Notes

Cranial nerves: Overview Cranial nerves are the nerves that emerge directly from the brain (mostly from the brainstem), in contrast to spinal nerves (which emerge from segments of the spinal cord). Cranial nerves are generally named according to their structure or function. They usually innervate areas close to where they are originated from. The cranial nerves provide motor and sensory innervation mainly to the structures within the head and neck. The sensory innervation includes sensation such as temperature and touch, and innervation such as taste, vision, smell, balance and hearing. The Vagus Nerve (X) provides sensory and autonomic (parasympathetic) innervation to most of the organs in the chest and abdomen. (It doesn't innervate the head/neck area).

Meninges: Overview

The Meninges are the three membranes that envelop the brain and spinal cord. In mammals, the meninges are the dura mater, the arachnoid mater, and the pia mater. Cerebrospinal fluid is located in the subarachnoid space between the arachnoid mater and the pia mater.

• Dura Mater
  • Leather-like, inflexible layer surrounding the CNS and spinal cord.
  • Inner and outer layers, containing large venous sinuses (large veins that bring the blood back to the heart) (e.g., superior sagittal sinus).
• Arachnoid Mater
  • Loose connective tissue bridging the liquor-filled space (subarachnoidal space) between dura mater and pia mater.
  • Contains all larger blood vessels.
• Pia Mater
  • Translucent, thin membrane directly covering the entire surface of the brain, follows all sulci and gyri.

Ventricles: Overview They are cavities containing fluid.

• Lateral Ventricles (Cerebral Hemispheres)
• 3rd Ventricle (Diencephalon)
• Aequaductus Mesencephali (Mesencephalon)
• 4th Ventricle (Pons, Midbrain)
• Central Canal (Spinal Cord).

Ventricles: Pathologies

• Neurodevelopmental Disorders (e.g., Schizophrenia).
• Neurodegenerative Disorders (e.g., Alzheimer's Disease, AD).

Cerebrospinal Fluid: Overview

• It is a clear fluid, high content of NaCl, contains glucose and K+, low in proteins, very few cells (lymphocytes).
• It does a turnover three times a day.
• It flows throughout the ventricular system ad is absorbed back into the bloodstream (via blood-brain-barrier).

Cerebrospinal Fluid: Main Functions

• Buoyancy: the actual mass of the human brain is approx. 1.5kg, however, the net weight of the brain suspended in the CSF is equivalent to a mass of 25gr. The brain therefore exists in neutral buoyancy, which allows the brain to maintain its density without being impaired by its own weight, which could cut off blood supply.
• Protection: CSF protects the brain tissue from injury when jolted or hit. In addition, it helps regulating intracranial pressure (lowering CSF production can help preventing brain ischemia).
• Homeostasis: through absorption back into the blood stream, CSF can rinse "metabolic waste" from the CNS allowing for a homeostatic regulation of the brain.

Cerebrospinal Fluid: Pathologies Hydrocephalus

• Abnormal accumulation of CSF within the brain.
• Congenital (neurodevelopmental disturbances) or acquired postnatally.
• Most common cause: Aqueductal Stenosis (mesencephalic passage between 3^rd^ and 4^th^ ventricles is blocked or too narrow to allow sufficient cerebral spinal fluid to drain fluid accumulates in the upper ventricles).

Cerebral Circulation The brain is one of the most metabolically active organs in the body!

• It uses approx. 20-25% of the body's total energy requirements (despite accounting for only 2% of the body's mass).
• The brain stores little energy as glycogen and relies mostly on circulating glucose.
• The rate of the cerebral blood flow in the adult is typically 750 milliliters per minute, representing 15% of the cardiac output.

Cerebral Circulation: Arteries Main branches of the internal carotids

• Anterior Cerebral Artery
• Middle Cerebral Artery

Main branches of the vertebral/basilar arteries

• 3 arteries supplying the cerebellum
• Posterior Cerebral Artery.

Cerebral Circulation: Veins