Central Nervous System: Spinal Cord & Meninges Study Notes

Central Nervous System Overview

Introduction to the Nervous System

The nervous system is divided into two main components: the Central Nervous System (CNS) and the Peripheral Nervous System (PNS). The CNS consists of the brain and spinal cord, while the PNS includes cranial nerves and spinal nerves.

• Central Nervous System: Brain and spinal cord

• Peripheral Nervous System: Cranial nerves (12 pairs), Spinal nerves (31 pairs)

Spinal Cord & Meninges

Structure of the Spinal Cord

The spinal cord is a cylindrical structure that extends from the base of the brain through the vertebral canal. It is protected by three layers of connective tissue called meninges.

• Pia mater: The innermost layer, closely adherent to the spinal cord and brain, following all surface irregularities.

• Arachnoid mater: The middle layer, forming the subarachnoid space which contains cerebrospinal fluid (CSF).

• Dura mater: The outermost, tough layer providing protection.

Meninges: Structure and Function

The meninges serve to protect the CNS and provide a supportive framework for blood vessels and CSF circulation.

• Pia mater: Thin, vascular layer directly on the CNS surface.

• Arachnoid mater: Web-like, avascular layer; forms subarachnoid space for CSF.

• Dura mater: Dense, fibrous connective tissue; forms dural folds and venous sinuses.

Dural folds (e.g., falx cerebri, tentorium cerebelli) divide the cranial cavity and help stabilize the brain, also housing venous sinuses for blood drainage.

Subarachnoid Space, Ventricles & Cerebrospinal Fluid (CSF)

The subarachnoid space is located between the arachnoid and pia mater and is filled with CSF, which cushions the CNS and removes waste products.

• CSF: Clear fluid produced by the choroid plexus (~500mL/day)

• Functions: Nutrient supply, waste removal, mechanical protection

Spinal Cord Anatomy

The spinal cord is organized into white and gray matter, with distinct regions for sensory and motor functions.

• Dorsal (posterior) side: Sensory input

• Ventral (anterior) side: Motor output

• Gray matter: Contains neuron cell bodies (e.g., anterior horn for motor neurons)

• White matter: Contains ascending (sensory) and descending (motor) tracts

Cauda Equina & Filum Terminale

Below the end of the spinal cord (conus medullaris), nerve roots continue as the cauda equina. The filum terminale is a fibrous extension anchoring the cord to the coccyx.

• Conus medullaris: Tapered end of the spinal cord (typically at L1-L2 in adults)

• Cauda equina: Bundle of lumbar and sacral nerve roots

• Filum terminale: Extension of pia mater anchoring the cord

Specific Features of Vertebrae

Cervical, Thoracic, and Lumbar Vertebrae

Vertebrae are classified by region, each with unique anatomical features.

Region	Features
Cervical (C1, C2, C7 atypical)	Bifid spine, transverse foramen, triangular/wide vertebral canal, small oval body
Thoracic (T1, T10, T11, T12 atypical)	Inferiorly projecting spine, large transverse processes, circular canal, triangular body, rib facets
Lumbar	Small stumpy spine, small transverse processes, small triangular canal, large round body

Ascending and Descending Tracts

Principles of Spinal Cord Tracts

Information travels in the spinal cord via distinct pathways:

• Ascending tracts: Carry sensory information to the brain

• Descending tracts: Carry motor commands from the brain to the body

Example: The dorsal columns transmit fine touch and proprioception, while the corticospinal tract carries voluntary motor signals.

Venous Sinuses and Dural Folds

Sinuses within Dural Folds

Venous sinuses are channels within the dura mater that drain blood from the brain.

Sinus	Location
Superior sagittal sinus	Along the midline, in the falx cerebri
Inferior sagittal sinus	Lower edge of falx cerebri
Straight sinus	Junction of falx cerebri and tentorium cerebelli
Transverse sinus	Along the tentorium cerebelli
Sigmoid sinus	Drains into internal jugular vein

Short Answer Questions (Review)

Sample Questions for Self-Assessment

• At what vertebral level does the spinal cord typically end in adults? L1-L2

• Which area of spinal cord gray matter contains cell bodies of lower motor neurons? Anterior (ventral) horn

• The sympathetic trunk is connected to the spinal cord at which segments? Thoracic and lumbar (T1-L2)

• The denticulate ligament is comprised by which layer of the meninges? Pia mater

• What is the term for the spinal cord's internal space filled by CSF? Central canal

Key Terms and Definitions

• Meninges: Three protective membranes covering the brain and spinal cord

• Subarachnoid space: Area between arachnoid and pia mater containing CSF

• Choroid plexus: Structure producing CSF in the ventricles

• Gray matter: Region of CNS containing neuron cell bodies

• White matter: Region of CNS containing myelinated axons

• Cauda equina: Bundle of nerve roots below the spinal cord

• Filum terminale: Fibrous extension anchoring the spinal cord

Additional info:

• The spinal cord grows more slowly than the vertebral column during development, resulting in its termination at L1-L2 in adults.

• CSF is produced by the choroid plexus and circulates through the ventricles and subarachnoid space, providing mechanical and chemical protection.

• Dural folds (falx cerebri, tentorium cerebelli) are important for compartmentalizing the brain and supporting venous drainage.