Cranial Nerves and Blood Supply to the Brain

Cranial Nerve Testing

  • Cranial Nerve I (Olfactory):
    • Function: Smell
    • Testing Method: Smell various substances.
  • Cranial Nerve II (Optic):
    • Function: Vision
    • Testing Method: Use a hand-held Snellen chart to assess visual acuity.
  • Cranial Nerves III (Oculomotor), IV (Trochlear), & VI (Abducens):
    • Function: Eye movements
    • Testing Method: Draw two large “H” in the air and have the patient follow the movement with their eyes.
  • Cranial Nerve V (Trigeminal):
    • Function: Sensation of the face, Motor to muscles of mastication
    • Testing Method: Clench teeth and palpate masseter and temporalis; stroke face with a cotton ball to test sensation.
  • Cranial Nerve VII (Facial):
    • Function: Facial expression, Taste from anterior 2/3 of the tongue
    • Testing Method: Raise eyebrows, close eyes tightly, puff out cheeks, and show teeth.
  • Cranial Nerve VIII (Vestibulocochlear):
    • Function: Hearing and balance
    • Testing Method: Use a tuning fork on the center of the forehead and mastoid process for auditory testing.
  • Cranial Nerve IX (Glossopharyngeal):
    • Function: Taste from posterior tongue, Motor to pharynx
    • Testing Method: Assess the gag reflex.
  • Cranial Nerve X (Vagus):
    • Function: Parasympathetic control of the heart, lungs, digestive tract
    • Testing Method: Ask the patient to say “ah” and observe the uvula for midline position.
  • Cranial Nerve XI (Accessory):
    • Function: Motor to sternocleidomastoid and trapezius
    • Testing Method: Ask the patient to shrug shoulders and turn head against resistance.
  • Cranial Nerve XII (Hypoglossal):
    • Function: Motor to the tongue
    • Testing Method: Ask the patient to stick out their tongue and observe for midline positioning.

Brain Blood Supply

  • Arterial Supply:
    • Aorta: Major artery that branches from the heart.
    • Brachiocephalic Artery: First branch off the aortic arch, bifurcates into the right common carotid artery.
    • Left Common Carotid Artery: Second branch of the aortic arch, supplies blood to the left side of the head and neck.
    • Internal Carotid Artery:
    • Branches from the common carotid artery.
    • Supplies the cerebrum.
    • Ends in the circle of Willis: anastomosis at the base of the brain, ensuring adequate blood supply.
  • Major Arteries of the Head and Neck:
    • Superficial Temporal Artery
    • Maxillary Artery
    • Occipital Artery
    • Facial Artery
    • Lingual Artery
    • Superior Thyroid Artery
    • Ophthalmic Artery
    • Basilar Artery: Formed by the joining of the vertebral arteries, supplies the brainstem and posterior cerebral circulation.
    • Circle of Willis: An important arterial circle that connects anterior and posterior blood supply to the brain, involving the Anterior Communicating Artery and Posterior Communicating Artery.

Venous Drainage in the Brain

  • Venous Sinuses:
    • Primary drainage systems for blood in the brain, located in the dura mater.
    • Characteristics:
    • Triangular shape, no valves, ultimately empty into the internal jugular veins.
    • Major sinuses include:
    • Superior Sagittal Sinus
    • Inferior Sagittal Sinus
    • Straight Sinus
    • Transverse Sinuses
    • Sigmoid Sinus
  • Veins of the Head and Neck:
    • Include the Internal Jugular Vein, External Jugular Vein, Facial Vein, Ophthalmic Vein, and others.

Cranial Nerve Characteristics

  • Cranial Nerve Features:
    • There are 12 pairs of cranial nerves, primarily serving the head and neck regions.
    • Wrapped in connective tissue:
    • Endoneurium: Surrounds individual axons.
    • Perineurium: Surrounds nerve fascicles.
    • Epineurium: Surrounds the entire nerve.
Specific Cranial Nerves
  1. Olfactory (CN I): Olfaction; originates from nasal mucosa.
  2. Optic (CN II): Vision; originates in the retina of the eye.
  3. Oculomotor (CN III): Motor control to eye muscles; carries parasympathetic fibers to iris.
  4. Trochlear (CN IV): Motor to superior oblique muscle of the eye.
  5. Trigeminal (CN V): Sensory for the face; motor to masticatory muscles.
  6. Abducens (CN VI): Motor to lateral rectus muscle of the eye.
  7. Facial (CN VII): Motor to facial expression muscles; parasympathetic to glands; taste from anterior tongue.
  8. Vestibulocochlear (CN VIII): Hearing and balance; from inner ear sensors.
  9. Glossopharyngeal (CN IX): Motor to pharynx, parasympathetic fibers to parotid gland, and taste/sensation from the posterior tongue.
  10. Vagus (CN X): Controls thoracic and abdominal parasympathetic functions, carrying sensory and taste fibers.
  11. Accessory (CN XI): Motor to sternocleidomastoid and trapezius muscles.
  12. Hypoglossal (CN XII): Motor to the tongue for speech and swallowing.