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Sensory receptors animal systems
and the CNS
Perennou Nuridsany/Science Source.
Involve four steps
• Sensory reception: sensory receptors
detect a stimulus
• Sensory transduction: in response to
the stimulus, ion channels open or close,
which changes the membrane potential
• Transmission: an action potential is
carried to the CNS
• Perception: awareness of the stimulus
occurs in the brain.
Integration: several weak stimuli are added into one
large perceived stimulus. Occurs at several steps:
• During signal transduction, separate stimuli are
added together to generate an action potential.
• During transmission, several rapid action potentials
are integrated into one.
• In the CNS, signals from multiple sensory cells are
integrated into one signal.
Sensitivity of sensory receptors changes
in response to constant stimulation
• Enables an animal to adjust to
changing environmental conditions.
• Enables an animal to ignore constant
stimuli that might otherwise be
Bind chemicals, responsible for senses of taste
Olfaction: sense of smell, involves detection of
airborne chemicals called odorants.
Gustation: sense of taste, involves detection of
dissolved chemicals called tastants.
Aquatic animals do not have distinct senses of
taste and smell.
by the larvae of their
species to navigate to
(a) Jacana/Science Source. (b)
Gary Meszaros/Science Source.
• Detect electromagnetic energy such as light,
electricity, and magnetism
• Photoreceptors detect light and are responsible for
Eyespots (planaria): sense light and dark
Compound eyes (insects): detect motion.
Single-lens eyes (vertebrates and some invertebrates):
Planaria move away from light sources using
use magnetite to orient
respect to Earth’s
magnetic field and
navigate during winter
Courtesy of Gene Nieminen/USFWS.
• Detect injurious stimuli such as extreme
heat, pressure, and dangerous chemicals.
• In humans, many nociceptors are naked
dendrites of other types of receptors;
thermoreceptors, mechanoreceptors, and
chemoreceptors can act as nociceptors.
MO Figure Auditory and
Courtesy of B. Peterson/USFWS.
Primary site of auditory sense reception. Contains
the fluid-filled vestibular and tympanic canals.
Vibration of the basilar membrane causes cilia on
hair cells to bend. Signals are transmitted to the
brain through the auditory nerve.