Central Nervous System (Brain)

Protection of the CNS

• Brain and spinal cord have a jelly-like consistency in natural state

  • Rare body tissues that lack supportive connective tissue

• Protections of CNS

  • Bony cranium and vertebral column

  • CSF

  • Meninges - 3 connective tissue layers between bone and CNS

Dura Mater

• Dura mater - “tough mother” >>> thick outermost layer

  • Periosteal layer - attached to inner surface of cranium (especially t suture lines)

    • Richly innervated by CN V and meningeal arteries (primary is middle meningeal a.)

    • Follows contours of skull

• Meningeal layer - avascular inner dural layer

  • Attached to underlying arachnoid

  • Continuous with spinal dura

  • Follows contours of skull except:

    • Dural sinus formations

    • Reflections (falx cerebri, tentorium cerebelli, etc)

Venous Drainage of Brain

• Dural venous sinuses - spaces between dura layers at dural reflections >> allow drainage of blood and CSF to internal jugular vv.

Arachnoid Mater

• “Spider-like mother” >> avascular thin membrane

  • Follows contours of meningeal dura

  • Arachnoid trabeculae - thin strands of connective tissue bridging subarachnoid space >> anchor arachnoid to pia mater

  • Arachnoid villi - invaginations into dural sinuses >> used in CSF reabsorption

  • Arachnoid granulations - macroscopic clusters of villi along the dural sinuses

Pia Mater

• “Tender mother” >> thin delicate membrane

  • Adheres to surface of brain and spinal cord

  • Follows contours of gyri and sulci

  • Saran wrap

actual space

a hollow space that is normally present

potential space

location in which no space is normally present but can occur in pathological conditions

Epidural space

• Cranium - potential space between skull and dura mater

• Spine - actual space between the vertebrae and dura mater

Subdural space

potential space between dura and arachnoid in both cranium and spine

subarachnoid space

• actual space between arachnoid and pia in cranium and spine

• contains CSF and cerebral arteries

no space deep to pia

astrocytes tightly adhere to inner surface of pia

ventricles

• elaborations of the developmental neural canal in the adult brain

  • all are interconnected and continuous with central canal of spinal cord AND subarachnoid space

  • Primary function — production and house for cerebrospinal final (CSF)

• Four spaces:

  • Paired lateral ventricles

  • Third ventricle

  • Fourth ventricle

Choroid Plexus

• extension of ventricular walls rich in capillaries

• eppendyma, endothelial cells form selectively permeable barrier to regulate CSF production

Buoyancy

brain floats in CSF >> reduces weight 1400 g → 45 g

• Prevents brain from collapsing under its own weight

• Prevents brain from squashing surrounding neurovasculature

Protection from trauma

cushions and protects brain/spinal cord from traumatic injury

Nutrition

provides nutrients to neurons and glia

Excretion and maintenance of stable environment

regulation of extracellular fluid composition in CNS

• no barrier between CSF and extracellular fluid of CNS

• CSF/ventricles acts like a lymphatic system

• Removes water-soluble cellular wastes which cannot drain into venous blood due to BBB (blood brain barrier)

Chemical communication

transportation biologically active signaling compounds within CNS (hormones, releasing factors, neurotransmitters)