topic 13

Anatomy of the Nervous System: CNS Protection

Overview

  • The central nervous system (CNS) is protected by various structures and fluid to ensure proper function and safety.

Protection of the CNS

  • Skull: Protects the brain through synarthroses (synostosis).

Layers of Meninges

  1. Dura Mater
        - Description: It is a double-layered structure within the brain that acts as a thick fibrous strong sheath covering the CNS.
        - Connections: Anchored to the cranium and vertebral cavity.
        - Special Features:
            - Forms folds (e.g., falx cerebri) to partition the brain.
            - Forms sinuses to drain blood and cerebrospinal fluid (CSF) to the internal jugular vein.
        - Spinal Cord Treatment: There is a single layer surrounding the spinal cord, with an epidural space located between the Dura and vertebrae.

  2. Arachnoid Mater
        - Description: A thin fibrous tissue that forms a loose sac around the CNS, resembling a spider web.
        - Function: Drains CSF into the superior sagittal sinus.

  3. Pia Mater
        - Description: A thin fibrous membrane that closely adheres to the surface of the brain and spinal cord, covering the sulci and gyri.
        - Special Features:
            - Thought to be fluid-impermeable.
            - Forms denticulate ligaments and the filum terminale within the spinal cord.

Ventricles of the Brain

  • Identification of Brain Structures (Refer to Figure 12.5):
        - Lateral Ventricle: Contains anterior and posterior horns and is separated by the septum pellucidum.
        - Third Ventricle: Located between the two halves of the thalamus.
        - Cerebral Aqueduct: Connects the third and fourth ventricles.
        - Fourth Ventricle: Located between the brainstem and cerebellum, leading to:
            - The central canal and lateral apertures.
            - The median aperture.

Cerebrospinal Fluid (CSF)

  • Description: Clear fluid surrounding the CNS.

  • Production: Produced by the choroid plexus.

  • Functions:
        - Buoyancy: Provides buoyancy to the brain, making it feel lighter and receiving protection.
        - Chemical Stability: Regulates the chemical environment within the CNS, containing higher concentrations of Na+ and Cl- compared to blood.

  • Production Rate: 500ml/day, with approximately 2/3 coming from the choroid plexus and 1/3 from the ependymal lining.

  • Pathway: CSF flows through the ventricles and central canal:
        1. Moves from lateral ventricles to third ventricle.
        2. Through cerebral aqueduct into the fourth ventricle.
        3. Then either into the central canal or the subarachnoid space.

Blood Brain Barrier (BBB)

  • Composition: Comprises endothelial cells, basal lamina, and astrocytes.

  • Function: It is selectively permeable, allowing certain substances to pass through, including:
        - H2O
        - Glucose
        - Selected gases
        - Amino acids
        - Caffeine
        - Nicotine

Problems Associated with CNS Protection

  1. Meningitis
        - Type: Can be bacterial or viral.
        - Effect: Affects pia and arachnoid mater, especially in toddlers.
        - Symptoms: Includes fever, stiff neck, headache, drowsiness, rash, and potentially leads to coma.

  2. Hydrocephalus
        - Description: Characterized as "water on the brain" due to excess CSF.
        - Consequences: Increased pressure on the brain leading to head enlargement (particularly in infants) and possibly symptoms like convulsions, tunnel vision, mental disabilities, and death.
        - Treatment: May involve inserting a tube to drain the excess fluid.

  3. Stroke
        - Definition: A loss of brain function caused by ischemia (lack of blood flow) or hemorrhage (bleeding).
        - Symptoms: Typically unilateral and appear suddenly.

Review Questions

  • How many layers of meninges are there?

  • What are the names of the meninges layers?

  • What are some problems we may experience regarding our CNS protection?

What's Up Next?

  • Quiz: Review materials will include checking folios and remembering packbacks.

  • Exam 4: Prepare for upcoming assessments.


  • How many layers of meninges are there?

  • What are the names of the meninges layers?

  • What are some problems we may experience regarding our CNS protection?