Central Nervous System (CNS) and Meninges

Central Nervous System (CNS) Overview:

• CNS consists of two main components:
• Brain
• Spinal Cord
• Other components like cranial nerves are not part of the CNS, but part of the Peripheral Nervous System (PNS).

Meninges:

• Protective coverings of the brain and spinal cord known as meninges, composed of three layers:

1. Dura Mater (outermost layer)
2. Arachnoid Mater (middle layer)
3. Pia Mater (innermost layer)

• Meninges provide protection and structural support to the brain and spinal cord.

Dura Mater:

• Also known as the "tough mother"
• Composed of dense, fibrous connective tissue, whitish in appearance.
• Two layers around the brain:
• Periosteal Layer: Closest to the skull (periosteum).
• Meningeal Layer: Inner layer.
• Around the spinal cord, there is only one layer.
• Creates sinuses that collect blood, different from bone sinuses.
• Forms partitions to limit brain movement:
• Falx Cerebri: Separates the two hemispheres of the brain along the longitudinal fissure.
• Tentorium Cerebelli: Separates the cerebrum and cerebellum, resembling a tent.
• Falx Cerebelli: Separates the two hemispheres of the cerebellum.

Subdural Space:

• Tiny space beneath the dura mater with minimal fluid to reduce friction.
• Subdural hematoma refers to bleeding in this space.

Arachnoid Mater:

• Known as the "spider mother" and appears spidery due to its fringes.
• Contains arachnoid villi which protrude into the venous sinuses.
• Subarachnoid Space:
• Space beneath the arachnoid mater filled with cerebrospinal fluid (CSF) that cushions the brain and spinal cord.

Pia Mater:

• The innermost layer that follows the contours of the brain (the "delicate mother").
• Extremely delicate and adheres closely to the brain and spinal cord.
• The pia mater extends from the crista galli of the ethmoid bone to the coccyx, ending at the terminal end known as filum terminale which anchors the spinal cord.

Spinal Cord vs. Brain:

• The pia mater conforms to the contours of the spinal cord, unlike the dura and arachnoid which do not follow all grooves.
• Epidural Space:
• Space that exists around the spinal cord but is almost non-existent around the brain.
• Epidurals are administered in this space, below where the spinal cord ends.

Order of Layers in the Spinal Cord:

• Epidural Space
• Dura Mater
• Subdural Space
• Arachnoid Mater
• Subarachnoid Space (CSF present)
• Pia Mater
• Spinal Cord (located at the bottom)

Next Topic:

• The next module will discuss the ventricles of the brain and their relationship to the spinal cord.