Brain Anatomy Parts 2 & 3 (Week 1, Mod 8)

What is the meninges of the skull and spinal cord?

A three layered membranous sheet that covers the brain and spinal cord

• Arrangement of meninges is different between skull and vertebral column

  • Same layers but different attachments to surrounding structures

What are the 3 layers of the meninges, from inside to outside? What are the names of the 3 spaces BETWEEN the layers?

Meninges layers: PAD

• Pia mater (innermost, comes into contact with the CNS)

• Arachnoid mater

• Dura mater (outermost)

Spaces BETWEEN layers:

• Epidural space (between bone (skull) and dura)

• Subdural space (between dura and arachnoid)

• Subarachnoid space (between arachnoid and pia) - CONTAINS CEREBRAL FLUID 

Describe the spinal cord’s meningeal arrangement… what is the dura’s interaction with the periosteum of the spine like?

• In spinal column dura is a free tube

  • Dura merges with periosteum at foramen

• Separation from periosteum is at foramen magnum

  • Though continues along floor of C1/C2

What is the meningeal arrangement in the skull? How is it different from the arrangement of the meninges in the spine?

In the skull: 

• Dura contributes to the inner periosteum, fusing the meninges directly to the skull bone (aka calvarium)

• Epidural space doesn’t really exist here anatomically like it does in the spine

  • If it IS present, usually indicates something is wrong (dura should not be separating from the calvarium)

The dura ALSO contributes to the division between the two hemispheres of the brain; dips into the longitudinal fissure and the transverse fissure (divides cerebrum from cerebellum) of the brain

What is the cisternae magna of the meninges?

Is the largest of the subarachnoid cisterns, which is a fluid-filled space at the back of the brain containing cerebrospinal fluid (CSF)

• Is essentially an enlargement of the subarachnoid space

• located below the cerebellum and above the medulla oblongata, crucial for CSF circulation, acting as a reservoir that connects to the spinal canal and fourth ventricle.

What 2 layers can the dura of the BRAIN be split into?

The two layers:

• Outer layer remains fused to bone

• Inner layer FOLDS BETWEEN THE MAJOR DIVISIONS OF THE BRAIN 

  • Falx cerebri - 

    • Is the dura fold that fills the longitudinal fissure

  • Tentorium cerebelli - 

    • Dura that fills the transverse fissure

What is another adaptation of the brain’s dura?

The Diaphragma sellae

• Dura that SURROUNDS STALK OF PITUITARY

• Offers protection

What exactly is the “fossa” of the brain supposed to describe? What are the two kinds of “fossa” of the brain?

Fossa describes a VOLUME of the brain, not necessarily an anatomical structure 

• Is used for the division of the brain on a clinical, anatomical, and imaging basis

• Is a straightforward way to describe the location of structures in tomographic images of the skull/brain

Is divided into the rostral fossa and the caudal fossa

Describe the rostral fossa… what is it composed of?

• Caudal border

  • The rostral aspect of the cerebellum and a line connecting the touching point of the cerebellum with the brainstem to the rostral border of the pons

• Forebrain

  • Cortex

  • Thalamus

  • Hypothalamus

  • Mid brain (part of)

• Cranial nerves

  • I and II (optic chiasm)

• Ventricles

  • Lateral ventricles

  • Third ventricle

Describe the caudal fossa… what is it composed of?

• Caudal border

  • line between most caudal point of the foramen magnum 

• Contents

  • Cerebellum

  • Mid-brain (part of)

  • Medulla oblongata

    • Majority of cranial nerves

    • III-XII

    • III course rostrally

  • Fourth ventricle (choroid plexus)

What does abnormal rostral and caudal fossa look like?  What can happen as a result of this?

• Chiari-like malformation

• Usually brachycephalic dogs

• Large brain and small skull

• Alters CSF flow between brain and spinal cord

• Can cause very severe symptoms