Nervous System: Sensory Modalities and Receptor Functions
Information and Directions
The nervous system functions through physical contact between cells, neural circuits, and specialized areas that receive information. These areas are responsible for detecting environmental stimuli.
Law of Specific Nerve Energy: Each receptor is specific to a sensory modality and transmits an action potential via a specific nerve fiber to a particular area of the nervous system.
- Effectors: Output systems (endocrine system, muscles, etc.).
- Senses: Mechanisms for information entry via sensory receptors.
- Sensory modalities are transmitted as action potentials.
Membrane receptors include: chemoreceptors, thermoreceptors, mechanoreceptors (hearing, touch, balance), electroreceptors, magnoreceptors, photoreceptors, and nociceptors (pain).
Taste buds and olfactory receptors use molecules to identify specific substances. Taste bud stimuli involve a mechanical response to membrane deformation.
Information is transmitted by slow fibers (C fibers) or fast fibers (Aα fibers).
Myelin Sheaths: Structures formed by Schwann cells coating the axon, increasing signal speed.
Autonomic Nervous System (Vertebrates)
The autonomic nervous system involuntarily ensures vital body functions and is responsible for reflex movements, often in response to pain.
An affected area transmits information to the spinal cord. An afferent cell sends a signal to a motor neuron, which controls muscles in the stimulated area, resulting in a fast response (Aα fibers).
Invertebrates: Have reflexes but lack a central core, maintaining vital functions independently of the brain.
Chemoreceptors: Animals respond to different substances based on their habitat, synthesizing membrane proteins for detection.
Sensory information results in action potentials.
The lateral line of fish forms a mechanoreceptor system, distributing receptors to the spinal cord and brain. This allows fish to detect sound by sensing pressure.
Sensory Modalities (Mechanoreceptors)
Hearing: Mechanoreceptors are excited by sound waves. The organ of balance consists of three rings.
SOFAR Channel: An area where sound propagates over long distances (common in large marine mammals).
Vision: Photoreceptors (invertebrates have ocelli). Vertebrate retina photoreceptor cells are cones and rods. Cones detect color, while rods detect light intensity.
Photoreceptor Excitation
White light produces maximum excitation in corresponding sensitive cells. Color vision results from the combination of the three types of cones.