CNS Neuroanatomy 2

Cranial meninges

Three connective-tissue membranes (dura mater, arachnoid mater, pia mater) that protect the brain, support blood vessels, and contain cerebrospinal fluid (CSF) in the subarachnoid space.

Dura mater

Outermost, toughest meningeal layer (“hard mother”); has two layers—periosteal cranial dura (outer) and meningeal cranial dura (inner)—that separate to form dural venous sinuses and dural folds.

Periosteal cranial dura

Outer dura mater layer fused to the inner surface of cranial bones; continuous with periosteum and felt in an infant’s anterior fontanelle.

Meningeal cranial dura

Inner layer of dura mater; forms dural septa (falx cerebri, tentorium cerebelli, falx cerebelli, diaphragma sellae) that partition the cranial cavity and stabilize the brain.

Dural septa

Dural folds formed by meningeal dura that extend inward to limit brain movement and support venous sinuses; include falx cerebri, tentorium cerebelli, falx cerebelli, diaphragma sellae.

Falx cerebri

Sickle-shaped dural fold in the longitudinal fissure separating cerebral hemispheres; attaches anteriorly to the crista galli and posteriorly to the tentorium cerebelli; contains the superior and inferior sagittal sinuses.

Tentorium cerebelli

Horizontal dural fold separating cerebrum (occipital lobes) from cerebellum; oriented perpendicular to the falx cerebri; contains the transverse sinus.

Falx cerebelli

Small dural fold extending between cerebellar hemispheres; contains the occipital sinus; continuous with the tentorium cerebelli.

Diaphragma sellae

Small circular dural fold forming the roof over the sella turcica of the sphenoid; anchors the dura mater and encases the pituitary gland while allowing passage of its stalk (infundibulum).

Dural venous sinuses

Endothelial-lined venous channels between dural layers that drain blood and some CSF from the brain into the internal jugular veins; examples include superior sagittal, inferior sagittal, transverse, and occipital sinuses.

Superior sagittal sinus

Large midline venous sinus in the superior border of the falx cerebri; receives CSF from arachnoid granulations and drains into transverse sinuses.

Inferior sagittal sinus

Smaller venous sinus in the inferior border of the falx cerebri; joins the straight sinus to drain deep cerebral structures.

Transverse sinus

Paired venous sinuses along the tentorium cerebelli that receive blood from superior sagittal and straight sinuses and continue as sigmoid sinuses → internal jugular veins.

Arachnoid mater

Middle meningeal layer; thin, avascular membrane bridging over sulci; beneath it lies the subarachnoid space containing CSF and blood vessels.

Subdural space

Potential space between meningeal dura and arachnoid mater; may fill with blood in a subdural hematoma.

Subarachnoid space

Real space between arachnoid and pia mater containing CSF, cerebral arteries and veins, and web-like arachnoid trabeculae.

Arachnoid trabeculae

Delicate collagenous filaments that connect arachnoid mater to pia mater and help suspend cerebral blood vessels within the subarachnoid space.

Arachnoid granulations (villi)

Protrusions of the arachnoid mater into dural venous sinuses (mainly the superior sagittal sinus) through which CSF is absorbed into venous circulation.

Pia mater

Innermost, delicate meningeal layer tightly adhered to the brain surface; follows all gyri and sulci; anchored by astrocyte processes and supports cerebral vessels.

Blood–brain barrier (BBB)

Selective barrier formed by tight junctions between endothelial cells of CNS capillaries; allows lipid-soluble substances (O₂, CO₂, some drugs) to pass, while water-soluble molecules require specific transporters.

Hypothalamus, Pineal, Choroid, posterior

Regions where BBB permeability is modified (“leaky” areas): (1) — (hormone exchange), (2) — gland (secretes melatonin), (3) — plexus (fenestrated capillaries forming blood–CSF barrier via ependymal cells), (4) — pituitary (release of oxytocin/ADH).

glucose, glycine

BBB transport selectivity: Endothelial cells use directional transporters; ___ is continuously transported into neurons regardless of blood level; ___ is actively removed from brain ECF to maintain low neural concentrations.

Cerebrospinal fluid (CSF)

Clear, low-protein plasma-like fluid cushioning the CNS; prevents brain–bone contact, supports neural tissue, delivers nutrients & removes waste.

Choroid plexus

Specialized vascular tissue with fenestrated capillaries and ependymal cells in each ventricle; actively transports nutrients and ions into CSF and removes waste; main plexuses in roof of 3rd and 4th ventricles.

Ependymal cells

Ciliated simple columnar cells lining ventricles; form the blood–CSF barrier of the choroid plexus and regulate composition and circulation of CSF.

choroid plexus, interventricular foramen, 3rd ventricle, cerebral aqueduct, 4th ventricle, lateral and median apertures, subarachnoid space, arachnoid granulations

CSF circulation pathway: CSF produced in (1) of lateral ventricles → (2) → (3) → (4) → (5) → (6) → (7) → (8) → venous sinuses.

Subarachnoid space role

Allows CSF to circulate around brain and spinal cord and provides a cushioned fluid environment for neurons and vessels.

internal carotid, vertebral arteries, venous, internal jugular veins

Blood supply to the brain: Delivered via (1) and (2) ; (3) return via (4); loss of flow

10 s causes unconsciousness and

minutes → irreversible neuronal damage due to high O₂/glucose demand.

Cerebrovascular accident (CVA, stroke)

Interruption of cerebral blood flow causing neuronal death within minutes; may result from ischemia or hemorrhage; highlights the brain’s dependency on continuous blood supply.

Traumatic brain injury (TBI)

Damage from external force (e.g., falls, accidents, blast injury); ranges from mild concussion to severe structural damage or chronic traumatic encephalopathy.

Concussion

Mild TBI causing transient neurological dysfunction (e.g., headache, confusion, memory loss); repetitive injury can lead to chronic changes (CTE).

Chronic traumatic encephalopathy (CTE)

Progressive neurodegeneration from repeated head trauma (sports injuries); historically called “dementia pugilistica.”

Epidural hematoma

Bleeding between skull and dura mater (usually arterial, often due to skull fracture); causes rapid ICP increase and requires emergency treatment.

Subdural hematoma

Bleeding between dura mater and arachnoid mater (usually venous); slower onset of symptoms such as headache and confusion.

Brain protection summary

Brain is protected by skull bones, meninges, CSF cushioning, blood–brain barrier, and robust blood supply; each system works together to preserve neural function and homeostasis.

Dura mater vs Arachnoid mater vs Pia mater

tough, fibrous outer layer forming protective folds and venous sinuses.

vs
thin, nonvascular middle layer bridging sulci, housing the subarachnoid space.

vs
delicate inner layer tightly following brain contours, anchoring vessels and supported by astrocytes.

Subdural space vs Subarachnoid space

potential space between dura and arachnoid; normally collapsed, can fill with blood (subdural hematoma).

vs
real CSF-filled space between arachnoid and pia containing arteries, veins, and trabeculae.

Falx cerebri vs Tentorium cerebelli

separates cerebral hemispheres vertically in longitudinal fissure; contains sagittal sinuses.

vs
separates cerebellum from occipital lobes horizontally; contains transverse sinuses.

Falx cerebelli vs Falx cerebri

small vertical fold separating cerebellar hemispheres; contains occipital sinus.

vs
large vertical fold separating cerebral hemispheres; contains superior and inferior sagittal sinuses.

Dural venous sinuses vs Typical veins

endothelial-lined spaces within dura lacking valves, drain brain blood and CSF into jugular veins.

vs
thin-walled vessels outside dura, with valves, returning blood from systemic tissues.

Arachnoid granulations vs Choroid plexus

absorb CSF into venous circulation (mainly superior sagittal sinus).
vs produces CSF from filtered blood plasma within ventricles via ependymal cell secretion.

Blood–brain barrier vs Blood–CSF barrier

tight junctions between endothelial cells restrict blood-brain solute exchange; maintained by astrocytes.

vs
formed by ependymal cells of choroid plexus; selectively regulates CSF composition.

CSF vs Blood supply

____cushions brain and maintains chemical stability; ___ delivers oxygen and glucose for metabolism.
Both systems are essential for protection and homeostasis, but blood provides nutrients while CSF provides mechanical and chemical protection.

Ependymal cells vs Astrocytes

line ventricles, produce and regulate CSF (blood–CSF barrier).

vs
glial cells that maintain BBB integrity, anchor neurons to capillaries, and provide metabolic support.

BBB normal regions vs BBB exception regions

Normal BBB: impermeable to large and water-soluble molecules.
Exception regions (e.g., hypothalamus, pineal gland, choroid plexus, posterior pituitary) allow controlled hormone exchange or secretion.

CSF flow direction vs Blood flow direction

CSF: produced by choroid plexus → ventricles → subarachnoid space → venous sinuses via arachnoid granulations.
Blood: flows via arteries → capillaries → venous sinuses → jugular veins → heart.
Both converge at venous sinuses but have separate regulatory barriers.

Brain vs Spinal cord meninges relationship

The same three meninges (dura, arachnoid, pia) surround both brain and spinal cord; continuous at foramen magnum.
However, spinal dura has a real epidural space (filled with fat), whereas cranial dura does not.

Epidural hematoma vs Subdural hematoma

arterial bleed between skull and dura, rapid onset, emergency.
vs
venous bleed between dura and arachnoid, slower onset, more chronic progression.

Hydrocephalus cause vs Stroke cause

excess CSF accumulation due to obstruction or impaired absorption (e.g., aqueductal blockage).

vs
loss of blood flow to brain tissue due to vessel blockage (ischemia) or rupture (hemorrhage).

Traumatic brain injury vs Cerebrovascular accident

mechanical injury (external trauma).

vs
vascular injury (blood flow interruption).
Both cause neuronal damage but via different mechanisms — physical vs ischemic.

glucose, oxygen

BBB endothelial cells transport ___ constantly into brain tissue regardless of blood concentration — crucial since neurons cannot store glucose or ____₂.

CSF and mechanical protection

CSF provides buoyancy reducing effective brain weight, preventing compression of cranial nerves and blood vessels, and absorbing mechanical shock.

Arterial vs Venous

____ system (internal carotid + vertebral arteries) provides oxygen and glucose; ____ system (dural sinuses → jugular veins) removes deoxygenated blood and CSF.

DURAL

Each —— fold (falx cerebri, tentorium cerebelli, falx cerebelli) houses major venous sinuses, combining structural support with drainage function.

Neural vs connective tissue components of protection

astrocytes, ependymal cells regulate environment.

vs
meninges, skull bones, CSF provide physical and fluid protection. Together maintain CNS homeostasis.

BBB vs CSF

____ restricts entry to extracellular fluid of neurons; __ barrier regulates composition of fluid bathing ventricles. Both ensure controlled microenvironment for neural function.