2. MENINGES
The meninges are three protective membranes that envelop the brain and
spinal cord, collectively known as the central nervous system (CNS). These
layers provide support, cushioning, and protection to the delicate neural
tissues of the CNS. The three layers of the meninges, from outermost to
innermost, are the dura mater, arachnoid mater, and pia mater.
3. DURA MATER
• The dura mater is the outermost layer of the meninges, the protective
membranes surrounding the brain and spinal cord.
• It is situated closest to the skull in the cranial region and closest to the
vertebral canal in the spinal region. It is the toughest and thickest of the
meningeal layers.
• The dura mater is composed of dense irregular connective tissue, primarily
collagen fibers, with scattered fibroblasts and elastic fibers. This
composition gives it its tough and fibrous characteristics.
4. • It consists of two layers:
1. The outer periosteal layer
2. The inner meningeal layer.
Spaces Associated with the Dura Mater:
1. Epidural Space: This space is located between the dura mater and the inner
surface of the skull in the cranial region or the periosteum of the vertebrae in the
spinal region. It contains adipose tissue, blood vessels, and loose connective
tissue.
2. Dural Venous Sinuses: These are large channels formed between the periosteal
and meningeal layers of the dura mater, where blood from the brain drains into
before being returned to the systemic circulation.
5. ARACHNOID MATER
• The arachnoid mater is the middle layer of the meninges, situated between
the dura mater (outer layer) and the pia mater (inner layer).
• It is composed of fibrous tissue, primarily collagen and elastic fibers. It is
thinner and more delicate than the dura mater but thicker than the pia
mater.
Structure:
1. Arachnoid Membrane: The main part of the arachnoid mater is a thin, web-like
membrane that lies directly beneath the dura mater.
6. 2. Arachnoid Trabeculae: Within the subarachnoid space, the
arachnoid mater extends fibrous strands called arachnoid trabeculae.
These trabeculae extend between the arachnoid membrane and the
pia mater and help support and suspend the structures of the CNS
within the cerebrospinal fluid (CSF).
Subarachnoid Space: The space between the arachnoid mater and
the pia mater is known as the subarachnoid space. This space is filled
with cerebrospinal fluid (CSF), which provides cushioning and support
to the brain and spinal cord. The subarachnoid space also contains
blood vessels and the arachnoid trabeculae.
7. PIA MATER
• The pia mater is the innermost layer of the meninges and is in direct contact
with the surface of the brain and spinal cord.
• It is a thin, delicate membrane composed of fibrous connective tissue. It is
highly vascularized and contains numerous blood vessels that supply
nutrients and oxygen to the underlying neural tissues.
• Unlike the dura mater and arachnoid mater, which consist of multiple layers,
the pia mater is a single layer of connective tissue.
8. • It adheres tightly to the surfaces of the brain and spinal cord, following their
contours and extending into the fissures and sulci.
• There are no significant spaces associated with the pia mater. It directly
covers the surfaces of the brain and spinal cord, forming a continuous
barrier between the neural tissues and the surrounding cerebrospinal fluid.
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12. FUNCTIONS OF MENINGES
1.Protection:
1. The meninges provide a physical barrier that protects the delicate
structures of the brain and spinal cord from mechanical trauma, impact,
and injury.
2. They serve as a shock-absorbing cushion, helping to distribute and
dissipate external forces that could potentially damage the CNS.
2.Support:
1. The meninges provide structural support for the brain and spinal cord,
helping to maintain their shape and position within the skull and vertebral
column.
2. They anchor the CNS in place, preventing excessive movement or
displacement during sudden head movements or changes in body
13. 3. Containment:
1. The meninges form a barrier that contains the cerebrospinal fluid (CSF), a clear
fluid that surrounds and bathes the CNS.
2. They help regulate the distribution and flow of CSF, ensuring proper fluid balance
and pressure within the brain and spinal cord.
4. Nutrient Supply:
1. The meninges contain blood vessels that supply oxygen and nutrients to the
underlying neural tissues of the brain and spinal cord.
2. They help regulate blood flow to the CNS, ensuring adequate oxygenation and
metabolic support for optimal neural function.
14. 5. Immune Defense:
1. The meninges play a role in the immune defense of the CNS by serving as a barrier
that prevents the entry of pathogens, toxins, and foreign substances into the brain
and spinal cord.
2. They contain specialized immune cells and signaling molecules that help protect
against infections and inflammatory responses within the CNS.
