Rucete ✏ Campbell Biology In a Nutshell
Unit 7 ANIMAL FORM AND FUNCTION — Concept 50.1 Sensory Receptors Transduce Stimulus Energy and Transmit Signals to the Central Nervous System
All sensory experiences begin with specialized sensory receptors that detect environmental or internal stimuli. These receptors convert energy into electrical signals, which the nervous system processes to produce perceptions and guide responses.
1. Four Key Functions of Sensory Pathways
- Sensory reception: detection of stimulus by sensory receptors (cells or organs)
- Transduction: conversion of stimulus into a receptor potential (graded electrical change)
- Transmission: relay of information as action potentials to the CNS
- Perception: interpretation of signals by the brain (e.g., light vs. sound based on neural pathway)
2. Sensory Receptors
- Can be neuronal (the receptor is a neuron) or non-neuronal (receptor regulates a neuron via neurotransmitters)
- Respond to internal (e.g., blood pressure) or external (e.g., light, touch) stimuli
- Stimuli trigger ion channel changes that produce receptor potentials, scaled by stimulus intensity
3. Transmission of Information
- Neuronal receptors generate action potentials directly
- Non-neuronal receptors release neurotransmitters that influence afferent neuron firing
- Stronger stimuli lead to higher receptor potentials and faster action potential rates
4. Perception Is Constructed in the Brain
- Sensory signals differ only by pathway, not form
- Brain identifies the stimulus type (e.g., sound, touch) by the neural circuit activated
- Perceptions are brain constructs—no sound exists unless sensed by an organism
5. Amplification and Adaptation
- Amplification: boosts signal strength during transduction (e.g., ear bones, enzymes)
- Adaptation: reduced sensitivity with prolonged exposure (e.g., tuning out clothing sensation)
6. Types of Sensory Receptors
- Mechanoreceptors: sense touch, pressure, vibration, motion
- Chemoreceptors: detect chemical cues like pH, CO₂, pheromones
- Electromagnetic receptors: detect light, electric fields, magnetic fields
- Thermoreceptors: detect temperature; some activated by capsaicin or menthol
- Pain receptors (nociceptors): sense harmful stimuli; enhanced by prostaglandins (blocked by aspirin)
7. Examples from Nature
- Star-nosed mole: detects prey by touch in dark tunnels
- Silkworm moths: smell pheromones from kilometers away
- Snakes: use pit organs to sense heat from prey
- Crayfish statocysts and insect tympanic membranes: detect balance and sound
- Humans map touch sensitivity based on receptor density and skin depth
In a Nutshell
Sensory systems convert environmental stimuli into electrical signals through specialized receptors. These signals are amplified, encoded, and transmitted to the brain, which interprets them as perception. Whether it’s detecting sound, light, pressure, or chemicals, the path taken by the signal defines the sensation. Adaptation and amplification fine-tune how we experience the world around us.