Biological Response Systems: Stimulus, Receptors, and Effectors

Biological Response Mechanisms

The Function Relationship

The function relationship involves roles that enable a living being to receive information from its external or internal environment and respond appropriately to ensure its survival. Within this function, we distinguish the stimulus, the receptor (which captures the stimulus and passes information), and the effector (which executes the most appropriate response).

Stimuli

A stimulus is a change in the environment surrounding a body or within it.

Types of Responses

Responses can be classified as:

• Static: Responses where no movement is produced.
• Dynamic (Taxias): Responses involving movement. These can be positive (approach to the stimulus) or negative (withdrawal from the stimulus).

Cellular Movements

Types of cell movements include:

• Amoeboid (via pseudopodia)
• Ciliary/Flagellar (via cilia and flagella)
• Contractility (via contractile filaments)
• Turgor movements (due to gain or loss of water, causing specific movements)

Plant Responses

Tropisms

Tropisms: These are movements related to plant growth or the growth of one of its parts. They are slow and irreversible responses. A tropism is positive if the movement is towards the stimulus, and negative if it is away from the stimulus.

Nasties

Nasties: These are rapid and temporary changes in certain parts of the plant, resulting from movements of turgid cells.

Photoperiodism

Photoperiodism: These responses are due to changes in light duration that occur throughout the seasons. Plants adapt vital activities, such as flowering, based on the relative duration of day and night.

Receptors

Receptors are specialized cells capable of perceiving certain stimuli. Receptors can be nerve cells or sensory cells.

Receptor Classification by Location

• External (Exteroceptors): Collect information from the outside environment.
• Internal (Interoceptors): Receive information from the internal environment.

Receptor Classification by Stimulus Type

• Photoreceptors: Capture light stimuli.
• Chemoreceptors: Stimulated by chemical substances.
• Mechanoreceptors: Respond to mechanical stimuli.
• Thermoreceptors: Discriminate heat and cold.
• Electroreceptors: Detect electrical energy.

The Hormonal (Endocrine) System

The hormonal (or endocrine) system is responsible for controlling and regulating responses through hormones. Hormones are produced in endocrine glands, which are organs distributed throughout the body. These hormones are released into the internal environment and the circulatory system, and through them, they are distributed to effector organs, especially those requiring slow and prolonged action.

The Nervous System

The nervous system regulates the body's activities using neurons, which are cells responsible for processing and transmitting information from receptors and coordinating effector responses.

Components of the Nervous System

• Nerves: These are long cords formed by thousands of extensions (axons) issued by neurons. They connect receptor organs and nerve centers to effector organs.
• Nerve Centers: These are organs that receive information from receptors, prepare appropriate responses, and send them to effector organs.