Meninges

→ Protective covering of brain

→ Made up of three layers: Dura mater, Arachnoid, Pia mater

Dura Mater

• Outermost layer

• Tough, dense, fibrous

• Two layers: outer, inner

  • Usually tightly connected

  • Separation of these layers creates venous sinuses

• Inner layer forms dural folds

Venous sinus (Dural sinus)

• Separation of inner and outer layers, creating a space

• Space collects:

  • Venous (deoxygenated) blood from brain

  • “Old” (depleted) cerebrospinal fluid from ventricular system

Dural folds

• Formed by inner layer of Dura mater

• Separates major brain divisions

• Stabilises brain within cranium

THREE TYPES: Falx= sickle shaped

1. Falx cerebri

   • Separates cerebral hemispheres

   • Median plane

2. Falx cerebelli

   • Separates cerebellar hemispheres

   • Median plane

3. Tentorium (‘tent’) cerebelli

   • Separates cerebrum and cerebellum

   • Horizontal plane

Arachnoid

→ “spider-like”

• Middle layer (beneath dura mater, above pia mater)

• Special features: Subarachnoid space and Arachnoid granulations

• Blood vessels sit within the subarachnoid space

• Does NOT extend into sulci

Subarachnoid Space

• Arachnoid layer suspended above pia mater on “legs”

• Filled with cerebrospinal fluid

  • Liquid layer for cushioning

• Blood vessels inside

Arachnoid Granulations

• Perforate dura mater

  • Into venous sinus

• Pumps CSF depleted of nutrients into venous sinus

Pia Mater

• Innermost layer, closest to the brain

• Thin, delicate, transparent

• Blood vessels sit on pia mater in arachnoid space

  • provides some cushioning

• Adheres closely to brain therefore providing some stability

  • follows gyri, extends into sulci

Ventricular System

• Network of interconnected ventricles (spaces) within brain

• Ventricles filled with CSF

  • nourishes and protects the brain

• Ventricles lined with ependymal cells (glia)

  • circulate CSF with cilia

• Choroid Plexus produces CSF

STRUCTURE, Superior to Interior

• Lateral ventricles (2)

  • One in each cerebral hemisphere

• Third ventricle

  • In diecephalon

• Cerebral aqueduct

  • Midbrain

  • Connects 3rd and 4th ventricles

• Fourth ventricle

  • at cerebellum level

• Central canal of spinal cord

Cerebrospinal Fluid (CSF)

• Produced by choroid plexus in ventricles

• Surrounds CNS

  • within arachnoid space

• Supports, cushions

• Transports nutrients and waste

Circulation

START: Lateral ventricles → Third ventricle → Cerebral aqueduct → Fourth ventricle (SOME: spinal canal) → Subarachnoid space → Arachnoid granulations → Venous sinus: EXIT