Sagittal section of the brain

Meninges and spaces

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1. Anatomical Relationships and Size of Spaces

The meninges consist of three layers surrounding the brain and spinal cord:

• Dura mater (outermost, tough layer)
• Arachnoid mater (middle, web-like layer)
• Pia mater (innermost, delicate layer adherent to the brain surface)

Between these layers, there are spaces:

• Epidural space: Between the dura mater and the skull (or vertebral bones).

  • In the cranial cavity, this space is a potential space because the dura is tightly adherent to the skull.
  • In the spinal canal, the epidural space is a real space containing fat and venous plexuses.
  • Thickness: In the spinal canal, approx. 1-3 mm, variable by location.

• Subdural space: Between dura mater and arachnoid mater.

  • This is a potential space; normally the arachnoid and dura are in close contact.
  • Thickness: Minimal under normal conditions, expands pathologically if bleeding occurs (subdural hematoma).

• Subarachnoid space: Between arachnoid mater and pia mater.

  • This is a real space filled with cerebrospinal fluid (CSF), trabeculae, and blood vessels.
  • Thickness: Variable depending on location; generally about 1-5 mm.
  • This space extends around the brain and spinal cord.

2. Functions of Each Layer and Their Spaces

• Dura Mater

  • Function: Provides a tough protective outer covering; dural septa compartmentalize brain regions (falx cerebri, tentorium cerebelli).
  • In spinal cord, dura mater forms a protective covering and encloses the epidural space.

• Epidural Space

  • In the spine: provides cushioning and a route for venous return.
  • Clinical use: Site for epidural anesthesia.

• Arachnoid Mater

  • Function: Thin, web-like membrane facilitating the passage of blood vessels.
  • Its trabeculae extend to the pia mater.

• Subdural Space

  • Normally a potential space; no major function.
  • Clinical: Site where blood can accumulate during traumatic injury (subdural hematoma).

• Subarachnoid Space

  • Function: Contains CSF, which cushions and nourishes the brain.
  • Its trabeculae suspend the brain within the skull.
  • Contains cerebral arteries and veins.

• Pia Mater

  • Delicate membrane tightly adherent to the brain surface.
  • Supports tiny blood vessels entering brain tissue.
  • Participates in blood-brain barrier and nutrient exchange.

3. Clinical Relevance

Space	Clinical Points
Epidural Space	- In spinal epidural analgesia/anesthesia - Epidural hematomas (cranial) occurring between dura and skull are arterial and rapid
Subdural Space	- Subdural hematomas from bridging vein tearing; venous, slower onset - Potential space expands with blood accumulation
Subarachnoid Space	- Site of CSF flow; lumbar puncture accesses this space - Subarachnoid hemorrhage (from ruptured aneurysm) is life-threatening

Ventricular system

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CSF flow: CSF production: produced by choroid plexuses in the lateral, third, and fourth ventricles by filtration of plasma → lateral ventricles → third ventricle (via interventricular foramina) → fourth ventricle (via cerebral aqueduct) → diffusion and active transfer into the subarachnoid space (via foramina of Luschka and Magendie) → reabsorption in the arachnoid granulations (a group of projections of the arachnoid mater into the dural sinuses) → drainage into the dural venous sinuses → internal jugular veins, ultimately heart

Cerebellum

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• Function
  • Control of balance and ocular movements
  • Planning of movements that are about to occur
  • Coordination of complex and sequential movements
  • Maintenance of muscle tone

Vasculature of the cerebellum

• Basilar artery
  • Superior cerebellar artery (SCA) → superior surface of the cerebellum
    • Also supplies the superior and middle cerebellar peduncles and the midbrain
  • Anterior inferior cerebellar artery (AICA)→ anterior surface of the cerebellum
    • Also supplies the middle cerebellar peduncle and inferolateral pons
• Vertebral artery
  • Posterior inferior cerebellar artery (PICA)→ posterior surface of the cerebellum
    • Also supplies the inferior cerebellar peduncles and the inferolateral medulla

Limbic system

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• Function: involved in emotional and behavioral responses, motivation, memory, olfaction, and autonomic nervous system function
• Components
  • Areas of the cerebral cortex: hippocampal formation (hippocampus, dentate gyrus, entorhinal cortex), cingulate gyrus
  • Nuclei: mammillary bodies, amygdala, anterior thalamic nuclei
  • Nerve fiber tracts
    • Cerebral fornix: C-shaped nerve fiber bundle that represents the major output tract of the hippocampus
    • Cingulum: nerve fiber bundle connecting cingulate gyrus and entorhinal cortex
    • Mammillothalamic tract
    • Striae terminalis