Cranium: Internal and External Configuration

• Internal and external configuration of the cranium.

General Information

• The skeleton is divided into axial, which includes the cranium, and appendicular sections.
• Bones are classified by shape: long, short, flat, irregular, pneumatic, sesamoid, and accessory.
• Flat bones have reduced thickness, with the rest of their dimensions dominating.
• Pneumatic bones contain air cavities.
• Flat bones consist of an external table, diploe, and an internal table.
• Skull articulations are joints or connections that can be classified by tissue type: synarthrosis, amphiarthrosis, and diarthrosis.
• Synarthrosis includes sutures, which are a type of synfibrosis, further classified as dentate, squamous, harmonic, and schindylesis.

Configuration of the Head

• The head is divided into the neurocranium and the viscerocranium.
• The cranium is the posterior and superior part that contains the encephalon.
• The face is the anterior and inferior part with viscera, including the orbit, nasal passages, and oral cavity.
• Key features include the glabella, superciliary arches, and zygomatic arch.
• Frankfurt's plane extends from the floor of the left orbit to the top of the external auditory canal.

Cranium Composition

• The cranium consists of frontal, parietal, temporal, occipital, sphenoid, and ethmoid bones.
• Some bones are flat or pneumatic
• Pneumatic bones include frontal (sinuses), ethmoid (ethmoid cells), sphenoid (sphenoid sinus), and temporal (mastoid cells). The maxilla is also pneumatic but is part of the viscerocranium.
• There are both paired (parietal and temporal) and unpaired (frontal, occipital, ethmoid, and sphenoid) bones.
• The cranial vault (bóveda) is composed of frontal, parietal, temporal, and occipital bones.
• The cranial base is composed of frontal, sphenoid, ethmoid, temporal, and occipital bones.
• The cranial vault's shape is ovoid, and its sutures include coronal (frontal-parietal), sagittal (interparietal), squamous (temporal-parietal), and lambdoid (parietal-occipital).
• Craniometric points include the bregma (coronal-sagittal) and lambda (sagittal-lambdoid).
• Fontanelles, or soft spots, are anterior (bregmatic) and posterior (lambdoid).
• Other craniometric points are asterion (lambdoid suture, occipitotemporal, or occipitomastoid) and inion (external occipital protuberance).
• The internal surface of the cranial vault shows sagittal suture, coronal suture, superior sagittal sinus groove, impressions of meningeal vessels, and arachnoid foveae.

Frontal Bone

• Characteristics of the frontal bone include that it is flat, pneumatic in its frontal sinus, and forms part of the roof of the orbit and the cranium/face. It also composes portion of the cranial floor.
• The frontal bone has the boveda (cranial floor) and the base, specifically the anterior cranial base.
• Faces of the skull include the exocranial and the endocranial.
• The exocranial face has upright, orbital, and nasal elements.
• The endocranial face has orbital areas, plus digitiform fossae and mamillary eminences.

Parietal Bone

• The exocranial surface of the parietal bone is characterized by the superior temporal line (STL), inferior temporal line (ITL), and parietal eminence.
• The endocranial of the parietal bone has an impression of the meningeal vessels, groove for the middle meningeal artery and vein, groove of the sigmoid sinus, parietal fossa, and granular foveae.

Occipital Bone

• The temporal bone is bilateral and symmetrical, forming the lateral wall and base of the cranium, housing the middle and inner ear.
• The temporal bone has certain relations and curves including an anterior border that sits behind the malar, with the external orbital apophysis and lateral crest of the frontal bone.
• The Arriba part of temporal bone has a temporal line of the parietal.
• The Abajo, or bottom portion of the temporal bone has a horizontal line passing through the zygomatic arch.

Tempora Bone - Vista exocraneal (External View)

• The squamosa part of the temporal bone form the lateral portion of the middle cranial fossa with a groove for the middle temporal artery, forming the temporal fossa.
• The apophysis of the temporal bone joins the zygomatic bone.
• The mastoid part of the temporal bone involves a conical projection pointing downward. It is the insertion point for the sternocleidomastoid muscle, splenius capitis, and longissimus capitis muscles, plus the posterior belly of the digastric muscle.
• The timpánica part of the temporal bone that a curved plate immediately below the origin of the zygomatic process, forming the anterior wall, bottom, and part of the posterior wall of the external auditory canal.
• The petrosa part of the temporal bone features a narrow, pointed apophysis projecting downward known as the APOFISIS ESTILOIDES.

Temporal Bone - Internal Features

• Key internal features of the temporal bone include the concha peñasco, cara cerebral de la porcion escamosa, eminencia arcuata, surco arterial, borde esfenoidal, tegmen timpany, and boveda caja timpan.

Base of the Skull - Openings

• Key openings include agujeros, foramenes and conductos. Examples are the foramina etmoidal (anterior and posterior).

Base of the Skull - External Part

• Notable structures include the foramen incisivum, foramen palatino mayor/menor, foramen ovale, foramen espinoso, foramen yugular, foramen mastoideo, and foramen magno.

Fractures

• Signs of skull base fractures include battle sign (retroauricular ecchymosis), raccoon eyes (periorbital ecchymosis), otolicorrhea/rhinolicorrhea, and cranial nerve palsies (VII-VIII).

Scalp Anatomy

• The scalp consists of several layers, including Skin (epidermis and dermis, 3-8 mm thick), connective tissue (collagenous, dense, vascularized, and innervated), aponeurosis (muscular: occipitofrontalis muscle and galea aponeurotica), loose connective tissue (permits free movement of upper layers, contains emissary veins), and pericranium (periosteum where fibrous tissue joins sutures).

Scalp - Blood and Nerves

• The external carotid artery supplies the temporal, occipital, and posterior auricular arteries.
• The internal carotid artery supplies the supratrochlear and supraorbital arteries in the frontal region.
• The scalp receives sensorial and motor nerves: Sensory include the frontal (N. frontal Interno y Ramas de N. supraorbitario), the temporal (N. Malar), the Parietal (N. Auriculotemporal), and the Occipital (N. Occipital Mayor).
• The occipital branch supplies motor control
• Venous return occurs through the, veins drain into the external jugular vein, while frontal and supraorbital veins drain into the ophthalmic vein and then the cavernous sinus.