Central Nervous System (CNS) Overview

Central Nervous System Protection

  • Components Protecting CNS:
    • Bones (skull and vertebrae)
    • Meninges
    • Ventricle
    • Blood-brain barrier

Meninges Structure and Function

  • Function of Meninges:
    • Cover and protect CNS
    • Protect blood vessels
    • Enclose venous sinuses
    • Contains cerebrospinal fluid (CSF)
    • Forms partitions in skull
  • Three Layers of Meninges:
    • Dura mater (outer layer)
    • Arachnoid mater (middle layer)
    • Pia mater (innermost layer)

Cerebrospinal Fluid (CSF)

  • CSF Functions:
    • Buoyancy to CNS, reducing brain weight by 97%
    • Protects CNS from trauma
    • Nourishes brain and carries signals
  • Formation and Circulation:
    • Formed in choroid plexus
    • Absorbed via arachnoid granulations into venous blood
    • Normal volume ~150 ml, replaced every 8 hours

Blood-Brain Barrier

  • Purpose:
    • Maintain stable environment for brain
  • Mechanisms of Action:
    • Tight junctions in capillary endothelium
    • Astrocytes and pericytes regulate junction formation
    • Substance movement via diffusion, specific transport, and transcytosis

Spinal Cord Anatomy and Protection

  • Protection Mechanisms:
    • Surrounded by bone, meninges, and CSF
    • Spinal dura mater single-layered
    • Epidural space contains fat and blood vessels
  • Key Features:
    • Conus medullaris (termination of spinal cord)
    • Filum terminale and denticulate ligaments secure the cord

Neuronal Pathways

  • Spinal Tracts:
    • Ascending Pathways:
    • Carry sensory information to the brain (3 neurons involved)
    • Descending Pathways:
    • Carry motor commands from the brain (2 neurons involved)

Brain Injuries and Disorders

  • Traumatic Brain Injuries:
    • Concussion, contusion, hemorrhage, cerebral edema
  • Cerebrovascular Accidents (Strokes):
    • Ischemia leads to tissue death; Transient ischemic attacks noted
  • Degenerative Disorders
    • Alzheimer’s, Parkinson’s, and Huntington’s diseases

Higher Mental Functions

  • Memory Types:
    • Declarative, procedural, motor, and emotional memories
    • Storage stages: Short-term, long-term
  • Language Processing:
    • Broca’s area (speech production), Wernicke’s area (language comprehension)

Sleep and Consciousness

  • Sleep Stages:
    • NREM (4 stages) and REM sleep characteristics
  • Consciousness:
    • Defined by perception, control, and higher processing capabilities

Clinical Considerations:

  • Homeostatic Imbalances:
    • Disorders like narcolepsy, insomnia, and amnesia
    • Developmental issues: cerebral palsy, spina bifida, anencephaly