Human Body Control: Nervous and Endocrine Systems Explained
The Human Nervous System: Coordination and Control
The Role of Relationship and Coordination
For us to perform the functions of nutrition and reproduction properly, we need a central system to coordinate all activities involved. This system also coordinates other events unrelated to these two primary functions, such as studying, shivering, or laughing, which allow us to interact with the external environment, with physical objects, or with other living beings. This crucial feature, called relationship, is primarily carried out by the nervous system.
The Neuron: Basic Unit of the Nervous System
The neuron is the anatomical and functional unit of the nervous system. The nerve impulse is electrical, saltatory, and unidirectional.
Central Nervous System (CNS)
The Central Nervous System (CNS) is responsible for receiving and processing the different sensations gathered by the senses and transmitting orders to respond accurately to various effectors.
Spinal Cord
The spinal cord is involved in simple acts or involuntary reflexes.
- Gray Matter: Consists of the grouping of cell bodies of neurons. It is responsible for the development of simple reflex actions.
- White Matter: Consists of the grouping of the axons of several neurons. It transmits information from the periphery to the brain and vice versa.
The Brain
Medulla Oblongata
The medulla oblongata is a vital nerve center involved in the control of basic life functions such as blood pressure, heartbeat, digestion, vomiting, respiratory rate, coughing, hiccups, and peristalsis. Damage to the medulla is usually fatal.
Cerebellum
The cerebellum is responsible for the coordination of movements and the control of body position. It plans and coordinates movements, providing fluidity and finesse, and controls the sense of balance. It is also responsible for coordinating and regulating movements that, through many repetitions, we have learned and now perform automatically (e.g., walking, writing, swimming).
Cerebrum
The cerebrum’s functions are related to thought, speech, and the reception of sensory information.
- Cerebral Cortex: Consists of gray matter. It is the area that receives and processes information from different senses and issues commands for all voluntary actions. It is also the seat of higher mental activity, including intelligence.
- The Limbic System: Consists of a part of the cerebral cortex located in the lower brain and several structures located deep beneath it. It is the center for emotions. It is capable of processing and storing information as emotional memories, enabling us to react to memories and express emotions, which in turn influence our behavior.
- The Hypothalamus: Has receptors that monitor the composition of the blood passing through it. If it detects variations from normal, it reacts by causing hunger, thirst, and other responses. It is considered the control center for vegetative life, managing the body’s internal functions by sending responses via the autonomic peripheral nervous system or by releasing hormones into the bloodstream. It also manages stress, fear, anxiety, and regulates sleep.
Nervous System Responses
The responses of the nervous system are varied, ranging from the most simple to the most complicated.
- Reflex Responses: Reflex responses are a series of rapid, involuntary reactions essential for survival, as they protect us in emergencies. The typical pathway involves:
- Stimulus
- Receptor stimulation
- Sensory current (afferent pathway)
- Reception and motor development (integration in CNS)
- Motor current (efferent pathway)
- Effector response
- Overall response
- Autonomic Responses: These are involuntary and fundamental to the maintenance of life. They are carried out by the autonomic peripheral nervous system, which is controlled by the hypothalamus and operates independently (i.e., involuntarily). Key divisions include the Parasympathetic and Sympathetic nervous systems.
Glands and Hormones: The Endocrine System
Types of Glands
Glands are cells or groups of cells forming a special type of epithelial tissue capable of secreting specific chemical substances:
- Exocrine Glands: Discharge their contents to the outside of the body or into internal cavities like the digestive tract (e.g., sweat glands, salivary glands).
- Endocrine Glands: Release their contents (hormones) directly into the bloodstream. They are the primary producers of hormones.
- Mixed Glands: Possess both exocrine and endocrine functions (e.g., pancreas).
Hormones: Chemical Messengers
Hormones are chemical substances produced by endocrine glands, released into the blood in small quantities, and carried by the blood to their specific site of action, known as the target organ. Hormones are eventually excreted, often in the urine.