Sensory Systems Study Guide

SENSORY SYSTEMS

Sensory Receptors

  • Definition: Sensory receptors are sensory nerve endings that are sensitive to stimuli and capable of converting stimuli into nerve impulses.

  • Types:

    • Exteroceptors: Detect stimuli from outside the body.

    • Interoceptors: Detect stimuli from inside the body.

Sensory Transduction

  • Definition: The process by which a stimulus is converted into a nerve impulse.

    • Process Overview:

    1. Stimulus: A change in the environment.

    2. Transduction of stimulus: The stimulus is converted into a receptor potential in sensory receptors.

    3. Transmission of action potential: An action potential is transmitted in the sensory neuron.

    4. Interpretation of stimulus: The central nervous system interprets the stimulus (perception).

Simple Response Pathway Example

  • Foraging by a Star-nosed Mole:

    • Scenario: The mole forages along a tunnel.

    • Outcomes:

    • Food Absent: The mole moves on.

    • Food Present: The mole bites, leading to sensory input and motor output.

Classification of Sensory Receptors

  • Neuronal Receptors:

    • The receptor itself is an afferent neuron.

    • Sends impulses directly to the Central Nervous System (CNS).

  • Non-neuronal Receptors:

    • The receptor regulates an afferent neuron.

    • Involves neurotransmitter release upon stimulation.

Receptor Potential

  • Relationship with Intensity: The receptor potential increases with the intensity of the stimulus.

    • Example:

      • Gentle Pressure: Low frequency of action potentials per receptor.

      • More Pressure: High frequency of action potentials per receptor.

Amplification and Adaptation

  • Amplification: Strengthening of a sensory signal during transduction.

  • Sensory Adaptation: A decrease in responsiveness to continued stimulation.

    • Importance: Sensory adaptation allows organisms to focus on changes in their environment rather than constant stimuli.

Types of Receptors and Their Functions

  1. Mechanoreceptors: Respond to pressure, touch, stretch, motion, and sound.

  2. Chemoreceptors: Respond to chemical changes both inside and outside the body.

  3. Electromagnetic Receptors: Respond to the electromagnetic spectrum (light, electricity, magnetism).

  4. Thermoreceptors: Respond to changes in temperature (cold and warmth receptors).

  5. Nociceptors (Pain Receptors): Sensitive to pain stimuli, which can be caused by chemical signals from damaged cells, intense pressure, or extreme temperatures.

  6. Proprioceptors: A subtype of mechanoreceptors that respond to stretch, important for body position recognition.

Specific Sensory Receptors

  • Thermoreceptors:

    • Free nerve endings responsive to temperature changes.

    • Cold receptors and warmth receptors are located throughout the skin and also in the hypothalamus, where they respond to the temperature of circulating blood.

  • Nociceptors:

    • Types: Chemoreceptors that detect pain stimuli induced by prostaglandins from damaged cells, intense pressure, or temperature extremes.

  • Baroreceptors:

    • Located in blood vessels and respond to changes in blood pressure.

Sensory Systems in Aquatic and Terrestrial Animals

  • Lateral Line System in Fish:

    • Composed of a series of canals along the sides of fish that detect water movement, vibrations, and pressure changes through hair cells.

Hearing Mechanics

  • Anatomy of the Ear:

    • Structures include:Eustachian Tube, Auditory Nerve, Organ of Corti, Cochlear Duct, various canals and membranes in the cochlea.

  • Sensory transduction in Cochlea: Involves the interaction of sound waves leading to action potentials in the auditory nerve.

Equilibrium and Balance

  • Sense of Equilibrium: Involves the vestibular system.

    • Structures include: Semicircular canals, Utricle, Saccule, and Otoliths.

  • Invertebrate Balance: Invertebrates use statocysts for balance, containing statoliths that help in orientation.