Nervous and Endocrine Systems: Cells, Hormones, and Plant Responses

Posted on Jan 20, 2025 in Biology

Neurons and the Nervous System

Neurons are specialized cells that transmit nervous impulses. Their filamentous structure, with characteristic extensions, allows them to connect to other neurons or organs. The extensions of neurons form fibers, which are grouped into bundles. Several of these bundles, in turn, form nerves.

Neuron Structure

• Cell body: Contains the nucleus and part of the cytoplasm.
• Axon: A long extension, branched at its end, that conducts the nerve impulse to another neuron or organ.
• Dendrites: Numerous short and highly branched extensions through which neurons connect with each other.
• Myelin: A lipoprotein that constitutes a system of phospholipid bilayers composed of sphingolipid. Located in the nervous system, it forms sheaths around the axons of neurons in vertebrates, enabling the transmission of nerve impulses between different parts of the body due to its insulating effect.

Synapse

Synapse: The process of communication between neurons. It starts with a chemical discharge that causes an electric current in the presynaptic cell membrane (sending cell).

The Endocrine System

The endocrine system consists of special organs called endocrine glands that produce hormones, chemicals that act as messengers.

Pheromones

Pheromones are chemicals secreted by an individual to induce a particular behavior in another individual of the same or another species. They are a means of signaling whose main advantages are their potency and ability to avoid obstacles, as they are carried through the air.

Plant Responses to Stimuli

Types of Stimuli

• Luminous: Light radiation or changes in light intensity.
• Gravitational: Stimulation by the force of gravity.
• Mechanical: Such as shock, friction, or pressure.
• Chemical: Due to the presence or variation of chemicals.
• Thermal: Changes in temperature.
• Water: Such as the amount of soil water or atmospheric moisture.

Tropism

Tropism: Permanent responses to a stimulus in which changes occur in the direction of plant growth.

• Phototropism: The stimulus is caused by light. Stems grow toward light.
• Geotropism: A response to gravity. Roots grow into the interior of the earth, making it easier to obtain water and minerals.
• Thigmotropism: A response to contact. Climbing plants and vines wind around a support.
• Hydrotropism: Caused by water. Plant roots grow toward areas of soil with water.

Nastic Movements

Nastic movements: Transient responses of certain areas of the plant in response to external stimuli.

Plant Hormones

Plant Hormones: These are chemicals that regulate and coordinate the vital functions of plants.

Endocrine Glands and Hormones