Neuroscience anatomy - The meninges and the cerebrospinal fluid

What is the meninges? What are its layers called? What are the functions of it?

• 3 protective membrane layers that envelop the brain and spinal cord

  1. Dura mater (outermost)

     • Thick, fibrous layer

     • Adhering to skull/vertebrae

     • Anchors CNS

     • Contains venous sinuses for blood/CSF drainage

  2. Arachnoid mater (middle)

     • Thin, avascular layer

     • Trabecular bridging to pia

     • Forms subarachnoid space filled with CSF for shock absorption/nutrient delivery

  3. Pia mater (innermost)

     • Thin layer

     • Hugging CNS surface

     • Nourishes tissue

     • Produces some CSF

     • Supports blood vessels

• Main functions → Protect against trauma, stabilize CNS, and facilitate circulation

Which are these 2 layers of the meninges?

1. Dura mater

2. Arachnoidea mater

Which are these 2 layers of the meninges (outermost and innermost)?

1. Dura mater

2. Pia mater

Which are these layers of the meninges?

1. Scull bone

2. Dura mater

3. Arachnoidea

4. Subarachnoidal space

   • Below arachnoidea

   • Filled with cerebrospinal fluid

5. Pia mater

What compartment in the meninges is this? What are its functions?

• The subarachnoid space

  • The fluid-filled compartment between the arachnoid mater and Pia mater

  • Surrounds the brain and spinal cord

  • Contains cerebrospinal fluid (CSF)

• Functions:

  1. Provides mechanical shock absorption

  2. Maintains intracranial pressure

  3. Circulates CSF

  4. Supports neuromuscular structures

What is the ventricular system?

• A network of 4 interconnected, CSF-filled cavities within the brain that produce, circulate, and house cerebrospinal fluid (CSF)

What are the 4 ventricles of the ventricular system called?

1. Left lateral ventricle (in left hemisphere)

2. Right lateral ventricle (in right hemisphere)

3. 3rd ventricle

4. 4th ventricle

What is this structure called? What is its main function?

• Choroid plexus

  • A highly vascularised network of capillaries and specialized ependymal cells located within the brain’s ventricles

• Responsible for producing ~70-80% of CSF

Which ventricles are these (horizontal section)?

• Lateral ventricles

How does the CSF circulate?

• CSF circulates through the brain's ventricular system and subarachnoid space in a unidirectional flow driven by choroid plexus production (~500 mL/day), arterial pulsations, respiration, and posture

Circulation Pathway

1. Produced in lateral ventricles by choroid plexus

2. Flows from lateral ventricles to 3rd ventricle

3. Flows from 3rd ventricle to 4th ventricle

4. Exits 4th ventricle into cisterna magna and subarachnoid space around brain/spinal cord

5. Circulates multidirectionally over brain convexities, basal cisterns, spinal subarachnoid space

How is the CSF reabsorbed into the blood?

• Reabsorbed into venous blood via extensions (villi) of the arachnoidea, which extends into large veins

• Pressure gradient favors one-way flow

What are the main functions of the CSF?

1. Mechanical protection

   • Acts as a shock absorber, protecting the brain and spinal cord against blows or sudden movements

2. Buoyancy

   • By suspending the brain in fluid, CSF effectively reduces the brain’s weight from about 1.5 kg to a few tens of grams → Preventing it from compressing its own blood vessels and tissue

3. Homeostasis, nutrion, and waste removal

   • Maintain a stable chemical environment (pH, electrolytes) necessary for proper neuronal function and regulation of blood flow and hormone signaling

   • Contributes to nutrient delivery and waste clearance, carrying metabolic by-broducts away from brain tissue and into venous or lymphatic circulation

How are diagnostic CSF samples taken? What can they detect?

• Collected via lumbar puncture (spinal tap)

  • A needle is inserted between the 3rd, 4th, or 5th lumbar vertebrae (below the spinal cord’s end) into the subarachnoid space to withdraw CSF for analysis of cells, proteins, glucose, infections, or biomarkers

• Analysis detects meningitis, haemorrhage, MS, tumours