Understanding the Central and Peripheral Nervous Systems

Central Nervous System (CNS) Components and Protection

The Central Nervous System (CNS) is composed of the brain and spinal cord. It is protected by membrane layers, called the meninges, and bone structures: the skull (for the brain) and the vertebrae (for the spinal cord).

Major CNS Structures Housed in the Cranium

The brain structure housed in the cranium includes the Cerebrum, Cerebellum, and Medulla.

The Cerebrum Structure and Function

The Cerebrum is divided into two hemispheres. Its surface features include protrusions called gyri and depressions called sulci or fissures. The cerebral cortex is the outer part, made up of gray matter that receives information from sense organs, produces response orders, and stores and processes information. The inner zone consists of white matter.

The Cerebellum: Coordination and Balance

The Cerebellum is located below the cerebrum. It is divided into two hemispheres and displays cerebellar gyri. It coordinates movements, such as walking, and allows us to maintain balance.

The Medulla Oblongata (Brainstem)

The Medulla connects the brain to the top of the spinal cord. It automatically controls vital bodily functions such as blood flow, breathing movements, and digestion.

The Spinal Cord Structure and Function

The Spinal Cord runs inside the spine (vertebral column). The outer part contains white matter, and the inner part contains gray matter. The spinal cord serves as a pathway through which sensory messages ascend to the brain and motor orders descend from the brain to other organs. There are 31 pairs of spinal nerves. It is also responsible for automatic reflex movements.

Peripheral Nervous System (PNS) Structure

The Peripheral Nervous System (PNS) consists of the cranial nerves and spinal nerves. These nerves connect the Central Nervous System (CNS) with all organs of the body.

Functional Classification of PNS Nerves

Nerves are functionally classified based on the direction of information flow:

• Sensory Nerves: Carry information from sense organs and viscera to the Central Nervous System.
• Motor Nerves: Carry orders from the Central Nervous System to muscles and organs responsible for executing a response.

Somatic Nervous System

The Somatic Nervous System involves nerves that connect the CNS to the skeletal muscles. It is responsible for voluntary acts, such as walking.

Autonomic Nervous System (ANS)

The Autonomic Nervous System (ANS) (also called the Vegetative Nervous System) involves nerves connecting the viscera to the CNS. It regulates involuntary organs, like the heart. These organs receive opposing orders via two systems:

• Parasympathetic Nervous System: Formed by parasympathetic nerves.
• Sympathetic Nervous System: Formed by sympathetic nerves.

Neurons: The Specialized Cells of the Nervous System

The nervous system is composed of a set of highly specialized cells: neurons. They possess a morphology perfectly suited for transmitting messages in the form of nerve impulses.

Neuron Operation and Synapses

Nerve impulses travel along neurons as short-duration electrical currents. The impulse enters the dendrite, moves toward the cell body, and exits via the axon. Connections called synapses are established, mediated by chemicals called neurotransmitters. During the growth stage of an organism, neurons establish new synapses, building a complex network required for nerve function. Notably, mature neurons are generally not capable of reproducing.