Temporal bone : easy lecture notes for viva

 

Temporal Bone: Key Points

🔹 Importance:

• Contains the entire internal ear, middle ear, and bony part of the external auditory meatus.

• Note: Only the cartilaginous part of the external auditory meatus and the auricle lie outside the temporal bone.

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• SN: Only cartilaginous part of external auditory meatus and auricle lies outside the temporal bone 

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Anatomical Points:

• Squamous Part: Convex surface directed laterally.

• Petrous Part Apex: Directed medially, forward, and upward.

• Zygomatic Process: Directed anteriorly.

Morphological Type:

• Pneumatic, irregular bone (air-containing).

Ossification:

• Both intramembranous (squamous & tympanic parts) and intracartilaginous ossification (rest of temporal bone).

Development:

• Petrous part: Derived from paraxial mesoderm.

• Other parts: Derived from neural crest.

Parts:

1️⃣ Squamous part
2️⃣ Petro-mastoid part
3️⃣ Tympanic part

Processes:

1️⃣ Zygomatic process
2️⃣ Mastoid process
3️⃣ Styloid process

Squamous Part:

• External Surface:
  1️⃣ Origin of temporalis muscle (except mandibular fossa & zygomatic process).
  2️⃣ Bears groove for middle temporal artery.

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  3️⃣ Suprameatal triangle: Landmark posterior to the external acoustic meatus, used in mastoidectomy.
  - Surgical Use: Guide for accessing the mastoid antrum.
  - Protection: Prevents damage to critical structures such as: - Facial nerve (anteriorly) - Sigmoid sinus (posteriorly) - Middle cranial fossa (superiorly).

iv)         Importance of suprameatal triangle : mastoid antrum lies 1.25 cm deep to it

Internal Surface of Squamous Part of Temporal Bone:

• Impressions: Impressions of the temporal lobe of the cerebrum.

• Groove: Groove for the middle meningeal artery.

Borders:

• Superior Border:

• Articulates with the inferior border of the parietal bone.

• Antero-Inferior Border:

• Articulates with the greater wing of the sphenoid bone.

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Petrous Part of the Temporal Bone

🔹 Apex: Directed medially, forward, and upward.
🔹 Base: Attached to squamous and mastoid parts.

Borders:

1️⃣ Anterior Border – Articulates with the greater wing of the sphenoid.
2️⃣ Superior Border – Lodges superior petrosal sinus and provides tentorium cerebelli attachment (except medially).
3️⃣ Posterior Border:

• Medially: Articulates with the basilar part of the occipital bone.

• Laterally: Articulates with the condylar part of the occipital bone.

• Jugular Foramen (between medial & lateral parts) – Transmits:

• Internal jugular vein

• Cranial nerves IX (Glossopharyngeal), X (Vagus), XI (Accessory)

Anterior Surface of the Petrous Part (Temporal Bone)

1️⃣ Irregular Surface – Accommodates sulci & gyri of the temporal lobe.
2️⃣ Trigeminal Impression – Depression near the apex for the trigeminal ganglion.
3️⃣ Arcuate Eminence – Elevation behind the trigeminal impression, caused by the superior semicircular canal.
4️⃣ Tegmen Tympani – Thin bony plate between the arcuate eminence and squamous part of the temporal bone.

🔹 Tegmen Tympani (Anteroposteriorly): formed
1️⃣ Roof of tensor tympani
2️⃣ Roof of middle ear cavity
3️⃣ Roof of mastoid antrum

🔹 Posterior Surface:

• Contains internal auditory meatus, transmitting:

• Entrance: Motor root of facial nerve, labyrinthine artery

• Exit: Sensory root of facial nerve, vestibulocochlear nerve, labyrinthine vein

🔹 Inferior Surface (Anteroposteriorly):
1️⃣ Near apex: Attachment of levator veli palatini & cartilaginous auditory tube
2️⃣ External opening of carotid canal
3️⃣ Jugular fossa : lodges the bulb of the internal jugular vein. The jugular bulb is the connection between the sigmoid sinus and the internal jugular vein.

  Sulcus related on petrous part of temporal bone 

The temporal bone houses important venous sinuses that play a crucial role in venous drainage of the brain. The major sinuses lodged on the temporal bone include:

1️⃣ Sigmoid Sinus

• It runs along the posterior surface of the petrous part of the temporal bone.

• It is a continuation of the transverse sinus and drains into the internal jugular vein via the jugular foramen.

2️⃣ Superior Petrosal Sinus

• Lies along the superior border of the petrous part of the temporal bone.

• Connects the cavernous sinus to the sigmoid sinus.

3️⃣ Inferior Petrosal Sinus

• Runs along the inferior border of the petrous part of the temporal bone.

• Connects the cavernous sinus to the internal jugular vein.

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Mastoid Part of the Temporal Bone

🔹 Forms the posterior part of the temporal bone.
🔹 Has:

• 2 Surfaces: External & Internal

• 2 Borders: Superior & Posterior

• 1 Process: Mastoid Process

External Surface – Muscle Attachments (from above downward & forward):

1️⃣ Auricularis posterior
2️⃣ Occipital belly of occipitofrontalis (origin)
3️⃣ Sternocleidomastoid (insertion)
4️⃣ Splenius capitis (insertion)
5️⃣ Longissimus capitis (insertion)

Internal Surface

• Sigmoid Sulcus: Deep groove lodging the sigmoid sinus

Borders

• Superior: Articulates with parietal bone

• Posterior: Articulates with occipital bone

Tympanic Part

• Thin bone between squamous & mastoid parts

• Anterior Surface: Forms non-articular part of mandibular fossa

• Posterior Surface: Forms most of the external auditory meatus

Processes of the Temporal Bone

1️⃣  Zygomatic Process:

• Muscle Attachment: Masseter (medial surface, lower border).

• Fascia Attachment: Temporal fascia (superior border).

• Articulation: Temporal process of the zygomatic bone (anterior end).

2️⃣ Mastoid Process:

• Muscle Insertions: Sternocleidomastoid, splenius capitis, longissimus capitis.

• Mastoid Notch: Origin of the posterior belly of the digastric muscle.

• Mastoid Foramen: Transmits an emissary vein (connects sigmoid sinus to the posterior auricular vein). Meningeal branch of the occipital artery – Supplies the dura mater in the posterior cranial fossa.

3️⃣ Styloid Process:

• Muscle Origins: Styloglossus, stylohyoid, stylopharyngeus.

• Ligaments: Stylohyoid and stylomandibular ligaments.

• Stylomastoid Foramen:

• Transmits: Facial nerve exit, entrance of stylomastoid branch of the posterior auricular artery.

• articulation: Temporal process of the zygomatic bone (anterior end).

Temporalis muscle originates from five skull bones within the temporal fossa:

1️⃣ Temporal Bone – Inferior temporal line and surface below it.
2️⃣ Parietal Bone – Temporal fossa region.
3️⃣ Frontal Bone – Temporal fossa anteriorly.
4️⃣ Sphenoid Bone – Greater wing contributing to the temporal fossa.
5️⃣ Zygomatic Bone – Temporal surface (minor contribution).