Architectonics of the meninges
The central nervous system is securely isolated from surrounding tissues. The brain and spinal cord are covered by three protective layers, which also envelop the cranial and spinal nerves as they exit their cavities.
- Dura mater (dura mater, or pachymeninx). It has a two-layer structure. Its outer layer fuses with the bone and acts as the periosteum, while the inner layer is the meninges proper. Where they diverge, the epidural (intradural) space is formed. In the cranial cavity, it is represented by venous sinuses, while in the spinal canal it is filled with venous plexuses and loose connective tissue. Meningeal arteries supplying the skull bones run between the layers of the membrane.
- Arachnoid mater (arachnoidea). Consists of an outer cellular membrane and an inner connective tissue layer. A network of delicate trabeculae resembling a spider's web extends from the inner layer. The membrane serves as a barrier against pathogens and attaches to the dura mater via specific villi — arachnoid granulations.
- Pia mater (pia mater, or leptomeninx). A thin layer of mesodermal cells. It lines the entire surface of the brain, except for the ventricular cavities. It is fixed to the nervous tissue by means of an ectodermal membrane that accompanies all entering and exiting blood vessels.
Ventricular system and CSF pathways
Interconnected cavities — ventricles — are located within the brain tissue. The system includes two paired lateral ventricles (each consisting of anterior, posterior, inferior horns, and a body), as well as the third and fourth ventricles.
The movement of fluid between them is strictly regulated:
- From the lateral ventricles, CSF enters the third ventricle through the interventricular foramina (foramina of Monro).
- The third and fourth ventricles are connected by the cerebral aqueduct.
- From the fourth ventricle, fluid exits into the subarachnoid space through the foramen of Magendie and the paired foramina of Luschka.
Cerebrospinal fluid (CSF)
The subarachnoid space is located between the arachnoid and pia maters. In places, it expands significantly, forming cisterns. It is here that the colorless and transparent cerebrospinal fluid circulates.
Production and resorption: CSF is produced by the choroid plexuses (plexus chorioideus), which are most prominent in the lateral ventricles. After passing the path from the ventricles to the subarachnoid space, the fluid is reabsorbed back into the blood. This occurs in the area of the superior sagittal sinus, where CSF enters the cranial venous sinuses through arachnoid granulations.
Main functions of CSF:
- Liquid buffer: mechanical protection of delicate brain tissue during trauma.
- Transport: movement of dissolved substances within the central nervous system.
- "Sewage system": removal of metabolic products into the bloodstream (hydrogen ions, ammonia, carbon dioxide, lactic acid salts).
Clinical significance: meningeal irritation syndrome
Pathological processes affecting the described structures lead to the development of meningeal syndrome. To detect this syndrome of meningeal irritation in neurological practice, special examination methods are used. They are based on the assessment of muscle tone: upon meningeal irritation, the tone of strictly defined muscle groups changes reflexively, which serves as a crucial diagnostic marker.
Briefly: answers to topical questions
What clinical symptoms (meningeal signs) are included in meningeal syndrome?
Meningeal syndrome includes symptoms of meningeal irritation, including a specific posture and reflex changes in muscle tone.
- Headache and general hyperesthesia (painful reaction to light, sound, touch).
- Nuchal rigidity — inability to passively flex the head toward the sternum.
- Kernig's sign — inability to straighten the leg flexed at a right angle.
- Brudzinski's sign (upper) — flexion of the legs upon passive flexion of the head.
- Brudzinski's sign (middle) — flexion of the legs upon pressure on the pubic symphysis.
- Brudzinski's sign (lower) — flexion of the opposite leg when testing Kernig's sign.
- Bechterew's sign — intensification of headache and appearance of a pain grimace on the side of percussion when tapping the zygomatic bone.
- Specific meningeal posture — the patient lies on their side, head thrown back, thighs pressed to the abdomen, lower legs pressed to the thighs.
What cisterns are formed by the subarachnoid space of the brain?
The subarachnoid space of the brain forms areas of significant expansion called cisterns. These include:
- Chiasmatic cistern and interpeduncular cistern (cisterns of the brain base).
- Interhemispheric cistern.
- Transverse cistern.
- Ambient (quadrigeminal) cistern.
- Cistern of the cerebellar vermis.
- Pontine cistern.
- Cerebellomedullary cistern (also known as the cisterna magna, or cisterna magna).
Which cranial nerves provide innervation to the dura mater?
Innervation of the dura mater is provided by branches of three cranial nerves:
- Trigeminal nerve (n. trigeminus) — innervates the dura above the tentorium cerebelli. The ophthalmic nerve gives off the tentorial branch (r. tentorii), the maxillary nerve gives off the meningeal branch (r. meningeus medius), and the mandibular nerve gives off the meningeal branch (r. meningeus spinosus).
- Vagus nerve (n. vagus) — gives off meningeal branches that innervate the dura mater below the tentorium cerebelli (in the posterior cranial fossa).
- Hypoglossal nerve (n. hypoglossus) — also gives off meningeal branches in the area of the posterior cranial fossa.
Which specific arteries supply blood to the dura mater?
Blood supply to the dura mater is provided by the following meningeal arteries:
- Anterior meningeal artery — is a branch of the anterior ethmoidal artery (originating from the ophthalmic artery).
- Middle meningeal artery (a. meningea media) — the largest meningeal vessel, supplying the dura and skull bones. It anastomoses with the lacrimal artery. It is also referred to in sources as the middle meningeal artery.
- Posterior meningeal artery — enters the cranial cavity through the jugular foramen and supplies the dura mater in the posterior cranial fossa.
What is the normal cellular and biochemical composition of cerebrospinal fluid?
The normal cellular and biochemical composition of cerebrospinal fluid (CSF) is characterized by the following parameters:
- Cell count (cytosis): no more than 4–5 cells per 1 µL (predominantly lymphocytes, up to 85%).
- Protein content: does not exceed 0.45 g/L.
- Glucose content: 2.2–3.9 mmol/L.
- Lactate: 3.5 mmol/L.
- Albumin quotient: > 20 × 10⁻³.
- Pandy's test: negative (–).
Normally, cerebrospinal fluid is a colorless and transparent fluid with a specific gravity of 1.005–1.008.
The names of the meninges from outer to inner are easy to remember by the abbreviation DPA: Dura mater (pachymeninx), Pachymeninx / arachnoid mater, Arachnoid / leptomeninx.
Class and exam questions
Where exactly does cerebrospinal fluid circulate?
CSF circulates in the cerebral ventricles and in the subarachnoid space, which is located between the arachnoid mater and the pia mater.
What is the blood-brain barrier (BBB)?
This is a protective physiological filter that prevents pathogens from entering the brain. It is formed by capillary endothelium, basement membrane, and choroid plexus epithelium.
What is the function of arachnoid granulations?
These are specific arachnoid villi. They provide absorption (resorption) of cerebrospinal fluid from the subarachnoid space into the dural venous sinuses.
What is the epidural space?
This is a space formed where the outer and inner layers of the dura mater diverge. In the cranium, it contains venous sinuses, while in the vertebral canal, it contains loose connective tissue and veins.
What else to study on this topic
- Method for examining muscle tone in meningeal syndrome
- Topography and clinical significance of subarachnoid space cisterns
- Structural features of capillary endothelium in the blood-brain barrier
- Anatomy of the choroid plexuses (plexus chorioideus) of the lateral ventricles
Master the entire topic in the "Neurology" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Meningeal Syndrome" and 907 more pages of the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 32 video lessons for the subject
Other topics in "Chapter 15. Meningeal and Hypertensive Syndromes, Hydrocephalus"
The entire section "Chapter 15. Meningeal and Hypertensive Syndromes, Hydrocephalus"Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.