OT104: Topic 7

• Ventricular System


  Communicating system of cavities lined with ependyma and filled with cerebrospinal fluid
• Ventricular System

  • Responsible for the production, transport and removal of CSF
  • Composed of 4 chambers: 2 lateral ventricles, 3rd ventricle (in diencephalon), 4th ventricle (in hindbrain)
• Ventriculus Terminalis (VT)


  5th ventricle present during early development, located at the conus medullaris
• Cerebrospinal Fluid (CSF)


  • Circulates in the surfaces of the brain and spinal cord (in the subarachnoid space)
  • Clear and colorless
  • Produced by the Choroid Plexus
• Functions of CSF

  • Shock absorption
  • Mechanical buoyancy
  • Nourishment/Reserve
  • Metabolite removal
  • Pineal secretion pathway
• • Normal CSF values: 150 mL in circulation, 400-500 mL produced and reabsorbed per day
  • Normal mean pressure: 70-180 mm H2O
• Spinal tap / Lumbar puncture


  • Diagnostic procedure done to collect spinal fluid to check for brain infections and content of fluid
  • Done at L3-L4 or L4-L5, avoiding spinal cord
• CSF Distribution


  1. Choroid Plexus (Lateral ventricles)

  2. Interventricular Foramina (Foramen of Monroe)

  3. Third ventricle

  4. Cerebral aqueduct of Sylvia

  5. Fourth ventricle

  6. Foramen of Luschka and Foramen of Magendie

  7. Subarachnoid space

  8. Arachnoid villi
• Ventricle Areas of the Brain Supplied

  Lateral Ventricle: Cerebral Cortex

  • Anterior horn → Frontal Lobe
  • Posterior horn → Occipital Lobe
  • Inferior horn → Temporal Lobe

  3rd Ventricle: Diencephalon

  4th Ventricle: Brainstem and Cerebellum
• CSF Absorption


  • Absorbed by the Arachnoid Villi and resorbed into the Dural Venous Sinuses
  • Initiated when CSF pressure exceeds venous sinus pressure
• Blood-Brain and Blood-CSF Barriers

  • Consists of: Blood–CSF barrier, Vascular–endothelial barrier, Arachnoid barrier
  • Isolates the nervous system from the blood supply to prevent poisonous or toxic substances from entering the brain
  • Permeable to: water, gas, electrolytes and glucose
  • Impermeable to: proteins and large organic molecules
  • More permeable in children than adults:

  Bilirubin → Brain damage in premature children

  Alcohol → Cerebellar damage
• Common Causes of Conditions

  • Infection
  • Obstruction / Stenosis
  • Herniation
  • Overproduction of CSF
  • Under-absorption and over-absorption of CSF
• Hydrocephalus


  Abnormal buildup of CSF volume in the ventricles

  • Communicating: (-) Obstruction in the brain; Overproduction or under-absorption
  • Non-communicating: (+) Obstruction in the brain:

  1. Cerebral aqueduct
  2. Interventricular foramen
  3. Foramen of Magendie (median) and Luschka (lateral)

  • Normal Pressure: Often caused by tumor, head injury, hemorrhage, infection or inflammation; No increase in ICP but with increase in CSF
  • Hydrocephalus Ex-Vacuo: Often in degenerative conditions and brain damage; Ventricles enlarge as a compensatory action
• Papilledema


  Swelling of the optic disc due to elevated intracranial pressure, leading to blindness or optic atrophy
• Vascular System: Arterial System

  Receives 18% of the total blood from the heart

  Uses 20% of the oxygen absorbed in the lungs

  • 10-180 seconds of oxygen loss - Loss of consciousness
  • 60 seconds of oxygen loss - Brain cells start dying
  • 3 minutes of oxygen loss - Neurons get extensively damages, lasting brain damage becomes more likely
  • 5 minutes of oxygen - loss Imminent death
• Circle of Willis


  Hexagonal network of arteries at the base of the brain that gives rise to all major cerebral arteries

  • Anterior Cerebral Artery
  • Anterior Communicating Artery
  • Internal Carotid Artery
  • Posterior Communicating Artery
  • Posterior Cerebral Artery
• Four Principal Arteries


  2 Internal Carotid Arteries (ICA)

  • Anterior circulation
  • Receive and supplies 80% of blood
  • Begin at the bifurcation of the common carotid artery

  2 Vertebral Arteries

  • Posterior circulation
  • Receive and supplies the remaining 20% of blood
  • Begin at the bifurcation of the subclavian arteries
• Anterior Circulation


  Pathway: Common Carotid Artery -> Internal Carotid Artery -> Ophthalmic Artery, Anterior Cerebral Artery, Middle Cerebral Artery, Posterior Communicating Artery, and Anterior Choroidal Artery
• ICA Branches and Areas Supplied

  • Ophthalmic Artery: Eyes, orbital structures, frontal scalp area, ethmoid & frontal sinuses, dorsum of nose
  • Anterior Cerebral Artery: Medial aspect of hemispheres, anterior frontal lobe, basal ganglia
  • Middle Cerebral Artery: Lateral aspect of hemisphere (except occipital lobe), basal ganglia
  • Anterior Choroidal Artery: Choroid plexus
• Cerebrovascular Accident (CVA) / Stroke

  Concepts to consider upon blood flow disruption:

  • Hemisphere location of disruption
  • Functions of the areas supplied

  
  

  • Cerebrum → C/L affectations
  • Cerebellum → I/L affectations
• Anterior Cerebral Artery


  • Involved in asymptomatic stroke (because there's a communicating artery)
• Middle Cerebral Artery


  • Largest and terminal branch; most commonly occluded in stroke patients
• Ophthalmic Artery


  Supplies eyes, other orbital structures, frontal scalp area, ethmoid & frontal sinuses, dorsum of nose
• Anterior Cerebral Artery (ACA)


  Supplies medial aspect of hemispheres, anterior frontal lobe, basal ganglia
• Middle Cerebral Artery (MCA)


  Supplies lateral aspect of hemisphere (except occipital lobe), basal ganglia
• Anterior Choroidal Artery (AChA)


  Supplies choroid plexus
• Anterior Cerebral Artery Lesion

  • LE > UE affected, contralateral hemiplegia, contralateral hemianesthesia, head or eye turning towards lesion, grasp reflex, paratonia (Gegenhalten Syndrome), disconnection apraxia, akinetic mutism (Abulia), personality changes, apathy, urinary incontinence, gait apraxia
• Middle Cerebral Artery Lesion

  • UE > LE affected, contralateral hemiplegia, contralateral hemianesthesia, contralateral homonymous hemianopsia, head or eye turning towards lesions, dysphagia, aprosody, neglect, aphasia (if left hemisphere affected), visual perceptual deficits (if right hemisphere affected)
• Posterior Circulation


  Pathway: Subclavian Artery → Vertebral Artery (VA) → PICA, AICA, SCA, PCA, Anterior Spinal Artery, and Pontine Artery
• Vertebral Artery Branches

  • Posterior Inferior Cerebellar Artery
  • Anterior Spinal Artery
  • Anterior Inferior Cerebellar Artery
• Basilar Artery Branches

  • Pontine Arteries
  • Superior Cerebellar Artery
• Posterior Cerebral Artery Branch

  Posterior Communicating Artery
• PICA


  Supplies posterior inferior quarter of cerebellum, medulla oblongata
• AICA


  Supplies anterior inferior quarter of cerebellum, inferior pons
• Basilar and Pontine Arteries


  Supply thalamus, midbrain, pons, medulla oblongata
• Superior Cerebellar Artery


  Supplies superior half of cerebellum, superior pons, midbrain
• Posterior Cerebral Artery


  Supplies occipital lobe, lower temporal lobe, lateral and Third ventricles, thalamus, midbrain
• Areas supplied by MCA and ACA


  • Corpus Striatum and Internal Capsule
• Areas supplied by PCA, Basilar A., Posterior Comm. A.


  • Thalamus
• Areas supplied by PCA, SCA, Basilar A.

  • Midbrain