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📚 SKULL BONES & SCALP - Week 1 Complete Notes

Gray's Anatomy for Students | Full Detail + Mnemonics

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TOPIC 1 - LAYERS OF SCALP

Mnemonic: "SCALP"

Key Points:

• Layers S + C + A are FIRMLY attached to each other = "Scalp proper" (torn together in scalping injuries)
• Layer L (Loose CT) = "Danger Zone" - infection/pus/blood can spread freely here
• Layer P = tightly attached to bone, CANNOT be lifted easily

Extent of Scalp:

• Anteriorly: Superciliary arches
• Posteriorly: External occipital protuberance + Superior nuchal lines
• Laterally: Zygomatic arch

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TOPIC 2 - VASCULAR SUPPLY OF SCALP

Mnemonic: "Super PASSion" (for arteries)

Arteries (5 pairs - all anastomose freely):

Mnemonic for blood supply origin: "2 from Inside, 3 from Outside"

• 2 from ICA (via ophthalmic): Supratrochlear + Supraorbital
• 3 from ECA: Superficial temporal + Posterior auricular + Occipital

Veins:

• Follow the same named arteries
• Important: Veins anastomose with diploic veins of skull and dural venous sinuses via emissary veins
• This connection = pathway for intracranial spread of infection

Lymphatics:

• Anterior to vertex → Parotid/preauricular nodes
• Posterior to vertex → Mastoid nodes (retro-auricular) → Upper deep cervical nodes
• Forehead → Submandibular nodes (follow facial artery)

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TOPIC 3 - NERVE SUPPLY OF SCALP

Mnemonic: "Scared Students Get Answers Quickly, Great Luck There"

Anterior to ears + vertex - TRIGEMINAL (CN V):

Posterior to ears + vertex - CERVICAL NERVES (C2, C3):

Mnemonic: "V before C - Ventral (anterior) = V5, Back (posterior) = Cervical"

• Front half = Trigeminal (CN V)
• Back half = Cervical plexus (C2, C3)

Motor Innervation of Scalp Muscles:

• Frontalis (frontal belly) → Temporal branches of CN VII (facial nerve)
• Occipitalis (occipital belly) → Posterior auricular branch of CN VII

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TOPIC 4 - APPLIED ASPECTS OF SCALP

Mnemonic: "SCALP problems = LABS"

1. Profuse Bleeding in Scalp Lacerations:

• Dense CT (Layer C) surrounds vessels and keeps them open (prevents vasoconstriction)
• Even small cuts bleed profusely
• Clinically: Even small scalp wounds may require suturing due to extensive bleeding

2. The "Dangerous Layer" (Layer L - Loose CT):

• Infection or hematoma in this layer can spread freely in all directions (no fascial barriers)
• Spread is limited: anteriorly by orbital septum, posteriorly by nuchal lines
• Infection here → can spread to intracranial sinuses via emissary veins = life-threatening

3. "Black Eye" after Scalp Injury:

• Blood from a forehead wound can track through loose connective tissue into periorbital tissue
• Produces bilateral periorbital bruising ("raccoon eyes" if bilateral)

4. Scalping Injuries:

• The first 3 layers (S+C+A) are firmly united = avulsed together
• Separation occurs at Layer L (loose CT) = the plane of cleavage

5. Subgaleal Hematoma (Cephalohematoma):

• Blood in Layer L (loose CT) - can spread across entire scalp
• Crosses suture lines (unlike cephalhematoma which is confined by periosteum)

6. Caput Succedaneum vs Cephalohematoma:

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TOPIC 5 - BASIC ANATOMY OF SKULL BONES

Mnemonic: "F.O.T.P.E.S.Z.N.M.V" - "Flip Over The Plate, Every Single Zygoma Needs More Vomers"

The 8 Cranial Bones:

The 14 Facial Bones:

• Nasal (x2), Lacrimal (x2), Maxilla (x2), Inferior nasal conchae (x2), Vomer (x1), Palatine (x2), Zygomatic (x2), Mandible (x1) = 14

Skull Structure:

• Calvaria = Skull cap (frontal + parietals + occipital)
• Cranial Base = Floor (ethmoid + sphenoid + temporal + occipital + frontal)
• Diploe = Cancellous bone between outer and inner tables of calvaria
• Contains diploic veins that communicate with emissary veins and dural sinuses

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TOPIC 6 - SUTURES

Mnemonic: "CLAMS" (or "Clever Lions Are Mostly Squamous")

The 5 Main Sutures:

Key Junctions:

Pterion - CLINICALLY IMPORTANT:

• Junction of frontal, parietal, temporal, and sphenoid bones
• Thinnest/weakest part of skull
• Located 2-3 cm posterior to zygomatic process of frontal bone
• Lies over middle meningeal artery (anterior division)
• Blow to pterion → Extradural (epidural) hematoma
• Mnemonic: "PTerion = Poor Temporal bone = breaks easily, bleeding from Middle Meningeal"

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TOPIC 7 - EXTERIOR AND INTERIOR OF SKULL

NORMA (5 views of skull):

• Verticalis (from above)
• Lateralis (from side)
• Basalis (from below)
• Occipitalis (from behind)
• Frontalis (from front)

Norma Verticalis (from above):

• Bregma (junction of coronal + sagittal sutures) - anteriorly
• Lambda (junction of lambdoid + sagittal sutures) - posteriorly
• Sagittal suture runs between them

Norma Lateralis (from side):

• Pterion (2.5-3 cm posterior to zygomatic arch)
• Temporal fossa
• Zygomatic arch (zygoma + temporal)
• Mastoid process
• External auditory meatus
• External occipital protuberance (inion)

Norma Basalis (base of skull - external):

• Hard palate (maxilla + palatine)
• Foramen magnum
• Occipital condyles
• Styloid process
• Mastoid process
• Carotid canal
• Jugular foramen
• Stylomastoid foramen

INTERIOR OF SKULL (3 cranial fossae):

Anterior Cranial Fossa:

• Bones: Frontal, Ethmoid (cribriform plate), Sphenoid (lesser wings)
• CN I (olfactory) passes through cribriform plate
• CN II exits via optic canal

Middle Cranial Fossa:

• Bones: Sphenoid (greater wings, body), Temporal (squamous + petrous part)
• Foramina: Mnemonic "ROSA"

Posterior Cranial Fossa:

• Bones: Occipital, Temporal (petrous), Sphenoid
• Foramen magnum: medulla, CN XI, vertebral arteries
• Internal acoustic meatus: CN VII + VIII
• Jugular foramen: CN IX, X, XI + IJV

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TOPIC 8 - FRONTAL AND OCCIPITAL BONES

FRONTAL BONE:

Parts:

1. Squamous part - Vertical plate (forehead)
2. Orbital parts (2) - Horizontal plates forming orbital roofs
3. Nasal part - Forms nasal bridge

Key Landmarks - Mnemonic: "Super Glabella Fills Orbits Neatly"

OCCIPITAL BONE:

Parts - Mnemonic: "CLAB" = Condylar, Lateral, Basilar, Squamous

1. Basilar part - Anterior to foramen magnum (clivus)
2. Condylar parts (2) - Bear occipital condyles
3. Squamous part - Posterior plate

Key Landmarks:

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TOPIC 9 - MAXILLA

Two maxillae articulate at the intermaxillary suture to form the upper jaw.

Parts - Mnemonic: "Freddy Ants Zigged Past"

Body of Maxilla:

• Contains maxillary sinus (largest of paranasal sinuses)
• Opens into middle meatus via ostium (infundibulum)
• 4 surfaces: Anterior, Posterior (infratemporal), Superior (orbital), Medial (nasal)

Key Foramina:

Applied:

• Cleft palate - failure of palatine processes to fuse
• Maxillary sinus infection - molar tooth roots project into floor of sinus
• Mnemonic: "Max Sinus DRANO: Drains Nasally (middle meatus), Roots Accessible from below (via teeth)"

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TOPIC 10 - SPHENOID AND TEMPORAL BONES

SPHENOID BONE

Shape: Resembles a bat/butterfly (with wings spread)

Parts - Mnemonic: "Big Bat Has Greatness, Little Bat Stands Proud"

• Body (central) - contains sphenoid sinuses
• Greater wings (2) - form middle cranial fossa floor + orbital walls
• Lesser wings (2) - form posterior orbital roof; optic canals
• Pterygoid processes (2) - hang down; medial and lateral pterygoid plates

Key Foramina of Sphenoid - Mnemonic: "ROSS + Carotid"

Sella Turcica ("Turkish Saddle"):

• Depression in sphenoid body
• Contains pituitary gland (hypophysis)
• Anterior: Tuberculum sellae
• Posterior: Dorsum sellae
• Floor of sella = pituitary fossa
• Clinical: Pituitary tumors → compress optic chiasm → bitemporal hemianopia

Pterygoid Plates:

• Medial pterygoid plate - ends in hamulus (hooks for tensor palati tendon)
• Lateral pterygoid plate - attachment of pterygoid muscles

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TEMPORAL BONE

Parts - Mnemonic: "PAST" = Petrous, (tympanic), Squamous, Styloid, (Mastoid)

Key Features:

Mnemonic for Styloid Muscle attachments: "Stylo-3 muscles"

Clinical Pearl - Mastoid:

• Mastoid air cells communicate with middle ear (via aditus)
• Infection (otitis media) → mastoiditis → potentially meningitis
• Digastric notch on medial mastoid = grooved for digastric posterior belly

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TOPIC 11 - FOETAL SKULL

Why different from adult skull?

• Bones separated by membranous junctions (future sutures + fontanelles)
• Brain grows rapidly after birth
• Fontanelles allow skull deformation during birth (molding)

Fontanelles (6 total):

Mnemonic: "Anterior Diamond-shape = 18 months; Posterior Triangle = 3 months"

Clinical Importance of Anterior Fontanelle:

• Bulging: ↑ ICP (meningitis, hydrocephalus, tumor)
• Sunken: Dehydration
• Closed early (craniosynostosis): premature fusion → abnormal skull shape
• Open too long: hypothyroidism, rickets, Down syndrome, hydrocephalus

Fontanelle Mnemonic: "MARCH" closes anterior

• Metabolic disease (rickets)
• Achondroplasia
• Rubella (congenital infection)
• Chromosomal (Down syndrome, trisomies)
• Hydrocephalus → These cause DELAYED closure of anterior fontanelle

Foetal Skull Proportions:

• Face:Cranium ratio = 1:8 (adult = 1:2.5)
• Frontal sinuses absent at birth (develop postnatally)
• Mastoid process absent at birth (develops after 2 years)
• Styloid process not ossified at birth

Moulding:

• Parietal bones can override frontal and occipital during labor
• Resolves within days of birth

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TOPIC 12 - HYOID BONE

"The ONLY bone in the body with NO articulation with any other bone"

Mnemonic: "H-Y-O-I-D = Hangs by ligaments, yields to swallowing, only floating bone, it's unique, different"

Structure:

• Body (corpus) - central horizontal part
• Greater horns (2) - project posteriorly from body
• Lesser horns (2) - small, project superiorly from body-greater horn junction

Position:

• Level of C3 vertebra
• Located between mandible and thyroid cartilage
• In the anterior neck

Attachments - Mnemonic: "Supra = above muscles, Infra = below (strap) muscles"

ABOVE (Suprahyoid muscles):

BELOW (Infrahyoid/strap muscles):

Ligaments:

• Stylohyoid ligament - From styloid process to lesser horn
• Thyrohyoid membrane - From body to thyroid cartilage
• Hyoepiglottic ligament - Body to epiglottis

Ossification:

• Body and greater horns: Ossify in fetal life (cartilage → bone by puberty)
• Lesser horns: Fibrocartilaginous throughout life
• Fusion of greater horns with body: 40s-50s

Clinical Importance:

1. Fracture - Rare but significant; associated with strangulation/throttling (forensic importance)
2. Thyrohyoid cyst - Thyroglossal duct cyst passes near hyoid body
3. Eagle syndrome - Elongated styloid process/calcified stylohyoid ligament → pharyngeal pain

Applied Mnemonic: "SHELF" for hyoid facts

• Strangulation fracture
• Hangs freely (no joint)
• Epiglottis attached
• Level C3
• Floating bone

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QUICK REVISION TABLE - ALL TOPICS

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MCQ POINTS TO REMEMBER (3 per topic format):

1. Layer "L" (loose CT) = dangerous space - infection/hematoma spreads here
2. Scalp bleeds profusely because dense CT holds cut vessels open
3. Scalp proper = S + C + A (avulsed together)

1. Supratrochlear and supraorbital from ophthalmic artery (ICA branch)
2. Emissary veins connect scalp veins to intracranial venous sinuses
3. Forehead lymphatics drain to submandibular nodes

1. Greater occipital nerve = posterior ramus of C2 (most important posterior scalp nerve)
2. Auriculotemporal nerve = branch of V3 (mandibular)
3. Anterior scalp = trigeminal; posterior scalp = cervical plexus

1. Pterion blow → middle meningeal artery tear → extradural hematoma
2. Caput succedaneum (loose CT) crosses sutures; cephalohematoma (subperiosteal) does NOT
3. Scalp infections can spread to intracranial sinuses via emissary veins

1. 8 cranial bones + 14 facial bones = 22 skull bones
2. Diploe = spongy bone between inner + outer tables of skull
3. Sphenoid = keystone bone of skull (articulates with all other cranial bones)

1. Pterion = thinnest skull; overlies anterior branch of middle meningeal artery
2. Bregma = junction of coronal + sagittal sutures (site of anterior fontanelle)
3. Lambda = junction of lambdoid + sagittal sutures (site of posterior fontanelle)

1. Anterior fontanelle = diamond-shaped, closes 18-24 months
2. Posterior fontanelle = triangular, closes 2-3 months
3. Caput succedaneum resolves in days; cephalohematoma takes weeks

1. Only bone with no joint to any other bone
2. Level C3; fracture suggests strangulation
3. Stylohyoid ligament connects styloid process to lesser horn

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