Chapter 10: Sensory Physiology

Overview of Sensory Physiology

Sensory physiology is the study of how sensory systems detect and process stimuli from the environment and the body. Sensory receptors convert physical or chemical stimuli into electrical signals, which are then interpreted by the nervous system to produce sensations and perceptions.

System: Senses External and Internal Environment

Introduction to Sensory Systems

• Sensory systems detect changes in the external and internal environment.

• They convert a stimulus into a neural signal (sensory transduction).

• Sensory cells are tuned to specific types of stimuli, either external (e.g., light, sound) or internal (e.g., blood pressure, pH).

Sensory Specificity Establishment

• Receptor specificity to an adequate stimulus: Each receptor is most sensitive to a particular type of stimulus.

• Stimulus threshold: The stimulus must be above a minimum strength to be detected.

• Stimulus location and modality: The type and location of the stimulus are encoded by the receptor and its neural pathway.

• Location of sensory projection: The origin of the signal is determined by where the sensory pathway projects in the brain.

• Stimulus intensity and duration: The strength and length of the stimulus are encoded and projected to the CNS.

Conscious and Unconscious Sensory Processing

• Not all sensory information reaches conscious awareness.

• Some information is ignored or processed without conscious interpretation (e.g., background noise).

• Threshold: The minimum amount of stimulus strength required for perception.

• Inhibitory modulation: Decreases perception by reducing the signal below threshold.

Sensory Receptors

Definition and Function

• A sensory receptor is a specialized cell or structure that detects an identifiable stimulus (e.g., light, chemicals, pressure).

• The adequate stimulus is the type of stimulus to which a receptor is most sensitive.

• Receptors may respond best to one type of stimulus but can sometimes be activated by others.

Receptor Potentials and Sensory Transduction

• Receptor potentials are graded electrical changes produced by sensory receptors in response to stimuli.

• Sensory transduction is the process of converting a physical or chemical stimulus into an action potential that the CNS can interpret.

Types of Sensory Receptors Based on Adequate Stimuli

• Mechanoreceptors: Respond to mechanical forces (e.g., touch, pressure, vibration).

• Thermoreceptors: Detect changes in temperature.

• Photoreceptors: Respond to light (e.g., rods and cones in the retina).

• Chemoreceptors: Detect chemical stimuli (e.g., taste, smell, blood pH).

• Nociceptors: Respond to potentially damaging stimuli (pain).

Examples of Sensory Receptors in the Skin

The skin contains several types of sensory receptors, each specialized for detecting different types of stimuli:

Example: Merkel Receptors

• Located in the basal epidermis and hair follicles.

• Specialized for sensing steady pressure and texture.

Example: Meissner's Corpuscles

• Found in the dermal papillae, especially in fingertips and lips.

• Detect light touch and low-frequency vibration.

Example: Pacinian Corpuscles

• Located deep in the dermis and subcutaneous tissue.

• Respond to deep pressure and high-frequency vibration.

Example: Free Nerve Endings

• Distributed throughout the skin and mucous membranes.

• Detect pain (nociception), temperature, and crude touch.

Summary Table: Sensory Receptors in the Skin

Key Terms and Concepts

• Stimulus: A detectable change in the internal or external environment.

• Transduction: The conversion of a stimulus into an electrical signal.

• Threshold: The minimum stimulus intensity required to produce a response.

• Modality: The type of sensation produced (e.g., touch, temperature, pain).

• Receptor potential: A graded change in membrane potential in response to a stimulus.

Additional info:

• Some sensory receptors adapt rapidly (phasic receptors), while others adapt slowly (tonic receptors).

• Adaptation allows the nervous system to ignore constant, unchanging stimuli.