction, sexual dysfunction and lower limb neurological deficits; urgent assessment is required.

Upper Limb — Shoulder to Hand

Trace osteology, joints, muscle compartments, peripheral nerves and arterial pathways.

805 Ulna and Radius — OpenStax College, CC BY 3.0. Tap image to enlarge.

Pectoral girdle & shoulder

803 The Scapula — OpenStax College, CC BY 3.0

Bones: clavicle and scapula. Glenohumeral joint is a ball-and-socket synovial joint. Rotator cuff = supraspinatus, infraspinatus, teres minor and subscapularis (SITS); stabilises humeral head in glenoid cavity.

Arm compartments

1120 Muscles that Move the Forearm — OpenStax, CC BY 4.0

Anterior compartment: biceps brachii, brachialis, coracobrachialis; mainly musculocutaneous nerve; elbow flexion/supination. Posterior compartment: triceps brachii; radial nerve; elbow extension.

Forearm compartments

Anterior flexor-pronator compartment is predominantly median nerve (ulnar nerve supplies selected intrinsic/flexor muscles). Posterior extensor-supinator compartment is predominantly radial nerve/posterior interosseous nerve.

Carpal tunnel

Gray422 — Henry Vandyke Carter, Public domain

Boundaries: carpal bones and flexor retinaculum. Contents: median nerve and nine flexor tendons (four FDS, four FDP, one FPL). Compression causes median neuropathy with paraesthesia in lateral 3½ digits and thenar weakness.

Brachial plexus

Gray808 — Henry Vandyke Carter, Public domain

Roots C5–T1 → trunks (upper, middle, lower) → divisions (anterior/posterior) → cords (lateral, posterior, medial) → terminal branches (musculocutaneous, axillary, radial, median, ulnar). Remember: Roots, Trunks, Divisions, Cords, Branches.

Major upper limb arteries

Subclavian → axillary (at lateral border of 1st rib) → brachial (at inferior border of teres major) → radial and ulnar arteries → superficial and deep palmar arches → digital arteries.

Hand anatomy

806 Hand and Wrist — OpenStax College, CC BY 3.0

Gray573 — Henry Vandyke Carter, Public domain

Eight carpal bones, five metacarpals and phalanges. Thenar muscles mainly median nerve; most hypothenar and interossei are ulnar nerve. Lumbricals flex MCP and extend IP joints. Interossei: DAB (dorsal abduct), PAD (palmar adduct).

Key joints & movements

802 Pectoral Girdle — OpenStax College, CC BY 3.0

Shoulder: flexion, extension, abduction, adduction, rotation. Elbow: flexion/extension. Radioulnar joints: pronation/supination. Wrist: flexion, extension, radial/ulnar deviation. MCP and IP joints enable grasp and fine motor control.

Clinical correlation: Axillary nerve injury may impair deltoid function and sensation over the “regimental badge” area. Radial nerve injury can cause wrist drop; ulnar neuropathy may impair finger abduction/adduction.

Lower Limb — Hip to Foot

Relate weight-bearing architecture to gait, balance, peripheral nerve function and vascular supply.

Gray245 — Henry Vandyke Carter, Public domain. Tap image to enlarge.

Pelvic girdle & hip joint

Gray339 — Henry Vandyke Carter, Public domain

Hip bone comprises ilium, ischium and pubis; acetabulum articulates with femoral head. Hip is a deep ball-and-socket joint stabilised by labrum, capsule and iliofemoral, pubofemoral and ischiofemoral ligaments.

Gluteal region

Gluteus maximus extends and laterally rotates hip; gluteus medius/minimus abduct and medially rotate hip and stabilise pelvis during single-leg stance. Superior gluteal nerve supplies medius/minimus; inferior gluteal nerve supplies maximus.

Thigh compartments

Gray434 — Henry Vandyke Carter, Public domain

Anterior: quadriceps femoris and sartorius; femoral nerve; knee extension. Medial: adductor group and gracilis; obturator nerve; adduction. Posterior: hamstrings; mainly tibial division of sciatic nerve; hip extension and knee flexion.

Knee joint

810 Femur and Patella — OpenStax College, CC BY 3.0

Modified hinge synovial joint. Menisci distribute load; ACL limits anterior translation of tibia, PCL limits posterior translation. MCL resists valgus stress; LCL resists varus stress. Patella improves quadriceps leverage.

Leg compartments

Gray440 — Henry Vandyke Carter, Public domain

Anterior: dorsiflexors, deep fibular nerve. Lateral: fibularis longus/brevis, superficial fibular nerve. Posterior: plantarflexors and toe flexors, tibial nerve; superficial and deep groups.

Lumbosacral plexus & major nerves

Gray822 — Henry Vandyke Carter, Public domain

Femoral nerve (L2–L4), obturator nerve (L2–L4), sciatic nerve (L4–S3), common fibular and tibial divisions. Common fibular nerve winds around fibular neck and is vulnerable to injury.

Arterial supply

2130 Lower Limb Arteries Chart — OpenStax College, CC BY 3.0

External iliac → femoral artery → popliteal artery → anterior tibial (continues as dorsalis pedis) and posterior tibial arteries (gives fibular artery and plantar branches). Femoral pulse is palpable inferior to inguinal ligament.

Foot arches & gait

812 Bones of the Foot — OpenStax College, CC BY 3.0

Medial and lateral longitudinal arches and transverse arch distribute load. Tibialis posterior, fibularis longus, plantar fascia and intrinsic muscles support arches. Gait cycle: stance phase and swing phase; ankle strategy, hip strategy and stepping responses contribute to balance.

Clinical correlation: Common fibular nerve injury can cause foot drop and impaired dorsiflexion/eversion. Weak hip abductors may produce Trendelenburg gait with contralateral pelvic drop during single-leg stance.

Pelvis & Perineum

Bony pelvis

809 Male Female Pelvic Girdle — OpenStax College, CC BY 3.0

Formed by two hip bones, sacrum and coccyx. Pelvic inlet separates greater (false) pelvis from lesser (true) pelvis; pelvic outlet is bounded by pubic arch, ischial tuberosities, sacrotuberous ligaments and coccyx.

Pelvic floor

Pelvic diaphragm consists chiefly of levator ani (puborectalis, pubococcygeus, iliococcygeus) and coccygeus. Supports pelvic viscera and contributes to urinary and faecal continence.

Perineum

Diamond-shaped region inferior to pelvic diaphragm, divided into urogenital and anal triangles by a line between ischial tuberosities. Perineal body is a central fibromuscular node for muscle attachment.

Pelvic organs

2605 The Bladder — OpenStax College, CC BY 3.0

Gray1167 — Henry Vandyke Carter, Public domain

Urinary bladder and urethra; rectum and anal canal; reproductive organs. Relationships differ by sex and are clinically important in pelvic examination, surgery and imaging.

Pelvic vessels & nerves

Internal iliac branches — Mikael Häggström. When using this image in external works, it may be cited as: , Public domain

Internal iliac artery supplies much of pelvic viscera, gluteal region and perineum. Sacral plexus gives rise to sciatic and pudendal nerves. Pudendal nerve (S2–S4) supplies much of perineum and external sphincters.

Continence mechanisms

Internal urethral sphincter (smooth muscle, autonomic control) and external urethral sphincter (skeletal muscle, pudendal nerve) contribute to urinary continence. Puborectalis maintains anorectal angle and supports faecal continence.

Urinary & Reproductive Systems

Kidney anatomy

2610 The Kidney — OpenStax College, CC BY 3.0

Renal capsule, cortex, medulla, renal pyramids, papillae, minor/major calyces and renal pelvis. Nephron comprises renal corpuscle (glomerulus and Bowman capsule), proximal tubule, loop of Henle, distal tubule and collecting system.

Gray1120 — Henry Vandyke Carter, Public domain. Tap image to enlarge.

Renal circulation

Renal artery → segmental → interlobar → arcuate → cortical radiate arteries → afferent arteriole → glomerular capillaries → efferent arteriole → peritubular capillaries/vasa recta. Renal vein drains to inferior vena cava.

Ureter, bladder & urethra

Ureters carry urine by peristalsis; common constriction sites are pelvi-ureteric junction, crossing iliac vessels and ureterovesical junction. Detrusor muscle forms bladder wall. Trigone lies between ureteric openings and internal urethral orifice.

Male reproductive anatomy

Gray1153 — Henry Vandyke Carter, Public domain

Testis → epididymis → ductus deferens → ejaculatory duct → prostatic urethra. Accessory glands: seminal vesicles, prostate and bulbourethral glands. Spermatic cord contains ductus deferens, testicular vessels, pampiniform plexus, nerves and lymphatics.

Female reproductive anatomy

Ovaries, uterine tubes (infundibulum, ampulla, isthmus, uterine part), uterus (fundus, body, cervix), vagina and external genitalia. Fertilisation most commonly occurs in the ampulla of uterine tube.

Autonomic & somatic control

2604 Nerves Innervating the Urinary SystemN — OpenStax College, CC BY 3.0

Sympathetic pathways contribute to storage and emission; parasympathetic pelvic splanchnic nerves (S2–S4) contribute to detrusor contraction and erection; pudendal nerve supplies external urethral sphincter and perineal muscles.

Clinical correlation: In older adults, urinary symptoms may reflect multiple contributors including detrusor overactivity or underactivity, outlet obstruction, medications, mobility and cognition. Anatomy informs assessment but does not replace clinical evaluation.

Endocrine & Lymphatic Systems

Hypothalamus & pituitary

Hypothalamus links nervous and endocrine systems. Anterior pituitary secretes ACTH, TSH, GH, prolactin, FSH and LH. Posterior pituitary releases ADH and oxytocin synthesised in hypothalamic nuclei.

1801 The Endocrine System — OpenStax College, CC BY 3.0. Tap image to enlarge.

Thyroid & parathyroid

1811 The Thyroid Gland — OpenStax College, CC BY 3.0

Thyroid follicles produce T3 and T4; parafollicular C cells produce calcitonin. Parathyroid chief cells secrete PTH, which increases serum calcium and regulates phosphate balance.

Adrenal glands

Cortex zones: zona glomerulosa (mineralocorticoids), fasciculata (glucocorticoids), reticularis (androgens). Medulla secretes catecholamines — epinephrine and norepinephrine.

Pancreatic islets

1820 The Pancreas — OpenStax College, CC BY 3.0

Beta cells secrete insulin; alpha cells glucagon; delta cells somatostatin. Insulin promotes glucose uptake/storage; glucagon raises blood glucose through hepatic glycogenolysis and gluconeogenesis.

Lymphatic organs

2201 Anatomy of the Lymphatic System — OpenStax College, CC BY 3.0

Primary lymphoid organs: bone marrow and thymus. Secondary: lymph nodes, spleen, tonsils and mucosa-associated lymphoid tissue (MALT). Lymph nodes filter lymph and support antigen presentation.

Lymphatic drainage

2202 Lymphatic Capillaries — OpenStax College, CC BY 3.0

Lymphatic capillaries collect interstitial fluid; lymph passes through afferent vessels, node sinuses and efferent vessels. Thoracic duct drains most of body; right lymphatic duct drains right upper quadrant.

Special Senses — Eye, Ear, Taste & Smell

Eyeball layers

Fibrous tunic: sclera and cornea. Vascular tunic (uvea): choroid, ciliary body and iris. Neural tunic: retina. Light pathway: cornea → aqueous humour → pupil → lens → vitreous body → retina.

1413 Structure of the Eye — OpenStax College, CC BY 3.0. Tap image to enlarge.

Retina & visual pathway

Gray773 — Henry Vandyke Carter, Public domain

Photoreceptors: rods (low-light vision) and cones (colour/high acuity). Signal travels via bipolar cells and ganglion cells; optic nerve → optic chiasm → optic tract → lateral geniculate nucleus → optic radiations → primary visual cortex.

Extraocular muscles

LR6 SO4, all others III: lateral rectus by CN VI, superior oblique by CN IV, remaining extraocular muscles by CN III. Levator palpebrae superioris elevates upper eyelid.

External, middle & inner ear

1404 The Structures of the Ear — OpenStax, CC BY 4.0

External auditory canal conducts sound to tympanic membrane. Ossicles: malleus, incus and stapes. Inner ear contains cochlea for hearing and vestibular apparatus (utricle, saccule, semicircular ducts) for balance.

Auditory & vestibular pathways

Hair cells transduce mechanical movement. Cochlear division of CN VIII carries auditory information; vestibular division conveys head position and acceleration signals to vestibular nuclei and cerebellum.

Olfaction & gustation

Olfactory receptor neurons project via CN I to olfactory bulb. Taste: anterior two-thirds of tongue via chorda tympani (CN VII); posterior one-third via CN IX; epiglottis/lower pharynx via CN X.

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