Cranium, Ventricles, and Meninges

Neurocranium function

Protects brain

Neurocranium bones

• Formed by 8 bones

• 4 singular bones - centered on the midline

  • Frontal

  • Ethmoid

  • Sphenoid

  • Occipital

• 2 sets of bones - bilateral pairs

  • Temporal

  • Parietal

Viscerocranium function

facial skeleton

Viscerocranium bones

• Formed by 15 irregular bones

• 3 singular bones - in the midline

  • Mandible

  • Ethmoid

  • Vomer

• 6 paired bones

  • Maxilla

  • Inferior nasal conchae

  • Zygomatic

  • Palatine

  • Nasal

  • Lacrimal bones

Cranial Sutures

• Coronal

• Sagittal

• Lambdoid

• Squamous

Anterior Cranial Fossae lobes

◦frontal lobes

Middle Cranial Fossae lobes

◦temporal lobes

Posterior Cranial Fossae lobes

◦cerebellum & brainstem

Anterior Cranial Fossa bones

◦ Frontal bone

◦ Ethmoid bone

◦ Lesser wings of sphenoid

Foramina of the Anterior Cranial Fossa

Foramen Cecum

Cribriform Foramina

Anterior & Posterior Ethmoidal Foramina

Middle Cranial Fossa bones

Sphenoid bone 

Temporal bone 

Foramina of the Middle Cranial Fossa

Optic Canal

Superior Orbital Fissure

Foramen Rotundum

Foramen Ovale

Foramen Spinosum

Posterior Cranial Fossa bones

◦ Occipital bone

◦ Temporal bone

◦ Sphenoid bone

Foramina of the Posterior Cranial Fossa

Foramen Magnum

Internal Acoustic (Auditory) Meatus

Jugular Foramen

Hypoglossal Canal

Cervicomedullary Junction

• transition between the medulla oblongata and upper cervical spinal cord at the level of the foramen magnum

• decussation

Epidural Hematoma

Arterial bleeding

Usually due to middle meningeal artery

Subdural hematoma

venous bleeding

Usually due to rupture of bridging veins

SCALP

Superficial Protection

1. Skin

2. Subcutaneous connective tissue

3. Galea aponeurotica

4. Loose areolar connective tissue

5. Pericranium

Meninges

◦Dura mater

◦Arachnoid mater

◦Pia mater

Dura Mater

Outermost meningeal layer, dense, pain-sensitive

Two layers periosteal layer (outer), meningeal layer (inner)

Dural reflections

◦ Falx cerebri

◦ Tentorium cerebelli

Falx Cerebri

Lies in the midline between the right and left cerebral hemispheres

Tentorium Cerebelli

Horizontal fold of meningeal dura mater, separates the cerebellum from the occipital

lobes

Dural Venous Sinuses

Drain venous blood and CSF from

the brain

◦ Superior sagittal sinus

◦ Inferior sagittal sinus

◦ Transverse and sigmoid sinuses

Arachnoid Mater

• Middle meningeal layer between dura mater and pia mater

Subarachnoid Space

• Filled with cerebrospinal fluid (CSF)

Arachnoid Granulations

protrude into venous sinuses, CSF reabsorption into venous system

Pia Mater

• Innermost meningeal layer covering the brain

Ventricles of the Brain filled with?

CSF

Lateral Ventricles

Contain choroid plexus for CSF production

Third Ventricle

Located between the thalami

Cerebral Aqueduct

• Connects third and fourth ventricles

• Located in the midbrain

Fourth Ventricle

Located between cerebellum and brainstem

Functions of CSF

protects, delivers nutrients and removes metabolic waste

CSF Production

• Produced by choroid plexus in ventricles, 500mL produced daily, 150mL at any given time

Cisterna magna (cerebellomedullary cistern)

◦ Between cerebellum and medulla

Interpeduncular cistern

◦ base of midbrain

Suprasellar (chiasmatic) cistern

◦ surrounds optic chiasm

Quadrigeminal cistern

◦ posterior to midbrain

Pontine cistern

◦ anterior to pons

Blood–Brain Barrier

Regulates what substances enter the brain and spinal cord via tight junctions

 Astrocyte end-feet surrounding capillaries

Primarily located in brain capillary endothelium

What Can and Cannot Cross the BBB

Can cross easily:

◦ Oxygen and carbon dioxide

◦ Lipid-soluble substances

Transported via carriers:

◦ Glucose (GLUT1)

◦ Amino acids

Restricted:

◦ Toxins, pathogens, most immune cells

Blood-CSF Barrier

 Maintains stable chemical environment for the CNS

Primarily located at the choroid plexus

Developmental and Aging Considerations for Barriers

immature in neonates

aging may reduce barrier efficiency

Elevated Intracranial Pressure (ICP)

Normal ICP:

◦ ~5–15 mmHg in adults

 Brain herniation

displacement of brain tissue due to elevated intracranial pressure

Subfalcine (cingulate) herniation

◦ Medial frontal lobe shifts under falx cerebri

Transtentorial (uncal) herniation

◦ Temporal lobe herniates through tentorial notch

Tonsillar herniation

◦ Cerebellar tonsils descend through foramen magnum

Central herniation

◦ Downward displacement of brainstem

Hydrocephalus

Excess CSF causing ventricular enlargement

Communicating:

◦ Impaired CSF absorption

Non-communicating

(Obstructive):

◦ Blockage within ventricular system

Craniotomy

bone flap replaced

Craniectomy

bone flap not replaced

Lumbar Puncture

Used to obtain cerebrospinal fluid (CSF) or measure opening pressure

L3–L4 or L4–L5, below termination of the spinal cord

Normal Pressure Hydrocephalus (NPH)

Communicating hydrocephalus with enlarged ventricles and normal ICP

Compression of frontal and periventricular white matter