A&P Lab Exam 2 Study Guide

Skeletal System

Thoracic Cage

The thoracic cage protects vital organs in the thorax and supports the shoulder girdles and upper limbs. It consists of the sternum, ribs, and thoracic vertebrae.

• Sternum: Flat bone at the anterior midline of the thorax, composed of the manubrium, body, and xiphoid process.

• Manubrium: Superior portion of the sternum; articulates with clavicles and first two pairs of ribs.

• Sternal angle: Junction between manubrium and body; important anatomical landmark.

• Xiphoid process: Inferior, cartilaginous tip of the sternum; ossifies with age.

• Clavicular notch: Articulation site for the clavicle on the manubrium.

• Jugular notch: Central indentation at the superior border of the manubrium.

• True ribs (1-7): Attach directly to the sternum via their own costal cartilages.

• False ribs (8-12): Attach indirectly or not at all to the sternum.

• Floating ribs (11-12): Do not attach to the sternum.

• Costal cartilage: Hyaline cartilage connecting ribs to sternum, providing flexibility.

Vertebral Column

The vertebral column supports the body, protects the spinal cord, and provides attachment points for ribs and muscles.

• Total number of vertebrae: 33 in early development; 26 in adults (after fusion).

• Cervical vertebrae (7): Smallest, located in the neck.

• Thoracic vertebrae (12): Articulate with ribs.

• Lumbar vertebrae (5): Largest, support lower back.

• Sacrum (5 fused): Forms posterior wall of pelvis.

• Coccyx (4 fused): Tailbone.

• Atlas (C1): Supports the skull; allows nodding motion.

• Axis (C2): Has the dens (odontoid process) for rotation of the head.

• Curvatures: Cervical and lumbar (concave posteriorly); thoracic and sacral (convex posteriorly).

General Vertebra Anatomy

• Vertebral body: Weight-bearing anterior portion.

• Vertebral arch: Posterior part forming the vertebral foramen.

• Spinous process: Posterior projection for muscle/ligament attachment.

• Transverse processes: Lateral projections for muscle/ligament attachment.

• Articular processes (superior/inferior): Form joints with adjacent vertebrae.

• Pedicle and lamina: Parts of the vertebral arch.

• Facets: Smooth surfaces for articulation.

• Vertebral foramen: Canal for the spinal cord.

• Intervertebral foramen: Openings for spinal nerves.

• Intervertebral disc: Fibrocartilage pad between vertebrae for cushioning.

Cervical Vertebrae

• Identifying features: Small body, bifid spinous process, transverse foramina.

• Transverse foramina: Passage for vertebral arteries/veins.

• Comparison: Cervical vertebrae are smaller and have unique foramina compared to thoracic/lumbar vertebrae.

Thoracic Vertebrae

• Costal facets: Articulate with ribs.

• Superior/transverse costal facets: For rib articulation.

• Spinous process: Long, angled downward.

• Identification: Presence of costal facets and downward spinous process.

Lumbar Vertebrae

• Thick vertebral body: Supports more weight.

• Short, blunt spinous process: For muscle attachment.

• Functional significance: Robust structure for weight-bearing.

Sacrum and Coccyx

• Sacrum: Five fused vertebrae; forms sacroiliac joints with pelvis.

• Coccyx: Four fused vertebrae; vestigial tailbone.

• Sacral promontory: Anterior projecting edge of the sacrum.

• Median sacral crest: Fused spinous processes.

• Sacral foramina: Openings for sacral nerves.

• Auricular surface: Articulates with ilium.

• Sacroiliac region: Area of articulation with pelvis.

Pectoral Girdle and Upper Limb

Pectoral Girdle Anatomy

The pectoral girdle attaches the upper limb to the trunk and consists of the clavicle and scapula.

• Clavicle: S-shaped bone; connects sternum to scapula.

• Scapula: Triangular bone; provides attachment for arm muscles.

• Relationship: Clavicle articulates with sternum (medially) and scapula (laterally); scapula rests on posterior thoracic cage.

Clavicle and Scapula Features

• Acromion: Lateral projection of scapula; articulates with clavicle.

• Coracoid process: Anterior projection for muscle attachment.

• Spine of scapula: Prominent ridge on posterior surface.

• Glenoid cavity: Shallow socket for humerus articulation.

• Fossae: Supraspinous, infraspinous, and subscapular fossae for muscle attachment.

• Angles and borders: Superior/inferior angles; medial/lateral borders.

• Acromial end of clavicle: Articulates with acromion.

• Sternal end of clavicle: Articulates with manubrium.

Upper Limb Bones

• Humerus: Arm bone; articulates with scapula (shoulder) and radius/ulna (elbow).

• Radius and Ulna: Forearm bones; radius is lateral (thumb side), ulna is medial (pinky side).

• Carpals: Eight wrist bones.

• Metacarpals: Five bones of the palm.

• Phalanges: Fourteen finger bones.

• Proximal/distal radioulnar joints: Allow rotation of forearm.

Humerus Features

• Head: Articulates with glenoid cavity.

• Anatomical/surgical neck: Sites of attachment and common fracture.

• Greater/lesser tubercle: Muscle attachment sites.

• Intertubercular sulcus: Groove for tendon of biceps brachii.

• Deltoid tuberosity: Attachment for deltoid muscle.

• Capitulum/trochlea: Articulate with radius/ulna.

• Epicondyles: Medial/lateral projections for muscle attachment.

• Coronoid/olecranon fossa: Accommodate ulna during flexion/extension.

Radius and Ulna Features

• Head of radius: Articulates with capitulum and radial notch of ulna.

• Radial tuberosity: Biceps brachii attachment.

• Olecranon: Proximal end of ulna; forms elbow point.

• Trochlear notch: Articulates with trochlea of humerus.

• Coronoid process: Anterior projection of ulna.

• Styloid processes: Distal projections of radius and ulna.

• Interosseous membrane: Connects radius and ulna along their length.

Hand

• Carpals: Proximal wrist bones.

• Metacarpals: Bones of the palm.

• Phalanges: Bones of the fingers (proximal, middle, distal).

Pelvic Girdle and Lower Limb

Hip Bone / Pelvic Girdle

The pelvic girdle supports the trunk and lower limbs, protects pelvic organs, and consists of two hip bones (each formed by fusion of ilium, ischium, and pubis).

• Acetabulum: Deep socket for femur head.

• Obturator foramen: Large opening for nerves and blood vessels.

• Ischial spine/tuberosity: Landmarks for muscle attachment.

• Pelvic brim: Edge of pelvic inlet.

• Greater (false) pelvis: Superior to pelvic brim.

• Lesser (true) pelvis: Inferior to pelvic brim; contains pelvic organs.

• Pelvic inlet/outlet: Openings at superior/inferior pelvis.

Hip Bone Articulations

• Sacroiliac joint: Articulation between sacrum and ilium.

• Pubic symphysis: Cartilaginous joint between pubic bones.

• Hip joint: Ball-and-socket joint between acetabulum and femur.

• Labrum: Fibrocartilage rim deepening the acetabulum.

• Joint cavity/capsule: Encloses synovial joint.

Femur

• Proximal features: Head, neck, greater/lesser trochanters.

• Distal features: Medial/lateral condyles, epicondyles.

• Identification: Largest bone; articulates with hip and knee.

Tibia and Fibula

• Tibia: Medial, weight-bearing bone of the leg.

• Fibula: Lateral, slender bone; stabilizes ankle.

• Landmarks: Tibial tuberosity, medial/lateral malleolus.

• Functional differences: Tibia bears weight; fibula provides muscle attachment.

Foot

• Tarsals: Seven ankle bones.

• Metatarsals: Five bones of the foot.

• Phalanges: Fourteen toe bones.

Joints

Structural / Functional Joint Categories

Joints are classified by structure and function, determining their movement capabilities.

• Synarthroses: Immovable joints (e.g., sutures of the skull).

• Amphiarthroses: Slightly movable joints (e.g., intervertebral discs).

• Diarthroses: Freely movable joints (e.g., synovial joints).

Synovial Joints

Synovial joints are diarthroses with a synovial cavity, articular cartilage, and joint capsule. They allow a wide range of movements.

• Six major types:

  • Plane (gliding) – e.g., intercarpal joints

  • Hinge – e.g., elbow

  • Pivot – e.g., proximal radioulnar joint

  • Condyloid (ellipsoid) – e.g., wrist

  • Saddle – e.g., thumb (1st carpometacarpal joint)

  • Ball-and-socket – e.g., shoulder, hip

• Joint shape and range of motion: The shape of articulating surfaces determines possible movements (e.g., ball-and-socket allows multiaxial movement).

Skeletal Muscle Physiology

Contractile Proteins and Regulation

Muscle contraction is regulated by the interaction of contractile proteins and calcium ions.

• Actin: Thin filament; contains binding sites for myosin.

• Myosin: Thick filament; forms cross-bridges with actin.

• Troponin: Regulatory protein; binds calcium to initiate contraction.

• Tropomyosin: Blocks actin binding sites at rest.

• Calcium regulation: Calcium binds troponin, shifting tropomyosin and exposing actin sites.

• Cross-bridge formation: Myosin heads bind actin, powered by ATP hydrolysis.

• Relaxation: Calcium is pumped back into the sarcoplasmic reticulum, tropomyosin covers actin sites.

Sarcomere / Banding Concepts

• I-band: Light band; contains only thin filaments.

• A-band: Dark band; contains thick filaments (with overlapping thin filaments).

• M-line: Center of A-band; holds thick filaments together.

• Contraction/relaxation: I-band and H-zone shorten during contraction; A-band remains constant.

• Expansion of I-band: Occurs during muscle relaxation.

Myogram

A myogram records muscle tension over time in response to stimulation.

• Single stimulus/twitch: One contraction-relaxation cycle.

• Latent period: Time between stimulus and contraction onset.

• Contraction period: Muscle tension increases.

• Relaxation period: Muscle tension decreases.

• Tension over time: Shows phases of muscle response.

Repeated Stimulation

• Wave summation: Increased tension from repeated stimuli before relaxation completes.

• Incomplete tetanus: Sustained, quivering contraction.

• Complete tetanus: Smooth, sustained contraction with no relaxation.

• Stimulus frequency: Higher frequency increases muscle tension.

Types of Contractions

• Concentric contraction: Muscle shortens while generating force (e.g., lifting a weight).

• Eccentric contraction: Muscle lengthens while maintaining force (e.g., lowering a weight).

• Isometric contraction: Muscle length does not change; tension increases (e.g., holding a weight steady).

• Isotonic contraction: Muscle changes length; includes concentric and eccentric types.

• Examples: Biceps curl (concentric up, eccentric down), plank (isometric).

Muscle Memorization Framework

• Origin (O): Fixed attachment point of muscle.

• Insertion (I): Movable attachment point.

• Function/Action (F/A): Movement produced by muscle contraction.

• Memorization: Learn O, I, and F/A for key muscles.

Muscles (Selected Groups)

Muscles of Breathing

• External intercostals: Elevate ribs; inspiration.

• Internal intercostals: Depress ribs; forced expiration.

• Diaphragm: Main muscle of inspiration; flattens to increase thoracic volume.

• Central tendon: Insertion for diaphragm muscle fibers.

• Relationship: Diaphragm attaches to ribs, xiphoid process, and lumbar vertebrae.

Muscles of the Chest / Anterior Trunk

• Trapezius: Elevates, retracts, and rotates scapula.

• Deltoid: Abducts arm.

• Pectoralis major: Flexes, adducts, and medially rotates arm.

• Pectoralis minor: Depresses scapula.

• Serratus anterior: Protracts scapula.

• External oblique: Compresses abdomen, flexes trunk.

• Rectus abdominis: Flexes vertebral column.

Muscles of the Back

• Trapezius: (see above)

• Deltoid: (see above)

• Rhomboid minor/major: Retract scapula.

• Latissimus dorsi: Extends, adducts, and medially rotates arm.

• Erector spinae: Extends vertebral column.

• Serratus posterior inferior: Depresses lower ribs.

Muscles of the Neck

• Sternocleidomastoid: Flexes and rotates head.

• Semispinalis capitis: Extends head.

• Splenius capitis: Extends and rotates head.

• Suprahyoid muscles: Elevate hyoid bone.

• Infrahyoid muscles: Depress hyoid bone.

Muscles of the Face

• Zygomaticus: Elevates corners of mouth (smiling).

• Orbicularis oculi: Closes eyelids.

• Orbicularis oris: Closes and protrudes lips.

• Frontalis: Raises eyebrows.

• Depressor anguli oris: Depresses corners of mouth.

• Buccinator: Compresses cheek.

Muscles of Mastication / TMD

• Symptoms of TMD: Jaw pain, clicking, limited movement.

• Strained muscles: Masseter, temporalis, pterygoids.

• Primary muscles: Masseter (elevates mandible), temporalis (elevates/retracts mandible), lateral pterygoid (protracts/depresses mandible), medial pterygoid (elevates/protracts mandible).

• Origin, insertion, function: Key for understanding muscle actions in mastication.

Joint Type	Movement Allowed	Example
Synarthrosis	Immovable	Sutures of skull
Amphiarthrosis	Slightly movable	Intervertebral discs
Diarthrosis (Synovial)	Freely movable	Shoulder, hip

*Additional info: Some explanations and examples were expanded for clarity and completeness based on standard anatomy and physiology curriculum.*