The Nervous and Endocrine Systems: A Comprehensive Overview

The Nervous System

Cranial Nerves

Twelve pairs of cranial nerves enter and exit the brain, comprising sensory, motor, and mixed types. They innervate the head, upper torso, and some internal organs. Some cranial nerves are associated with the autonomic nervous system. Along their pathways, ganglia—groups of neuronal cell bodies—can be observed.

Spinal Nerves

Thirty-one pairs of mixed spinal nerves emerge from the spinal cord. Each nerve originates as two distinct roots—dorsal and ventral—which merge to form a single nerve cord. Sensory neurons enter the spinal cord through the dorsal root, while motor neurons exit through the ventral root.

The Autonomic Nervous System

The autonomic nervous system (ANS) regulates involuntary bodily functions. Its higher centers reside in the spinal cord's gray matter, the medulla oblongata (spinal bulb), and the hypothalamus. Nerves originating from these areas transmit signals to organs. The ANS is divided into two branches with opposing actions: the sympathetic and parasympathetic nervous systems.

The Endocrine System

Pituitary Gland

Posterior Lobe

• Antidiuretic Hormone (ADH): Decreases excess water in urine.
• Oxytocin: Contracts uterine muscles during childbirth.

Anterior Lobe

• Stimulating Hormones: Activate other glands.
• Growth Hormone (GH): Promotes bone lengthening and overall growth.

Thyroid Gland

Thyroxine: Stimulates metabolism.

Parathyroid Glands

Parathyroid Hormone (PTH): Regulates calcium and phosphorus levels in the blood.

Pancreas

• Insulin: Stimulates glucose utilization by tissues and muscles.
• Glucagon: Stimulates the conversion of glycogen to glucose.

Adrenal Glands

• Adrenaline (Epinephrine): Prepares the body for action, similar to the sympathetic nervous system.
• Corticosteroids: Regulate metabolic processes and tissue water balance.
• Aldosterone: Controls sodium and potassium concentrations in the blood.

Ovaries

• Estrogens: Produce and maintain female sexual characteristics.
• Progesterone: Facilitates embryo implantation in the uterus.

Testes

Androgens: Produce and maintain male sexual characteristics.

The Spinal Cord

The spinal cord is a nerve tissue cord running through the spinal canal. Gray matter is centrally located, while white matter surrounds it. A small channel within the gray matter, the central canal, contains cerebrospinal fluid. Nerves branching from the spinal cord reach the entire body, excluding the head.

Spinal Cord Functions

• Reflex Actions: These are immediate responses to stimuli, occurring without brain involvement.
• Nerve Impulse Transmission: Carries sensory nerve impulses to the brain and motor nerve impulses from the brain to effector organs, allowing the brain to process information and modify reflex actions.