4.1 Sensory receptor types and transduction mechanisms
3 min read•august 7, 2024
Sensory receptors are specialized cells that detect and respond to various stimuli. From sensing touch to capturing light, these cells form the foundation of our sensory experiences. Understanding their types and functions is key to grasping how we perceive the world around us.
is the process of converting stimuli into electrical signals. This involves , receptor potentials, and . mechanisms allow our senses to adjust to constant stimuli, ensuring we remain sensitive to changes in our environment.
Sensory Receptor Types
Mechanoreceptors and Thermoreceptors
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Mechanoreceptors detect physical stimuli such as pressure, touch, vibration, and sound waves
Includes in the inner ear that detect sound waves and motion (vestibular system)
detect deep pressure and vibration (mesentery)
detect light touch and texture (fingertips)
detect changes in temperature
Cold receptors increase firing rate when temperature drops below normal body temperature
Warm receptors increase firing rate when temperature rises above normal body temperature
Located in the skin, hypothalamus, and other internal organs
Chemoreceptors and Photoreceptors
detect chemical stimuli such as taste and smell
Taste buds contain that detect sweet, salty, sour, bitter, and umami (savory) tastes
in the nasal cavity detect a wide variety of odorants
in the brainstem detect changes in blood pH and CO2 levels
Photoreceptors detect light energy and transduce it into electrical signals
Rods are highly sensitive to light and enable vision in dim light conditions
Cones are less sensitive to light but enable color vision and visual acuity
Located in the of the eye
Nociceptors
detect potentially damaging stimuli and give rise to the sensation of pain
Respond to mechanical, thermal, and chemical stimuli that may cause tissue damage
Have high thresholds and continue to fire in the presence of sustained stimuli (slow adaptation)
Classified as (fast, sharp pain) and (slow, dull pain)
Distributed throughout the skin, muscles, joints, and internal organs
Sensory Transduction Mechanisms
Sensory Transduction and Receptor Potential
Sensory transduction is the process by which sensory receptors convert stimuli into electrical signals (receptor potentials)
Involves the opening or closing of ion channels in the receptor cell membrane
Leads to a graded change in the membrane potential called the
The amplitude and duration of the receptor potential depend on the intensity and duration of the stimulus
Receptor potential is a graded, localized change in the membrane potential of a sensory receptor cell
Can be depolarizing (excitatory) or hyperpolarizing (inhibitory) depending on the type of receptor and stimulus
Triggers action potentials in the sensory neuron if the depolarization reaches the
Ion Channels and Action Potentials
Ion channels are pores in the cell membrane that allow specific ions to pass through
Gated by specific stimuli (ligand-gated, voltage-gated, or mechanically-gated)
Opening or closing of ion channels leads to changes in the membrane potential
Examples include the cyclic nucleotide-gated (CNG) channels in photoreceptors and the transient receptor potential (TRP) channels in nociceptors
Action potentials are all-or-none electrical signals that propagate along the axon of a neuron
Generated when the receptor potential reaches the threshold for activation of voltage-gated sodium channels
Enables long-distance transmission of sensory information to the central nervous system
Frequency of action potentials encodes the intensity of the stimulus
Adaptation
Adaptation is the decrease in responsiveness of a sensory receptor to a constant stimulus over time
Allows the receptor to remain sensitive to changes in the stimulus rather than absolute levels
Phasic receptors adapt quickly and respond mainly to changes in the stimulus (Pacinian corpuscles)
Tonic receptors adapt slowly and continue to respond to sustained stimuli (nociceptors)
Involves mechanisms such as inactivation of ion channels, depletion of neurotransmitters, and inhibitory feedback from the central nervous system