Chapter 7: Skeletal System Notes
Chapter 7: Skeletal System
Overview of the Skeleton
The skeleton consists of 206 bones along with associated cartilage.
It is divided into two main divisions:
Axial Skeleton (80 bones)
Components include:
Skull: 22 bones
Vertebral Column: 33 bones
Ribs: 24 bones
Sternum: 1 bone
Appendicular Skeleton (126 bones)
Components include:
Pectoral Girdle: 4 bones
Upper Limb: 60 bones
Pelvic Girdle: 2 bones (plus sacrum, which is part of the axial skeleton)
Lower Limb: 60 bones
Visual Representation:
Figure 7.1 shows divisions of the skeletal system, with the axial skeleton shaded orange and the appendicular skeleton shaded tan.
Module 7.1: Overview of the Skeletal System
Bone Markings: Surface features of bones categorized into three types:
Depressions: Indentations that allow blood vessels and nerves to travel along a bone or provide space for two bones to articulate.
Openings: Structures that enclose delicate structures and allow them to pass through a bone.
Projections: Features providing sites for ligament and tendon attachment or articulation points between bones.
Module 7.2: Overview of Skull Structure
General Characteristics:
All skull bones are united in adults by immovable joints called sutures, except for the mandible.
1. Cranial Bones (8 total)
List of Cranial Bones:
Frontal
Occipital
Ethmoid
Sphenoid
2 Temporal
2 Parietal
2. Facial Bones (14 total)
List of Facial Bones:
Mandible
Vomer
2 of the following: Maxilla, Zygomatic, Nasal, Lacrimal, Palatine, and Inferior Nasal Concha.
Cavities of the Skull
Functions and Components:
Cranial Cavity: Protects the brain; includes a superior cranial vault (calvaria) and an inferior cranial base.
Orbits: Formed by 7 bones, house the eyeballs.
Nasal Cavity: Houses sensory receptors for smell.
Oral Cavity: Contains teeth, tongue, and salivary glands.
Paranasal Sinuses: Air-filled, membrane-lined spaces that connect to the nasal cavity.
Other small cavities house sense organs for hearing and balance.
Special Features of the Skull
Internal View of the Skull: Provides insight into the arrangement of cranial bones and features for lab practical identification.
Bones of the Orbit: Formed by seven bones including Palatine, Maxilla, Lacrimal, Ethmoid, Sphenoid, Frontal, and Zygomatic.
Mnemonic for orbit bone arrangement: "Please Make Lily Eat Spinach From Zimbabwe."
Nasal Cavity Details
Function: First part of respiratory tract, facilitating the passage of air to the lungs.
Composition: Formed by several bones lined with mucous membranes:
Sphenoid Bone: Includes body and pterygoid processes.
Ethmoid Bone: Contains perpendicular and cribriform plates.
Inferior Nasal Conchae
Maxilla
Palatine Bone
Nasal Septum: Divides the two sides of the nasal cavity, composed of hyaline cartilage anteriorly and perpendicular plate of ethmoid and vomer posteriorly.
Paranasal Sinuses
Definitions: Located within frontal, sphenoid, ethmoid, and maxillary bones.
Functions: Lighten the skull, enhance voice resonance; infections can result in sinusitis.
Oral Cavity Characteristics
Function: Houses teeth, tongue, and salivary glands, serving as the first part of the gastrointestinal tract.
Constitution: Formed by bones and other soft tissues:
Roof: Hard palate.
Walls: Maxillae and mandible.
Floor and Posterior: Soft tissues, including muscle and connective tissue.
Fetal Skull Anatomy
Composition: Bones and membranous tissue called Fontanels.
Specific Fontanels:
Anterior Fontanel: Largest; closes between 18-24 months, located between frontal and parietal bones.
Posterior Fontanel: Closes around 2 months; located between parietal and occipital bones.
Sphenoid Fontanels: Closure around 6 months after birth.
Mastoid Fontanels: Closure between 6-18 months.
Hyoid Bone
Description: Small U-shaped bone suspended in the superior neck by muscles and ligaments.
Unique Feature: Does not articulate with any other bone in the human body; serves as an attachment point for muscles involved in swallowing and speech.
Module 7.3: Overview of the Vertebral Column
Structure: Composed of 33 vertebrae in adults.
Common Features:
7 Cervical Vertebrae (C1-C7):
Atlas: The first cervical vertebra articulated with occipital condyles allowing the head to nod “yes”.
Axis: The second cervical vertebra with dens, allowing the head to shake “no”.
Unique marking: Transverse foramen.
12 Thoracic Vertebrae (T1-T12):
Additional features: Superior, inferior, and transverse costal facets.
5 Lumbar Vertebrae (L1-L5):
Characteristics: Largest and heaviest, supports torso weight.
5 fused Sacral Vertebrae (S1-S5): Form the sacrum, fusing by ages 20-25.
3-5 fused Coccygeal vertebrae: Form the coccyx, fusing around age 25.
Structure of Vertebrae
Basic Anatomy: Important for lab practical identification.
Spinal Curvatures
Primary Curvatures: Thoracic and sacral; present during fetal development.
Secondary Curvatures: Cervical and lumbar; develop after fetal period for head support and bipedalism.
Abnormal Spinal Curvatures
Examples: Illustrated in Figure 7.17, covering various abnormal conditions.
Intervertebral Discs
Function: Pads between vertebrae that absorb shock, bind vertebral column, and support body weight.
The Thoracic Cage
Components:
Composed of the sternum, 12 pairs of ribs, and thoracic vertebrae.
Sternum: Three parts:
Manubrium: Articulates with sternal end of clavicles and first rib.
Body: Articulates directly with ribs 2-7 and indirectly with ribs 8-10.
Xiphoid Process: Composed of hyaline cartilage, generally ossified by age 40.
Ribs: 12 pairs categorized by attachment to sternum:
True Ribs (1–7): Attach via their own costal cartilage.
False Ribs (8–10): Attach indirectly through the cartilage of rib 7.
Floating Ribs (11–12): Do not attach to the sternum.
Module 7.4: Bones of the Pectoral Girdle and Upper Limb
Pectoral Girdle Configuration:
Consists of two bones, the Clavicle and Scapula.
Clavicle:
S-shaped bone:
Medial (sternal) end articulates with the manubrium.
Lateral (acromial) end articulates with the acromion of the scapula.
Conoid Tubercle: Ligament attachment site.
Scapula:
Coracoid Process: Muscle attachment point.
Glenoid Cavity: Articulates with the humerus, forming glenohumeral joint.
Acromion: Forming acromioclavicular joint.
Humerus Anatomy
Proximal Epiphysis: Ball-shaped head that articulates with the glenoid cavity for the shoulder joint.
Diaphysis: Includes the Deltoid Tuberosity for muscle attachment.
Distal Epiphysis: Forms elbow joint; includes features:
Capitulum: Articulates with the head of the radius.
Trochlea: Articulates with the ulna.
Radial Fossa: For radial head.
Coronoid Fossa: For coronoid process of the ulna.
Olecranon Fossa: For olecranon of the ulna.
Radius and Ulna Details
Forearm Configuration:
Composed of lateral Radius and medial Ulna, connected by the Interosseous Membrane.
Radius:
Proximal epiphysis includes Radial Head, articulating with capitulum for elbow joint.
Distal epiphysis forms distal radioulnar joint and articulates with carpal bones for wrist joint.
Ulna:
Proximal features include Trochlear Notch for articulation with humerus, and Olecranon.
Distal features for distal radioulnar joint.
Carpals, Metacarpals, and Phalanges
Carpals (8 bones) arranged in two rows:
Proximal Carpal Bones: articulating with radius and ulna.
Distal Carpal Bones: including trapezium, trapezoid, capitate, hamate.
Metacarpals (5 bones): Numbered I-V, with distinctions of bases, bodies, and heads (knuckles).
Phalanges (14 bones):
Each finger has proximal, middle, and distal phalanx.
Each thumb consists of just proximal and distal phalanx.
Module 7.5: Bones of the Pelvic Girdle
Pelvic Girdle Composition:
Comprises sacrum and two pelvic bones which form the pelvic inlet and brim, surrounding the coccyx.
Greater (False) Pelvis: Superior to pelvic brim.
Lesser (True) Pelvis: Inferior to pelvic brim.
Pelvic Outlet: The inferior boundary of the lesser pelvis.
Pelvic Bone Structure
Each pelvic bone (hip bone or os coxae) is made from three fused bones: Ilium, Ischium, and Pubis.
Acetabulum: Deep socket articulating with femur head.
Ilium: Largest, articulates with sacrum to form sacroiliac joint.
Features: Greater Sciatic Notch.
Ischium: Forms the posterior part of the pelvic bone with a lesser sciatic notch.
Pubis: Anterior part meeting at the pubic symphysis.
Differences Between Pelves
Visual Distinctions: Figure 7.36 illustrates differences between female and male pelves.
Module 7.5: Bones of the Lower Limb
Femur:
Largest and strongest bone in the body.
Proximal Epiphysis: Features the head that articulates with acetabulum for hip joint.
Fovea Capitis: Attaches ligament connecting femur head to acetabulum.
Distal Epiphysis: Features condyles for articulation with tibia to form the knee joint, including patellar surface for patella attachment.
The Patella
Definition: Sesamoid bone within the tendon of the rectus femoris muscle, continuing as the patellar ligament attaching to the tibial tuberosity.
The Tibia and Fibula
Tibia:
Proximal Epiphysis: Articulates with femur and fibula.
Distal Epiphysis: Ends with medial malleolus forming the ankle joint.
Fibula:
Proximal and Distal Ends: Articulate with tibia at proximal and distal tibiofibular joints, forming lateral malleolus at distal end.
Tarsals, Metatarsals, and Phalanges of the Foot
Tarsals (7 bones): Forming ankle, including:
Talus: Connects to both tibia and fibula.
Calcaneus: Heel bone, attaching to the calcaneal tendon.
Other Tarsals: Contain navicular, medial, intermediate, and lateral cuneiforms, and cuboid.
Metatarsals (5 bones): Numbered I-V from lateral to medial.
Phalanges (14 bones): Toes consist of similar phalanx structure to fingers, differing in number for big toe as it has only proximal and distal phalanx.
Arches of the Foot
Function: Support ligaments and muscles to maintain foot shape during standing or walking.
Medial Longitudinal Arch: Formed from calcaneus to metatarsals I-III.
Lateral Longitudinal Arch: Formed from calcaneus to metatarsals IV-V.
Transverse Arch: Located in the midfoot, formed by distal tarsals and bases of metatarsals.