Surrounding the brain and spinal cord are three layers of protective tissue, collectively called the meninges. Meninges are a necessary cushion between these vital organs and the cranium (or skull) and vertebrae (spine). They also prevent cerebrospinal fluid (CSF), the clear fluid the brain and spinal cord sit in, from leaking, while providing structural support for important blood vessels and nerves.
Given their critical role, it’s little wonder that anatomical variations and health issues in the meninges can have a serious impact. Birth defects, such as spina bifida and anencephaly, as well as infection (meningitis) and bleeding (as in cerebral hematoma or hemorrhage), can lead to chronic disability or become fatal.
Anatomy
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Location
Broadly speaking, the meninges, though completely interconnected, are identified by the part of the body these membranes cover. The portion that surrounds the brain is the cranial meninges. The spinal meninges, as the name suggests, surrounding the spinal cord.
Spinal meninges also encase the cauda equina, the bundle of nerves and nerve roots at the base of the spine. This includes nerves corresponding to lumbar (low back) vertebrae, as well as the sacrum (the bony, triangular structure at the base of the spine).
Structure
Both cranial and spinal meninges are broken down into three layers, with the inner two collectively referred to as the leptomeninges:
- Outermost (dura mater): Also known as the pachymeninx or dura mater, the outermost layer is tough and fibrous. The cranial dura mater is, itself, composed of two layers: the periosteal cranial dura on the outside, and the meningeal covering the middle layers. In the spine, it consists only of a meningeal layer.
- Middle layers (arachnoid): Resembling spider webs, the arachnoid or middle layers of the meninges project arachnoid trabeculae, which are strands of connective tissue to the innermost layer. This is membrane is marked by granulations, which are protrusions at areas of contact with the outermost layer. Unlike the innermost layer, the cranial middle layers straddle the edges of the cortical sulci, or depressions in the brain.
- Innermost (pia mater): The pia mater, or innermost membrane, follows the shape of the brain, and lines the spine. It consists of two layers: the outer (epipial) and inner (intima pia). The outer layer has stiffer fibers that support vessels that pass through the space between the innermost and middle layers. The pia intima is more elastic and attaches to the outer parts of the brain and spinal cord.
In places, the meningeal layers are separated by gaps, and there also are spaces between the surrounding bone, as well as the enveloped brain and spinal cord. These important anatomical features are:
- Epidural space: Separating the dura mater and the bones and tissues surrounding it is the epidural space. The cranial epidural space separates the inside of the skull and the outermost layer, whereas in the spine, additional tissues line the area.
- Subdural space: Beneath the outermost layer, and above the middle layers, you find the subdural space, which is continuous between spinal and cranial meninges. It’s a thin layer, with some suggesting it’s filled with fluid.
- Subarachnoid space: The innermost layer of the meninges is separated from the surface of the brain and spinal cord by the subarachnoid space. Filled with cerebrospinal fluid (CSF), it allows major blood vessels to pass. In areas where the innermost layer completely separates from the middle layers, it has projections called cisterns.
Nerve and Blood Supply
The cranial meninges primarily receive blood from by the middle meningeal artery (MMA), which is a branch of the internal carotid artery, which progresses up the neck. On each side, the MMA enters the skull through an opening in its side called the foramen spinosum and continues through the epidural space.
At the same opening—and running alongside the MMA—is the meningeal branch of the mandibular nerve. Its two branches transmit signaling between the outermost meningeal layer and the brain, with its anterior branch communicating with the meningeal branch of the maxillary nerve.
Blood supply for the spinal meninges comes from a single anterior artery, as well as two paired posterior spinal arteries. Branches of the vertebral arteries, they arise at the base of the neck and take an upward course.
Anatomical Variations
As with all parts of the body, the meninges can be significantly impacted by genetic mutations. These coding errors lead to neural tube defects, in which the meninges never fully forms. These potentially very severe diseases of the meninges include:
- Spina bifida: This condition occurs when a part of the neural tube surrounding the spine—including the meninges—never forms completely. Without adequate protection, spinal fluid-filled sacs form and even stick out from the spine. Especially in its most severe form, myelomeningocele, spina bifida can lead to skin problems, paralysis, neurological issues, incontinence, and learning disabilities, among other symptoms.
- Anencephaly: This is another neural tube defect. It affects the development of the brain, skull, spine, and spinal cord in the embryo. Because the meninges never fully form while the fetus is still in the womb, developing neurons degenerate and die. As a result, those born with anencephaly lack significant portions of the brain, including those involved with thinking, hearing, vision, emotion, and movement. Bones of the skull may be malformed or missing.
- Encephalocele: This is a rare condition. During the third and fourth weeks of pregnancy, malformation of the neural tube causes babies to be born with parts of the brain, meninges, or sacs of CSF poking through an opening in the skull. This sac usually protrudes from the back of the head but is able to emerge from anywhere along its centerline. Encephalocele can cause a range of symptoms, including developmental delays, seizures, microcephaly (a skull that is too small), intellectual disabilities, vision problems, and many others.
Function
The primary task of the meninges is to provide protection and support for the brain and spine. This involves:
- Structural support: The tough meningeal membranes in the spine help attach it to the surrounding spinal column, keeping the spinal cord in position and appropriately shaped. This is done by fibrous projections from the inner layer (pia), called denticulate ligaments, which pass through the middle layers and attach to the outer layer.
- Nutrition support: The subarachnoid space—between the middle and inner layers—contains CSF, which is necessary for providing the brain and spinal cord with nutrition and removing waste.
- Protection: In providing space for CSF to flow—essentially keeping your brain and spine covered in a liquid that cushions impact—the meningeal layers help protect the central nervous system. The inner layer of the cerebral meninges serves to keep vessels separate from neural tissues. This forms an essential part of the blood-brain barrier. This structure works to prevent infections or pathogens from accessing the brain.
Associated Conditions
When the health of the meninges is affected, the consequences can be severe. This part of the body can be affected by bleeds and blood circulation problems, infections, and cancer, among other medical conditions. Skull or spinal fracture can also significantly damage these membranes and warrants medical attention.
Hemorrhage and Hematoma
Two closely related types of blood circulation issues that affect the meninges are hemorrhage and , hematoma. A hemorrhage occurs when there is bleeding in the brain or spine. Hematoma is a complication of a hemorrhage, where blood pools outside of blood vessels. These potentially serious bleeding problems may arise due to trauma, bone fracture, or other health conditions.
These intracranial bleeding problems are dangerous because they raise intracranial pressure (ICP), or blood pressure within the skull, which can damage the brain. These issues are categorized based on the meningeal space being affected.
Here’s a quick breakdown:
- Epidural hematoma arises when bleeding in the arteries or veins, often the MMA, causes blood to fill in the epidural space between the outer layer and the skull.It’s often associated with blunt trauma to the head or skull fracture.
- Subdural hematoma occurs when there’s bleeding in the subdural space due to tearing and hemorrhage in a blood vessel, usually a vein. A type of traumatic brain injury (TBI), it occurs in about 25% of cases of blunt trauma. This bleeding can be slow and gradual or very rapid, with the latter being a medical emergency.
- Subarachnoid hematoma is pooling of blood due to bleeding in the subarachnoid space. This can arise due to trauma or can occur due to spontaneous ruptures at weak points in vessels. This condition is often associated with cases of brain aneurysm, in which a cerebral artery (which brings oxygen from the heart to the brain) balloons or even bursts due to structural insufficiency.
- Intraparenchymal hematoma, sometimes called intracerebral hemorrhage or hematoma, is caused by bleeding in the parenchyma. This potentially fatal condition can also cause impairment of cognitive ability.
Infection
Infection of the meninges, known as meningitis, leads to inflammation of these membranes, causing a range of significant and dangerous health effects. Meningitis is classified based on what’s causing these issues:
- Bacterial meningitis: Several types of bacteria, including two strains of streptococcus and Neisseria meningitides, can be spread and infect the meninges. Associated with sepsis (bacterial infection of the blood), inflammation due to this condition can be fatal or lead to permanent disability.
- Viral meningitis: Infection of the meninges can also occur due to non-polio enteroviruses, as well as others, including viruses that cause mumps, measles, herpes, and influenza (the flu), among others. This type tends to be milder than bacterial meningitis, with most able to recover on their own.
- Fungal meningitis: Meningitis due to fungal infection is very rare but arises when spores of cryptococcus, histoplasma, Blastomyces, or coccidioide are breathed in. Another fungus that lives in the body, candida, can also enter the bloodstream and infect the meninges.
- Parasitic and amebic meningitis: When certain infectious parasites, as found in infected eggs, produce, freshwater fish, poultry, among other foods, are ingested, noncommunicable parasitic meningitis arises. Another cause is brain infection with Naegleria fowler, a tiny amoeba, invisible to the human eyes, that lives warmer, fresh waters. Both of these types of meningitis are seldomly reported in the US.
- Non-infectious meningitis: Cancers, autoimmune disorders like lupus, and some medications (including non-steroidal anti-inflammatory drugs (NSAIDs), certain antibiotics, immunosuppressant drugs, and others) can also cause meningitis. This condition may also arise following head injury and brain surgery, which is why these patients are closely monitored during recovery.
Cancer and the Meninges
When cancer cells spread to the meninges, tumors, called meningiomas, form. The majority of these are actually benign; however, depending on their location and the activity of the cancer cells, these can be dangerous and fatal, or malignant.
Tests
Many factors determine the specific approach to clinical testing and diagnosis of meningeal health conditions. Doctors may need to figure out the root causes of any infection or inflammation, assess the extent of congenital malformation, or take on hematoma and bleeding. Luckily, there are many tests and examinations they can use, including:
- Physical and neurological exams entail testing vision, balance, coordination, and cognitive function, as well as blood pressure and other vital checks. Doctors also assess medications you’re taking, lifestyle factors, as well as any family history of problems.
- Imaging, such as magnetic resonance imaging (MRI) or computerized tomography (CT or CAT) scanning may be used to let doctors identify the hematoma or hemorrhage or assess the scope ofdamage or bleeding.
- Blood or CSF tests help doctors diagnoses causes of meningitis. Small samples of these fluids are taken to a lab to isolate the bacteria, virus, fungus, or other cause of the infection.
- Maternal blood alpha fetoprotein (MSAF) screening is performed at 16 to 18 weeks of pregnancy. This detects the presence of the alpha-fetoprotein (AFP) in fetuses or embryo’s blood or amniotic fluid (amniocentesis), which can be signs of spina bifida.
- Ultrasound or other imaging techniques are used during pregnancy to assess any congenital malformations of the neural tube due to spina bifida or other inborn conditions. This is especially indicated if AFP levels are higher.
- Genetic testing is considered when neural tube defects are detected. Though environmental factors are always relevant, mutations in certain genes can lead to spina bifida, among other congenital disorders. Samples of fetal or parental blood are clinically tested.
A Word From Verywell
There’s no doubt that the health of the meninges is closely associated with overall wellness. These layers are tasked with the essential job of protecting and nourishing the brain and spine. No doubt the burden due to congenital conditions, infections, injuries, or other disorders of these crucial membranes can be heavy.
But as researchers learn more about causes and effects of meningeal problems, and as doctors develop even better treatment approaches, prognoses and outlook for those suffering with them will continue improve. Management of conditions impacting the meninges requires the help of dedicated medical staff, as well as the support of family, friends and loved ones.
If you’re concerned about meningitis, congenital issues during pregnancy, or other issues impacting this crucial part of the body, be sure to talk to your doctor.
Congenital Conditions and Diseases
FAQs
How do meninges protect the nervous system? ›
What do the meninges do? The meninges: Protect your CNS (central nervous system) from trauma injury to your brain, such as a blow to your head by acting as a shock absorber. They anchor your CNS and keep your brain from moving around within your skull.
What are the meninges of the nervous system and what are their functions? ›Three layers of membranes known as meninges protect the brain and spinal cord. The delicate inner layer is the pia mater. The middle layer is the arachnoid, a web-like structure filled with fluid that cushions the brain. The tough outer layer is called the dura mater.
Are the meninges part of the nervous system? ›The meninges are the fibrous covering of the central nervous system (CNS) which contain vastly heterogeneous cell types within its three layers (dura, arachnoid, and pia).
Where do the meninges that protect and support the brain attach? ›From superficial to deep, the meningeal layers are the dura mater, arachnoid mater and pia mater. The dura mater is a thick fibrous layer and a strong protective sheath over the entire brain. It is anchored to the inner surface of the cranium and vertebral cavity.
What part of the nervous system protects the brain? ›The meninges support and protect the brain. A clear fluid called cerebrospinal fluid runs between the meninges. The cerebrospinal fluid, or CSF, is made by tissue that lines the brain ventricles. The CSF flows in and around the brain and the spinal cord.
What are the 3 main functions of the meninges? ›The meninges are layers of tissue that surround the brain and spinal cord. They function to protect the nervous system, to hold it in place, to produce cerebrospinal fluid, and to provide a passageway for fluids, nerves, and vessels.
What is the nervous supply of meninges? ›The meninges primarily receives innervation by the vagus and trigeminal nerves, with some cervical spinal nerves contributing to a lesser degree.
Which of the following is a main function of the nervous system? ›The nervous system helps all the parts of the body to communicate with each other. It also reacts to changes both outside and inside the body. The nervous system uses both electrical and chemical means to send and receive messages.
What's the meaning of meninges? ›(meh-NIN-jeez) The three thin layers of tissue that cover and protect the brain and spinal cord.
Where are the meninges in the brain? ›The meninges are the three membranes that envelop the brain and spinal cord and separate them from the walls of their bony cases (skull and vertebral column). Based on their location, meninges are referred to as the cranial meninges which envelop the brain, and spinal meninges which envelop the spinal cord.
What is the function of the meninges immune system? ›
Meningeal immunity is not only involved in the normal physiological functions of the brain but also plays a role in immune surveillance to determine whether the immune effector response is required to address the existence of pathogens or the occurrence of tissue damage.
Which of the meninges is closest to the nervous tissue of the central nervous system? ›The pia mater is the innermost layer of meninges. This thin, delicate membrane is tightly bound to the surface of the brain and spinal cord and cannot be dissected away without damaging the surface.
What is the function of the meninges quizlet? ›The primary function of the meninges and of the cerebrospinal fluid is to protect the central nervous system. The pia mater is the meningeal envelope that firmly adheres to the surface of the brain and spinal cord.
How do the meninges CSF and blood brain barrier protect the central nervous system? ›The meninges help anchor the brain and spinal cord to the bones, keeping them in place. This prevents any unnecessary movements that may damage the brain. The central nervous system is also filled with a liquid called the cerebrospinal fluid (CSF).
Which is a part of the meninges membranes that cover and protect the brain attach to the Crista Galli? ›The dura mater is the thickest and most superficial membranous layer of the meninges. It forms the falx cerebri, which separates the left and right cerebral hemispheres like a curtain. The falx cerebri is attached anteriorly to the crista galli of the ethmoid bone, so the correct answer is a) Crista galli .
What are the 4 main functions of the nervous system? ›- Control of body's internal environment to maintain 'homeostasis' An example of this is the regulation of body temperature. ...
- Programming of spinal cord reflexes. An example of this is the stretch reflex. ...
- Memory and learning. ...
- Voluntary control of movement.
Recap. The CNS is protected by structures including the skull, spinal vertebrae, meninges, and cerebrospinal fluid.
What is the brain and the nervous system? ›The brain is a complex organ that controls thought, memory, emotion, touch, motor skills, vision, breathing, temperature, hunger and every process that regulates our body. Together, the brain and spinal cord that extends from it make up the central nervous system, or CNS.
What happens if the meninges are damaged? ›The meninges are a collection of membranes that line the central nervous system and help protect brain and spinal cord tissue from various forms of injury. Damage to the meninges can cause cell death in underlying brain tissue.
What is the function of meninges in biology? ›The meninges provide a protective cover to the underlying soft neural tissue of the brain and the spinal cord. Furthermore, they attach the CNS parenchyma to the bony skull or the vertebral column. The meninges also contain space through which cerebrospinal fluid (CSF) travels around CNS.
Which bone protect the brain? ›
The skull is anterior to the spinal column and is the bony structure that encases the brain. Its purpose is to protect the brain and allow attachments for the facial muscles.
Do the meninges have blood supply? ›The blood supply of the meninges generally concerns the blood supply of the outer layer of dura mater rather than the inner layer of dura mater, arachnoid or pia mater which do not require a large blood supply. There are several arteries that supply the dura in the anterior, middle, and posterior cranial fossae 1,2.
What does the meningeal branch supply? ›The meningeal branches supply nerve function to the vertebrae themselves, including the ligaments, dura, blood vessels, intervertebral discs, facet joints, and periosteum. The rami communicantes contain autonomic nerves that carry visceral motor and sensory information to and from the visceral organs.
What is the main blood supply to the meninges? ›Arterial Supply
The largest meningeal artery is the middle meningeal artery, which is a branch of the maxillary artery that arises from the external carotid artery and provides the major blood supply to the dura mater. This artery enters the skull via the foramen spinosum (sphenoid bone).
The nervous system is involved in receiving information about the environment around us (sensation) and generating responses to that information (motor responses). The nervous system can be divided into regions that are responsible for sensation (sensory functions) and for the response (motor functions).
What are the two main parts of the nervous system? ›The body's nervous system is made up of two major parts, the central nervous system, and the peripheral nervous system.
What are the three main parts of the nervous system? ›The human nervous system is made up of three basic parts: the central nervous system, the peripheral nervous system, and the autonomic nervous system.
What causes brain meninges? ›Viral infections are the most common cause of meningitis. That's followed by bacterial infections and, rarely, fungal and parasitic infections. Because bacterial infections can lead to death, learning the cause is essential.
What are the benefits of meninges? ›Together, your meninges stabilize your brain, protect sensitive areas, and give support to nerves, blood vessels, lymphatics, and the cerebrospinal fluid found in your central nervous system.
What is meninges of the brain disease? ›Meningitis is an inflammation (swelling) of the protective membranes covering the brain and spinal cord. A bacterial or viral infection of the fluid surrounding the brain and spinal cord usually causes the swelling. However, injuries, cancer, certain drugs, and other types of infections also can cause meningitis.
Which of the meninges is the strongest? ›
[1] The dura mater is the strongest of the three layers, with some animal studies showing that the thickness of the dura decreases as it descends towards the coccyx.
Do meninges feel pain? ›Answer: There are no pain receptors in the brain itself. But he meninges (coverings around the brain), periosteum (coverings on the bones), and the scalp all have pain receptors.
Are the meninges part of the blood brain barrier? ›The meninges reside in the space between the skull and the brain parenchyma's glial limitans, the outer layer of the blood–brain barrier.
Does meninges nourish the brain? ›The primary functions of the meninges and of the cerebrospinal fluid (produced in and circulating in the meninges) is to protect, cushion, nourish, and support the brain and spinal cord.
How does meningitis avoid the immune system? ›Meningitis-Causing Bacteria May Evade Our Immune System by Sensing Fever.
Which layer of the meninges is connected to the brain? ›The arachnoid is a meningeal layer adherent to the inner surface of the dura. The innermost meningeal layer is a very thin layer of cells called the pia mater. Unlike the arachnoid, the pia is closely adherent to the surface of the brain and follows into the depths of the sulci.
Which layer of cells forms the brain and nervous system? ›The ectoderm is also sub-specialized to form the (2) neural ectoderm, which gives rise to the neural tube and neural crest, which subsequently give rise to the brain, spinal cord, and peripheral nerves.
What type of tissue is the meninges? ›It is the meningeal envelope that firmly adheres to the surfaces of the brain and spinal cord, following all of the brain's contours (gyri and sulci). It is a very thin membrane composed of fibrous tissue covered on its outer surface by a sheet of flat cells thought to be impermeable to fluid.
What is the function of the spinal meninges of the spinal cord? ›The principal function of the spinal meninges is to protect and support the spinal cord.
Which spinal nerve root carry sensory nerve signals? ›The spinal ganglia or posterior or dorsal root ganglia associated with the spinal nerves contain the unipolar neurons of the sensory nerve fibers that carry signals to the cord.
Which layer of the meninges is connected to the brain quizlet? ›
The pia mater is the innermost of the cranial meninges. It is a thin layer of delicate areolar connective tissue that tightly adheres to the brain and follows every contour of the brain surface. Arachnoid trabeculae.
How does the nervous system protect the brain and spinal cord? ›They are coated in myelin, which is a fatty insulation. The brain and spinal cord are protected from damage by a clear liquid called cerebrospinal fluid, 3 layers of membranes called the meninges, and the hard bones of the skull and backbone.
What is the importance of the blood-brain barrier How does it protect the brain from toxins and harmful chemicals? ›The blood-brain barrier (BBB) is the specialized system of brain microvascular endothelial cells (BMVEC) that shields the brain from toxic substances in the blood, supplies brain tissues with nutrients, and filters harmful compounds from the brain back to the bloodstream.
Which support cells of the nervous system maintain the blood-brain barrier? ›The blood-brain barrier (BBB) is maintained by glial cells, including astrocytes.
What do the structures called the meninges and the cerebrospinal fluid help to protect? ›The primary function of the meninges and of the cerebrospinal fluid is to protect the central nervous system. The pia mater is the meningeal envelope that firmly adheres to the surface of the brain and spinal cord.
What is the name of the protective membranes that cover the spinal cord and brain? ›Meninges are formed by three tissue membranes that are primarily known as wrappers of the brain. They consist of dura mater, arachnoid and pia mater.
What structure forms the cerebrospinal fluid? ›Cerebrospinal fluid is made by tissue called the choroid plexus in the ventricles (hollow spaces) in the brain. Also called CSF.
How does CSF protect the central nervous system? ›CSF provides hydromechanical protection of the neuroaxis through two mechanisms. First, CSF acts as a shock absorber, cushioning the brain against the skull. Second, CSF allows the brain and spinal cord to become buoyant, reducing the effective weight of the brain from its normal 1,500 grams to a much lesser 50 grams.
What protects the spinal cord in the nervous system? ›The spinal cord is protected by bones, discs, ligaments, and muscles. The spine is made of 33 bones called vertebrae. The spinal cord passes through a hole in the center (called the spinal canal) of each vertebra. Between the vertebrae there are discs that act as cushions, or shock absorbers for the spine.
What is the immune function of meninges? ›Meningeal immunity is not only involved in the normal physiological functions of the brain but also plays a role in immune surveillance to determine whether the immune effector response is required to address the existence of pathogens or the occurrence of tissue damage.
What nerves supply the meninges surrounding the brain? ›
The meninges primarily receives innervation by the vagus and trigeminal nerves, with some cervical spinal nerves contributing to a lesser degree.
What fluid functions to protect the brain and nervous system? ›The fluid that flows in and around the hollow spaces of the brain and spinal cord, and between two of the meninges (the thin layers of tissue that cover and protect the brain and spinal cord).
What is the meninges and blood-brain barrier? ›Whereas the skull, meninges and cerebrospinal fluid protect against physical damage, the blood–brain barrier provides a defence against disease-causing pathogens and toxins that may be present in our blood.
What is cerebrospinal fluid most likely to protect the brain from damage from? ›The CSF supports the weight of the brain estimated at 1500 gm and suspends it in neutral buoyancy to a net weight of about 25 gm. Hence, the entire brain density is cushioned, protecting it from crushing into the bony cranium. It protects the brain from damage during head trauma.
What does CSF protect the brain and spinal cord from? ›Cerebrospinal fluid acts like a cushion that helps protect your brain and spinal cord from sudden impact or injury. The fluid also removes waste products from the brain and helps your central nervous system work properly.
What are the 5 ways the CSF protects? ›CSF serves five primary purposes: buoyancy, protection, chemical stability, waste removal, and prevention of brain ischemia.
What part of the central nervous system is protected by your backbone? ›The spinal cord is made up of bundles of nerve fibers. It runs down from the brain through a canal in the center of the bones of the spine. These bones protect the spinal cord.
What bone protects the brain? ›The Skull. The skull is made up of 22 bones: the cranium includes eight bones that surround and protect the brain and 14 bones that form the face. In adults, all but one of the skull bones are fused together by immovable joints called sutures.
How does meningitis enter the brain? ›The bacteria or infective organism spreads through the blood. They reach the meninges by one of two main routes: through the bloodstream or through direct contact between the meninges and either the nasal cavity or the skin. The infection begins in one part of the body – e.g. throat or lungs and spreads to the brain.
What does meningitis do to the covering of the brain? ›Meningitis is an inflammation (swelling) of the protective membranes covering the brain and spinal cord. A bacterial or viral infection of the fluid surrounding the brain and spinal cord usually causes the swelling.