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    From Musculoskeletal System

    Glenohumeral Ligaments
    Shoulder ligaments that stabilize the shoulder joint.
    Fibula
    Smaller bone in the lower leg, located alongside the tibia.
    Temporalis
    Muscle involved in closing the jaw.
    Gluteus Maximus
    Largest muscle in the buttocks responsible for hip extension.
    Facial Bones
    Bones forming the structure of the face.
    Phalanges (14 bones)
    14 bones forming the toes.
    Rectus Abdominis
    Abs muscle that flexes the trunk.
    Trapezius
    Muscle responsible for moving, rotating, and stabilizing the scapula.
    Latissimus Dorsi
    Back muscle responsible for arm adduction and extension.
    Sesamoid Bones
    e.g., patella, some found in hands/feet.
    Hinge Joints
    e.g., elbow, knee
    Thoracic Vertebrae (T1 - T12)
    Vertebrae in the upper and mid-back (T1-T12).
    Parietal Bones
    Bones forming the sides and roof of the skull.
    Zygomatic Bones
    Cheekbones that form part of the orbit.
    Metatarsals (5 bones)
    5 bones forming the mid-foot.
    Synchondroses
    Cartilaginous joints where bones are connected by hyaline cartilage.
    Humerus
    Upper arm bone connecting the shoulder to the elbow.
    Hyoid Bone
    U-shaped bone in the neck that supports the tongue.
    Sartorius
    Longest muscle in the body responsible for hip flexion.
    Cervical Vertebrae (C1 - C7)
    Vertebrae in the neck region (C1-C7).
    Anterior Cruciate Ligament (ACL)
    Knee ligament that stabilizes the joint.
    Rotator Cuff Muscles
    Supraspinatus, Infraspinatus, Teres Minor, Subscapularis.
    Adductors
    Muscles that bring the thighs toward the midline.
    Vomer Bone
    Bone forming the nasal septum.
    Temporal Bones
    Bones forming the lower sides of the skull and housing the ears.

    Sphenoid Bone

    Reviewed by our medical team

    Bone forming part of the base of the skull and sides of the orbits.

    1. Overview

    The sphenoid bone is a complex, butterfly-shaped bone situated at the base of the skull. It forms a central part of the cranial floor and articulates with nearly every other cranial bone. Because of its central location and articulations, it is often referred to as the "keystone of the cranial floor." The sphenoid bone plays critical roles in protecting neurovascular structures and supporting the brain.

    2. Location

    The sphenoid bone is located in the middle cranial fossa:

    • Anteriorly: Articulates with the frontal and ethmoid bones.

    • Posteriorly: Articulates with the occipital and temporal bones.

    • Laterally: Contributes to the floor and side walls of the skull and forms part of the orbit.

    • Medially: Its body lies on the midline and contains the sphenoidal sinus.

    3. Structure

    The sphenoid bone is a single, irregular, unpaired bone with multiple anatomical components:

    • Body: Central portion housing the sphenoidal sinuses and the sella turcica, which holds the pituitary gland.

    • Greater wings: Extend laterally to form part of the floor of the middle cranial fossa and the lateral wall of the orbit.

    • Lesser wings: Smaller, triangular projections that form part of the floor of the anterior cranial fossa and the superior orbital fissure.

    • Pterygoid processes: Project downward from the junction of the body and greater wings, providing attachment points for muscles of mastication.

    • Foramina and canals:

      • Optic canal: Transmits the optic nerve (CN II) and ophthalmic artery.

      • Superior orbital fissure: Transmits cranial nerves III, IV, V1, and VI, and the superior ophthalmic vein.

      • Foramen rotundum, ovale, and spinosum: Transmit branches of the trigeminal nerve and middle meningeal artery.

    4. Function

    The sphenoid bone has structural and functional roles critical to skull integrity and neurovascular protection:

    • Forms part of the skull base: Contributes to both the anterior and middle cranial fossae.

    • Protects vital structures: Surrounds and supports the pituitary gland within the sella turcica.

    • Supports muscle attachment: Pterygoid processes serve as origins for muscles involved in chewing and speech.

    • Allows passage of neurovascular structures: Multiple foramina allow transmission of cranial nerves and arteries to and from the brain.

    5. Physiological role(s)

    Beyond its skeletal function, the sphenoid bone participates in various physiological processes:

    • Endocrine support: Houses the pituitary gland, a major endocrine organ, in the sella turcica.

    • Sinus ventilation: Contains paired sphenoidal sinuses that open into the nasal cavity, contributing to humidification and voice resonance.

    • Vision: Forms the optic canal and part of the orbit, guiding and protecting the optic nerve and associated vessels.

    • Cranial nerve routing: Forms bony channels for multiple cranial nerves crucial to eye movement, facial sensation, and more.

    6. Clinical Significance

    The sphenoid bone's central location and relationships make it clinically important:

    • Pituitary tumors:

      • Because the pituitary gland sits in the sella turcica, tumors can expand and impinge on the optic chiasm, leading to visual disturbances.

    • Sphenoid sinusitis:

      • Infection or inflammation of the sphenoidal sinus can cause deep-seated headaches and may spread to nearby structures like the cavernous sinus.

    • Trauma:

      • Fractures can damage multiple cranial nerves due to the bone’s foramina-rich structure.

    • Surgical access route:

      • The transsphenoidal approach is a common surgical route to access pituitary tumors.

    • Cavernous sinus syndrome:

      • Pathologies near the sphenoid bone can affect the cavernous sinus and its contained cranial nerves, leading to ophthalmoplegia and facial numbness.

    Did you know? The pelvic girdle consists of the ilium, ischium, and pubis.