BIO 004 · Human Anatomy
CNS Meninges and CSF
Block 5 · Module 4: The Meninges and Cerebrospinal Fluid
A reference for the meninges and CSF video and lab. This page covers the cranial and spinal meninges, the dural reflections, the meningeal spaces, where the spinal cord ends and the lumbar puncture, the ventricles, cerebrospinal fluid and its circulation, and the blood-brain barrier.
How to use this sheet Toggle the toolbar above. Notes prints the full reference for review. Study prints as a fill-in-the-blank worksheet. Print it, then write each definition while you watch the video or read your book. Quiz me is on-screen typing practice: type the term, click Reveal to check yourself. The comparison grids respond to Study and Quiz too, with a Reveal button on each row.
The Foundations video gives you a complete foundational understanding of this topic, enough on its own for a foundational course. Learn it first, then move on to the Deep dive, which adds the majors-level material: the dural reflections, the spinal meninges and the lumbar puncture, and the circulation of CSF.
- Name the cranial and spinal meninges and the spaces between them.
- Identify where the spinal cord ends and the layers a lumbar puncture passes.
- Describe cerebrospinal fluid, where it is found, and where it is made.
- Trace the circulation of CSF from production to reabsorption.
Your pre-work
Work through these the evening before class. None of it is turned in. It is how you learn the material and build your spaced recall.
This is more than a checklist. Ticking these boxes is the start, not the finish. Committing this material to memory and being able to apply it takes considerable time and repeated effort. You are not done when the boxes are checked. Put in the real hours, and keep coming back for frequent recall and review until the material is genuinely yours.
The meninges
Add a labeled section showing the dura, arachnoid, and pia mater and the spaces between them.
The ventricles
Add a labeled view of the lateral, third, and fourth ventricles and their connections.
The circulation of CSF
Add a labeled diagram tracing CSF from the choroid plexus to the arachnoid granulations.
An Overview
The brain and spinal cord are soft and irreplaceable, so they are protected four ways: by bone, by the meninges, by a cushioning fluid, and by a barrier that screens the blood.
- Protection of the CNSthe brain and spinal cord are shielded by bone, by membranes, by fluid, and by a blood barrier
- Bony protectionthe cranium encloses the brain; the vertebral column encloses the spinal cord
- Meningesthe three connective tissue membranes that wrap the brain and spinal cord
- Cerebrospinal fluidthe clear fluid that surrounds, cushions, and floats the central nervous system
- Blood-brain barrierthe barrier that controls what passes from the blood into the brain tissue
The Cranial Meninges
Three connective tissue membranes wrap the brain. Their Latin names run from tough mother on the outside to tender mother within. Compare them.
| Layer | Position | Description |
|---|---|---|
| Dura mater | the outermost layer | a tough membrane with two layers: an outer periosteal layer against the skull and an inner meningeal layer; the two are fused except where they part to form the dural venous sinuses |
| Arachnoid mater | the middle layer | a delicate, lace-like membrane |
| Pia mater | the innermost layer | a thin membrane, rich in blood vessels, that clings directly to the surface of the brain |
- No cranial epidural spacethe periosteal dura is attached directly to the skull, so there is no epidural space inside the cranium, unlike the vertebral canal
The Dural Reflections
In a few places the inner meningeal dura folds inward as a partition that anchors the brain and separates its parts. These folds are the dural reflections, also called the dural extensions.
- Dural reflectionsinward folds of the meningeal dura that partition the cranial cavity
- Falx cerebrithe fold that dips into the longitudinal fissure, separating the right and left cerebral hemispheres
- Falx cerebellithe fold that separates the right and left cerebellar hemispheres
- Tentorium cerebellithe fold that separates the cerebrum above from the cerebellum below
Where the two dural layers part within these folds, they form the dural venous sinuses. The sinuses collect venous blood from the brain, along with the CSF returned by the arachnoid granulations, and drain it toward the heart. Follow the main drainage route.
- Superior sagittal sinusruns along the top edge of the falx cerebri; receives CSF from the arachnoid granulations
- Confluence of sinusesthe meeting point of the major sinuses, at the internal occipital protuberance
- Transverse sinusesthe paired sinuses running laterally from the confluence
- Sigmoid sinusesthe S-shaped sinuses that curve down toward the jugular foramen
- Internal jugular veinscarry the blood out of the skull and back toward the heart
The Spinal Meninges
The same three membranes continue down around the spinal cord, with one important difference: the vertebral canal has a true epidural space, and the cranium does not.
- Spinal dura matera single tough layer around the cord, not fused to bone, unlike the two-layered cranial dura
- Spinal arachnoid materthe middle membrane, continuous with the cranial arachnoid
- Spinal pia materthe innermost membrane, clinging to the surface of the cord
- Epidural spacethe space between the spinal dura and the vertebral bone, filled with fat and veins; the site of an epidural injection
- Denticulate ligamentstooth-like extensions of pia mater that anchor the cord to the dura along its length
- Filum terminalea thread of pia mater that extends from the end of the cord and anchors it to the coccyx
The Meningeal Spaces
The gaps around and between the meninges are named spaces. Each one matters in the clinic, whether for an injection, a bleed, or a spinal tap. Compare them.
| Space | Location | Contents |
|---|---|---|
| Epidural space | between the spinal dura and the vertebral bone | fat and veins; present in the vertebral canal but not the cranium |
| Subdural space | between the dura mater and the arachnoid mater | a potential space only, with a thin film of fluid |
| Subarachnoid space | between the arachnoid mater and the pia mater | cerebrospinal fluid; this is where CSF is found around the brain and cord |
Where the Spinal Cord Ends
The spinal cord is shorter than the vertebral column. It ends high in the lumbar region, and the subarachnoid space continues below it as a pool of CSF.
- Conus medullaristhe tapered end of the spinal cord, at the level of the L1 to L2 intervertebral disc in the adult
- Cauda equinathe hair-like bundle of nerve roots that descends past the conus medullaris within the vertebral canal
- Filum terminalethe pia mater thread running from the conus medullaris to anchor on the coccyx
- Lumbar cisternthe enlarged subarachnoid space below the conus medullaris, filled with CSF and the floating cauda equina
The Lumbar Puncture
A lumbar puncture, or spinal tap, draws CSF from the lumbar cistern. The needle enters in the midline between the L3 to L4 or L4 to L5 spines, safely below the end of the cord. Follow the structures it passes, superficial to deep.
- Skinthe epidermis and dermis of the lower back
- Subcutaneous fatthe superficial fascia beneath the skin
- Supraspinous ligamentthe ligament running along the tips of the spinous processes
- Interspinous ligamentthe ligament between adjacent spinous processes
- Ligamentum flavumthe tough elastic ligament joining the laminae of adjacent vertebrae
- Epidural spacethe fat-filled and vein-filled space inside the vertebral canal
- Dura materthe tough outer meningeal membrane
- Arachnoid materthe delicate middle meningeal membrane
- Subarachnoid spacethe needle reaches the lumbar cistern, where CSF is withdrawn
The Ventricles of the Brain
The ventricles are connected, fluid-filled chambers deep within the brain, lined by ependymal cells. Cerebrospinal fluid is made in them. Compare them.
| Ventricle | Location | Connects to |
|---|---|---|
| Lateral ventricles | one in each cerebral hemisphere | the third ventricle, through the interventricular foramina of Monro |
| Third ventricle | in the diencephalon | the fourth ventricle, through the cerebral aqueduct of Sylvius |
| Fourth ventricle | between the brainstem and the cerebellum | the central canal and the subarachnoid space, through three apertures |
| Central canal | runs the length of the spinal cord | continuous above with the fourth ventricle |
- Choroid plexusnetworks of capillaries, wrapped in ependymal cells, that produce CSF; found in the lateral, third, and fourth ventricles
- Ependymal cellsthe glial cells that line the ventricles and central canal and help circulate CSF
Cerebrospinal Fluid
Cerebrospinal fluid is the clear liquid cushion of the central nervous system. It is made, circulated, and reabsorbed continuously, keeping a steady volume.
- Cerebrospinal fluidCSF, the clear, watery fluid that surrounds and fills the central nervous system
- Where CSF is foundin the four ventricles, in the central canal of the spinal cord, and in the subarachnoid space around the whole brain and cord, including the lumbar cistern
- Site of productionthe choroid plexus within the ventricles
- Site of reabsorptionthe arachnoid granulations, which return CSF to the venous blood of the dural sinuses
- Buoyancythe fluid floats the brain, reducing its effective weight so it does not crush its own base
- Protectionthe fluid cushions the CNS against jolts and blows
- Chemical stabilitythe fluid carries nutrients, removes wastes, and keeps a stable environment around the neurons
The Circulation of CSF
Cerebrospinal fluid follows a one-way loop, produced in the ventricles and reabsorbed into the blood. The ventricles below hold choroid plexus, where ependymal cells produce CSF. Follow it in order.
- Lateral ventricleshold choroid plexus, where ependymal cells produce CSF; one ventricle sits in each cerebral hemisphere
- Interventricular foramina of MonroCSF passes through these paired openings into the third ventricle
- Third ventriclein the diencephalon; also holds choroid plexus, adding more CSF
- Cerebral aqueduct of SylviusCSF flows down this channel through the midbrain
- Fourth ventriclebetween the pons and the cerebellum; also holds choroid plexus
- Apertures of the fourth ventricleCSF exits through the two lateral apertures of Luschka and the median aperture of Magendie
- Subarachnoid spaceCSF bathes the whole surface of the brain and spinal cord; some passes into the central canal
- Arachnoid granulationsCSF is reabsorbed here into the venous blood of the superior sagittal sinus, completing the loop
The Blood-Brain Barrier
The blood-brain barrier is the structural seal that keeps brain tissue separate from the changing chemistry of the blood. It is built from three components.
- Blood-brain barrierthe BBB, a selective barrier between the blood and the brain tissue
- Capillary endothelial cellsthe cells lining brain capillaries, joined by tight junctions and lacking the pores of ordinary capillaries
- Basement membranethe supporting layer that wraps the capillary endothelium
- Astrocyte end-feetthe foot-like projections of astrocytes that envelop the capillary and help control the barrier
Disorders of the Meninges and CSF
Compare the common disorders by the structure each one affects.
| Disorder | Structure affected | What it is |
|---|---|---|
| Meningitis | the meninges | inflammation of the meninges, usually from infection; diagnosed by testing CSF drawn at a lumbar puncture |
| Hydrocephalus | the ventricles | a buildup of CSF that enlarges the ventricles and raises intracranial pressure |
| Epidural hematoma | the epidural space | bleeding between the dura mater and the skull |
| Subdural hematoma | the subdural space | bleeding between the dura mater and the arachnoid mater |
| Subarachnoid hemorrhage | the subarachnoid space | bleeding into the CSF-filled space around the brain |
See also: The Brain and The Spinal Cord for the structures these membranes protect, and The Peripheral Nervous System.
Study questions
Work on answering these in writing, in your own words. They are the questions to bring to class, and good practice for the reasoning the exams ask for.
- Name the three meningeal layers from superficial to deep and what sits between them.
- Trace the circulation of cerebrospinal fluid from where it is made to where it is reabsorbed.
- Name the four ventricles and describe how they connect.
- Explain why the spinal cord ends where it does, and how that makes a lumbar puncture safe.
Step 2 . Retrieval check
Now explain it back, in your own words.
In 60 words or more, pull together what the video just taught you. Include the key concepts. This is the point where the learning actually sticks. After you submit, your spaced-recall cards for this topic unlock.