Nervous System: Structure, Development, and Major Regions

Nervous System Overview

Central vs Peripheral Nervous System

The nervous system is divided into two main parts: the Central Nervous System (CNS) and the Peripheral Nervous System (PNS). Each plays a distinct role in processing and transmitting information throughout the body.

• Central Nervous System (CNS): Consists of the brain and spinal cord. Responsible for integrating sensory information and responding accordingly.

• Peripheral Nervous System (PNS): Composed of nerves and ganglia outside the CNS. Connects the CNS to limbs and organs, serving as a communication relay.

Nervous System Development

Stages and Influences on Development

The development of the nervous system begins early in embryogenesis and is influenced by genetic and environmental factors.

• Early Development: Begins during the first month of embryonic growth. Critical events include neural tube formation and differentiation into major brain regions.

• Influences: Maternal infection, lifestyle choices (e.g., smoking, alcohol), and nutrition can impact neural development.

• Brain Growth: The brain reaches maximum weight in early adulthood. With aging, brain weight and volume decline due to neuronal damage.

• Cerebral Palsy: A disorder of muscle coordination resulting from damage to the developing brain, often before birth.

• Spina Bifida: A defect in vertebral formation that can impact the spinal cord or nerves.

Brain Development

Formation of Brain Vesicles and Adult Structures

Brain development involves the transformation of the neural tube into distinct regions through the formation of primary and secondary brain vesicles.

• Primary Brain Vesicles: Prosencephalon (forebrain), Mesencephalon (midbrain), Rhombencephalon (hindbrain).

• Secondary Brain Vesicles: Telencephalon, Diencephalon, Mesencephalon, Metencephalon, Myelencephalon.

• Adult Brain Structures: Cerebrum, diencephalon (thalamus, hypothalamus, epithalamus), brain stem (midbrain, pons, medulla oblongata), cerebellum, spinal cord.

Primary Vesicle	Secondary Vesicle	Adult Structure
Prosencephalon	Telencephalon	Cerebrum (cortex, white matter, basal nuclei)
Prosencephalon	Diencephalon	Diencephalon (thalamus, hypothalamus, epithalamus), retina
Mesencephalon	Mesencephalon	Midbrain
Rhombencephalon	Metencephalon	Pons, cerebellum
Rhombencephalon	Myelencephalon	Medulla oblongata

Growth and Folding of the Brain

During development, the brain grows rapidly, causing the cerebral hemispheres to fold and envelop other regions, increasing surface area for neural processing.

• Flexures: Bending of the neural tube forms the adult brain shape.

• Folding: The cerebral hemispheres double back and envelop the diencephalon, forming gyri and sulci.

• Surface Area: Increased by folding, allowing for more neurons and complex processing.

Major Regions of the Brain

Functional Anatomy

The adult brain is organized into several major regions, each with specialized functions.

• Cerebral Hemispheres: Responsible for higher cognitive functions, voluntary movement, and sensory interpretation.

• Diencephalon: Includes the thalamus (sensory relay), hypothalamus (homeostasis), and epithalamus.

• Brain Stem: Composed of the midbrain, pons, and medulla oblongata; controls vital functions such as breathing and heart rate.

• Cerebellum: Coordinates movement and balance.

Region	Main Function
Cerebrum	Conscious thought, memory, voluntary movement
Diencephalon	Sensory relay, autonomic control, hormone regulation
Brain Stem	Basic life functions (breathing, heart rate)
Cerebellum	Coordination, balance

Example: Precentral Gyrus and Central Sulcus

The precentral gyrus (primary motor cortex) and central sulcus are key landmarks in the cerebral cortex, involved in voluntary motor control and separating the frontal and parietal lobes.

• Precentral Gyrus: Initiates voluntary movements.

• Central Sulcus: Divides the frontal and parietal lobes.

Additional info:

• Neural tube defects such as spina bifida and anencephaly are important clinical considerations in nervous system development.

• Gyri (ridges) and sulci (grooves) increase the surface area of the cerebral cortex, allowing for greater cognitive capacity.