Study Guide: The Skeleton (Anatomy & Physiology)

Introduction to the Skeleton

Skeletal System Overview

The skeletal system consists of bones, cartilages, joints, and ligaments, forming the structural framework of the body. It is divided into two main parts: the axial skeleton and the appendicular skeleton.

• Axial Skeleton: Includes the skull, vertebral column, and thoracic cage (80 bones). Provides structure and protection for internal organs.

• Appendicular Skeleton: Comprises the limbs and pectoral/pelvic girdles (126 bones). Enables movement and interaction with the environment.

Distinguishing Axial vs. Appendicular Skeleton

• Axial: Skull, vertebral column, ribs, sternum.

• Appendicular: Shoulder blades, arms, hands, pelvic girdle, legs, feet.

The Skull

Introduction to the Skull

The skull is a complex structure composed of cranial bones, facial bones, and associated bones. It houses the brain, forms the face, and provides openings for air and food.

• Cranial Bones: Protect the brain.

• Facial Bones: Shape the face and anchor teeth.

• Associated Bones: Involved in hearing and swallowing.

• Cavities & Sinuses: Air-filled spaces that lighten the skull and enhance vocal resonance.

Functions of the Skull

• Protects the brain.

• Creates facial structure.

• Provides openings for air and food.

• Anchors teeth.

• Houses sensory organs (eyes, ears, nose).

Overview of Cranial Bones

The cranium is made of eight bones connected by sutures. These bones include:

• Frontal: Forehead bone.

• Parietal: Upper sides of the head.

• Occipital: Back of the head; contains the foramen magnum for the spinal cord.

• Temporal: Sides of the head; houses auditory structures.

• Sphenoid: Butterfly-shaped bone forming the base of the cranium; contains the sella turcica for the pituitary gland.

• Ethmoid: Spongy bone between the orbits and nasal cavity; includes crista galli and cribriform plate.

Overview of Facial Bones

The face is composed of 14 bones, many of which are paired. Key facial bones include:

• Maxilla: Main facial bone; forms the upper jaw and anchors teeth.

• Mandible: Lower jaw; only freely moving bone in the skull.

• Zygomatic: Cheekbones; form the zygomatic arch.

• Nasal: Bridge of the nose.

• Lacrimal: Inner wall of the orbit; associated with tear production.

• Palatine: Forms part of the hard palate.

• Vomer: Part of the nasal septum.

• Inferior Nasal Conchae: Form walls of the nasal cavity.

Cavities of the Face

Cranial and facial bones form functional cavities:

• Orbital Cavity: Houses the eyes; formed by maxilla, lacrimal, ethmoid, sphenoid, palatine, frontal, and zygomatic bones.

• Nasal Cavity: Formed by maxilla, nasal, sphenoid, vomer, inferior nasal conchae, palatine, and ethmoid bones.

• Septum: Separates right and left sides of the nose; made of cartilage, ethmoid, and vomer bones.

Overview of Sinuses

Sinuses are air-filled cavities lined with mucosa, located within certain skull bones and connected to the nasal cavity. They function to lighten the skull, warm and moisten air, and enhance vocal resonance.

• Paranasal Sinuses: Found in the frontal, ethmoid, maxilla, and sphenoid bones.

The Spine (Vertebral Column)

Overview of the Spine

The vertebral column consists of 24 vertebrae, the sacrum, and the coccyx. It is divided into regions:

• Cervical: 7 vertebrae (C1-C7); supports the head.

• Thoracic: 12 vertebrae (T1-T12); articulate with ribs.

• Lumbar: 5 vertebrae (L1-L5); lower back.

• Sacrum: 5 fused vertebrae (S1-S5); part of the pelvis.

• Coccyx: 3-5 fused vertebrae; tailbone.

The spine has four curvatures (cervical, thoracic, lumbar, sacral) that act as a spring to absorb shock. Intervertebral discs are connective tissue pads between vertebrae, absent between the atlas and axis.

Spinal Regions Table

Region	Letter from diagram	# of bones in region	Curvature: Concave or convex posteriorly
Cervical	Additional info: A	7	Concave
Thoracic	Additional info: B	12	Convex
Lumbar	Additional info: C	5	Concave
Sacrum	Additional info: D	5 (fused)	Convex
Coccyx	Additional info: E	3-5 (fused)	Convex

The Thoracic Cage

Structure and Function

The thoracic cage protects the thoracic cavity and provides structure for the lungs. It consists of the thoracic vertebrae, ribs, sternum, and intercostal cartilage.

• Ribs: 12 pairs; wrap the chest.

• True Ribs: First 7 pairs; attach directly to sternum via cartilage.

• False Ribs: Next 5 pairs; attach indirectly or not at all to sternum.

• Floating Ribs: Last 2 pairs of false ribs; no sternal attachment.

• Sternum: Flat bone; consists of manubrium, body, and xiphoid process.

• Intercostal Cartilage: Connects ribs 1-10 to sternum; provides flexibility.

The Pectoral Girdle

Structure and Function

The pectoral girdle attaches the arms to the axial skeleton and is part of the appendicular skeleton. It consists of two bones:

• Clavicle: Collar bone; articulates with sternum and scapula.

• Scapula: Shoulder blade; articulates with clavicle and humerus.

• Acromion Process: Where scapula meets clavicle.

• Glenoid Cavity: Shoulder socket; articulates with humerus.

Bones of the Upper Limb

Arm and Forearm

• Humerus: Single bone of the upper arm; head fits into shoulder.

• Radius: Lateral to ulna; same side as thumb; circular head articulates with humerus.

• Ulna: Medial to radius; forms a "U" shape; articulates with humerus.

Wrist and Hand

• Carpals: 8 short bones of the wrist.

• Metacarpals: Long bones of the palm; numbered 1 (thumb) to 5 (pinky).

• Phalanges: 14 bones in the fingers; each finger has proximal, middle, and distal phalanges; thumb has only proximal and distal.

The Pelvic Girdle

Structure and Function

• Pelvic Girdle: Made of right and left coxal bones; pelvis = coxal bones + sacrum.

• Coxal Bone: Formed from three fused bones: ilium (superior), ischium (inferior), pubis (anterior).

• Acetabulum: Hip socket; formed by all three bones.

Differences Between Male and Female Pelvis

• Female pelvis is adapted for childbirth; wider pelvic arch.

• Male pelvic arch is more acute.

Bones of the Lower Limb

Thigh and Leg

• Femur: Largest long bone; head fits into acetabulum.

• Patella: Kneecap; sesamoid bone.

• Tibia: Larger, medial bone; bears most weight.

• Fibula: Smaller, lateral bone.

Foot and Ankle

• Tarsals: 7 short bones of the ankle; talus (top), calcaneus (heel).

• Metatarsals: Long bones creating the arch of the foot; numbered 1 (medial) to 5 (lateral).

• Phalanges: 14 bones in the toes; each toe has proximal, middle, and distal phalanges; big toe has only proximal and distal.

Summary Table: Major Bones and Functions

Region	Main Bones	Function
Skull	Frontal, parietal, occipital, temporal, sphenoid, ethmoid, maxilla, mandible, zygomatic, nasal, lacrimal, palatine, vomer, inferior nasal conchae	Protect brain, form face, anchor teeth, house sensory organs
Spine	Cervical, thoracic, lumbar, sacrum, coccyx	Support body, protect spinal cord, allow movement
Thoracic Cage	Ribs, sternum	Protect lungs and heart, support breathing
Pectoral Girdle	Clavicle, scapula	Attach arms to axial skeleton, allow mobility
Upper Limb	Humerus, radius, ulna, carpals, metacarpals, phalanges	Movement, manipulation
Pelvic Girdle	Ilium, ischium, pubis	Attach legs to axial skeleton, support weight
Lower Limb	Femur, patella, tibia, fibula, tarsals, metatarsals, phalanges	Support, locomotion

Additional info: Some content was inferred for completeness and clarity, such as the number of bones in each region and the specific functions of certain bones.