Comprehensive Laboratory Notes on Human Musculoskeletal Anatomy and Dissection Practical Review

Laboratory Protocols, Model Labeling, and Exam Structure

• Nomenclature and Spelling Precision:

  • Precise spelling is mandatory across all practical assessments. Incorrect spelling results in loss of credit.
  • Clear distinction must be maintained between skeletal landmarks (the bone or specific bony feature of the scapula) and the overlying muscular tissue.
  • Two-part anatomical names must always be written in full (e.g., Biceps brachii and Biceps femoris cannot be identified merely as "biceps").

• Examination Architecture:

  • The comprehensive practical examination consists of $50$ questions covering both the skeletal system and the muscular system.
  • The testing format utilizes $5$ primary exam versions, with each version containing $5$ to $6$ sub-variations to prevent duplication.
  • Stations feature physical models with pinned structures corresponding to blank spaces and letter keys located in the corner of the station tag.

• Anatomical Modeling Systems Used:

  • Standard full-arm muscle model.
  • Isolated lower-extremity leg model.
  • Miniature full-body model ("little guy").
  • Medium-sized full-body muscular model.
  • Large full-body muscular model ("big guy").
  • Digital visualization software: Visible Body (VB) and eMind feline dissection software.

Shoulder and Scapular Musculature

• General Stabilizing Musculature of the Shoulder:

  • The complete anatomical unit stabilizing the glenohumeral joint comprises: Pectoralis major, Deltoid, Latissimus dorsi, Supraspinatus, Infraspinatus, Subscapularis, Teres major, Teres minor, and Coracobrachialis.

• Identified Shoulder Muscles and Numerical Key:

  • Subscapularis (Model #5): Located on the anterior costal surface of the subscapular fossa.
  • Supraspinatus (Model #6): Occupies the supraspinous fossa superior to the spine of the scapula.
  • Infraspinatus (Model #7): Located in the infraspinous fossa inferior to the scapular spine.
  • Teres minor (Model #8): Positioned superior to teres major; spans higher up onto the shoulder joint and is relatively longer in muscle belly contour.
  • Teres major (Model #9): Located inferior to teres minor; features a slightly shorter, thicker muscle belly.
  • Coracobrachialis (Model #15): Located deep within the axillary region (armpit); identified by locating the subscapularis and proceeding toward the bone to locate a long, slender, cylindrical muscle.

Rotator Cuff Musculature and Functional Biomechanics

• Rotator Cuff Muscle Components (The SITS Group):

  • Supraspinatus (#6).
  • Infraspinatus (#7).
  • Subscapularis (#5).
  • Teres minor (#8).
  • Note on Exclusion: Teres major (#9) is not a component of the rotator cuff.

• Primary Physiological Roles:

  • Medial and lateral rotation of the humerus.
  • Dynamic stabilization of the head of the humerus within the shallow glenoid cavity.
  • Execution of high-velocity overhead kinetic movements, such as throwing a ball or rowing a boat.

• Frequent Exam Prompts:

  • Direct prompt requiring identification of two distinct rotator cuff muscles.
  • Functional prompt explaining the mechanical purpose of the rotator cuff complex (rotation and shoulder joint stabilization).

Anterior Arm and Elbow Flexors

• Primary Action:

  • Flexion of the elbow joint by drawing the forearm anteriorly and superiorly toward the brachium.

• Muscle Identifications and Key Features:

  • Biceps brachii (Model #11): Located on the anterior upper arm. Composed of two distinct structural bellies converging into a single distal tendon: the long head (Model #12) and the short head (Model #13), both ascending deep to the deltoid toward the shoulder girdle.
  • Brachialis (Model #14): Positioned directly deep and lateral to the biceps brachii on the distal anterior humerus above the elbow joint.
  • Brachioradialis (Model #19): Originates at the lateral supracondylar ridge of the elbow and courses inferolaterally down the radial side of the forearm toward the styloid process of the radius (thumb side).

• Critical Distinctions:

  • The prefix radialis consistently denotes anatomical orientation toward or functional involvement with the thumb side (radius).
  • Students frequently confuse Biceps brachii and Brachialis; their distinct numbers (#11 and #14) and structural depths must be memorized.

Posterior Arm and Elbow Extensors

• Agonist vs. Antagonist Dynamic:

  • Biceps brachii and brachialis function as the agonists for forearm flexion.
  • Triceps brachii serves as the primary antagonist, mediating extension of the forearm at the elbow.

• Muscle Identifications and Key Features:

  • Triceps brachii (Models #16, #17, and #18): Positioned on the posterior compartment of the brachium. For examination labeling purposes, differentiation between the long, lateral, and medial heads is not required; labeling all heads as Triceps brachii is sufficient.
  • Anconeus (Arm Model #33; "Little Guy" #53): A small, triangular muscle located immediately inferior to the lateral epicondyle on the posterior elbow. Functions synergistically with the triceps brachii in elbow extension.

• Common Pitfall:

  • Anconeus (#33) and Brachioradialis (#19) are positioned on opposing lateral/posterior surfaces of the elbow joint and are frequently confused on practical examinations.

Forearm Pronators and Supinators

• Pronation Complex (Turning Palm Downward / Posteriorly):

  • Pronator teres (Model #22): Located on the proximal medial anterior forearm/inside of the elbow. Medially rotates the radius across the ulna.
  • Pronator quadratus (Model #29): A deep, flat, quadrangular muscle located on the anterior distal forearm directly superior to the wrist joint.
  • Both muscles act in concert to execute full pronation of the hand.

• Supination Complex (Turning Palm Upward / Anteriorly):

  • Supinator (Model #34): The sole dedicated muscle for rotating the palm into the supine position.
  • Dissection Anatomy & Exam Warning: The supinator is a deep muscle positioned directly beneath Extensor digitorum (#30) and deep to Brachioradialis (#19). Practical exam configurations frequently require removal of superficial model piece #30 to visualize #34 beneath it.

Anterior Forearm Flexors and Digital Flexion

• Compartmental Mechanics:

  • Located on the anterior superficial and intermediate forearm compartment.
  • In standard anatomical position (palms facing forward), these muscles flex the wrist, carpals, metacarpals, and phalanges.

• Muscle Identifications and Trajectories:

  • Flexor carpi radialis (Model #23): Located superficially on the lateral (thumb) side of the anterior forearm; flexes and abducts the wrist and thumb.
  • Palmaris longus (Model #24): Runs down the exact centerline of the anterior forearm to insert into the palmar aponeurosis; anchors and flexes the entire palm (identified in Visible Body occasionally as flexor pollicis longus, but designated strictly as palmaris longus for laboratory practical purposes).
  • Flexor carpi ulnaris (Model #25): Located along the medial (pinky) border of the anterior forearm; flexes and adducts the wrist.
  • Flexor digitorum superficialis (Model #26): Deep to the superficial carpal flexors; branches into separate tendons traversing to digits II through V to flex the digits into a clenched fist.

Posterior Forearm Extensors and Digital Extension

• Compartmental Mechanics:

  • Located on the posterior forearm compartment; functions to extend the wrist, extend digits back into hyperextension, and abduct digits.

• Muscle Identifications and Trajectories:

  • Extensor carpi radialis longus (Model #20) & Extensor carpi radialis brevis (Model #21): Positioned along the lateral radial border; extend and abduct the wrist and thumb (analogous to the "hitchhiker thumb" gesture pulling out and back). Acceptable exam labeling allows the collective term Extensor carpi radialis without designating longus or brevis.
  • Extensor digitorum (Model #30): Centrally positioned on the posterior forearm; divides into four distinct distal tendons inserting onto digits II through V to extend all fingers and pull the wrist dorsally.
  • Extensor carpi ulnaris (Model #32): Located along the medial ulnar border; extends and adducts the hand and extends the fifth digit (pinky outward, analogous to sipping tea).

• Common Pitfall:

  • Extensor carpi radialis (#20, #21) and Extensor carpi ulnaris (#32) are frequently mixed up because they run in parallel alignment toward adjacent sides of the dorsal wrist joint.

Hip, Pelvic, and Gluteal Musculature

• Iliopsoas Complex:

  • Formed by the anatomical combination of Psoas major, Psoas minor, and Iliacus.
  • Individual divisions do not require separate identification; the combined term Iliopsoas must be utilized.
  • Leg Model representation: #25.
  • "Little Guy" representation: Groin region #68.

• Gluteal Muscle Group:

  • Gluteus maximus (Model #11): Superficial, broad, dominant posterior muscle of the buttock; guaranteed practical station item across all model sizes.
  • Gluteus medius (Model #12): Located directly deep and lateral to the gluteus maximus on the leg model, medium model, and large model.
  • Gluteus minimus: The deepest gluteal layer, located immediately subjacent to the gluteus medius. Missing entirely on the isolated leg model, but visible on both the medium-sized and large full-body models.

• Deep Lateral Hip Rotators:

  • Piriformis (Model #13): Located inferior to the gluteus medius along the bottom of the hip rotator schematic.
  • Obturator Group (Models #14 & #15): Collective unit consisting of Obturator externus (#14) and Obturator internus (#15). Acceptable practical designation is the plural Obturators or Obturator group (caution against misspelled non-anatomical terms like "operators").
  • Quadratus femoris (Model #17): Rectangular muscle situated inferior to the obturator group.
  • Tensor fasciae latae (Model #18): Short proximal muscular belly transitioning into a long fascial band (iliotibial tract) traversing down the lateral thigh to the knee; highly tested on practicals.

• Functional Role:

  • All pelvic and gluteal components act cooperatively as internal and external hip rotators to execute medial and lateral femoral rotation.

Anterior Thigh Musculature: Sartorius and Quadriceps Group

• Sartorius (Model #24):

  • An elongate, ribbon-like muscle spanning obliquely from the anterior superior iliac spine (ASIS) of the outer hip, across the anterior groin, to insert upon the medial proximal condyle of the tibia.
  • Often designated colloquially as the "sexy sartorius" due to its long diagonal drape.

• Quadriceps Femoris Group:

  • Generalizing the group simply as "quads" or "quadriceps" is prohibited; all four individual muscle bellies must be differentiated.
  • Rectus femoris (Model #20): Large, prominent, central anterior superficial muscle overlying the femur; primary knee extensor and hip flexor.
  • Vastus medialis (Model #23): Located on the anteromedial compartment toward the big-toe side of the knee.
  • Vastus lateralis (Model #21): Located on the anterolateral compartment toward the pinky-toe side of the thigh.
  • Vastus intermedius (Model #22): Located deep directly beneath the detached belly of Rectus femoris (#20).

Medial Thigh Compartment: Adductor Group and Pectineus

• Pectineus ("Little Guy" Model #69):

  • Positioned directly inferior and medial to the Iliopsoas (#68) in the proximal femoral triangle.
  • Exam Alternation Rule: Exam forms utilize a mutual-exclusion pattern: if Iliopsoas (#68) is tagged, Pectineus (#69) will not be tagged, and vice versa.

• Adductor Muscle Complex:

  • Functional Role: Adducts the femur medially toward the anatomical midline.
  • Adductor longus (Model #26): Positioned anteriorly within the medial groin compartment.
  • Gracilis (Model #27): A long, broad, ribbon-like muscle spanning from the pubic symphysis down the medial margin of the thigh to the knee; positioned between adductor longus and adductor magnus.
  • Adductor magnus (Model #28): Massive muscle mass situated posterior to the gracilis extending down to the posterior medial thigh below the ischium ("big butt magnus").
  • Note on Omission: Adductor brevis is omitted from testing identification requirements.

Posterior Thigh Musculature: Hamstring Complex

• Functional Role:

  • Flexes the lower leg at the knee joint (pulling the heel backward toward the gluteal region) and extends the thigh at the hip.
  • Collective labeling as "hamstrings" is not permitted; each of the three distinct anatomical components must be labeled individually.

• Muscle Identifications and Spatial Arrangement:

  • Biceps femoris (Models #31 & #32): Located on the lateral posterior thigh; comprised of long and short heads. Must be explicitly labeled with both genus and specific terms to avoid confusion with Biceps brachii.
  • Semitendinosus (Model #30): Positioned on the medial posterior thigh superficially; characterized by a long, cord-like insertion tendon.
  • Semimembranosus (Model #29): Positioned medial and deep/adjacent to Semitendinosus; broad and membranous.

Anterior and Lateral Compartments of the Lower Leg

• Anterior Compartment (Dorsiflexors and Toe Extensors):

  • Tibialis anterior (Model #33): Positioned directly lateral to the anterior crest of the tibia; executes dorsiflexion and inversion of the foot.
  • Extensor digitorum longus (Model #34): Positioned lateral to tibialis anterior; sends multiple tendons across the superior ankle to digits II through V to extend the toes.
  • Extensor hallucis longus (Model #44): Extends deep from the fibula and interosseous membrane down to the distal phalanx of the hallux (digit I/big toe); mediates extension of the great toe (e.g., a ballerina balancing en pointe).

• Lateral Compartment (Evertors):

  • Peroneus Group (Models #35 & #36): Overlies the lateral fibular surface; serves to evert the foot and abduct the lower extremity outward.
  • Peroneus longus (Model #35): More superficial and proximal belly.
  • Peroneus brevis (Model #36): Shorter and more distal belly.
  • Historical Nomenclature Caveat: Historically designated as fibularis longus and fibularis brevis; laboratory testing standards explicitly mandate the updated term Peroneus.

Posterior Lower Leg Compartment and Deep Plantar Flexors

• Superficial Posterior Compartment:

  • Gastrocnemius (Models #37 & #38): Features prominent medial and lateral superficial heads; colloquial term "calf muscle" is unacceptable.
  • Achilles Tendon (Model #10): Tendocalcaneus inserting gastrocnemius and soleus into the calcaneus.
  • Soleus (Model #39): Broad, flat muscle located deep to the gastrocnemius, extending along the distal leg down toward the calcaneus. Functions jointly with gastrocnemius in plantarflexion (standing on tiptoes, rocking on heels).

• Deep Posterior Compartment and Popliteal Space:

  • Popliteus (Model #41): Small, oblique muscle located across the posterior capsule of the knee; unlocks the knee during flexion; heavily tested on practicals.
  • Plantaris (Model #43): Small belly situated in the posterior popliteal space with an elongate tendon; rarely featured on practicals.
  • Tibialis posterior (Model #40): Centrally positioned deep posterior leg muscle; inverts and plantarflexes the foot.
  • Flexor digitorum longus (Model #42): Courses along the medial posterior leg to the plantar surface; curls digits II through V into plantarflexion.
  • Flexor hallucis longus (Models #51 & #52): Courses along the posterior distal leg to the plantar surface of the hallux; flexes the great toe.

Comparative Feline Anatomy (Cat Dissection via eMind)

• Testing Specifications for Cat Dissection:

  • Practical assessment relies on digital photographic stations derived directly from the eMind dissection modules.
  • Students are responsible for memorizing all four standard photographic views provided in the eMind software.
  • Station setups use pinned anatomical regions with letters keyed to blanks alongside an alphabetized or randomized reference bank in the corner.
  • The practical exit ticket assesses two specific cat muscle identifications.

• High-Yield Feline Dissection Muscles:

  • Clavotrapezius: Superficial dorsal neck/shoulder region.
  • Latissimus dorsi: Broad superficial lateral-thoracic muscle.
  • Pectoralis major & Pectoralis minor: Ventral chest musculature.
  • Secondary Identified Lower Limb Muscles: Biceps femoris, Rectus femoris, and Gastrocnemius.

In-Class Dialogue, Anecdotes, and Discussion

• Bowling League Anecdote:

  • A student in a local bowling league reported that their regular bowling partner suffered an injury requiring surgery a couple of weeks prior and is sidelined for the remainder of the season.
  • The league rules mandate that any replacement substitute partner must be over the age of $60$.

• Questions & Discussion on Exam Scope:

  • Student Query regarding lower leg testing priorities: Which muscles of the lower leg are guaranteed to be on the practical exam?
  • Instructor Response: Gastrocnemius and Soleus are the most probable items on the lower leg; all secondary deep flexors and extensors remain potential inclusions.
  • Student Query on exam labeling rules: Are distinctions between longus and brevis required for Extensor carpi radialis?
  • Instructor Response: No; whether pointing to #20 or #21, writing Extensor carpi radialis receives full credit without differentiating longus versus brevis.