chp14 pt1

Central Nervous System

Directional Terminology

  • Rostral: Defined as toward the forehead.
  • Caudal: Defined as toward the spinal cord.

Anatomical Features of the Brain

  • Longitudinal Fissure: A deep groove that separates the cerebral hemispheres (the right and left sides of the brain).
  • Gyri: Ridges present on the surface of the brain.
  • Sulci: Dips or shallow grooves on the brain's surface.
  • Corpus Callosum: A specialized structure that links the right and left sides of the brain.

Major Parts of the Brain

  • Cerebrum:
    • Also known as the cerebral hemispheres; it constitutes the bulk of the brain and is responsible for conscious control and thought.
    • Often referenced in common terminology when discussing the brain.
  • Cerebellum:
    • The second-largest brain structure, making up about 50% of all neurons (approximately 10% of the brain's volume).
    • Located at the posterior portion of the brain.
  • Brain Stem:
    • Comprised of major structures: diencephalon, midbrain, pons, and medulla oblongata.

Brain Surface Anatomy

  • Frontal Lobe: Separated from the parietal lobe by the frontal sulcus.
  • Parietal Lobe: Located posterior to the frontal lobe.
  • Occipital Lobe: Located at the back of the cerebral hemispheres.
  • Temporal Lobe: Located under the temporal bone of the skull.
  • Insula: A lobe behind the temporal lobe not visible unless the temporal lobe is pulled down.

Functional Organization of the Brain

  • Cerebral Hemispheres: Focus on conscious thought processes. Everything else managed is involuntary control.

Neuron and Matter in Central Nervous System (CNS)

  • Gray Matter:
    • Predominantly composed of neuron cell bodies.
    • Some instances of unmyelinated axons.
    • Represents the areas of processing (information sent and received).
  • White Matter:
    • Mostly consists of myelinated axons, contributing to fast signal transmission.
    • Myelin is the substance giving a whitish color to these areas.

Development of the Nervous System

  • Originates from the ectoderm, the outermost germ layer during embryonic development.
    • Formation includes:
    • The thickening of the dorsal midline to form a neural plate.
    • The plate sinks and forms neural folds that fuse to create a neural tube (the precursor to the spinal cord and brain).
  • The tube expands at the anterior end, yielding the brain regions:
    • Forebrain
    • Midbrain
    • Hindbrain
    • Extends into the spinal cord.

Ventricles of the Brain

  • Ventricles: Cavities or empty spaces within the brain developed during the formation of the neural tube.
    • Lined with ependymal cells.
    • Largest Ventricles: Lateral ventricles (left and right).
    • Followed by the third ventricle and fourth ventricle.

Cerebrospinal Fluid (CSF) Circulation

  • Origin of CSF:
    • Produced mainly at the choroid plexus located in the lateral ventricles.
    • Circulation pathways include:
    • Lateral Ventricles → Interventricular Foramen → Third Ventricle → Cerebral Aqueduct → Fourth Ventricle.
  • Functions of CSF:
    • Provides nutrients and oxygen to neurons without direct blood supply.
    • Offers buoyancy, allowing the brain to float and reducing the risk of damage during impact.
    • Maintains chemical stability for brain and spinal cord.

Protective Layers of the CNS

  • Meninges: Special membranes covering the brain and spinal cord, consisting of three layers:
    • Dura Mater: The outermost layer, composed of two layers (peripheral periosteal layer and the inner meningeal layer).
    • Arachnoid Mater: Middle layer, characterized by a web-like appearance. Contains the subarachnoid space filled with cerebrospinal fluid.
    • Pia Mater: Innermost layer, thin and closely adheres to the brain’s surface contours.

Meningitis

  • Definition: Inflammation of the meninges, typically caused by bacterial or viral infections.
  • Explained Types:
    • Bacterial Meningitis: Serious and can lead to death.
    • Viral Meningitis: Generally less severe.
  • Spinal Tap: Diagnostic technique used to collect cerebrospinal fluid, often performed in the lumbar region.

Blood-Brain Barrier (BBB)

  • Function: Protects the brain by allowing selective passage of substances from the blood.
    • Permits crossing of: water, glucose, lipid-soluble substances (e.g., alcohol, caffeine).
    • Restricts: sodium, potassium, chloride, and other larger molecules including many medications.

Stroke

  • Definition: Any interruption in blood supply to the brain leading to tissue death.
  • Types of Stroke:
    • Hemorrhagic Stroke: Results from a ruptured blood vessel.
    • Ischemic Stroke: Caused by obstructions, such as blood clots (thrombosis) or atherosclerotic deposits.

Upcoming Study Focus

  • Preparing to examine the detailed functions and anatomy of each part of the brain.
  • Practicing the identification and understanding of the ventricular system and CSF dynamics.