Anatomy: Axial and Appendicular Skeleton Overview

Chapter 8 Lecture Outline

• The skeletal system is organized into two divisions: axial and appendicular.
• The axial skeleton includes bones along the central body axis, such as the skull, vertebral column, and thoracic cage.
• The appendicular skeleton includes bones of the upper and lower limbs, and the girdles that attach them to the axial skeleton (pectoral and pelvic).
• Learning objectives include comparing and contrasting the functions and composition of the axial and appendicular skeletons, becoming familiar with terminology for common bone markings.

8.1 Components of the Skeleton

• The skeletal system is composed of 22 bones for the skull.
• The axial skeleton is composed of bones arranged along the central body axis.
• The appendicular skeleton is composed of bones that support the upper and lower limbs.

8.1a Axial and Appendicular Skeleton

• The axial and appendicular skeleton are two divisions of the human skeletal system.

8.1b Bone Markings

• The study of bone markings is important for learning skeletal anatomy.

8.2 Bones and Features of the Skull

• Learning objectives include distinguishing between cranial and facial bones, identifying their locations, learning bone markings and features, and comparing cranial fossae.

8.2a General Anatomy of the Skull

• The skull is the most complex structure in the skeleton, with 22 bones.
• It's composed of cranial and facial bones.

8.2a General Anatomy of the Cranial Bones

• Surround and enclose the brain.
• The roof of the cranium or calvaria is composed of frontal, parietal, and parts of occipital bones.
• The base of the cranium is composed of portions of ethmoid, sphenoid, occipital, and temporal bones.

8.2a General Anatomy of the Facial Bones

• Form the face.

8.2a Cavities of the Skull

• The cranial cavity is the largest cavity, enclosing and protecting the brain.
• The orbits are eye sockets.
• The nasal cavity houses the nasal passages.

8.2b Views of the Skull and Landmark Features

• Landmark features and views of the skull are essential for understanding its structure.

8.2c Sutures

• Sutures are immovable joints connecting cranial bones.
• Coronal suture: articulates frontal and parietal bones.
• Lambdoid suture: articulates parietal and occipital bones.
• Sagittal suture: connects the left and right parietal bones.
• Squamous suture: articulates parietal and temporal bones.

8.2d Orbital and Nasal Complexes, Paranasal Sinuses

• The orbital complex encloses the eyes and eye muscles, composed of multiple bones.
• The nasal complex encloses nasal cavity and paranasal sinuses.
• Paranasal sinuses are air-filled chambers open to nasal cavity with mucous membranes warming and humidifying the inhaled air; these also provide voice resonance.

8.3 Bones Associated with the Skull

• Learning objectives include locating and identifying auditory ossicles and describing the structure and function of the hyoid bone.

8.3.1 Auditory Ossicles

• Three tiny ear bones (malleus, incus, stapes) housed within petrous part of each temporal bone.

8.3.2 Hyoid Bone

• Slender, curved bone inferior to the skull, between the mandible and larynx.
• Doesn't articulate with any other bone. Has a medial body with two hornlike processes (greater and lesser cornua).
• Attachment sites for tongue and larynx muscles and ligaments.

8.4b Aging of the Skull

• Cranial bones interconnected by dense regular CT ("soft spots" on baby's head)
• Enable some flexion and body plate ease during birth.
• Fontanelles (mastoid, sphenoidal, posterior, anterior) close at different times; posterior closes around 9 months, anterior closes around 15 months.

8.5 Bones of the Vertebral Column

• Learning objectives include describing the functions of the vertebral column, listing the five types of vertebrae, and naming the four spinal curvatures of an adult vertebral column..

8.5a Types of Vertebrae

• The vertebral column consists of 24 individual vertebrae and the fused sacrum and coccyx.
• Vertebral column divided into 5 distinct regions: cervical, thoracic, lumbar, sacrum, coccyx.

8.5b Spinal Curvatures

• Spinal curvatures include four types: cervical, thoracic, lumbar, and sacral curvatures.
• Primary curves are present at birth, the thoracic and sacral curves.
• Result in a C-shaped column.
• Secondary curves appear after birth, cervical and lumbar curves..
• These help shift trunk weight over legs. The curves help support body weight, provide flexibility, and appear sequentially during fetal, newborn and childhood development stages.

8.5c Vertebral Anatomy

• Common vertebral features include body (weight-bearing), vertebral arch (posterior), vertebral foramen (opening for spinal cord), intervertebral foramina (openings for spinal nerves), pedicles and laminae (arch components), spinous and transverse processes.
• Intervertebral discs separate vertebral bodies, composed of anulus fibrosus (outer ring) and nucleus pulposus (inner gelatinous region) acting as shock absorbers.

8.5c Vertebral Anatomy (continued)

• Cervical vertebrae (7, C1-C7): have transverse foramina, the atlas (C1) lacks body and spinous process, for nodding “yes,” and axis (C2) has dens for lateral rotation shaking the head “no”.
• Thoracic vertebrae (12, T1-T12): articulates with ribs. Costal facets & demifacets.
• Lumbar vertebrae (5, L1-L5): largest vertebrae; thick oval bodies. Bears most body weight.
• Sacrum (5 fused vertebrae, S1-S5): triangular bone forms pelvic cavity posterior wall. Completely fused by 20-30 years old.
• Coccyx (4 fused coccygeal vertebrae, Co1-Co4): tailbone. Unites during puberty.
• Cervical Vertebrae (C7-prominens): has longest spinous process.

8.6 Bones of the Thoracic Cage

• Describes features on ribs, differentiating between true and false ribs, and detailing their connections to the sternum.
• Includes the sternum, 12 pairs of ribs, and thoracic vertebrae, encloses thoracic organs.

8.6a Sternum

• Sternum (breastbone), components: manubrium (most superior), body (longest), xiphoid process (tip)
• Clavicular notches, sternal angle made by junctions of manubrium and body
• Costal notches (first seven rib connections).

8.6b Ribs

• Twelve pairs of ribs, elongated, curved, and flattened bones originate on thoracic vertebrae in the anterior wall of the thorax.
• Classified as true ribs (1–7), connected individually to sternum with cartilaginous extensions, also called costal cartilages
• False ribs (8–10), their costal cartilages fuse to that of rib 7; floating ribs (11–12) without sternal connection.

8.7 The Upper and Lower Limbs: A Comparison

• Upper and lower limbs share features based on evolutionary history, but differ based on primary limb functions (e.g., weight-bearing).
• The proximal part is supported by a "girdle" of bones, pectoral girdle for upper limb, pelvic girdle for lower limb
• Each distal end with multiple bones allow greater range of motion.

8.8 The Pectoral Girdle and Its Functions

• The pectoral girdle connects the upper limbs to the trunk, and consists of clavicles and scapulae.
• The clavicle is an elongated S-shaped bone attaching the sternum to the scapula forming the sternoclavicular and acromioclavicular joints.
• The scapula (shoulder blade) is a broad flattened bone, has borders and angles with muscle attachment sites like the spine, acromion, coracoid process.

8.9 Bones of the Upper Limb

• Includes the humerus, radius, ulna, carpals, metacarpals, and phalanges.
• Differentiates between supination and pronation of the forearm (e.g., palm facing forward or backward).
• Describes features and articulations of each bone, including humerus, radius, and ulna.
• Describes how the radius, ulna, and humerus articulate.
• Identifies the carpals, metacarpals, and phalanges.

8.10 Pelvic Girdle and its Functions

• Compares true and false pelves, male and female pelvic features and anatomical differences.
• The pelvic girdle consists of the sacrum, coccyx and two ossa coxae.

8.10a Os Coxae

• Each os coxae is composed of fused ilium, ischium, and pubis which fuse between ages 13-15.

8.10b True and False Pelves

• Pelvic brim divides pelvic cavity to true and false pelves.
• True pelvis is inferior and contains pelvic cavity and organs, false is superior.

8.10c Sex Differences in the Pelvis

• Discusses features of ossa coxae that differ substantially between sexes.

8.11 Bones of the Lower Limb

• Describes articulations, features, functions of femur, tibia and fibula, patella including their tarsals, metatarsals and phalanges.

8.11a Femur and Patella

• Longest, heaviest bone in body.
• Spherically shaped head articulates with acetabulum of os coxae, has a fovea capitis,
• Has an elongated neck and greater & lesser trochanters, Linea aspera, and medial and lateral condyles.
• Patella: large sesamoid bone in quadriceps tendon, allows smooth gliding, protects knee joint.

8.11b Tibia and Fibula

• Tibia: weight-bearing tibia and fibula bones are parallel. The tibia has medial and lateral condyles with a prominent ridge (intercondylar eminence) between them.
• Fibula: non-weight-bearing lateral bone, with a knob-like head & distal tip (malleolus) connected by interosseous membrane.

8.11c Tarsals, Metatarsals, and Phalanges

• 7 tarsal bones form ankle and proximal foot. Proximal row includes talus, calcaneus, and navicular bone; distal includes cuneiforms (three wedge-shaped) and cuboid.
• 5 metatarsal bones, parallel in the palm of the foot; Roman numerals identify from medial to lateral.
• 14 phalanges, form toes; hallux (great toe) has 2 phalanges, other toes have 3 each.

8.11d Arches of the Foot

• 3 arches help support body weight.
• The arches are maintained by shaped bones, ligaments, and tendons.

Test your knowledge on the axial and appendicular skeleton in this quiz. Explore the functions and classifications of bones, including cranial, facial, and key structures like the pectoral girdle. Ideal for students studying human anatomy.