Nervous System Divisions and Endocrine Regulation

Divisions of the Nervous System

Central Nervous System (CNS)

The CNS consists of the brain and the spinal cord. Its primary role is processing information and preparing appropriate responses.

Peripheral Nervous System (PNS)

The PNS connects the CNS to the rest of the body and the external environment. It is divided into two main systems:

Somatic Nervous System

This system is built by nerves leaving the brain (cranial nerves) and the spinal cord (spinal nerves).

• Function: Connects the CNS with the rest of the body and the environment.
• Action: Its action is voluntary and conscious.

Autonomic Nervous System

This system is built by nerves and ganglia. Two systems are distinguished: the sympathetic and the parasympathetic.

• Function: Connects the CNS with the viscera (internal organs).
• Action: Its action is involuntary and unconscious.

Structure and Function of CNS Components

The Brain

The brain interprets sensory stimuli, coordinates motor responses, and handles emotional and intellectual functions.

Diencephalon

• Thalamus: Controls emotions.
• Hypothalamus: Controls the functions aimed at maintaining internal balance (homeostasis). It also controls the operation of the main endocrine gland, the pituitary gland.

Cerebellum

The cerebellum controls fine, coordinated movements, body posture, and balance.

Brain Stem

The brain stem controls vital functions for the body. It is divided into three parts:

• Mesencephalon: Transmits motor impulses.
• Pons: Connects and integrates the various parts of the brain.
• Medulla Oblongata: Lodges control centers for vital functions (those that regulate blood pressure and cardiac and respiratory frequencies).

Spinal Cord

The spinal cord is housed within the vertebral column (spine). The cord acts as a nerve center that coordinates involuntary reflex actions.

The Pituitary Gland and Hypothalamus

The Pituitary Gland (Hypophysis)

The pituitary is a gland located at the base of the brain that regulates the functioning of other glands. It is divided into three parts:

Adenohypophysis (Anterior Lobe)

The anterior lobe releases six major hormones:

• Somatotropin: Promotes the growth of bones and tissues of the body.
• Adrenocorticotropin (ACTH): Regulates the activity and growth of the adrenal cortex.
• Thyrotropin (TSH): Stimulates the production and secretion of hormones by the thyroid gland.
• Gonadotropins (FSH/LH): Act on the structure and function of the gonads.
• Prolactin: Stimulates milk secretion during pregnancy and lactation.

Intermediate Lobe

In fish, amphibians, and reptiles, this lobe releases melanocyte-stimulating hormone (MSH), which changes skin color. In humans, its secretion is low, and it is believed to have a function similar to that observed in other vertebrates.

Neurohypophysis (Posterior Lobe)

The posterior lobe stores and releases hormones that are secreted by the hypothalamus:

• Vasopressin (ADH): Increases water reabsorption in the kidneys.
• Oxytocin: Released during childbirth to help expel the fetus, and also involved in breastfeeding by stimulating milk ejection.

Neurosecretion

Neurosecretion is the process where hormones produced by living neurons in the hypothalamus are transported, stored in the pituitary gland, and eventually released into the bloodstream.