Anatomy of Central Nervous System

The primary unit of the central nervous system is the neuron or the nerve cell. Millions of neurons allow the various parts of the body to coordinate with each other through the brain and the spinal cord. The nerve cells are coated with a fatty material called myelin that insulates them and helps them in communicating easily. The central nervous system (CNS) is covered with meninges, a three layered protective coat that almost separates CNS from the rest of the body. This envelope controls the import and export of nourishing substances, pivotal electrolytes, and also prevents the entry of potentially harmful material like toxins, bacteria and viruses. The brain and the spinal cord are surrounded by cerebrospinal fluid that circulates between two meningeal layers called the pia mater and the arachnoid (or pia-arachnoid membranes). The outer, thicker meningeal layer acts as a protective shield and is called the dura matter.

The Central Nervous System

The anatomy of CNS comprises two main parts: the brain (cerebrum) and the spinal cord.

Brain (Cerebrum)

The brain consists of millions of nerve cells that cluster together and interact with each other through the process of neurotransmission. It controls most of the bodily functions like movements, thoughts, speech, sensations and memory. The brain is divided into three main subsections: the forebrain (Prosencephalon), midbrain (Mesencephalon) and hindbrain (Rhombencephalon).

Hindbrain (Rhombencephalon)
The hindbrain comprises three components:
Medulla oblongata (Myelencephalon) lies at the transition zone between the brain and the spinal cord, towards the posterior end of the body. Its internal structure and gross aspect resembles the appearance of the spinal cord. Pons connects the Medulla oblongata with the midbrain region. Cerebellum is a distinct brain region connected to the rest of the brain by three stalks on each side: the Pedunculus cerebellaris superior, Pedunculus cerebellaris medius and Pedunculus cerebellaris inferior. It is connected to the dorsal aspect of the Pons. The cerebellum controls and coordinate the muscle tone and also contributes to muscle tone generation. It also displays a distinction of gray and white matter like the Prosencephalon.

Midbrain (Mesencepalon)
The midbrain is intervened between the hindbrain and the forebrain. It has a similar functional composition as the spinal cord and the hindbrain. Ventral areas of the brain are responsible for the motor functions and hold tracts that convey motor information. Dorsal regions are related to the sensory information circuits of the body.

Forebrain (Prosencephalon)
The forebrain is the largest part of the brain and is mainly made up of cerebrum. It consists of important structures like the thalamus, hypothalamus and limbic system. The thalamus works to pass sensory information to the cerebral cortex and the hypothalamus controls visceral functions, like reproductive functions, sleeping, temperature, eating and the display of emotion. The limbic system is also known as the 'emotional brain' and helps in controlling emotions, learning skills and decision making.

Spinal Cord

The spinal cord is a continuation of the brain and is surrounded by the vertebral bodies that form the spinal column. The central structures of the spinal cord are formed of gray matter and the external tissues are formed of white matter. The spinal cord has 30 segments that are categorized into 4 sections:

• Eight cervical segments transfer signals from or to the areas of neck, arms, head and shoulder.
• Twelve thoracic segments transfer signals from or to the part of the arms, anterior and posterior chest and abdominal areas.
• Five lumbar segments transfer signals from or to the legs, feet and pelvic organs.
• Five sacral segments transfer signals from or to the lower back, buttocks, pelvic organs, genital areas and some areas in the legs and feet.
• A coccygeal remnant is situated at the bottom of the spinal cord.

The central nervous system plays a fundamental role in controlling human behavior. It is held within the dorsal cavity, the brain in the cranial cavity and the spinal cord within the spinal cavity.