Nervous and Hormonal Control: Homeostasis and Behavior in Animals

Posted on Jan 20, 2025 in Biology

Nervous and Hormonal Control

Changes in the internal environment trigger a set of physiological responses, called homeostasis. Changes in the external environment cause a variety of responses that constitute behavior.

Control Systems Coordination in Animals

  • The nervous system is responsible for regulation and coordination of the functions of the body through nerve impulses.
  • The hormonal system regulates bodily functions through hormones.

Integrated Operation

  • Stimulus: The external or internal environment.
  • Receptor: Detects and converts the stimulus into a nerve impulse.
  • Central Nervous System: Receives information.
  • Answer: Reaction to a stimulus.
  • Effector: Executes the response.

Types of Responses

  • Motor response: Locomotion, which allows animals to move.
  • Secretory responses: The secretion of a substance from glands.

Components of the Nervous System

  • Neurons:
    • Soma: Contains the core of neurofilaments, groups of membranous sacs, the rough endoplasmic reticulum, and mitochondria.
    • Dendrites: Ramifications of the cell body that receive nerve impulses.
    • Axon: Conducts the nerve impulse.

Neuron Classification by Function

  • Sensory Neurons: Lead from receptor stimulation to the nerve centers.
  • Association Neurons: Are within the nervous system and are responsible for connecting the neurons.
  • Motor Neurons: Lead the response from the nerve centers to the effector organs.
  • Neuroglia: Performs supportive, nutrition, and protection functions for the nervous system. The main cells are astrocytes, oligodendrocytes, and Schwann cells. They have a plasma membrane rich in a white lipid called myelin.

Types of Nerve Fibers

  • Unmyelinated: Several axons that are covered by a single Schwann cell.
  • Myelinated: Rolled by several Schwann cells. The cell bodies are grouped into structures that constitute the peripheral nervous system ganglion and form the gray matter.

Transmission of Nerve Impulse

The main function of a neuron is the generation and propagation of nerve impulses, which correspond to electrochemical changes.

Origin and Nerve Impulse Propagation

A neuron is polarized. Inside there are cations K+, with a negative charge; on the outside, there is a positive charge. The potential difference is called resting potential. When a nerve impulse reaches the membrane, it is disturbed, large amounts of Na+ ions penetrate inside the neuron, and to a lesser extent, K+ ions exit. This process is called depolarization. The potential difference between the outside and inside of the membrane is called the action potential. When the action potential has traveled a few millimeters, the point where the disturbance began is repolarized.

Invertebrate Nervous System

  • Neural Networks: Consisting of neurons that form a diffuse network, there is no supervisory body.
  • Annular Nervous System: In echinoderms (sea stars), known as a nerve ring formed by a periesophageal collar.
  • Cord Nervous System: In flatworms, the cerebral ganglia form neurons.
  • Ganglionic Nervous System: In annelids, arthropods, crustaceans, and mollusks; cerebral ganglia leaving the periesophageal collar.