The Nervous and Endocrine Systems: Anatomy and Physiology
1. The Nervous System
The nervous system, through sensory organs, allows interaction with the external environment. It is divided anatomically into:
a) Central Nervous System (CNS)
- Brain: Telencephalon, Brainstem, Cerebellum
- Spinal Cord: White matter, Gray matter
b) Peripheral Nervous System (PNS)
- Cranial nerves
- Spinal nerves
According to their functional characteristics, they are divided into:
a) Somatic Nervous System (Voluntary)
Nerves that innervate muscles.
b) Autonomic Nervous System
- Sympathetic
- Parasympathetic
2. Central Nervous System
The CNS transmits information throughout the body through electrical signals via a network of neurons. It is composed of neurons, glial cells, blood vessels, and connective tissue. It is covered by the meninges and bathed in cerebrospinal fluid.
Brain
Can be divided into the telencephalon, brainstem, and cerebellum.
Telencephalon
Includes the cerebral cortex, which surrounds the brain and is composed of two layers: a surface layer that forms the gray matter and a deeper layer forming the white matter.
Brainstem
Includes the hypothalamus, pituitary gland, medulla oblongata, etc.
Cerebellum
Controls agonist and antagonist muscles, skeletal muscle, body movements, and balance.
Spinal Cord
Part of the CNS that extends from the brain to the first lumbar vertebra inside the vertebral column. The gray matter is in the form of an H, and the white matter is on the surface.
3. Meninges and Cerebrospinal Fluid
The brain and spinal cord are bathed in cerebrospinal fluid and protected by two surfaces: an external one (formed by bone) and an internal one that consists of layers or membranes called meninges.
Meninges
From outside to inside, the three layers are:
1. Dura Mater
Outer layer formed by fibrous tissue that surrounds the brain and spinal cord.
2. Arachnoid Mater
Middle layer that presents a number of villi or extensions that serve as conduits for the absorption of cerebrospinal fluid into the nervous system.
3. Pia Mater
Inner layer; the vascular layer that nourishes the nervous tissue.
4. Cerebrospinal Fluid
A colorless, crystalline liquid located between the meninges, the brain, and the spinal cord. Its function is to protect the brain and spinal cord, acting as a cushion and offsetting changes in intracranial blood volume.
5. Peripheral Nervous System
Cranial Nerves
Consists of three types: sensory, motor, and mixed.
Vagus Nerve
Also known as the pneumogastric nerve (X cranial nerve), it originates in the medulla oblongata and supplies the following organs: pharynx, esophagus, larynx, trachea, bronchi, heart, stomach, and liver. Its function is the movement of visceral muscles and visceral sensitivity.
6. Autonomic Nervous System
Sympathetic Nervous System
Responsible for stimulating activities required in emergency situations, such as the fight-or-flight response.
Parasympathetic Nervous System
Conserves energy. Preganglionic fibers originate in the brainstem and sacral segments of the spinal cord.
7. Endocrine System
The major glands of the endocrine system are: pituitary, thyroid, parathyroid, adrenal, pancreas, gonads (ovaries, testes), and pineal gland. These glands secrete hormones directly into the bloodstream to be transported to different parts of the body where they exert their actions.
8. Pituitary Gland
Located at the base of the skull below the hypothalamus. It is an endocrine gland that produces numerous hormones.
- Thyroid-Stimulating Hormone (TSH): Stimulates the thyroid gland.
- Antidiuretic Hormone (ADH) or Vasopressin: Acts on the nephron, favoring the reabsorption of sodium and water. It also produces vasoconstriction, leading to increased arterial blood pressure.
- Oxytocin: Acts on the myometrium during childbirth, stimulating contractions. It also stimulates the release of milk during lactation.
9. Thyroid Gland
An endocrine gland located in the front of the neck, below the larynx. It secretes three hormones: thyroxine, triiodothyronine, and calcitonin. These hormones produce the following effects:
- Generalized increase in metabolism
- Stimulation of growth in children
- Increased heart and respiratory rates
10. Parathyroid Glands
Four glands located on the posterior aspect of the thyroid gland. Their function is related to the metabolism of calcium and phosphorus.
11. Adrenal Glands
Two small glands located in the abdomen, on both sides of the vertebral column and on top of the kidneys. They secrete adrenaline and noradrenaline, which act in response to stress, promoting alertness and wakefulness. They also secrete a group of hormones called corticosteroids.
- Glucocorticoids: Involved in the metabolism of carbohydrates, proteins, and fats. They also block inflammatory responses and allergic reactions.
- Androgens (Testosterone): Have masculinizing effects.
- Epinephrine: Stimulates involuntary movements or processes of the body, such as breathing, heart activity, blinking, and digestive processes.
- Noradrenaline: Has antagonistic effects to epinephrine.
12. Pancreas
A gland located in the upper abdomen, below the stomach. It consists of two types of glandular tissue: endocrine tissue, consisting of Langerhans cells, which secrete insulin and glucagon; and exocrine tissue, which secretes pancreatic juice that is released into the duodenum. It also secretes amylase and peptidase enzymes.
- Insulin: Regulates blood glucose levels.
13. Gonads (Sex Glands)
Glands that produce gametes and hormones. In males, these are the testes, and in females, the ovaries.
Female Hormones
- Estrogen: Stimulates the growth and development of female sexual organs and the development of breasts.
- Androgens (Testosterone): Stimulate female libido and the development of pubic and axillary hair.
- Progesterone: Assists in the process of gestation.
Male Hormones
- Testosterone: Responsible for the development of the male sexual apparatus (growth of pubic hair, deepening of the voice, etc.).
14. Physiology of the Neuroendocrine System
The Neuron
One of the most important cells in the body. It is formed by the cell body or soma and extensions called dendrites and axons. The axon is responsible for conducting the nerve impulse to other neurons. There are three types of neurons: sensory neurons, motor neurons, and interneurons.