In-depth Notes on Sensory Physiology

Sensory physiology focuses on how sensory system works, including the sensory receptors and the neural pathways that transmit information.
Involves transformation of stimulus energy into graded potentials and action potentials.

Sensory Receptors: Specialized structures that convert external and internal environmental stimuli into electrical signals (graded potentials).
- Types of sensory receptors:
- Mechanoreceptors: respond to touch, pressure, and stretch.
- Thermoreceptors: respond to temperature changes.
- Photoreceptors: respond to light.
- Chemoreceptors: respond to smell and taste.
- Nociceptors: respond to pain.
Neural Pathways: Conduct information from receptors to the CNS for processing.
CNS Processing: Involves interpretation and perception of sensory information, differentiating between simple sensation and complex perception.

Sensory Processing: Involves the transformation of stimulus energy into graded potentials (receptor potential) which can lead to action potentials in afferent neurons.
Sensory Transduction: Activation of sensory receptors can alter ion channels, influencing receptor potential and action potential frequency.
- Receptor potential varies with:
- Strength of stimulus
- Rate of stimulus application
- Temporal summation of potentials
- Adaptation (decrease in sensitivity)

Modality: Determined by activated receptor types, with all receptors in a sensory unit responding to the same modality (e.g., all respond to touch).
Stimulus Intensity: Coded by:
- Frequency of action potentials from individual sensory units.
- Number of activated sensory units (recruitment).
Localization: Determined by size of receptive fields and overlap, along with lateral inhibition effects.

Specific Ascending Pathways: Convey information about a single stimulus type (e.g., pain, temperature) to specific brain areas for processing sensory modalities such as somatosensory and visual cortex.
Nonspecific Ascending Pathways: Convey information from multiple sensory types to brainstem and thalamus, alerting the body to stimulus presence without detailed information.

Factors Affecting Perception:
- Emotional state, past experiences, personality traits, receptor adaptation, neural damage, drug effects, and mental illnesses.
Processing of sensory information is multi-faceted and often integrates inputs from different sensory modalities.

Types of Somatic Sensations:
- Touch, pressure, temperature, pain, and itch.
Different receptors encode specific types of somatic sensations (e.g., muscle spindle receptors for kinesthesia, cold/warm receptors for temperature).