Human Nervous System: Central and Peripheral Divisions

The Human Nervous System: Divisions and Functions

The human nervous system is a complex network responsible for controlling all body activities. It is broadly divided into two main parts:

• Central Nervous System (CNS): Protected by bones (skull and spine) and three membranes called meninges.
• Peripheral Nervous System (PNS): Composed of nerves that connect receptors and effectors to the central nervous system.

Central Nervous System (CNS)

The Central Nervous System (CNS) is the body's control center, formed by the brain (located inside the skull) and the spinal cord (located inside the spine).

The Brain: Control Center of the Body

The brain is the most complex organ in the human body, responsible for thought, emotion, memory, and movement. It comprises several key parts:

• Cerebrum

  The Cerebrum is the largest part of the brain and is responsible for conscious thought. Its functions include:

  • Receiving and processing stimuli from sensory organs.
  • Producing voluntary responses.
  • Higher functions such as memory, reasoning, intelligence, and will.

  Its structure is divided into two hemispheres, each folded into ridges called convolutions, which carry out specific functions. A cross-section reveals grey matter (formed by neuron cell bodies) on the outside, known as the cerebral cortex, and white matter (formed by axons) on the inside. Neuronal plasticity allows for constant changes, enabling new learning and memories to be stored.

• Cerebellum

  The Cerebellum has a structure similar to the cerebrum. It operates unconsciously and is primarily responsible for maintaining equilibrium and executing learned movements.

• Diencephalon (Thalamus & Hypothalamus)

  The Thalamus (unconscious) associates emotions with stimuli, controls our necessities and desires, regulates sleep, and manages visual and auditory reflexes. The Hypothalamus connects the nervous system with the endocrine system, playing a vital role in hormone regulation.

• Brainstem (Medulla Oblongata)

  The Medulla Oblongata (often referred to as the "spinal bulb" in some contexts) is an unconscious part of the brainstem that regulates vital body organ functions such as breathing, heartbeat, and digestion.

The Spinal Cord: Reflexes and Information Relay

The Spinal Cord is a long, tube-like structure extending from the brainstem. It is responsible for producing body reflexes and carrying information between the brain and the rest of the body. A cross-section shows grey matter (formed by neuron cell bodies) on the inside, shaped like a butterfly, and white matter (formed by axons) on the outside.

Peripheral Nervous System (PNS)

The Peripheral Nervous System (PNS) consists of nerves that extend throughout the body, connecting the CNS to limbs and organs. Unlike the CNS, it is not protected by bones. The PNS is divided into two main functional components:

• Somatic Nervous System

  The Somatic Nervous System carries information via nerves that control skeletal muscles, which are under conscious, voluntary control.

• Autonomic Nervous System

  The Autonomic Nervous System carries information via nerves that manage internal organs, which operate under unconscious, involuntary control. It is further divided into two opposing branches:

  • Sympathetic Nervous System: Activates organs in situations of stress or "fight-or-flight" responses.
  • Parasympathetic Nervous System: Acts on organs to promote relaxation and "rest-and-digest" functions.