Anatomy Exam 4 — Study Guide

1 · Anatomy of the Appendicular Skeleton

1.1 · Objective 1 — Bones of the appendicular skeleton and their landmarks

The appendicular skeleton (126 bones) is the two girdles (Objectives 2–3) plus the bones of the limbs. In the upper limb, the humerus is the single arm bone: its rounded proximal head articulates with the glenoid cavity, flanked by the greater and lesser tubercles (rotator-cuff attachments), with the deltoid tuberosity along the shaft and, distally, the capitulum (for the radius) and trochlea (for the ulna) between the coronoid and olecranon fossae. The forearm has the medial ulna (its trochlear notch, bounded by the olecranon and coronoid process, forms most of the elbow) and the lateral radius (its radial head rotates for pronation/supination; radial tuberosity is the biceps insertion), bound by an interosseous membrane. The hand has 8 carpals (proximal row scaphoid-lunate-triquetrum-pisiform; distal row trapezium-trapezoid-capitate-hamate), 5 metacarpals, and phalanges (three per finger, two for the thumb). The lower limb mirrors this: the femur (longest bone — head, neck, greater/lesser trochanters, intertrochanteric line, distal condyles), the sesamoid patella, the weight-bearing medial tibia (tibial tuberosity, medial malleolus), the thin lateral non-weight-bearing fibula (lateral malleolus), and the foot's 7 tarsals (incl. the calcaneus), 5 metatarsals, and phalanges (same 2-for-great-toe / 3-for-others pattern).

1.2 · Objective 2 — Bones of the pectoral girdle

The pectoral (shoulder) girdle is just two bones — the clavicle and scapula — anchoring the upper limb to the axial skeleton loosely, trading stability for mobility. The clavicle is S-shaped: its medial (sternal) end meets the manubrium, its lateral (acromial) end meets the scapular acromion, with the conoid tubercle near the acromial end and the costal tuberosity near the sternal end. The scapula is a flat triangular bone whose posterior scapular spine divides the supraspinous and infraspinous fossae and continues laterally into the acromion (forming the acromioclavicular joint). The coracoid process hooks forward for muscle/ligament attachment, and the shallow lateral glenoid cavity receives the humeral head to form the glenohumeral joint.

1.3 · Objective 3 — Bones of the pelvic girdle

The pelvic girdle is the two coxal (hip) bones, each a fusion of three bones — the ilium (superior flared wing), ischium (posteroinferior, what you sit on), and pubis (anteroinferior, meeting at the pubic symphysis) — that converge at the deep acetabulum receiving the femoral head. Landmarks include the anterior inferior iliac spine, the greater/lesser sciatic notches, the obturator foramen, and the internal arcuate line and auricular surface (sacroiliac joint). With the sacrum and coccyx, the coxal bones form the bony pelvis. Unlike the mobility-built pectoral girdle, the pelvic girdle is built for weight-bearing stability — and shows a sex difference: the female pelvis is wider and shallower with a larger outlet for childbirth.

2 · Anatomy of the Axial Skeleton

2.1 · Objectives 1, 3 & 11 — Osteon, compact vs. trabecular bone, and osseous histology

Bone tissue comes in two structural forms. Compact bone is dense and solid, forming the outer shell of every bone and bearing most of the mechanical load. Spongy (trabecular/cancellous) bone is a lattice of thin bony struts with large spaces between them, found at the interior of bones (especially near the ends of long bones). A medullary (marrow) cavity — the space where blood cells and platelets are produced — replaces spongy bone at the center of many bones. The entire external surface of a bone (except at joint surfaces) is wrapped in the periosteum, a fibrous connective-tissue covering that carries the blood supply and nerve fibers into the bone and serves as an attachment site for tendons and ligaments.

At the microscopic level, compact bone's structural unit is the osteon: concentric rings of bone matrix (concentric lamellae) surrounding a central canal that carries blood vessels and nerves, with perforating canals running perpendicular to connect neighboring osteons and link the whole system to the periosteum's surface vessels. Interstitial lamellae — the remnants of older, partially resorbed osteons — fill the gaps between intact ones.

By shape, bones fall into four classes: long bones (tubular — humerus, phalanges), short bones (cuboidal, found only in the wrist and ankle), flat bones (thin and protective — the cranium), and sesamoid bones (develop within tendons to reduce wear — the patella).

2.2 · Objective 2 — Ossification and growth of long bones

Long-bone growth begins at a primary ossification center in the diaphysis (shaft) during fetal development, where bone tissue first replaces the original cartilage model. After birth, secondary ossification centers appear in the epiphyses (bone ends). Between the diaphysis and each epiphysis sits the epiphyseal plate (growth plate) — a layer of hyaline cartilage that is the site of longitudinal bone growth throughout childhood and adolescence, organized into zones (a resting zone of inactive chondrocytes, a proliferative zone of rapidly dividing chondrocytes, a hypertrophic zone of enlarging chondrocytes, and a calcification zone). The plate eventually ossifies completely once growth is finished, fusing the epiphysis to the diaphysis.

2.3 · Objective 4 — Types of marrow

Bone marrow fills the spongy-bone spaces and medullary cavities in two forms. Red marrow is hematopoietic — it produces red blood cells, white blood cells, and platelets — and in adults is found chiefly in the spongy bone of flat and irregular bones (sternum, ribs, vertebrae, ilium) and the proximal epiphyses of the femur and humerus. Yellow marrow is mostly adipose (fat storage) and fills the medullary cavities of long-bone shafts. At birth nearly all marrow is red; much of it converts to yellow with age, but yellow marrow can revert to red under high demand (such as chronic blood loss).

2.4 · Objectives 5 & 6 — Bones of the skull; cranial vs. facial bones

The skull is built from 29 named bones grouped into three categories: 14 facial bones (which shape the face and support the teeth and jaws), 8 cranial bones (which enclose and protect the brain), and 7 associated bones (including the hyoid and the middle-ear ossicles). Most cranial and facial bones are joined by immovable, interlocking joints called sutures — the sagittal suture runs between the two parietal bones, the coronal suture between the frontal bone and the parietals, and the lambdoid suture between the occipital bone and the parietals.

Among the cranial bones: the occipital bone forms the back and base of the skull, pierced by the foramen magnum (through which the spinal cord passes) and bearing the paired occipital condyles that articulate with the atlas (C1). The frontal bone forms the forehead; its supra-orbital foramen transmits the supra-orbital nerve and artery. The temporal bones house the middle and inner ear structures within their petrous portions, and their stylomastoid foramen is the exit point for the facial nerve. The sphenoid, a butterfly-shaped bone at the base of the skull, carries the saddle-shaped sella turcica, which houses the pituitary gland, along with the foramen ovale and foramen spinosum (transmitting branches of the trigeminal nerve). The ethmoid contributes to the nasal cavity and orbit; its crista galli anchors the dural fold called the falx cerebri, and its perforated cribriform plate transmits olfactory nerve fibers from the nose to the brain.

The base of the skull's interior is divided into three stepped depressions — the anterior, middle, and posterior cranial fossae — that cradle the frontal/temporal lobes and cerebellum respectively, with the middle fossa extending from the posterior nasal apertures back to the petrous portions of the temporal bones.

Among the facial bones: the maxillae form the upper jaw and contain the air-filled maxillary sinuses (one of the four paranasal sinuses, alongside the frontal, sphenoidal, and ethmoid sinuses). The vomer and the perpendicular plate of the ethmoid together form the bony nasal septum. The mandible, the only mobile skull bone, articulates with the temporal bone's mandibular fossa at the temporomandibular joint (TMJ) via its condylar process; its coronoid process is a muscle attachment site, and its mandibular foramen/canal carries the neurovascular bundle to the lower teeth, exiting anteriorly at the mental foramen. The hyoid bone, suspended in the neck by ligaments rather than articulating with any other bone, anchors muscles of the tongue and larynx.

The infant skull is not yet fully ossified: membranous gaps called fontanelles — most famously the anterior fontanelle ("soft spot") — sit where sutures will eventually form, allowing the skull to compress slightly during birth and accommodate rapid brain growth afterward.

2.5 · Objective 7 — Cranial foramina and their contents

Each cranial foramen transmits specific neurovascular structures — a high-yield table to memorize:

2.6 · Objectives 8 & 10 — Bones of the axial skeleton, their landmarks & the different vertebrae

The adult vertebral column contains 26 bones: 24 individual vertebrae (7 cervical, 12 thoracic, 5 lumbar), plus the sacrum (5 fused vertebrae) and coccyx (3–5 fused vertebrae). It encloses and protects the spinal cord, supports the head/neck/trunk, and transfers body weight down to the lower limbs. Viewed from the side, it has four curves — cervical, thoracic, lumbar, and sacral — alternating in direction to balance the trunk over the pelvis; the thoracic and sacral curves are primary (present before birth), while the cervical and lumbar curves are secondary (developing after birth, as an infant learns to hold up its head and then to stand).

A typical vertebra has an anterior weight-bearing body, separated from its neighbors by a cartilaginous intervertebral disc, and a posterior vertebral arch (made of paired pedicles and laminae) enclosing the vertebral foramen. Stacked vertebral foramina form the vertebral canal housing the spinal cord, while gaps between adjacent vertebrae — the intervertebral foramina — allow spinal nerves to exit. A spinous process projects posteriorly and paired transverse processes project laterally, both serving as muscle/ligament attachment sites, while superior and inferior articular processes let adjacent vertebrae articulate with each other.

Each region has a distinct signature. Cervical vertebrae (C1–C7) all have a transverse foramen for the vertebral artery and a spinous process that is bifid (forked) except at C7. C1 (the atlas) has no body at all — just anterior/posterior arches — and articulates directly with the occipital condyles, letting the head nod "yes." C2 (the axis) has a peg-like dens that projects up into the atlas's ring, held by the transverse ligament, letting the head rotate "no." C7, the "vertebra prominens," has an unusually long, easily palpable spinous process that anchors the ligamentum nuchae.

Thoracic vertebrae (T1–T12) carry costal facets for rib articulation (T1–T8 have both superior and inferior facets; T9–T12 have only one) and spinous processes that point sharply inferiorly. Lumbar vertebrae (L1–L5) have the largest, thickest vertebral bodies of the spine — built for weight-bearing — with a spinous process that points straight posteriorly. The sacrum, five fused vertebrae, articulates with the ilium at the auricular surface to form the sacroiliac joint, with landmarks including the sacral promontory, sacral canal, and sacral foramina; the coccyx caps the column below it (angled anteriorly in males, inferiorly in females).

2.7 · Objective 9 — The thoracic cage

The thoracic cage protects the heart, lungs, and thymus, and anchors the muscles of respiration. Its 12 pairs of ribs split two ways: true ribs (1–7) attach directly to the sternum via their own costal cartilage (also called vertebrosternal), while false ribs (8–12) don't — ribs 8–10 (vertebrochondral) attach indirectly via shared cartilage, and ribs 11–12 ("floating ribs") have no anterior attachment at all. The sternum itself has three parts: the manubrium (superior, with the palpable jugular notch and clavicular articulations), the body, and the xiphoid process (the inferior cartilaginous/bony tip).

3 · Appendicular Musculature

3.1 · Objective 1 — Connective tissue coverings of muscles

Three nested connective-tissue layers organize a skeletal muscle: the epimysium wraps the whole muscle, the perimysium wraps bundles of fibers called fascicles, and the endomysium wraps each individual muscle fiber (whose plasma membrane is the sarcolemma). These layers are continuous with and converge into the tendon (a cord) or aponeurosis (a flat sheet) that attaches the muscle to bone, while the surrounding deep fascia binds muscle groups into compartments.

3.2 · Objective 2 — Components of muscle

A skeletal muscle is built as a nested hierarchy: muscle → fascicles → muscle fibers (long, multinucleate cells) → myofibrils → sarcomeres (the functional contractile unit). Within each fiber, the sarcoplasm contains the sarcoplasmic reticulum (stores calcium), T-tubules (carry the impulse inward), and abundant mitochondria. Each sarcomere contains overlapping thick filaments (myosin) and thin filaments (actin), whose ordered overlap produces the striated appearance.

3.3 · Objective 3 — Histology of the three muscle types

The three muscle tissues differ histologically. Skeletal muscle has long, cylindrical, striated, multinucleate fibers and is voluntary. Cardiac muscle has short, branching, striated, usually uninucleate cells joined end-to-end by intercalated discs and is involuntary. Smooth muscle has spindle-shaped, non-striated, uninucleate cells in the walls of hollow organs and vessels and is involuntary.

3.4 · Objective 5 — Muscle morphologies

Muscles are classified by the arrangement of their fascicles, which trades force against range of motion: parallel/fusiform (fascicles run with the long axis — biceps brachii; more shortening/range), convergent (broad origin narrowing to one tendon — pectoralis major), pennate (feather-like around a central tendon — unipennate, bipennate, or multipennate as in the deltoid; more force), and circular/sphincter (concentric rings closing an opening — orbicularis oris).

3.5 · Objective 6 — Structures involved in muscle contraction

Contraction occurs within the sarcomere, bounded by Z-discs. The thin actin filaments (with regulatory troponin and tropomyosin) slide over the thick myosin filaments as myosin heads form cross-bridges — the sliding-filament mechanism, powered by ATP. The trigger is calcium released from the sarcoplasmic reticulum when the action potential travels along the sarcolemma and down the T-tubules, exposing actin's binding sites.

3.6 · Objective 7 — The neuromuscular junction

The neuromuscular junction (NMJ) is the synapse where a motor neuron meets a muscle fiber. The presynaptic axon terminal releases acetylcholine (ACh) from synaptic vesicles across the synaptic cleft; ACh binds nicotinic receptors on the folded postsynaptic motor end plate of the sarcolemma to trigger contraction, and is then broken down by acetylcholinesterase to end the signal. Schwann cells cap and support the junction.

3.7 · Objective 9 — Innervation of striated muscle

Striated skeletal muscle is voluntary, innervated by somatic motor neurons whose cell bodies sit in the spinal cord's ventral horn (or cranial-nerve motor nuclei). One motor neuron plus all the muscle fibers it innervates is a motor unit — small units (few fibers) allow fine control, large units produce powerful force. The neuron signals its fibers by releasing ACh at the NMJ, and graded whole-muscle force is achieved by recruiting more motor units.

3.8 · Objective 4 — Differentiating axial and appendicular muscles

Skeletal muscle divides by what it moves. Axial musculature has both origin and insertion on the axial skeleton — it positions the head and vertebral column and moves the rib cage (covered in Section 4). Appendicular musculature stabilizes and moves the limbs and girdles, absorbing shock during locomotion and reinforcing the joints. A muscle's action line relative to a joint predicts its effect: crossing the anterior aspect gives flexion, the posterior aspect extension, the medial aspect adduction/medial rotation, and the lateral aspect abduction/lateral rotation.

3.9 · Objective 8 (appendicular) — Origin, insertion, innervation & supply of the pectoral girdle and upper limb

Muscles that position the pectoral girdle — trapezius, rhomboid major/minor, levator scapulae, serratus anterior, pectoralis minor, subclavius — coordinate with the muscles that move the arm itself. The trapezius has the broadest range, able to elevate, depress, and rotate the scapula/clavicle and extend the neck. The serratus anterior protracts the shoulder and rotates the scapula so the glenoid cavity faces upward; it's innervated by the long thoracic nerve, and a lesion there causes serratus anterior paralysis (a "winged scapula").

Muscles that move the arm at the shoulder include the prime movers — pectoralis major (flexion, adduction, medial rotation), deltoid (abduction), coracobrachialis (adduction), and latissimus dorsi (extension, adduction, medial rotation) — plus the four rotator cuff muscles that stabilize the humeral head in the glenoid cavity: supraspinatus (abduction), infraspinatus (lateral rotation), teres minor (adduction, lateral rotation), and subscapularis (medial rotation).

Most muscles that move the forearm and hand originate on the humerus (elbow flexors biceps brachii, brachialis, brachioradialis; the elbow extensor triceps brachii, all three heads inserting on the ulna's olecranon; and the pronator/supinator pairs pronator teres/pronator quadratus versus supinator). The wrist flexors (flexor carpi radialis, flexor carpi ulnaris, palmaris longus) and extensors (extensor carpi radialis longus/brevis, extensor carpi ulnaris) are named for their side-to-side action (radial = abduct, ulnar = adduct) as well as flexion/extension. Hand muscles split into extrinsic (large, originate in the forearm, provide strength and crude control — the flexor/extensor digitorum and pollicis groups) and intrinsic (small, live within the hand itself, provide fine control — thenar muscles like opponens pollicis, hypothenar muscles like abductor digiti minimi, plus the lumbricals and interossei that fine-tune finger flexion/extension and abduction/adduction).

Blood supply and lymphatic drainage (upper limb): these muscles are supplied by branches of the subclavian → axillary → brachial arterial chain, with venous and lymphatic drainage following the arteries back toward the axillary lymph nodes.

3.10 · Objective 8 (appendicular) — Origin, insertion, innervation & supply of the pelvic girdle and lower limb

Lower-limb muscles are larger and more powerful than their upper-limb counterparts, split into three groups: muscles that move the thigh, the leg, and the foot/toes. Thigh movers originate on the pelvis and fall into four groups: the gluteal group (gluteus maximus extends the hip; gluteus medius/minimus and tensor fasciae latae abduct it), the lateral rotator group (piriformis, obturators, gemelli, quadratus femoris — mostly lateral rotation plus abduction), the adductor group (adductor brevis/longus/magnus, pectineus, gracilis), and the iliopsoas group (iliacus and psoas major, the primary hip flexors).

At the knee, the quadriceps femoris (vastus lateralis, medialis, intermedius, plus rectus femoris, which also flexes the hip) extends the leg, while the hamstrings (biceps femoris, semimembranosus, semitendinosus) flex the leg and extend the hip. Sartorius, the long strap-like muscle that lets you cross your legs, flexes both the hip and knee; together with gracilis and semitendinosus, it converges on the medial tibia to form the pes anserine.

Below the knee, extrinsic muscles originating on the leg move the foot and toes: tibialis anterior dorsiflexes the foot, gastrocnemius/soleus (joined at the calcaneal/Achilles tendon) plantar-flex it, tibialis posterior plantar-flexes and inverts it, and fibularis longus/brevis evert it. Intrinsic foot muscles (abductor hallucis, flexor digitorum brevis, lumbricals, interossei, and others) mirror the hand's intrinsic layout, providing fine control of the toes.

Fascial compartments group functionally related muscles within connective-tissue sheaths that still allow independent movement: the arm has anterior (biceps brachii, brachialis, coracobrachialis) and posterior (triceps brachii) compartments; the thigh has anterior/extensor (quadriceps, iliopsoas, sartorius), medial/adductor (the adductor group, gracilis), and posterior/flexor (hamstrings) compartments.

Blood supply and lymphatic drainage (lower limb): these muscles are supplied by branches of the femoral → popliteal arterial chain (with the gluteal region supplied by the internal iliac's gluteal arteries), and venous and lymphatic drainage follows the arteries toward the deep and superficial inguinal lymph nodes.

Muscle-by-Muscle Reference — Origin, Insertion, Action & Innervation

Every appendicular muscle named above, in one table, organized the same way the source lecture groups them.

4 · Axial Musculature

4.1 · Objective 8 (axial) — Muscles of the head and neck

The muscles of facial expression are all innervated by the facial nerve (CN VII) and are grouped by the region of the face they act on: mouth (orbicularis oris purses the lips; zygomaticus major/minor elevate the corner of the mouth; buccinator compresses the cheeks; risorius, mentalis, depressor labii inferioris, depressor anguli oris, levator labii superioris round out the group), eyes (orbicularis oculi closes the eye; corrugator supercilii furrows the brow; levator palpebrae superioris elevates the eyelid — its dysfunction causes ptosis, and unlike the others it's innervated by CN III), nose (procerus, nasalis), scalp (occipitofrontalis, temporoparietalis), and neck (platysma).

The four muscles of mastication — masseter, temporalis, and medial pterygoid (all close/elevate the jaw) plus lateral pterygoid (the lone jaw-opener) — are all innervated by the mandibular branch of the trigeminal nerve (CN V). The temporalis passes medial to the zygomatic arch to insert on the mandible's coronoid process; the masseter inserts on the mandibular angle.

The six extra-ocular muscles follow the classic "LR6 SO4 3" innervation rule: the lateral rectus (abducts the eye) is innervated by CN VI, the superior oblique (rotates the eye down and out) by CN IV, and the remaining four — medial rectus, superior rectus, inferior rectus, inferior oblique — by CN III. Tongue muscles (genioglossus, hyoglossus, styloglossus) are innervated by CN XII, except palatoglossus, which is innervated by CN X. In the neck, the sternocleidomastoid (CN XI) flexes the neck when both sides contract together and rotates the head to the opposite side when acting alone, while the infrahyoid/suprahyoid muscles (omohyoid, sternohyoid, sternothyroid, thyrohyoid, digastric, mylohyoid) position the hyoid and larynx. The pharyngeal constrictors (CN X), laryngeal elevators (CN IX & X), and palatal muscles (CN V & X) round out the swallowing musculature.

4.2 · Objective 8 (axial) — Muscles of the vertebral column, rib cage & pelvic floor

Back muscles come in two broad categories. Extrinsic back muscles — really appendicular muscles that happen to attach the limbs to the trunk — form a superficial layer (trapezius, latissimus dorsi, levator scapulae, rhomboids) and an intermediate layer (serratus posterior superior/inferior, which elevate/depress the ribs for ventilation). Intrinsic back muscles are the true "deep back" muscles, subdivided into superficial, intermediate, and deep layers that together flex, extend, and laterally stabilize the spine — because they act as a functional group, dysfunction of one usually can't be pinpointed clinically. The intermediate layer's erector spinae group (spinalis, longissimus, iliocostalis — medial to lateral) extends the column, while the deep layer (multifidus, rotatores, interspinales, intertransversarii) fine-tunes extension, rotation, and lateral flexion. Anteriorly, longus capitis/colli flex and rotate the neck, and quadratus lumborum laterally flexes the lumbar spine.

The rib cage and abdominal wall use opposing muscle pairs to drive ventilation and support the trunk: the external intercostals elevate the ribs (inhalation) while the internal intercostals depress them (exhalation), assisted by the scalene muscles (elevate) and transversus thoracis (depress). The diaphragm, innervated by the phrenic nerves (C3–C5), is the major muscle of inhalation: it contracts and flattens/descends to increase thoracic volume on inhalation, then relaxes and rises on exhalation. The abdominal wall's external oblique, internal oblique, and transversus abdominis compress the abdomen (the obliques also depress the ribs and laterally flex the trunk), while the midline rectus abdominis — bounded by the linea alba and segmented by tendinous inscriptions — flexes the vertebral column and depresses the ribs.

The pelvic floor supports the pelvic organs, flexes the sacrococcygeal joints, and controls the passage of urine and stool; because its individual muscles can't be told apart clinically, dysfunction is worked up by imaging (innervation is S2–S4). The perineum splits into an anterior urogenital triangle (superficial transverse perineal, ischiocavernosus, bulbospongiosus; deep transverse perineal, external urethral sphincter) and a posterior anal triangle (levator ani — its iliococcygeus and pubococcygeus parts — plus coccygeus, obturator internus, and the external anal sphincter), separated by the superficial transverse perineal muscle. Levator ani and coccygeus together form the bulk of the pelvic diaphragm, the muscular floor of the entire pelvic cavity.

Blood supply and lymphatic drainage (axial muscles): the head and neck muscles are supplied by branches of the external carotid artery (facial, maxillary, occipital, superficial temporal) draining to the cervical lymph nodes; the thoracic and abdominal wall muscles are supplied by posterior intercostal, subcostal, and lumbar arteries draining to parasternal, axillary, and lumbar nodes; and the pelvic floor is supplied by branches of the internal iliac artery draining to internal iliac and sacral nodes.

Muscle-by-Muscle Reference — Origin, Insertion, Action & Innervation

Every axial muscle named above (facial expression, mastication, anterior neck, perineum, and pelvic diaphragm — the muscle groups with dedicated origin/insertion/action/innervation tables in the source lecture), organized the same way.