Human Anatomy Atlas — Husain Farooqui

Nervous System — The Brain

CNSNeuroanatomy

The nervous system coordinates and regulates body activity through electrical and chemical signalling. It is divided into the central nervous system (brain and spinal cord) and peripheral nervous system (cranial nerves, spinal nerves, and their ganglia). The brain is the most information-dense structure in the body, so it anchors this atlas — the sections below move from the cerebral surface inward to the ventricles, vasculature, and meninges.

Cerebral Hemispheres & Lobes

Lateral view of the cerebral hemisphere showing the frontal, parietal, temporal and occipital lobes separated by the central and lateral sulci, after Gray's Anatomy plate 728.

Medial (sagittal) view of the cerebral hemisphere and brainstem, after Gray's Anatomy plate 727.

KEY LANDMARKS

Longitudinal fissure
Deep midline groove separating the right and left cerebral hemispheres.
Central sulcus (of Rolando)
Separates the frontal lobe from the parietal lobe; marks the boundary between primary motor and primary sensory cortex.
Lateral sulcus (Sylvian fissure)
Separates the temporal lobe below from the frontal and parietal lobes above; the insula lies buried within it.
Parieto-occipital sulcus
Marks the boundary between parietal and occipital lobes, best seen medially.
Precentral gyrus
Immediately anterior to the central sulcus; site of the primary motor cortex.
Postcentral gyrus
Immediately posterior to the central sulcus; site of the primary somatosensory cortex.
Insula (Island of Reil)
A fifth lobe hidden beneath the frontal, parietal and temporal opercula.

Anatomical Description

Each cerebral hemisphere has a convex outer surface thrown into folds — gyri — separated by grooves called sulci, an arrangement that triples cortical surface area within the confines of the skull. By convention the cortex is divided into four visible lobes named for the overlying cranial bones (frontal, parietal, temporal, occipital), plus the insula. The frontal lobe extends from the frontal pole to the central sulcus and is concerned with voluntary movement, executive function, expressive language (Broca's area) and personality/judgement. The parietal lobe lies between the central and parieto-occipital sulci and processes somatosensation, spatial orientation and sensory integration. The temporal lobe, inferior to the lateral sulcus, houses the primary auditory cortex, receptive language (Wernicke's area), and — on its medial surface — the hippocampus and amygdala. The occipital lobe, the most posterior lobe, is dominated by the primary visual cortex around the calcarine sulcus.

Function

Frontal — planning, voluntary motor control, expressive speech, judgement, inhibition
Parietal — touch, proprioception, spatial awareness, calculation
Temporal — hearing, language comprehension, memory encoding, emotion
Occipital — visual processing

Important Relations

Superior: calvarium (skull vault), covered by meninges
Inferior (frontal lobe): orbital plate, olfactory bulb/tract
Inferior (temporal lobe): middle cranial fossa, tentorium cerebelli
Medial: falx cerebri separates the two hemispheres
Deep to lateral sulcus: insula and middle cerebral artery branches

Blood Supply

Cortex is supplied by the three cerebral arteries arising from the Circle of Willis: the anterior cerebral artery (medial frontal/parietal cortex — the "leg area" of the motor/sensory homunculus), the middle cerebral artery (lateral surface — face and arm representation, and language areas in the dominant hemisphere), and the posterior cerebral artery (occipital and inferior temporal lobe).

Innervation

The cortex itself does not have "innervation" in the peripheral sense; rather, it originates the corticospinal, corticobulbar and corticopontine pathways and receives thalamocortical projections relaying sensory, visual and auditory input to their respective primary cortical areas.

Clinical Anatomy

Because the three cerebral arteries supply broadly predictable cortical territories, the pattern of a patient's neurological deficit after a stroke often localises the occluded vessel: contralateral leg-predominant weakness suggests an anterior cerebral artery territory infarct; contralateral face-and-arm weakness with aphasia (if the dominant hemisphere is involved) suggests middle cerebral artery territory; and a contralateral homonymous hemianopia suggests posterior cerebral artery territory. Damage to Broca's area (posterior inferior frontal gyrus) produces non-fluent, effortful speech with preserved comprehension, while damage to Wernicke's area (posterior superior temporal gyrus) produces fluent but nonsensical speech with poor comprehension.

Did You Know?

Cortical folding is not decorative — it is a space-saving solution. If the human cerebral cortex were flattened out, it would cover roughly 2,000–2,500 cm², about the size of a large pizza, yet it fits inside a skull with an internal volume of only around 1,400 cm³ because roughly two-thirds of the cortical surface lies buried within sulci.

Diencephalon, Basal Nuclei & Limbic System

Anatomical Description

Deep to the cortex, the two hemispheres are interconnected by the corpus callosum, the largest commissure in the brain, arching over the diencephalon and lateral ventricles. The diencephalon comprises the thalamus (a paired, egg-shaped mass of grey matter that relays essentially all sensory input — except olfaction — to the cortex), the hypothalamus (below the thalamus, forming the floor and part of the walls of the third ventricle), and the epithalamus (including the pineal gland). The basal nuclei (caudate nucleus, putamen, globus pallidus, subthalamic nucleus and substantia nigra) form subcortical grey-matter loops that modulate movement. The internal capsule, a compact white-matter band between the thalamus/basal nuclei and the lentiform nucleus, carries nearly all ascending and descending fibres connecting cortex to brainstem and spinal cord — a small lesion here can cause a disproportionately large deficit. The limbic system — hippocampus, amygdala, cingulate gyrus, fornix and related structures — forms a functional loop governing memory, emotion and motivation.

Function

Thalamus: sensory relay and gating to cortex; some motor relay
Hypothalamus: autonomic regulation, temperature, hunger/thirst, circadian rhythm, pituitary control via the hypophyseal portal system
Basal nuclei: initiation and smoothing of voluntary movement, procedural learning
Hippocampus: consolidation of new declarative (episodic) memories
Amygdala: fear processing, emotional salience, autonomic/endocrine responses to threat

Blood Supply

Thalamic perforating branches from the posterior cerebral and posterior communicating arteries; hypothalamus from the circle of Willis directly; basal nuclei chiefly from the lenticulostriate branches of the middle cerebral artery — small, end-artery-like vessels that are a classic site of hypertensive lacunar infarcts and haemorrhage.

Clinical Anatomy

Because motor, sensory, visual and cortico-cortical fibres are tightly packed into the small cross-sectional area of the internal capsule, even a lacunar infarct only a centimetre across can produce a dense contralateral hemiparesis affecting face, arm and leg equally — unlike a cortical stroke, which tends to favour one body part over another. Damage to the hippocampus (for example in herpes encephalitis or after prolonged hypoxia) produces anterograde amnesia — an inability to form new long-term memories — while older memories, stored diffusely in cortex, are often relatively spared.

Did You Know?

The hippocampus is named for its resemblance to a seahorse (Greek hippokampos) when dissected out of the temporal lobe — the curved shape is easiest to appreciate on a coronal section through the medial temporal lobe.

Cerebellum & Brainstem

Anatomical Description

The brainstem connects the cerebrum to the spinal cord and comprises, from rostral to caudal, the midbrain (mesencephalon), pons, and medulla oblongata. It contains the nuclei of cranial nerves III–XII, major ascending and descending tracts, and the reticular formation governing arousal, respiration and cardiovascular tone. The cerebellum sits in the posterior cranial fossa behind the pons and medulla, connected to the brainstem by three paired peduncles (superior, middle, inferior), and consists of two hemispheres joined by a midline vermis.

Function

Midbrain: relay for vision/hearing reflexes (superior/inferior colliculi), origin of CN III and IV, contains substantia nigra
Pons: relay between cerebrum and cerebellum, origin of CN V–VIII, respiratory centres
Medulla: cardiovascular and respiratory control centres, decussation of pyramids, origin of CN IX–XII
Cerebellum: coordination, balance, motor learning, fine-tuning of movement timing

Blood Supply

Vertebrobasilar system: vertebral arteries and their branches (posterior inferior cerebellar artery) supply the medulla; the basilar artery and its branches (anterior inferior cerebellar, superior cerebellar, pontine perforators) supply the pons, midbrain and remaining cerebellum.

Cranial nerves overview: I Olfactory · II Optic · III Oculomotor · IV Trochlear · V Trigeminal · VI Abducens · VII Facial · VIII Vestibulocochlear · IX Glossopharyngeal · X Vagus · XI Accessory · XII Hypoglossal. All except I and II attach to the brainstem.

Clinical Anatomy

Because long tracts, cranial nerve nuclei and cerebellar connections are packed closely together in the small cross-section of the brainstem, brainstem strokes classically produce "crossed" syndromes — an ipsilateral cranial nerve deficit combined with a contralateral long-tract (motor or sensory) deficit — which localises the lesion precisely along the brainstem's rostrocaudal axis.

Ventricular System, Meninges & CSF Circulation

Cast of the ventricular cavities viewed from the side, showing the lateral ventricles, third ventricle and fourth ventricle, after Gray's Anatomy plate 739.

CSF PATHWAY (IN ORDER)

Lateral ventricles (×2)
Produced mainly by choroid plexus here.
Interventricular foramina (of Monro)
Third ventricle
Cerebral aqueduct (of Sylvius)
Narrowest point — common site of obstructive hydrocephalus.
Fourth ventricle
Foramina of Luschka (×2, lateral) & Magendie (midline)
Exit into subarachnoid space.
Subarachnoid space → arachnoid granulations → dural venous sinuses
Reabsorbed into venous blood.

Meninges (superficial to deep)

Dura mater — tough outer layer; forms the falx cerebri and tentorium cerebelli; encloses the dural venous sinuses
Arachnoid mater — delicate middle layer; subarachnoid space beneath it contains CSF and the cerebral vessels
Pia mater — thin, vascular layer intimately applied to the brain surface, following every gyrus and sulcus

Function

CSF cushions the brain against mechanical injury, provides buoyancy (effectively reducing the brain's weight from ~1,400 g to about 50 g), removes metabolic waste, and helps maintain a stable chemical environment for neurons.

Clinical Anatomy

Obstruction anywhere along the CSF pathway — most classically at the narrow cerebral aqueduct — causes obstructive (non-communicating) hydrocephalus, with dilation of the ventricles upstream of the block. Bleeding into the subarachnoid space (subarachnoid haemorrhage, often from a ruptured berry aneurysm on the Circle of Willis) presents with sudden severe headache and can be sampled at lumbar puncture, performed below the spinal cord's termination (around L1–L2 in adults) to avoid cord injury, in the subarachnoid space of the lumbar cistern.

Cerebral Circulation

Arterial Supply

The brain receives blood from two paired systems that anastomose at the base of the brain to form the Circle of Willis: the internal carotid system anteriorly (giving the anterior and middle cerebral arteries plus the posterior communicating artery) and the vertebrobasilar system posteriorly (the paired vertebral arteries join to form the basilar artery, which terminates as the two posterior cerebral arteries). The circle is completed by the anterior communicating artery joining the two anterior cerebral arteries. This arrangement provides a potential collateral pathway if one feeding vessel is occluded, though the degree of anatomical completeness of the circle varies considerably between individuals.

Venous Drainage

Cerebral veins are valveless and drain into a system of dural venous sinuses — the superior and inferior sagittal sinuses, straight sinus, transverse and sigmoid sinuses, and the cavernous sinus — which ultimately empty into the internal jugular veins.

High-Yield Facts

The brain receives ~15% of resting cardiac output despite being ~2% of body weight.
The middle cerebral artery is the most commonly occluded vessel in ischaemic stroke.
The cavernous sinus is traversed by the internal carotid artery and CN VI, with CN III, IV, V1 and V2 running in its lateral wall.

Quick Revision — Nervous System

4 visible lobes + insula per hemisphere
Central sulcus = motor/sensory boundary
ACA–leg, MCA–face/arm, PCA–vision
Thalamus = sensory relay hub
Internal capsule = dense motor/sensory bottleneck
Basal nuclei fed by lenticulostriate vessels
Hippocampus → new memory formation
CSF: lateral → 3rd → aqueduct → 4th → subarachnoid space
3 meningeal layers: dura, arachnoid, pia
Circle of Willis unites carotid + vertebrobasilar systems

Skeletal System — Osteology

206 bones (adult)Osteology

The skeleton provides structural support, protects vital organs, enables movement through muscle attachment and lever action, stores calcium and phosphate, and houses the bone marrow responsible for haematopoiesis. An adult skeleton has 206 bones, grouped into the axial skeleton (skull, vertebral column, ribs, sternum) and the appendicular skeleton (limb bones and girdles).

Bone Classification & Long Bone Architecture

Bone Classification (by shape)

Long bones — femur, humerus, phalanges; length > width, act as levers
Short bones — carpals, tarsals; roughly cuboidal, absorb shock
Flat bones — sternum, skull vault, scapula; protection and broad muscle attachment
Irregular bones — vertebrae, hip bone, facial bones; complex shapes
Sesamoid bones — patella; embedded within a tendon, protects it from friction
Pneumatic bones — some skull bones (frontal, maxilla, sphenoid, ethmoid) contain air-filled sinuses that lighten the skull

Functions of the Skeleton

Mechanical support and shape
Protection of viscera (cranium, thoracic cage, pelvis)
Movement, via muscle attachment and joints acting as levers
Mineral storage and homeostasis (calcium, phosphate)
Haematopoiesis in red marrow
Fat storage in yellow marrow

Long Bone Architecture

A typical long bone has a shaft, the diaphysis, composed of dense compact (cortical) bone surrounding a central medullary cavity that houses bone marrow. At each end lies an epiphysis, made largely of spongy cancellous (trabecular) bone covered by articular cartilage at the joint surface. Between diaphysis and epiphysis is the metaphysis, containing the epiphyseal (growth) plate in a growing bone — a layer of hyaline cartilage where longitudinal growth occurs through endochondral ossification until it fuses in early adulthood. The outer surface of bone (except at articular cartilage) is covered by the periosteum, a fibrous membrane carrying blood vessels, nerves and osteoprogenitor cells important for repair; the internal marrow cavity surface is lined by the thinner endosteum. A nutrient artery typically pierces the diaphysis obliquely to supply the medullary cavity and inner cortex.

Bone Cells

Osteoprogenitor cells — mesenchymal stem cells that differentiate into osteoblasts
Osteoblasts — synthesise osteoid (unmineralised bone matrix); line growing bone surfaces
Osteocytes — mature osteoblasts entombed in lacunae, maintaining bone matrix and sensing mechanical strain
Osteoclasts — large multinucleate cells of monocyte lineage that resorb bone, enabling remodelling and calcium release

Microscopic Structure (Compact Bone)

Compact bone is organised into cylindrical units called osteons (Haversian systems), each built around a central Haversian canal carrying blood vessels and nerves, surrounded by concentric rings of matrix called lamellae. Osteocytes sit in small spaces (lacunae) between lamellae and communicate via thin channels (canaliculi). Volkmann's (perforating) canals run perpendicular to Haversian canals, linking them and connecting to the periosteal and medullary circulation.

Clinical Anatomy

Because the epiphyseal plate is the weakest part of an immature long bone — weaker than the surrounding ligaments — traumatic injury in children more often produces a growth plate (physeal) fracture than a ligament tear, unlike in adults. Fractures through the growth plate are graded by the Salter–Harris classification, and depending on the pattern can disturb future bone growth.

Did You Know?

Bone is a living, constantly remodelling tissue: an estimated 5–10% of the adult skeleton is replaced every year through the coordinated action of osteoblasts and osteoclasts, meaning the skeleton you have today is, matrix-wise, largely different from the one you had a decade ago.

The Skull

MAJOR CRANIAL BONES

Frontal bone
Forehead, orbital roof, anterior cranial fossa floor.
Parietal bones (×2)
Form most of the cranial vault; meet at the sagittal suture.
Temporal bone
Houses the middle and inner ear; contains the mastoid and styloid processes.
Occipital bone
Contains the foramen magnum; articulates with C1 (atlas).
Sphenoid bone
"Keystone" of the skull base; houses the sella turcica/pituitary fossa.
Ethmoid bone
Between orbits; forms part of the nasal septum and cribriform plate.
Maxilla
Upper jaw; forms the hard palate and orbital floor.
Mandible
Lower jaw; the only mobile bone of the skull, via the temporomandibular joint.

Important Foramina

Foramen	Location	Transmits
Foramen magnum	Occipital bone	Medulla/spinal cord, vertebral arteries, CN XI (spinal root)
Foramen ovale	Sphenoid, middle cranial fossa	Mandibular nerve (CN V3)
Foramen rotundum	Sphenoid	Maxillary nerve (CN V2)
Superior orbital fissure	Between greater/lesser sphenoid wings	CN III, IV, V1, VI; ophthalmic veins
Jugular foramen	Between temporal & occipital bones	CN IX, X, XI; internal jugular vein
Internal acoustic meatus	Temporal bone	CN VII, VIII
Cribriform plate foramina	Ethmoid bone	Olfactory nerve (CN I) fibres

Clinical Anatomy

The pterion, where frontal, parietal, temporal and sphenoid bones meet on the lateral skull, is the thinnest part of the calvarium and overlies the anterior division of the middle meningeal artery. A blow to this region can fracture the bone and lacerate the artery, producing an extradural (epidural) haematoma — classically presenting with a lucid interval followed by rapid neurological decline as the arterial bleed strips dura from bone.

Vertebral Column

Anatomical Description

The vertebral column consists of 33 vertebrae in the young adult: 7 cervical (C1–C7), 12 thoracic (T1–T12), 5 lumbar (L1–L5), 5 fused sacral vertebrae forming the sacrum, and 3–4 fused coccygeal vertebrae forming the coccyx. A typical vertebra has a body (weight-bearing, anteriorly) and a vertebral arch (formed by pedicles and laminae) enclosing the vertebral foramen, through which the spinal cord passes; the arch bears spinous and transverse processes for muscle/ligament attachment and paired articular processes forming facet joints with adjacent vertebrae. Adjacent vertebral bodies are separated by intervertebral discs, each with a central gelatinous nucleus pulposus and a surrounding fibrous annulus fibrosus, which absorb axial load and permit movement.

Regional Distinguishing Features

Cervical: small bodies, bifid spinous processes (C3–C6), transverse foramina for vertebral vessels; C1 (atlas) has no body, C2 (axis) bears the odontoid process (dens)
Thoracic: costal facets for rib articulation, long downward-sloping spinous processes
Lumbar: large, kidney-shaped bodies bearing most axial load; no costal facets or transverse foramina

Function

Supports the trunk and head, protects the spinal cord, transmits load from the head/trunk to the pelvis, provides muscle attachment, and its curvatures (cervical and lumbar lordosis, thoracic and sacral kyphosis) absorb shock during upright locomotion.

Clinical Anatomy

The spinal cord ends around the L1–L2 vertebral level as the conus medullaris, well above the end of the bony vertebral canal — this is why a lumbar puncture is performed lower, typically at the L3/L4 or L4/L5 interspace, where only the cauda equina (lumbar and sacral nerve roots floating in CSF) is present and the needle is unlikely to injure neural tissue. Degeneration and posterolateral herniation of the intervertebral disc — most common at L4/L5 and L5/S1 — can compress an exiting or traversing nerve root, producing radicular pain (sciatica) along its dermatomal distribution.

Thoracic Cage

Description

Formed by 12 pairs of ribs, the sternum (manubrium, body, xiphoid process) anteriorly, and the 12 thoracic vertebrae posteriorly. Ribs 1–7 ("true ribs") attach directly to the sternum via their own costal cartilage; ribs 8–10 ("false ribs") attach indirectly via the cartilage of rib 7; ribs 11–12 ("floating ribs") have no anterior attachment.

Function

Protects the heart, lungs and great vessels, and provides attachment for respiratory muscles; its compliance allows the bucket-handle and pump-handle movements that expand thoracic volume during inspiration.

Clinical Anatomy

The manubriosternal joint (sternal angle/angle of Louis) marks the level of the second costal cartilage, T4/T5 vertebral level, tracheal bifurcation and aortic arch borders — a key surface landmark for counting ribs and intercostal spaces.

Upper Limb Bones

Bone	Key landmarks	Major articulations
Clavicle	S-shaped; sternal & acromial ends	Sternum, acromion of scapula
Scapula	Spine, acromion, coracoid process, glenoid fossa	Humerus (glenohumeral), clavicle
Humerus	Surgical/anatomical neck, deltoid tuberosity, epicondyles, radial groove (radial nerve)	Scapula, radius, ulna
Radius	Head, radial tuberosity, styloid process	Humerus, ulna, carpals
Ulna	Olecranon, coronoid process, trochlear notch, styloid process	Humerus, radius
Carpals (8)	Scaphoid, lunate, triquetrum, pisiform, trapezium, trapezoid, capitate, hamate	Radius, metacarpals
Metacarpals (5) & phalanges (14)	Base, shaft, head	Carpals, each other

Clinical Anatomy

The scaphoid receives a retrograde blood supply entering distally, so a fracture through its waist (the commonest carpal fracture, typically from a fall on an outstretched hand) risks avascular necrosis of the proximal fragment. The surgical neck of the humerus is a common fracture site and lies close to the axillary nerve; the radial (spiral) groove carries the radial nerve, vulnerable in mid-shaft humeral fractures ("Saturday night palsy" pattern of wrist drop).

Lower Limb Bones

Bone	Key landmarks	Major articulations
Hip bone (ilium + ischium + pubis)	Acetabulum, iliac crest, ischial tuberosity, pubic symphysis	Sacrum, femur, opposite hip bone
Femur	Head, neck, greater/lesser trochanters, linea aspera, medial/lateral condyles	Hip bone, tibia, patella
Patella	Largest sesamoid bone; within quadriceps tendon	Femur (patellofemoral joint)
Tibia	Medial/lateral condyles, tibial tuberosity, medial malleolus	Femur, fibula, talus
Fibula	Head, lateral malleolus; non-weight-bearing shaft	Tibia, talus
Tarsals (7)	Talus, calcaneus, navicular, cuboid, 3 cuneiforms	Tibia/fibula, metatarsals
Metatarsals (5) & phalanges (14)	Base, shaft, head	Tarsals, each other

Clinical Anatomy

The femoral neck is a common fracture site in elderly osteoporotic patients, especially after a fall; because its retinacular blood supply can be disrupted, displaced fractures carry a significant risk of avascular necrosis of the femoral head. The classic clinical sign is a shortened and externally rotated limb.

Quick Revision — Skeletal System

206 bones: axial + appendicular
Long bone: epiphysis–metaphysis–diaphysis
Osteoblast builds, osteoclast resorbs
Osteon = Haversian canal + lamellae
Pterion overlies middle meningeal artery
Spinal cord ends ~L1–L2; LP done lower
Scaphoid: retrograde blood supply → AVN risk
Sternal angle = T4/5, 2nd rib level

Joints (Arthrology)

Skeletal system

Structural Classification

Fibrous — bones united by dense connective tissue (sutures of the skull, interosseous membranes, gomphoses of teeth); little to no movement
Cartilaginous — united by cartilage: primary/synchondroses (hyaline cartilage, e.g. epiphyseal plate) or secondary/symphyses (fibrocartilage, e.g. pubic symphysis, intervertebral discs)
Synovial — bones separated by a fluid-filled joint cavity enclosed by a capsule lined with synovium; the most mobile joint type

Synovial Joint Subtypes

Plane — flat surfaces, gliding (intercarpal joints)
Hinge — one-axis flexion/extension (elbow, knee)
Pivot — rotation around a single axis (atlantoaxial joint)
Condyloid — biaxial, ovoid surfaces (wrist/radiocarpal)
Saddle — biaxial, reciprocally curved surfaces (first carpometacarpal/thumb)
Ball-and-socket — multiaxial (shoulder, hip)

Major Joints — Summary

Joint	Bones	Type	Key stabilisers	Clinical note
Shoulder (glenohumeral)	Humerus, scapula	Synovial, ball-and-socket	Rotator cuff (supraspinatus, infraspinatus, teres minor, subscapularis)	Most mobile but least stable joint — most commonly dislocated large joint, usually anteriorly
Elbow	Humerus, radius, ulna	Synovial, hinge (+ pivot at radioulnar)	Medial (ulnar) & lateral (radial) collateral ligaments	"Nursemaid's elbow" = radial head subluxation in young children
Wrist (radiocarpal)	Radius, scaphoid, lunate, triquetrum	Synovial, condyloid	Extrinsic radiocarpal & ulnocarpal ligaments	FOOSH injury pattern — scaphoid or distal radius fracture
Hip	Femur, acetabulum	Synovial, ball-and-socket	Iliofemoral, pubofemoral, ischiofemoral ligaments; deep acetabular labrum	Deep socket → inherently stable, dislocation usually needs major trauma
Knee	Femur, tibia, patella	Synovial, modified hinge	ACL, PCL, MCL, LCL, medial & lateral menisci	ACL injury classic in pivoting sports; "unhappy triad" = ACL+MCL+medial meniscus
Ankle (talocrural)	Tibia, fibula, talus	Synovial, hinge	Lateral ligament complex (ATFL most often injured), deltoid ligament medially	Inversion sprain injures ATFL most commonly

Did You Know?

The shoulder trades stability for mobility: its shallow glenoid fossa contacts only about a third of the humeral head's surface at any time, which is precisely what allows the enormous range of motion at the cost of being the most frequently dislocated major joint in the body.

Muscular System

~600 skeletal muscles

Skeletal muscle produces voluntary movement by contracting across joints, acting through origin (fixed attachment), insertion (mobile attachment) and action. Below are the clinically and functionally most important muscle groups by region rather than an exhaustive list.

Region	Muscle	Origin → Insertion	Action	Innervation
Shoulder	Deltoid	Clavicle/scapula → deltoid tuberosity	Arm abduction (middle fibres)	Axillary nerve (C5–C6)
Shoulder	Supraspinatus	Supraspinous fossa → greater tubercle	Initiates abduction (first 15°)	Suprascapular nerve
Arm	Biceps brachii	Scapula → radial tuberosity	Elbow flexion, forearm supination	Musculocutaneous nerve (C5–C6)
Arm	Triceps brachii	Scapula/humerus → olecranon	Elbow extension	Radial nerve (C6–C8)
Back	Trapezius	Occiput/spinous processes → clavicle/scapula	Scapular elevation, rotation, retraction	Accessory nerve (CN XI)
Back	Latissimus dorsi	Lower spine/ilium → humerus	Arm adduction, extension, internal rotation	Thoracodorsal nerve
Abdomen	Rectus abdominis	Pubic crest → xiphoid/costal cartilages	Trunk flexion, compresses abdomen	Thoracoabdominal nerves (T7–T12)
Thorax	Diaphragm	Xiphoid, costal margin, lumbar vertebrae → central tendon	Principal muscle of inspiration	Phrenic nerve (C3–C5)
Gluteal	Gluteus maximus	Ilium/sacrum → gluteal tuberosity/IT band	Hip extension, lateral rotation	Inferior gluteal nerve
Gluteal	Gluteus medius	Ilium → greater trochanter	Hip abduction; stabilises pelvis in stance	Superior gluteal nerve
Thigh	Quadriceps femoris (4 heads)	Ilium/femur → tibial tuberosity (via patella)	Knee extension	Femoral nerve
Thigh	Hamstrings (biceps femoris, semitendinosus, semimembranosus)	Ischial tuberosity → tibia/fibula	Knee flexion, hip extension	Sciatic nerve (tibial division)
Leg	Gastrocnemius/soleus (triceps surae)	Femoral condyles/tibia-fibula → calcaneus (Achilles tendon)	Ankle plantarflexion	Tibial nerve

Clinical Anatomy

The rotator cuff (SITS — supraspinatus, infraspinatus, teres minor, subscapularis) dynamically stabilises the glenohumeral joint; supraspinatus tendinopathy or tear is the commonest rotator cuff injury and classically produces a painful arc of abduction. The phrenic nerve's origin from C3–C5 ("C3, 4, 5 keep the diaphragm alive") explains why high cervical spinal cord injury above this level is immediately life-threatening.

Did You Know?

The gluteus maximus is the largest single muscle in the human body by mass, an adaptation closely tied to upright bipedal walking and running — it contributes relatively little during slow walking but becomes strongly active during running, climbing and rising from a seated position.

Cardiovascular System — The Heart

Mediastinum~72 beats/min at rest

The heart is a four-chambered muscular pump lying in the middle mediastinum, enclosed within the pericardium. It drives two circuits in series — the pulmonary circulation (right heart → lungs) and the systemic circulation (left heart → body) — and generates its own rhythmic electrical impulse independent of nervous input.

Chambers & Valves

Interior of the right atrium and right ventricle, showing the tricuspid valve and chordae tendineae, after Gray's Anatomy plate 493.

Interior of the left atrium and left ventricle, showing the mitral valve, after Gray's Anatomy plate 496.

BLOOD FLOW — IN ORDER

1. Venae cavae → right atrium
2. Tricuspid valve → right ventricle
3. Pulmonary valve → pulmonary trunk → lungs
4. Pulmonary veins → left atrium
5. Mitral valve → left ventricle
6. Aortic valve → aorta → systemic circulation

Anatomical Description

The heart has four chambers. The right atrium receives deoxygenated blood from the superior and inferior venae cavae and the coronary sinus, and empties through the tricuspid valve into the right ventricle, which is crescent-shaped in cross-section and has a thinner wall than the left ventricle since it only needs to generate the lower pressure of the pulmonary circuit. The right ventricle ejects blood through the pulmonary valve into the pulmonary trunk. Oxygenated blood returns via four pulmonary veins to the left atrium, passes through the mitral (bicuspid) valve into the left ventricle — the most muscular chamber, generating systemic arterial pressure — and is ejected through the aortic valve into the ascending aorta. The interatrial septum separates the two atria (marked by the fossa ovalis, the remnant of the fetal foramen ovale); the muscular interventricular septum separates the ventricles. The atrioventricular valves are anchored by fibrous chordae tendineae attached to conical papillary muscles, which contract during systole to prevent valve prolapse into the atria.

Function

Right heart = low-pressure pump to the lungs (pulmonary circulation); left heart = high-pressure pump to the body (systemic circulation). Both sides contract synchronously and eject equal stroke volumes to keep the two circuits balanced.

Great Vessels

Superior & inferior vena cava → right atrium
Pulmonary trunk → right and left pulmonary arteries
Pulmonary veins (×4) → left atrium
Ascending aorta → arch → descending aorta

Clinical Anatomy

Valve surface anatomy matters for auscultation: aortic (2nd right intercostal space), pulmonary (2nd left intercostal space), tricuspid (4th/5th left intercostal space near sternum) and mitral (5th left intercostal space, midclavicular line — the cardiac apex). Left ventricular hypertrophy occurs because this chamber does most of the pressure-generating work against systemic vascular resistance; chronic pressure overload (e.g. hypertension, aortic stenosis) thickens its wall further and can eventually impair filling and function.

Coronary Circulation

Arterial Supply

The heart's own blood supply arises from the right and left coronary arteries, the first branches of the ascending aorta, originating from the aortic sinuses just above the aortic valve — meaning they fill primarily during diastole, when the valve cusps are not obstructing their ostia. The left coronary artery divides into the left anterior descending (LAD) branch, supplying the anterior interventricular septum and anterior left ventricular wall, and the circumflex artery, supplying the lateral and posterior left ventricular wall. The right coronary artery supplies the right atrium, right ventricle and, in most people, the inferior wall of the left ventricle and the AV node (right-dominant circulation).

Venous Drainage

Most cardiac veins (great, middle, small cardiac veins) drain into the coronary sinus, which empties directly into the right atrium; some anterior cardiac veins drain directly into the right atrium.

Clinical Anatomy — Coronary Territories

Because each coronary artery supplies a relatively predictable myocardial territory, the ECG pattern of a myocardial infarction localises the culprit vessel: anterior/septal ST changes suggest LAD occlusion, inferior changes suggest right coronary artery occlusion, and lateral changes suggest circumflex occlusion. The LAD is often called the "widow-maker" because it supplies a large portion of the left ventricle including the interventricular septum, and proximal occlusion can be catastrophic.

Conduction System & Blood Flow Sequence

Sequence of Electrical Conduction

SA node (sinoatrial node) — in the right atrial wall near the entry of the superior vena cava; the heart's natural pacemaker, initiating each heartbeat
Internodal pathways spread the impulse across both atria, causing atrial contraction
AV node (atrioventricular node) — near the interatrial septum; delays the impulse briefly, allowing the atria to finish contracting before ventricular contraction begins
Bundle of His (AV bundle) — penetrates the fibrous skeleton of the heart, the only normal electrical connection between atria and ventricles
Left & right bundle branches — run down either side of the interventricular septum
Purkinje fibres — spread rapidly through ventricular myocardium, producing coordinated, near-simultaneous ventricular contraction

Clinical Anatomy

Because the AV node is the sole normal electrical bridge between atria and ventricles, disease or injury there (including surgical trauma, as it lies near the septal leaflet of the tricuspid valve and the membranous interventricular septum) can produce heart block, ranging from delayed conduction to complete dissociation of atrial and ventricular rhythms requiring a pacemaker.

Did You Know?

The SA node's own cells depolarise spontaneously roughly 60–100 times a minute even with no external nerve input — this is why a transplanted, fully denervated heart still beats rhythmically; it simply loses the moment-to-moment autonomic adjustment that vagal and sympathetic input normally provide.

Quick Revision — Heart

Right heart = pulmonary; left heart = systemic
Tricuspid (right) vs mitral/bicuspid (left) AV valves
LAD → anteroseptal wall; RCA → inferior wall + AV node (usually); circumflex → lateral wall
SA node → AV node → bundle of His → Purkinje fibres
Coronary arteries fill in diastole
Apex beat = 5th left intercostal space, midclavicular line

Respiratory System

Gas exchange

The respiratory system moves air between the atmosphere and the alveoli, where gas exchange with pulmonary capillary blood occurs, and is functionally divided into a conducting zone (no gas exchange) and a respiratory zone (gas exchange).

Airway Pathway

Inspired air passes through the nasal cavity (warmed, humidified, filtered) or mouth, through the pharynx (naso-, oro-, laryngopharynx — shared with the digestive tract), through the larynx (voice box, containing the vocal folds and the epiglottis which protects the airway during swallowing), into the trachea, which bifurcates at the carina (T4/5 level, at the sternal angle) into the right and left main bronchi. The right main bronchus is wider, shorter and more vertical than the left, so inhaled foreign bodies more often lodge there. Bronchi branch progressively through lobar, segmental and smaller bronchi into bronchioles, terminating in alveoli, tiny sacs where gas exchange occurs across an extremely thin blood-air barrier.

Lung Lobes & Segments

The right lung has 3 lobes (upper, middle, lower) separated by horizontal and oblique fissures; the left lung has 2 lobes (upper, lower) separated by an oblique fissure, and is smaller due to the cardiac notch accommodating the heart. Each lung is further divided into bronchopulmonary segments (10 on the right, 8–10 on the left), each with its own segmental bronchus and artery — a clinically useful unit for localising disease and for surgical resection.

Pleura

Each lung is invested by a visceral pleura and enclosed within a parietal pleura lining the thoracic wall, diaphragm and mediastinum; the potential space between them, the pleural cavity, contains a thin film of fluid that allows the layers to slide over each other during breathing while remaining coupled, so the lung expands as the chest wall expands.

Blood Supply

Pulmonary circulation (functional, for gas exchange): deoxygenated blood via pulmonary arteries, oxygenated blood returned via pulmonary veins. Bronchial circulation (nutritive, from the aorta): supplies the lung tissue itself, particularly the airway walls.

Innervation

The diaphragm, the principal muscle of inspiration, is supplied by the phrenic nerve (C3–C5). Airway smooth muscle and glands receive autonomic innervation — parasympathetic (vagus) causing bronchoconstriction and secretion, sympathetic causing bronchodilation.

Clinical Anatomy

Because the right main bronchus is wider, shorter and more vertically oriented than the left, aspirated foreign bodies and aspirated gastric contents preferentially enter the right lung, most often the right lower lobe in an upright patient. Pneumothorax (air in the pleural space) collapses the lung because the normally negative intrapleural pressure that keeps the lung expanded is lost.

Digestive System

GI tract + accessory organs

The digestive system is a continuous muscular tube from mouth to anus, specialised regionally for ingestion, digestion, absorption and elimination, supported by accessory glands that secrete digestive enzymes and bile.

Anatomical Description

Food enters the oral cavity, where the tongue and salivary glands (parotid, submandibular, sublingual) begin mechanical and enzymatic digestion, then passes through the pharynx and oesophagus — a muscular tube roughly 25 cm long descending through the posterior mediastinum and diaphragm — into the stomach, a J-shaped reservoir with cardia, fundus, body, antrum and pylorus, where acid and pepsin begin protein digestion. Chyme passes through the pyloric sphincter into the duodenum (C-shaped, receiving bile and pancreatic secretions), then the jejunum and ileum (together the rest of the small intestine, the principal site of nutrient absorption), then through the ileocaecal valve into the caecum, from which the vermiform appendix arises. The colon (ascending, transverse, descending, sigmoid) reabsorbs water and electrolytes, and the rectum and anal canal store and expel faeces.

Accessory Organs

Liver — largest internal organ; produces bile, metabolises nutrients and drugs, synthesises plasma proteins
Gallbladder — stores and concentrates bile, releasing it via the cystic duct into the common bile duct on stimulation by cholecystokinin
Pancreas — exocrine (digestive enzymes into the duodenum via the pancreatic duct) and endocrine (insulin, glucagon from the islets of Langerhans) functions

Blood Supply & Portal Circulation

The gut is supplied by three unpaired branches of the abdominal aorta following embryological foregut/midgut/hindgut divisions: the coeliac trunk (foregut — stomach, duodenum proximal to the ampulla, liver, pancreas, spleen), the superior mesenteric artery (midgut — distal duodenum to proximal two-thirds of the transverse colon), and the inferior mesenteric artery (hindgut — distal transverse colon to upper rectum). Venous blood from the entire GI tract, spleen and pancreas drains via the hepatic portal vein to the liver before reaching the systemic circulation — allowing first-pass metabolism of absorbed nutrients and drugs.

Clinical Anatomy

The appendix's position is variable, but pain classically begins as poorly localised periumbilical pain (referred, via the midgut's shared visceral innervation) before migrating to the right iliac fossa (McBurney's point) as inflammation irritates the overlying parietal peritoneum — a textbook example of the transition from visceral to somatic pain. Portal hypertension (e.g. from cirrhosis) can force blood through portosystemic anastomoses, causing oesophageal varices, caput medusae, and haemorrhoids.

Urinary System

Kidney · Nephron

Kidney & Nephron

Gross Anatomy

Each bean-shaped kidney lies retroperitoneally at approximately T12–L3, the right slightly lower than the left due to the liver. Internally, an outer cortex surrounds an inner medulla, organised into 8–18 conical renal pyramids separated by renal columns (cortical tissue extending inward). Each pyramid's apex, the papilla, drains urine into a minor calyx; minor calyces converge into 2–3 major calyces, which join to form the funnel-shaped renal pelvis, continuous with the ureter. Vessels, nerves, lymphatics and the ureter enter/exit at the medially-facing hilum.

The Nephron (Functional Unit)

Each kidney contains roughly a million nephrons. Blood is filtered at the renal corpuscle, comprising a capillary tuft, the glomerulus, invaginated into Bowman's capsule. Filtrate then passes through the proximal convoluted tubule (bulk reabsorption of glucose, amino acids, ions, water), the loop of Henle (descending and ascending limbs, generating the medullary concentration gradient via countercurrent multiplication), the distal convoluted tubule (fine regulation of Na⁺/K⁺, under aldosterone influence), and finally the collecting duct (final water reabsorption, under ADH influence), before draining into a minor calyx.

Downstream Structures

Ureter — muscular tube carrying urine from renal pelvis to bladder by peristalsis; crosses the pelvic brim near the bifurcation of the common iliac vessels
Urinary bladder — distensible muscular reservoir; the trigone (between the two ureteric orifices and the internal urethral orifice) is a smooth, relatively fixed region
Urethra — conducts urine to the exterior; considerably shorter in females, a factor in higher female rates of ascending urinary tract infection

Blood Supply

Renal artery (direct branch of the abdominal aorta) → segmental → interlobar → arcuate → interlobular arteries → afferent arteriole → glomerulus → efferent arteriole → peritubular capillaries/vasa recta → interlobular/arcuate/interlobar/renal veins → inferior vena cava.

Clinical Anatomy

Kidney stones typically become symptomatic when they lodge at one of three physiological narrowings of the ureter — the pelvi-ureteric junction, where the ureter crosses the pelvic brim, or the point where it enters the bladder wall — producing classic colicky loin-to-groin pain as peristalsis tries to push the stone through.

Endocrine System

Hormonal regulation

Gland	Location	Key hormones
Hypothalamus	Base of brain, floor of 3rd ventricle	Releasing/inhibiting hormones controlling the anterior pituitary; produces ADH & oxytocin (stored in posterior pituitary)
Pituitary gland	Sella turcica of sphenoid bone	Anterior: GH, TSH, ACTH, FSH/LH, prolactin. Posterior: ADH, oxytocin (released, not made, here)
Pineal gland	Posterior to third ventricle	Melatonin — circadian rhythm regulation
Thyroid gland	Anterior neck, either side of trachea, below larynx	T3/T4 (metabolic rate), calcitonin
Parathyroid glands (×4)	Posterior surface of thyroid lobes	Parathyroid hormone — raises blood calcium
Adrenal glands	Superior pole of each kidney	Cortex: cortisol, aldosterone, androgens. Medulla: adrenaline, noradrenaline
Pancreas (endocrine)	Islets of Langerhans, scattered through the gland	Insulin (β cells), glucagon (α cells)

Clinical Anatomy

Because the parathyroid glands are small, variably located, and sit directly behind the thyroid, they are at risk of inadvertent removal or devascularisation during thyroidectomy, which can cause acute post-operative hypocalcaemia. The pituitary's location just below the optic chiasm means a pituitary macroadenoma can compress the chiasm and produce bitemporal hemianopia.

Lymphatic / Immune System

Fluid balance & defence

Anatomical Description

A network of blind-ending lymphatic capillaries collects interstitial fluid that has leaked from blood capillaries and cannot be reabsorbed directly; this fluid, now called lymph, passes through lymph nodes — small filtering stations packed with lymphocytes and macrophages — before returning to the venous system. Lymph from the lower body, left upper limb and left side of the thorax and head drains into the thoracic duct, which empties into the venous system near the junction of the left subclavian and internal jugular veins; lymph from the right upper limb, right thorax and right head/neck drains via the smaller right lymphatic duct. The spleen, in the left upper quadrant, filters blood (removing old erythrocytes) and mounts immune responses to blood-borne antigens. The thymus, in the superior mediastinum, is the site of T-lymphocyte maturation and is largest in childhood, involuting with age. The tonsils (palatine, pharyngeal/adenoid, lingual) form a ring of lymphoid tissue guarding the entrance to the pharynx.

Regional Drainage (High-Yield)

Breast (lateral) → axillary nodes
Stomach → coeliac nodes
Testis → para-aortic (lumbar) nodes — follows testicular embryological descent
Anal canal (below pectinate line) → superficial inguinal nodes

Clinical Anatomy

Lymph node drainage patterns matter for cancer staging: because the testis drains to para-aortic nodes rather than inguinal nodes (a consequence of its embryological origin high in the abdomen before descent), testicular cancer characteristically spreads to retroperitoneal para-aortic nodes rather than groin nodes, even though the testis itself sits in the scrotum.

Reproductive Anatomy

Male & female

Male Reproductive System

The testes produce sperm and testosterone within the scrotum, where a slightly lower temperature than core body temperature supports spermatogenesis. Sperm mature in the epididymis, a coiled tube on the posterior testis, then travel through the vas deferens (ductus deferens), which ascends through the inguinal canal into the pelvis, joining the duct of the seminal vesicle to form the ejaculatory duct. The prostate, surrounding the proximal urethra, adds secretions that support sperm viability. The penis contains erectile tissue (paired corpora cavernosa, single corpus spongiosum surrounding the urethra) supplied by branches of the internal pudendal artery.

Clinical Anatomy

Benign prostatic hyperplasia, common with age, compresses the prostatic urethra and can obstruct urinary outflow, because the prostate surrounds the urethra just distal to the bladder neck.

Female Reproductive System

The ovaries produce oocytes and sex hormones (oestrogen, progesterone) and are suspended by the suspensory and ovarian ligaments. Released oocytes are captured by the fimbriae of the uterine (fallopian) tubes, where fertilisation typically occurs, and travel to the pear-shaped uterus, a thick-walled muscular organ that houses a pregnancy. The uterus's lower narrow portion, the cervix, projects into the vagina, the muscular canal connecting the uterus to the exterior. The broad ligament, a peritoneal fold, supports the uterus, tubes and ovaries.

Clinical Anatomy

Because fertilisation normally occurs in the ampulla of the uterine tube, a fertilised ovum that fails to reach the uterine cavity can implant there — an ectopic (tubal) pregnancy, a surgical emergency if the tube ruptures.

Special Senses — Eye & Ear

VisionHearing & balance

The Eye

Anatomical Description

Light enters through the transparent cornea, the eye's main refractive surface, and passes through the anterior chamber (filled with aqueous humour, produced by the ciliary body and draining via the trabecular meshwork) before reaching the iris — the pigmented diaphragm whose central aperture, the pupil, regulates light entry. Behind the iris, the lens, suspended by zonular fibres from the ciliary body, fine-tunes focus through accommodation. The posterior segment is filled with gel-like vitreous humour and lined by the retina, the light-sensing layer containing rods (low-light, monochrome) and cones (colour, high acuity, concentrated at the fovea). The outer fibrous coat, the sclera, provides structural support (the "white" of the eye), continuous anteriorly with the cornea. Visual signals leave via the optic nerve (CN II) at the optic disc.

Visual Pathway (Overview)

Retina → optic nerve → optic chiasm (nasal retinal fibres cross) → optic tract → lateral geniculate nucleus of thalamus → optic radiation → primary visual cortex (occipital lobe).

Clinical Anatomy

Because only nasal retinal fibres (carrying temporal visual field information) cross at the optic chiasm, a lesion compressing the chiasm from below — classically a pituitary tumour — cuts these crossing fibres and produces bitemporal hemianopia, loss of the outer visual field in both eyes.

The Ear

Anatomical Description

The external ear (auricle and external acoustic meatus) channels sound to the tympanic membrane (eardrum), which vibrates and transmits sound through the air-filled middle ear via three small ossicles — malleus, incus, stapes — the smallest bones in the body, which mechanically amplify the signal before it reaches the fluid-filled inner ear. The auditory (Eustachian) tube connects the middle ear to the nasopharynx, equalising pressure across the tympanic membrane. The inner ear houses the cochlea (a fluid-filled, spiral duct converting mechanical vibration into neural signals for hearing) and the vestibular apparatus (semicircular canals, utricle and saccule, detecting head rotation and linear acceleration/gravity). Both structures are innervated by the vestibulocochlear nerve (CN VIII).

Clinical Anatomy

Because the auditory tube in young children is shorter, wider and more horizontal than in adults, middle ear infections (otitis media) are more common in childhood, as bacteria from the nasopharynx more readily reach the middle ear.

Integumentary System — Skin

Largest organ

Anatomical Description

Skin is organised into three layers. The epidermis, a keratinised stratified squamous epithelium with no blood vessels of its own, is continuously renewed from its basal layer and provides the primary barrier against water loss, microbes and UV radiation. The dermis, beneath it, is a vascularised connective tissue layer containing collagen and elastin (providing strength and elasticity), hair follicles, sweat glands, sebaceous glands, and sensory receptors. The hypodermis (subcutaneous layer), technically not part of the skin itself, anchors it to underlying structures and stores fat for insulation and energy.

Appendages

Hair — thermoregulation, sensation, protection
Nails — protect fingertips, aid fine manipulation
Sweat glands (eccrine) — thermoregulation via evaporative cooling
Sebaceous glands — secrete sebum, lubricating skin and hair

Sensory Receptors

Meissner's corpuscles (light touch), Pacinian corpuscles (deep pressure/vibration), Merkel cells (sustained pressure/texture), Ruffini endings (skin stretch), and free nerve endings (pain, temperature) are distributed through the dermis and epidermal junction.

Clinical Anatomy

Burn depth is classified by which skin layers are involved: superficial (epidermis only), partial-thickness (extends into dermis, typically blistering and painful because dermal nerve endings are intact), and full-thickness (destroys the entire dermis, often painless at the burn centre because nerve endings are destroyed, and unable to heal without grafting since regenerative epidermal cells are lost).

Regional Anatomy Explorer

Cross-system view

Regional anatomy studies everything within one body area together — bones, muscles, vessels, nerves and spaces — the way a surgeon or examiner encounters it, rather than one system at a time.

Head & Neck

CN foramina · carotid sheath · triangles of the neck

Skull, cervical vertebrae, hyoid bone
Carotid arteries, jugular veins, thyroid
Anterior & posterior triangles of the neck
Cranial nerve exit points

Thorax

Mediastinum · pleural cavities · great vessels

Heart within the middle mediastinum
Lungs and pleura
Oesophagus, thoracic duct, descending aorta (posterior mediastinum)
Intercostal neurovascular bundles

Abdomen

Peritoneum · retroperitoneum · 9-region grid

Stomach, liver, spleen, pancreas, kidneys
Coeliac, superior & inferior mesenteric arteries
Portal venous system
Peritoneal reflections and mesenteries

Pelvis

Pelvic floor · viscera · perineum

Bladder, rectum, internal reproductive organs
Pelvic floor musculature (levator ani)
Internal iliac vessel branches
Sacral plexus

Back

Vertebral column · spinal cord · paraspinal muscles

Vertebral column and intervertebral discs
Spinal cord, meninges, epidural space
Erector spinae and deep back muscles

Upper Limb

Brachial plexus · axilla · compartments

Brachial plexus (roots, trunks, divisions, cords, branches)
Axillary, brachial, radial/ulnar arteries
Anterior/posterior compartments of arm and forearm

Lower Limb

Lumbosacral plexus · femoral triangle · fascial compartments

Femoral triangle (nerve–artery–vein, lateral to medial)
Sciatic nerve and its divisions
Anterior, lateral, posterior leg compartments

Spotlight: Brachial Plexus

The brachial plexus is formed by the ventral rami of C5–T1, organised (medial to lateral, proximal to distal) into roots → trunks (upper, middle, lower) → divisions (anterior/posterior) → cords (lateral, posterior, medial, named for their relation to the axillary artery) → branches — classically remembered by the mnemonic "Randy Travis Drinks Cold Beer." Major terminal branches include the musculocutaneous, axillary, radial, median and ulnar nerves, supplying essentially all motor and sensory innervation to the upper limb.

Clinical Anatomy

Traction injuries can selectively damage the upper (C5–C6) or lower (C8–T1) plexus: upper trunk injury (Erb's palsy, from excessive stretching between the head and shoulder, e.g. in a difficult birth) produces the "waiter's tip" posture; lower trunk injury (Klumpke's palsy, from excessive arm traction) produces a claw hand.

Anatomy in Imaging

X-ray · CT · MRI · Ultrasound

Recognising normal anatomy on medical images is a core skill for learners. This section is for anatomical orientation only — it is not a diagnostic tool, and no interpretation here should be treated as a clinical read of any image.

Licensed chest X-ray image can be added here.
Learner task: identify the cardiac silhouette, hila, hemidiaphragms and costophrenic angles.

Chest X-ray (PA view)

Orient using the heart border, lung fields, ribs and the gastric air bubble under the left hemidiaphragm.

Licensed axial CT (brain) image can be added here.
Learner task: identify the lateral ventricles, basal ganglia and cerebellum.

CT — Axial Brain

Grey matter appears denser (brighter) than white matter; CSF-filled ventricles appear dark.

Licensed sagittal MRI (brain) image can be added here.
Learner task: identify the corpus callosum, brainstem and cerebellum.

MRI — Sagittal Brain (T1)

Excellent soft-tissue contrast; T1-weighted images show CSF as dark, fat as bright.

Licensed abdominal ultrasound image can be added here.
Learner task: identify the liver, gallbladder and right kidney.

Ultrasound — Right Upper Quadrant

Real-time, radiation-free imaging; the liver is a common acoustic window to the kidney and gallbladder.

Self-Test — Anatomy Quiz

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