HB

Detailed Anatomical Landmarks of the Brain

Brain Anatomy

Main Brain Regions

  • Cerebrum:
    • The outermost part containing the cortex.
    • Majority of the brain's mass.
    • Features gyri (folds) and sulci (grooves).
  • Diencephalon:
    • Deeper structures: thalamus and hypothalamus.
    • Involved in information transfer and hormonal regulation/homeostatic feedback loops.
  • Cerebellum:
    • Posterior region, meaning "little brain".
    • High neuron density.
  • Brain Stem:
    • Most ancient part.
    • Components: midbrain, pons, and medulla oblongata.
    • Regulates autonomic functions (e.g., respiratory rate).

Hemispheres and Lobes

  • Cerebral Hemispheres:
    • The cerebrum is split into left and right hemispheres by the longitudinal fissure.
    • Connected by the corpus callosum (a mass of axons).
  • Lobes:
    • Frontal Lobe: Anterior (rostral) to the central sulcus.
    • Parietal Lobe: Posterior (caudal) to the central sulcus.
    • Occipital Lobe: At the posterior part of the brain.
    • Temporal Lobe: Located near the ears (not shown in the initial diagrams).
  • Sulci and Gyri:
    • Sulci are grooves (valleys), singular: sulcus.
    • Gyri are folds (hills), singular: gyrus.
    • The central sulcus separates the frontal and parietal lobes.

Cerebral Cortex and Meninges

  • Cerebral Cortex:
    • Surface layer of the cerebrum, consisting of gray matter (cell bodies).
    • Cortex means “bark” in Latin, as in the bark of a tree.
  • Meninges:
    • Protective layers of connective tissue and membranes surrounding the central nervous system (brain and spinal cord).
    • Three layers:
      • Dura Mater: Outermost, tough membrane.
      • Arachnoid Mater: Middle layer, web-like structure.
      • Pia Mater: Innermost layer, adheres directly to brain tissue, following sulci and gyri.
    • Subarachnoid Space: Between pia mater and arachnoid mater; contains blood vessels and cerebrospinal fluid (CSF).

Ventricles and Cerebrospinal Fluid (CSF)

  • Ventricles:
    • Internal chambers within the central nervous system that contain and circulate CSF.
    • Lateral ventricles (left and right) in the cerebral hemispheres.
    • Third ventricle: Single vertical space under the corpus callosum.
    • Cerebral aqueduct: Runs through the midbrain.
    • Fourth ventricle: Chamber between the pons and cerebellum.
    • Central canal of the spinal cord.
  • CSF Production and Circulation:
    • Produced by the choroid plexus within the brain ventricles.
    • Choroid plexus contains ependymal cells.
    • Functions:
      • Removes waste.
      • Provides buoyancy to the brain and spinal cord.
      • Protects from trauma.
      • Nourishes the brain (nutrients, hormones).
  • CSF Flow:
    • Circulates through ventricles, central canal, and around the meninges.
    • Drains at arachnoid granulations in the superior sagittal sinus.

Blood-Brain Barrier

  • Structure:
    • Endothelium of blood vessels with tightly packed cells.
    • Limits entry of substances into the brain.
  • Permeability:
    • Freely permeable to lipid-soluble substances (e.g., alcohol, O2, CO2, nicotine, anesthetics).
    • Water-soluble substances require regulated uptake through endothelial cells.
  • Function:
    • Protects the brain from hazardous chemicals, drugs, and infectious agents.
  • Breaks in the Barrier:
    • Circumventricular organs in the third and fourth ventricles.
    • Allow the brain to monitor glucose concentration, pH, osmolarity, etc., for homeostasis.
  • Importance of Monitoring:
    • Neurons don't store energy; constant glucose supply is crucial.
    • Neurons are susceptible to pH changes.
    • Osmolarity must be tightly regulated to prevent cell swelling.

White and Gray Matter

  • White Matter:
    • Myelinated axons of neurons (white due to lipid-rich myelin).
    • Allows communication between brain regions and between the brain and spinal cord; action potential carrier.
    • Found in deeper tissues of the brain (subcortical) and outer portion of the spinal cord.
  • Gray Matter:
    • Cell bodies and dendrites of neurons (unmyelinated, hence gray).
    • Processes information.
    • Found in the cerebral cortex, cerebellum, brain stem, and inner portion of the spinal cord.
  • Distribution Pattern:
    • Brain: Gray matter (cortex) overlies white matter.
    • Spinal Cord: White matter on the outside, gray matter on the inside.

Tracts in the Central Nervous System

  • Definition:
    • Groups of axons in the central nervous system (analogous to nerves in the peripheral nervous system).
    • Protected by the skull and vertebral column, so they lack the layered structure of peripheral nerves.
  • Types of Tracts:
    • Projection Tracts:
      • Project from the brain to the spinal cord and vice versa.
      • Link ascending (spine to brain) and descending (brain to spine) neurons.
      • Decussation (crossover) point at the pyramids around the brain stem.
    • Commissural Tracts:
      • Cross between hemispheres, linking the left and right sides of the brain.
      • Example: corpus callosum.
    • Association Tracts:
      • Connect lobes and gyri within a hemisphere.
      • Facilitate matching information from different brain regions (e.g., occipital lobe for visual information with temporal and parietal lobes for memory and spatial awareness).