Lecture 12: Intracranial Anatomy

What are the two subsections of the neurocranium?

Cranial vault

Cranial base

How is the cranial vault developed?

Via intramembranous ossification (mesenchyme)

How is the cranial base developed?

Via endochondral ossification

What are the derivatives of the viscerocranium?

Face

Mandible

How is the viscerocranium developed?

Branchial arches

Neural crest cells

The bones of the cranial vault are composed of two layers. The outer and inner layers are called ____ bone while the middle, spongy layer is called ____.

Compact

Diploë

What type of joint are cranial sutures? How are these joints held together?

Fibrous joints

Via Sharpey’s fibers (Type III Collagen)

What are sutural (wormian) bones?

Small, irregular bones that develop within the sutures in cranial development

Prior to having adult sutures, babies have soft spots called ____.

Fontanelles

What are emissary veins?

External veins that drain through diploic veins to the internal, dural sinuses

Why are emissary veins of note?

They allow for a potential route of infection from the scalp to the cranial cavity

What are the four paranasal sinuses?

Frontal

Ethmoidal

Sphenoidal

Maxillary

*Mastoid air cells

What is the semilunar hiatus?

A crescent-shaped groove located in the lateral wall of the nasal cavity where several paranasal sinuses can drain into the nasal cavity

What sinuses drain into the nasal cavity via the semilunar hiatus?

Frontal

Ant. ethmoidal

Maxillary

What sinuses drain into the nasopharynx?

Post. ethmoidal

Sphenoidal

What is the cranial nerve innervation and modality of the maxillary region?

CN V2

GSA

What is another name for the maxillary sinus?

Antrum

What are the meningeal layers from superficial to deep?

Dura mater

Arachnoid mater

Pia mater

From what artery does the middle meningeal artery branch from?

Maxillary artery

What is the innervation of the anterior and middle cranial fossae?

CN V

What is the innervation of the posterior cranial fossae?

CN IX

CN X

C1-C3

What additional layer of dura mater is found only in the cranial cavity?

Endosteal or periosteal layer

What layer of dura mater continues from outside the cranial cavity to the spinal cord?

Meningeal layer

What are dural sinuses?

Areas of venous drainage in the cranial region, formed between layers

What are the functions of the dural sinuses?

Returns CSF to venous circulation

From what are dural folds formed?

Meningeal layer of the dura mater

What is the falx cerebri?

A dural fold that separates the left and right hemispheres of the brain

What is the tentorium cerebelli?

A dural fold that separates the cerrebrum and cerebellum

What are arachnoid granulations?

Protrusions in the arachnoid mater that aid in draining CSF from the subarachnoid space into the venous system via the dural sinuses

What produces CSF?

Choroid plexus of the ventricles

What are some important characteristics of the pia mater?

Impermeable to CSF

Forms perivascular space acting as brain’s lymphatic system

What is the calvaria?

The dome-shaped, cranial vault of the skull

What forms the impressions found on the inner part of the calvaria?

Middle meningeal artery

What are the five categories of dural sinuses?

Sup and inf sagittal sinuses

Straight sinus

Transverse sinus

Sigmoid sinus

Cavernous sinus

Where are the sup and inf sagittal sinuses located?

Falx cerebri

Where is the straight sinus located?

Junction of falx cerebri and tentorium cerebelli

Where is the transverse sinus located?

Tentorium cerebelli

Where does the sigmoid sinus drain into?

Internal jugular vein

Where is the cavernous sinus located?

Around the internal carotid artery

Through what veins does venous blood exit the skull?

Internal jugular vein (sigmoid sinus)

Vertebral veins

Maxillary vein (cavernous sinus and pterygoid veins)

What are foramen?

Holes where cranial nerves and vasculature can enter/exit the skull

What are fossae?

Depressions in the cranial base

What is found in the anterior cranial fossa?

Frontal lobe

Olfactory bulbs

What is found in the middle cranial fossa?

Temporal lobe

Pituitary gland

CN II-CN VII, CN IX

Lots of vasculature

What is found in the posterior cranial fossa?

Cerebellum

Medulla

Pons

What structures are associated with the cavernous sinus?

Internal carotid artery

CN III

CN IV

CN V1, CN V2

CN VI

What is anastomosis?

Multiple ways of getting blood to and from the same source

What are opthalmic veins?

Veins that connect the facial vein and cavernous sinus

What is antegrade flow?

Facial blood flow at rest, where blood drain inferiorly from the facial vein to the internal jugular vein

What is retrograde flow?

Facial blood flow when the brain is hot! This is when the blood drains posteriorly through the opthalmic veins into the cavernous sinus. This cools arterial blood.

Why is retrograde flow potentially dangerous?

It can spread skin infections into the cavernous sinus, meninges and brain (danger triangle)