Because the brain processes all of the body’s signals, it houses major nerves to collect the information and get it to the proper section of the brain.

There are 12 pairs of major nerves called cranial nerves and serve both sides of the body. All but two pairs—olfactory and optic—arise from the brain stem. These two pairs emerge from the brainstem.

The cranial nerves and their responsibilities include:

  • Olfactory: smell
  • Optic: sight
  • Oculomotor: contraction of eye muscles
  • Trochlear: one muscle of the eye
  • Trigeminal: large sensory nerve of the face and head
  • Abducens: one muscle of the eye
  • Facial: facial expression
  • Vestibulocochlear: hearing and equilibrium of the inner ear
  • Glossopharyngeal: back of tongue, including taste senses, and the sylopharyngeus muscle in the throat
  • Vagus: thoracic and abdominal cavities as well as larynx
  • Accessory: larynx, neck, and lower neck muscles
  • Hypoglossal: muscles of the tongue

The head’s blood supply comes mainly from the external and internal carotid arteries. These are the arteries you use to check your pulse in your neck. Damage to these arteries poses severe, immediate health risks that can be fatal.

The internal carotid artery travels up from the aortic arch just outside the heart. It travels into the brain to provide oxygenated blood to the eyes, the front of the brain, and portions of the scalp.

The external carotid artery helps supply part of the brain through its many branches, and it also gives blood to the thyroid gland in the neck. The thyroid gland is one of the largest endocrine glands in the body. Hormones from the thyroid gland control how quickly the body uses energy, when to make proteins, and how the body responds to other hormones.

Inside the brain, important areas get blood from more than one source, which involves communication between two blood vessels. This is called anastomosis. This process also occurs in the hands, feet, and intestinal tract.

In the brain, a circle consisting to of two carotid arteries and the basilar artery form the circle of Willis. This supplies blood in the center of the brain and branches to the cerebrum, pons, medulla oblongata, cerebellum, and the beginning of the spinal cord. 

Deoxygenated blood leaves the brain and goes back to the heart through veins such as the superficial temporal vein, frontal vein, occipital vein, the anterior facial vein, and others.

The cranial venous sinuses also remove blood from the head. Unlike normal veins, these are large channels that drain blood. They run in various places in the brain, including along the back, through the middle, and through the outermost membrane as well as behind the eyes.