Skeletal System Part 2 - Axial Skeleton 2024 PDF

SKELETAL SYSTEM part 2 The Axial Skeleton By: Dr Mary Hazel Bolanon, RMT, MD Sept 2024 Overview of the Skeletal System: Comprises bones, cartilages, and ligaments -> support and shape the body Total adult bones : 206 -Bone count is higher in children...

SKELETAL SYSTEM part 2 The Axial Skeleton By: Dr Mary Hazel Bolanon, RMT, MD Sept 2024 Overview of the Skeletal System: Comprises bones, cartilages, and ligaments -> support and shape the body Total adult bones : 206 -Bone count is higher in children : bone fusion during growth Primary Functions: Provides a rigid internal structure to support body weight against gravity. Serves as a framework for muscle action to produce movement Specialization of Skeleton: Lower Skeleton: Specialized for stability during walking and running. Upper Skeleton: Provides greater mobility and range of motion for lifting, carrying, and turning movements. Additional Functions: Protection: Shields internal organs like the brain, spinal cord, heart, lungs, and pelvic organs. Storage: Stores essential minerals like calcium and phosphate. Bone marrow within bones stores fat and produces blood cells. Divisions of the Skeleton: The skeleton is divided into two major divisions: AXIAL and APPENDICULAR Axial Skeleton: Forms the vertical, central axis of the body. Consists of bones of the head, neck, chest, and back. Functions: Protects the brain, spinal cord, heart, and lungs. Serves as an attachment site for muscles that move the head, neck, back, and limbs.  Components: Skull: 22 bones. Vertebral Column: 24 vertebrae, sacrum, and coccyx. Thoracic Cage: 12 pairs of ribs and the sternum. Associated Bones: Hyoid bone and ear ossicles (3 in each ear). Total bones in axial skeleton: 80.  Appendicular Skeleton: Includes: 1. all bones of the upper and lower limbs 2. bones that attach limbs to the axial skeleton Total bones in appendicular skeleton: 126. Overview of the Skull: CRANIUM (skull) = skeletal structure of the head. Functions: Supports the face and protects the brain. Subdivisions: Facial Bones: Underlie facial structures, form the nasal cavity, enclose eyeballs, support upper and lower teeth. Brain Case (Cranial Vault): Surrounds and protects the brain, houses middle and inner ear structures. Composition of the Skull: Total Bones: 22 individual bones. Immobile Bones: 21 bones are immobile and form a single unit. Movable Bone: The mandible (lower jaw) is the only movable bone of the skull. Anterior View of the Skull: Facial Bones: Provide bony support for eyes and facial structures. Orbits: Bony sockets that house the eyeballs and related muscles. Supraorbital Margin: Upper margin of the anterior orbit. Contains the Supraorbital Foramen: Passage for a sensory nerve to the forehead. Infraorbital Foramen: Below the orbit, supplies the anterior face below the orbit with a sensory nerve.  Nasal Cavity: Divided by the nasal septum (upper portion: perpendicular plate of ethmoid bone, lower portion: vomer bone). Nasal Conchae: Inferior Nasal Concha: Independent bone. Middle and Superior Nasal Conchae: Parts of the ethmoid bone. Lateral View of the Skull: Brain Case: Large, rounded upper portion. Jaws and Teeth: Upper and lower jaws with teeth dominate the lower portion. Zygomatic Arch: Bony arch on the side of the skull, from cheek to above the ear canal. Formed by: Temporal Process: Anterior component from the zygomatic bone (cheekbone). Zygomatic Process: Posterior component from the temporal bone. Supports muscles involved in biting and chewing. Overview of the Brain Case: Function: Contains and protects the brain. Cranial Cavity: Interior space occupied by the brain. Calvaria (Skullcap): Rounded top of the skull. Base of the Skull: Floor of the brain case, complex area with openings for cranial nerves, blood vessels, and the spinal cord. Cranial Fossae: Subdivided into anterior, middle, and posterior fossae, each corresponding to different brain regions. Bones of the Brain Case: Total Bones: 8 bones (paired and unpaired). Paired: Parietal and Temporal bones. Unpaired: Frontal, Occipital, Sphenoid, and Ethmoid bones. Parietal Bone: Forms most of the upper lateral side of the skull. Boundaries: Anterior: Frontal bone. Inferior: Temporal bone. Posterior: Occipital bone. Temporal Bone: Forms the lower lateral side of the skull. Regions: Squamous Portion: Flattened upper portion. Zygomatic Process: Anterior projection forming part of the zygomatic arch. Mastoid Portion: Posterior area with the mastoid process, a large prominence for muscle attachment. Petrous Portion: Internal region forming the petrous ridge, housing middle and inner ear structures. (Temporal Bone continuation) Key Landmarks: External Acoustic Meatus: Ear canal opening on the lateral side. Internal Acoustic Meatus: Opening inside the cranial cavity connecting to the ear cavities. Mandibular Fossa: Depression for the mandible, forming part of the temporomandibular joint. Articular Tubercle: Ridge contributing to the temporomandibular joint. Styloid Process: Elongated projection for muscle and ligament attachment. Stylomastoid Foramen: Exit point for the cranial nerve supplying facial muscles. Carotid Canal: Tunnel for the artery supplying the brain. (Temporal Bone continuation) Key Landmarks: External Acoustic Meatus: Ear canal opening on the lateral side. Internal Acoustic Meatus: Opening inside the cranial cavity connecting to the ear cavities. Mandibular Fossa: Depression for the mandible, forming part of the temporomandibular joint. Articular Tubercle: Ridge contributing to the temporomandibular joint. Styloid Process: Elongated projection for muscle and ligament attachment. Stylomastoid Foramen: Exit point for the cranial nerve supplying facial muscles. Carotid Canal: Tunnel for the artery supplying the brain. Frontal Bone: Forms the forehead. Glabella: Slight depression between the eyebrows. Supraorbital Margin: Upper margin of the orbit with the supraorbital foramen for sensory nerve passage. Brow Ridges: Thickened areas above the supraorbital margin, varying in size. Internal Structure: Extends posteriorly to form the roof of the orbit and floor of the anterior cranial cavity. Occipital Bone: Forms the posterior skull and base of the cranial cavity. External Occipital Protuberance: Small bump serving as an attachment site for neck ligaments. Nuchal Lines: Superior attachment points for neck muscles. Foramen Magnum: Large opening for the spinal cord's passage. Occipital Condyles: Oval-shaped structures forming joints with the first cervical vertebra, supporting the skull. Occipital Bone: Forms the posterior skull and base of the cranial cavity. External Occipital Protuberance: Small bump serving as an attachment site for neck ligaments. Nuchal Lines: Superior attachment points for neck muscles. Foramen Magnum: Large opening for the spinal cord's passage. Occipital Condyles: Oval- shaped structures forming joints with the first cervical vertebra, supporting the skull. Sphenoid Bone Overview: Single, complex bone of the central skull. Acts as a "keystone" bone, joining with almost every other skull bone. Contributes to the base and sides of the skull. Structure: Lesser Wings: Resemble bird wings. Form the boundary between the anterior and middle cranial fossae. Sella Turcica: "Turkish saddle" region at midline of the middle cranial fossa. Houses the hypophyseal (pituitary) fossa, which contains the pituitary gland.  Greater Wings: Extend laterally from the sella turcica. Form the anterior floor of the middle cranial fossa. Visible on the lateral skull, anterior to the squamous portion of the temporal bone. Pterygoid Plates: Medial Pterygoid Plate: Forms posterior, lateral walls of the nasal cavity. Lateral Pterygoid Plate: Larger, serves as attachment sites for chewing muscles in the infratemporal space. Ethmoid Bone Overview: Single, midline bone. Forms the roof and lateral walls of the upper nasal cavity, upper portion of the nasal septum, and medial wall of the orbit. Contributes to the floor of the anterior cranial cavity. Structure: Perpendicular Plate: Forms the upper portion of the nasal septum. Contributes to the lateral walls of the upper nasal cavity. Superior and Middle Nasal Conchae: Thin, curved projections extending into the nasal cavity.  Cranial Cavity: Crista Galli: "Rooster's comb" projection at midline. Attachment point for one of the brain's covering layers. Cribriform Plate: Flattened area with numerous olfactory foramina. Allows passage of olfactory nerves from the nasal cavity to the brain. Lateral Portions: Form the lateral wall of the nasal cavity and a portion of the medial orbit. Contain air-filled spaces as part of the paranasal sinus system. Sutures of the Skull Definition: An immobile joint between adjacent skull bones. Narrow gap between bones filled with dense, fibrous connective tissue. Irregular, twisting lines interlock bones, adding strength for brain protection. Major Sutures: Coronal Suture: Runs side to side across the skull in the coronal plane. Joins the frontal bone to the right and left parietal bones.  Sagittal Suture: Extends posteriorly from the coronal suture along the midline in the sagittal plane. Unites the right and left parietal bones. Terminates at the lambdoid suture on the posterior skull. (continuation Sutures) Lambdoid Suture: Extends downward and laterally from its junction with the sagittal suture. Joins the occipital bone to the right and left parietal and temporal bones. Named for its upside-down "V" shape, resembling the Greek letter lambda (Λ). Squamous Suture: Located on the lateral skull. Unites the squamous portion of the temporal bone with the parietal bone. Pterion: Intersection of four bones: frontal, parietal, squamous portion of the temporal bone, and greater wing of the sphenoid bone. Shaped like a small capital-H. Located approximately two finger widths above the zygomatic arch and a thumb’s width posterior to the zygomatic bone. The weakest part of the skull. Facial Bones of the Skull Overview: The facial bones form the upper and lower jaws, nose, nasal cavity, nasal septum, and orbit. Comprises 14 bones: six paired and two unpaired. Paired Bones: Maxilla: Forms the upper jaw, hard palate, medial floor of the orbit, and lateral base of the nose. Palatine: Contributes to the lateral walls of the nasal cavity, medial wall of each orbit, and the posterior quarter of the hard palate. Zygomatic: Known as the cheekbone, forms the lateral wall of the orbit and anterior portion of the zygomatic arch. Nasal: Forms the bony base of the nose and supports the lateral walls of the nose. Lacrimal: Forms the anterior, medial wall of the orbit; contains the lacrimal fossa and nasolacrimal canal. Inferior Nasal Conchae: Curved bony plates projecting from the lower lateral wall of the nasal cavity. Unpaired Bones: Vomer: Forms the posterior- inferior part of the nasal septum. Mandible: The lower jaw, only moveable bone of the skull, includes the alveolar process, mental protuberance, mental foramen, mylohyoid line, mandibular foramen, and lingula. Maxillary Bone: Contains the alveolar process for upper teeth. Infraorbital foramen: exit point for a sensory nerve supplying the nose, upper lip, and anterior cheek. Palatine process forms the anterior three-quarters of the hard palate. Palatine Bone: Irregularly shaped; forms the posterior quarter of the hard palate. Best seen in an inferior view of the skull. Zygomatic Bone: Forms much of the lateral wall of the orbit and the zygomatic arch. Nasal Bone: Forms the bridge of the nose, often damaged in nasal fractures. Lacrimal Bone: Small, forms the anterior- medial wall of the orbit, contains the lacrimal fossa, and nasolacrimal canal for tear drainage. Inferior Nasal Conchae: Largest of the nasal conchae; projects into the nasal cavity to help warm, moisturize, and filter incoming air. Vomer Bone: Triangular-shaped; forms the lower and posterior part of the nasal septum. Mandible: Consists of a horizontal body and vertical ramus, with important features including: Coronoid Process: Attachment for a biting muscle. Condylar Process: Articulates with the temporal bone to form the temporomandibular joint. Alveolar Process: Anchors the lower teeth. Mental Protuberance: Forms the chin. Mandibular Foramen: Passage for sensory nerves supplying the lower teeth. Lingula: Small flap of bone, attachment site for a ligament. The Orbit: Cone-shaped bony socket for the eyeball, contains muscles for eye movement. Contributions from seven skull bones (frontal, zygomatic, maxilla, palatine, ethmoid, lacrimal, sphenoid). Contains the optic canal and superior orbital fissure for nerve passage. Nasal Septum and Nasal Conchae: Nasal Septum: Formed by the perpendicular plate of the ethmoid bone, vomer bone, and septal cartilage. Nasal Conchae: Superior, middle, and inferior conchae; help swirl and filter incoming air. Cranial Fossae Overview: The cranial cavity floor is divided into three cranial fossae (spaces): anterior, middle, and posterior. These fossae increase in depth from anterior to posterior, corresponding to the shape of the brain regions they contain. Each fossa has anterior and posterior boundaries, divided at the midline by significant bony structures or openings. Anterior Cranial Fossa: Most anterior and shallowest of the three fossae. Contains the frontal lobes of the brain, situated above the orbits. Bounded anteriorly by the frontal bone, which forms most of the floor. The lesser wings of the sphenoid bone mark the boundary between the anterior and middle fossae. Features the ethmoid bone with the crista galli and cribriform plates at the midline. Middle Cranial Fossa: Deeper and located posterior to the anterior fossa. Bounded anteriorly by the lesser wings of the sphenoid bone and posteriorly by the petrous ridges of the temporal bones. Houses the temporal lobes of the brain, with a butterfly shape due to the petrous ridges. Divided at the midline by the sella turcica, part of the sphenoid bone. Contains several openings for the passage of blood vessels and cranial nerves: Optic Canal: Passage for the optic nerve into the orbit, located at the anterior lateral corner of the sella turcica. Superior Orbital Fissure: Irregular opening in the anterior wall, lateral to the optic canal, allows passage of nerves to the eyeball and forehead.  Foramen Rotundum: Rounded opening, inferior to the superior orbital fissure, for the passage of a sensory nerve to the cheek, nose, and upper teeth. Foramen Ovale: Large, oval-shaped opening for a sensory nerve to the lateral head, cheek, chin, and lower teeth. Foramen Spinosum: Small opening, posterior-lateral to the foramen ovale, entry point for an artery that supplies the brain's covering layers. Carotid Canal: Zig-zag passageway for a major artery to the brain, entering the skull anteromedial to the styloid process. Foramen Lacerum: Irregular opening filled with cartilage in life, located immediately inferior to the exit of the carotid canal. Posterior Cranial Fossa: Most posterior and deepest of the cranial fossae. Contains the cerebellum of the brain. Anterior boundary formed by the petrous ridges; floor and posterior wall formed by the occipital bone. Divided at the midline by the foramen magnum, the opening for the spinal cord. Internal Acoustic Meatus: Opening on the medial wall of the petrous ridge for the passage of nerves related to hearing, equilibrium, and facial muscles. Hypoglossal Canal: Located at the anterior-lateral margin of the foramen magnum, allows passage of a nerve to the tongue. Jugular Foramen: Large, irregularly shaped opening inferior to the internal acoustic meatus, exit point for cranial nerves and venous blood from the brain. Paranasal Sinuses Overview: Paranasal sinuses are hollow, air-filled spaces located within certain bones of the skull. All sinuses communicate with the nasal cavity and are lined with nasal mucosa. Functions: Reduce bone mass, lightening the skull. Add resonance to the voice. Sinus congestion or infection can cause swelling, mucus buildup, and obstruction, leading to voice changes, pain, and discomfort. Frontal Sinus: Located just above the eyebrows within the frontal bone. The most anterior of the paranasal sinuses. May be divided at the midline into bilateral spaces or fused into a single sinus space. Maxillary Sinus: The largest of the paranasal sinuses. Paired sinuses located within the right and left maxillary bones, just below the orbits. Most commonly involved during sinus infections. Difficult to drain due to their connection to the nasal cavity being located high on their medial wall. Sphenoid Sinus: A single, midline sinus located within the body of the sphenoid bone. Positioned just anterior and inferior to the sella turcica, making it the most posterior of the paranasal sinuses. Ethmoid Air Cells: Multiple small spaces located within the lateral aspects of the ethmoid bone. Separated by very thin bony walls. Located on both sides of the ethmoid bone, between the upper nasal cavity and medial orbit, just behind the superior nasal conchae. Hyoid Bone Overview: The hyoid bone is an independent, U-shaped bone located in the upper neck, near the level of the inferior mandible. It is unique because it does not contact any other bone, making it distinct from the skull. Location and Structure: The tips of the "U" shape point posteriorly. Positioned at the base of the tongue above, and attached to the larynx below and the pharynx posteriorly. Function: Serves as the base for the tongue. Coordinates with movements of the tongue, larynx, and pharynx during swallowing and speaking. Muscular Attachment: Held in place by small muscles that attach to it from above or below. These muscles allow for movement of the hyoid up/down or forward/back, aiding in swallowing and speech. The Vertebral Column Overview: Also known as the spinal column or spine. Composed of vertebrae, separated and united by intervertebral discs, forming a flexible column that supports the head, neck, and body, and protects the spinal cord. Regions of the Vertebral Column: Develops initially with 33 vertebrae, reduced to 24 vertebrae, plus the sacrum and coccyx. Subdivided into five regions: Cervical (C1–C7): Seven vertebrae in the neck, with C1 articulating with the skull. Thoracic (T1–T12): Twelve vertebrae in the upper back. Lumbar (L1–L5): Five vertebrae in the lower back. Sacrum: Fusion of five sacral vertebrae, part of the pelvis. Coccyx: Fusion of four coccygeal vertebrae, forming the tailbone. Curvatures of the Vertebral Column: Four curvatures along its length: Primary Curvatures (thoracic and sacrococcygeal curves): Retained from the fetal curvature, concave anteriorly. Secondary Curvatures (cervical and lumbar curves): Develop after birth, concave posteriorly. Disorders include kyphosis (excessive thoracic curvature), lordosis (excessive lumbar curvature), and scoliosis (abnormal lateral curvature). General Structure of a Vertebra: Common features across regions: Body: Anterior portion, supports body weight, increases in size descending the column. Vertebral Arch: Posterior portion, forms the vertebral foramen housing the spinal cord. Processes: Transverse Processes: Project laterally, serve as muscle attachment sites. Spinous Process: Projects posteriorly, forms the bumps down the back. Articular Processes: Superior and inferior, forming joints between adjacent vertebrae.  Regional Modifications of Vertebrae Cervical Vertebrae: Typical Cervical Vertebrae (e.g., C4, C5): Small body, reflecting lower weight-bearing needs. Usually have a bifid (Y-shaped) spinous process, short in C3–C6 but longer in C7. Transverse processes are U- shaped, allowing passage of cervical spinal nerves and an artery supplying the brain. Superior and inferior articular processes are flattened and face upward and downward, respectively.  Atlas (C1): Supports the skull, lacks a body or spinous process. Ring-shaped with an anterior and posterior arch. Superior articular processes are deeply curved for articulation with the skull, while the inferior processes are flat for articulation with C2. Axis (C2): Serves as the axis for head rotation. Distinguished by the dens (odontoid process), a bony projection that joins with the anterior arch of the atlas. Thoracic Vertebrae: Larger bodies compared to cervical vertebrae. Characterized by a long spinous process with a downward angle, overlapping the next inferior vertebra. Superior articular processes face anteriorly, and inferior processes face posteriorly, affecting movement. Have costal facets for rib attachment: two on the lateral sides of the body for rib heads and one on the transverse process for rib tubercles. Lumbar Vertebrae: Largest and thickest vertebrae due to high weight-bearing requirements. Short transverse processes and a short, blunt spinous process. Large articular processes, with superior processes facing backward and inferior facing forward. Sacrum and Coccyx: Sacrum: Triangular-shaped, formed by the fusion of five sacral vertebrae after age 20. Features include the median sacral crest, sacral promontory, auricular surface (for sacroiliac joints), and sacral canal (ending at the sacral hiatus). Sacral foramina allow sacral spinal nerves to exit. Superior articular processes articulate with the inferior processes of L5. Coccyx (Tailbone): Formed by the fusion of four small coccygeal vertebrae. Articulates with the inferior tip of the sacrum. Not weight-bearing when standing, but may bear some weight when sitting. Intervertebral Discs Overview: Intervertebral discs are fibrocartilaginous pads that anchor adjacent vertebrae and provide cushioning during weight-bearing activities. Ligaments run along the length of the vertebral column, providing support and stability. Intervertebral Disc: Structure: Each disc fills the gap between adjacent vertebral bodies, firmly uniting them. Discs are thinner in the cervical region and thickest in the lumbar region, which bears the most weight. Intervertebral discs account for about 25% of the body height between the top of the pelvis and the base of the skull. The Thoracic Cage Overview: The thoracic cage, or rib cage, forms the chest portion of the body, consisting of 12 pairs of ribs with their costal cartilages and the sternum. It is anchored posteriorly to the 12 thoracic vertebrae (T1–T12) and serves to protect vital organs like the heart and lungs. Sternum: The sternum is an elongated bone that anchors the anterior thoracic cage and consists of three parts: the manubrium, body, and xiphoid process. Manubrium: The superior, wider portion of the sternum. Features the jugular notch at its top, which can be felt at the base of the neck. The clavicular notches on either side are sites of the sternoclavicular joint, where the sternum meets the clavicle. The first ribs attach here. (Sternum continuation) Body: The central, elongated portion of the sternum. Joins the manubrium at the sternal angle, which forms a slight bend rather than a flat junction. The second rib attaches to the sternum at the sternal angle, making it an important landmark for identifying and counting lower ribs. Ribs 3–7 attach to the sternal body. Xiphoid Process: The small, inferior tip of the sternum. It is cartilaginous early in life and becomes ossified during middle age. Ribs: Each rib is a curved, flattened bone contributing to the thoracic wall. Ribs articulate posteriorly with the T1–T12 thoracic vertebrae, and most attach anteriorly to the sternum via costal cartilages. Parts of a Typical Rib: Head: The posterior end, which articulates with the costal facet on the body of the corresponding thoracic vertebra and to a lesser extent, the vertebra above. Neck: The narrowed region lateral to the head. Ribs cont Tubercle: A small bump on the posterior rib surface that articulates with the facet on the transverse process of the same- numbered vertebra. Body (Shaft): The remainder of the rib, with the angle marking its greatest degree of curvature and aligning with the medial border of the scapula. A shallow costal groove along the inferior margin of the rib allows for the passage of blood vessels and a nerve. Rib Classifications: True Ribs (1–7): Attach directly to the sternum via their costal cartilages, also called vertebrosternal ribs. False Ribs (8–12): Do not attach directly to the sternum, also called vertebrochondral ribs. Ribs 8–10: Attach to the cartilage of the next higher rib, with rib 8 eventually connecting to rib 7. Floating Ribs (11–12): These are short ribs that do not attach to the sternum. Their small costal cartilages end within the lateral abdominal wall muscles. Skull Bone Development Origin: The bones of the skull develop from mesenchyme during embryonic development through two different mechanisms. Intramembranous Ossification: The bones forming the top and sides of the brain case arise through intramembranous ossification. Mesenchymal cells accumulate at the future bone site and directly differentiate into bone-producing cells, which form the skull bones. Fontanelles The Infant Skull Grows rapidly Is large compared to the body Has many ossification centers  Fontanelles Are areas of fibrous connective tissue (soft spots) Cover unfused sutures in the infant skull Allow the skull to flex during birth After birth: enable continued growth and expansion of the skull to accommodate the enlarging brain largest fontanelle: junction of the frontal and parietal bones on the anterior head decrease in size and usually disappear by the age of 2 Fontanelles Anterior Fontanelle Frontal, sagittal, and coronal sutures Occipital Fontanelle Lambdoid and sagittal sutures Sphenoidal Fontanelles Squamous and coronal sutures Mastoid Fontanelles Squamous and lambdoid sutures  Anterior Fontanelle Frontal, sagittal, and coronal sutures Occipital Fontanelle Lambdoid and sagittal sutures Sphenoidal Fontanelles Squamous and coronal sutures Mastoid Fontanelles Squamous and lambdoid sutures  Sutures: Even after fontanelles close, the skull bones remain separated by sutures—dense fibrous connective tissue that unites adjacent bones. Sutures allow for the continued growth of the skull bones as the brain enlarges during childhood. Thank you