The Central Nervous System

Overview of the Central Nervous System (CNS)

  • Central Nervous System: Composed of the brain and spinal cord.

  • Cephalization: Evolutionary development of anterior CNS, leading to higher neuron counts in the human brain.

Brain Development

  • Embryological Origin: Begins as a neural tube, which expands and constricts to form three primary vesicles:

    • Prosencephalon (forebrain)

    • Mesencephalon (midbrain)

    • Rhombencephalon (hindbrain)

  • Growth: Brain grows faster than skull, causing folding to occupy space.

Brain Regions and Organization

  • Adult Brain Regions:

    • Cerebral Hemispheres

    • Diencephalon

    • Brain Stem (Midbrain, Pons, Medulla Oblongata)

    • Cerebellum

  • Gray Matter: Nonmyelinated neurons and cell bodies.

  • White Matter: Myelinated and nonmyelinated axons.

Ventricles of the Brain

  • Structure: Fluid-filled chambers filled with cerebrospinal fluid (CSF).

    • Lateral Ventricles: Large chambers separated by the septum pellucidum.

    • Connections: Interventricular foramen connects lateral and third ventricles; cerebral aqueduct connects third and fourth ventricles.

Cerebral Hemispheres

  • Structure: Comprise 83% of brain mass, divided into five lobes:

    • Frontal Lobe

    • Parietal Lobe

    • Temporal Lobe

    • Occipital Lobe

    • Insula

  • Surface Markings: Include gyri (ridges), sulci (shallow grooves), and fissures (deep grooves).

Cerebral Cortex

  • Functionality: Site of conscious mind, processing sensory input, initiating voluntary movements.

  • Areas: Motor areas, sensory areas, and association areas.

  • Lateralization: Division of labor between hemispheres; involves specialization, particularly in left hemisphere for language.

Basal Nuclei

o- Components: Include caudate nucleus, putamen, and globus pallidus; associated with regulating motor functions.

  • Functions: Influence muscle movements and play a role in cognition and emotion.

Diencephalon Components

  • Thalamus: Relay station for sensory impulses; mediates sensations and motor activities.

  • Hypothalamus: Key for homeostasis; regulates autonomic nervous system, behavior, temperature, hunger, and thirst.

    • Pineal Gland: Part of the epithalamus, secretes melatonin for sleep regulation.

Brain Stem Structure

  • Regions: Midbrain, Pons, Medulla Oblongata; controls automatic behaviors necessary for survival.

  • Cranial Nerve Association: Involved with 10 of the 12 cranial nerves.

Cerebellum Functions

  • Processes input from various parts of the brain and coordinates movements; involved in balance.

Protection of the Brain

  • Meninges: Protective cover consisting of the dura mater, arachnoid mater, and pia mater.

  • Cerebrospinal Fluid (CSF): Provides buoyancy and protection; formed by choroid plexus.

Blood-Brain Barrier

o- Protects the brain from chemical variations in blood; only specific substances can pass through.

Spinal Cord Overview

  • Enclosed in the vertebral column; a major reflex center and pathway for communication between the brain and body.

  • Comprised of dorsal and ventral roots, with gray matter at the core surrounded by white matter.