Chapter 18. Sensory System
Recommended Article : 【Biology】 Biology Table of Contents
1. Overview
c. Equilibrium Receptors : Ears
e. Gustatory Receptors : Tongue
1. Overview
⑴ Stimulus
① Definition : Changes in the surrounding environment
② Characteristics : Modality, intensity, location, timing
⑵ Sensation : Subjective experience triggered when sensory receptors are activated by a stimulus
① Mechanism : Sensory transformation → Amplification → Transmission → Integration → Consciousness
○ Sensory receptors : Generate action potential when physical stimulus exceeds the threshold
○ Sensory transduction : Conversion of light, chemical, mechanical, thermal energy to electrical energy directly or through GPCR mediation
② Sensory Encoding : Mechanisms to distinguish stimuli
○ Modality of stimulus : Labeled-line sensory channel by specific sensory receptors
○ Law of specific nerve energy : Nature of sensation is determined by the type of sensory receptor, not the type of stimulus
○ Intensity of stimulus : Magnitude of sensory receptor voltage, frequency of action potential, repetition
○ Location of stimulus : Topographical organization
○ Examples : Somatosensory homunculus, Retinotopic map, Tonotopic map
③ Types of Sensory Receptors
○ Types of sensory receptors based on stimuli
○ Electromagnetic receptors
○ Chemical receptors
○ Mechanical receptors
○ Nociceptors
○ Thermoreceptors
○ Types of sensory receptors based on structure
○ Simple receptors : Neurons with free nerve endings
○ Complex neural receptors : Nerve endings encased in connective tissue sheath
○ Specialized sensory receptors : Release neurotransmitters to initiate action potentials in sensory neurons
○ Types of sensory receptors based on principles
○ Tonic receptors : Slowly adapting receptors
○ Maintain depolarization even during sustained stimulus
○ Convey stimulus magnitude (e.g., proprioceptors, nocioceptors)
○ Phasic receptors : Rapidly adapting receptors
○ Cease firing if stimulus intensity remains constant (e.g., olfactory receptors, touch receptors)
○ Detect onset, offset, and changes of stimulus primarily
④ When Neurons are Sensory Cells
○ Olfactory receptors
○ Cutaneous receptors
○ Pacinian receptors
○ Thermoreceptors
○ Renal receptors (e.g., Proximal feedback in cerebellum, unconscious sensation)
⑵ Characteristics of the Sensory System
① Decussation (chiasm): Sensory and motor tracts in the brain cross over, governing opposite side (contralateral) regions of the body
○ Reasons remain unclear
② Synaptic Integration: Sensory information interaction due to connection structure
○ Convergence
○ Divergence
○ Facilitation
○ Occlusion
③ Lateral Inhibition: Sensory receptor excitation inhibits nearby receptor activity
○ Two-point discrimination: Ability to distinguish two adjacent stimuli
○ Example : Recognizing spikes in food
Figure. 1. Effect of lateral inhibition on two-point discrimination [Note: 1]
④ Adaptation: Gradual decrease in sensory receptor voltage due to sustained stimulus
○ SA (slowly adapting receptor)
○ RA (rapidly adapting receptor)
○ TA (transiently adapting receptor)
⑤ Parallel Processing
⑥ Descending Control: Sensory information feedback regulation downwards as well
○ Example: Temporarily forgetting touch through other senses
Figure. 2. Example of descending control [Note: 2]
⑦ Except for olfactory information, all sensory information passes through the visual cortex
⑧ Plasticity
○ Advantage: Increased efficiency in brain’s information processing
○ Disadvantage: May lead to conditions like hallucinogenic pain
Figure. 3. Effects of finger amputation and training on brain cortex [Note: 3]
⑷ Psychophysics
① Principles: Physical reality ≠ Psychological reality, active, evolutionary
② Psychophysical Measurement Functions
○ Different reactions from different individuals
○ Measuring reactions when stimulus is suddenly introduced in absence of prior stimuli
○ Concepts : Detection rate, theoretical threshold curve, threshold-below stimulus, absolute threshold, obtained threshold curve
③ Just Noticeable Difference (JND)
○ Weber’s Law: ΔI/Ii = constant
○ Light: ΔIlight / Ii, light × 100 = 8 (%)
○ Weight: ΔIweight / Ii, weight = 2 (%)
○ Sound: ΔIsound / Ii, sound = 0.3 (%)
Figure. 4. Intensity-response curve of stimuli [Note: 4]
④ Signal Detection Theory (SDT)
○ Detecting faint signals in noise
○ Assumption: No single absolute threshold
○ Concepts: Liberal criterion, conservative criterion, noise, signal
⑤ Psychophysical Adaptation
⑸ McGurk Effect
① Definition: Integrating different sensory information to perceive when perceiving sensory information
② Example: Seeing ‘ga’ but hearing ‘ba’ results in perception as ‘da’
2. Types of Sensory Receptors
⑼ Chemical Receptors
① Chemical Sensation
○ Oldest and most widespread sensory organs
○ Detect chemical signals in our internal and external environment
○ All species and cells detect various chemicals
② Olfactory Receptors in Vertebrates: Nose
③ Gustatory Receptors in Vertebrates: Tongue
④ Moth’s Chemical Receptors: Antennae
○ Male’s receptors respond to a molecule of female’s pheromone
○ Pheromone → Male’s antenna → Sensory cells → Olfactory receptors → Dissolved in liquid → Interacts with receptor membrane → Dissolution
⑽ Electromagnetic Receptors
① Lorenzini Organs: Found in sharks, rays, can sense electrical signals
⑾ Interoception
① Example: Knowing the position of your arm even with closed eyes
⑿ Thermal Receptors
① Example: Snakes have pit organs, thermal sensors
Input: 2015.07.26 22:50
Modified: 2018.07.15 08:09