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Sensory Perception
Chapter 34 Part 1
Impacts, Issues
A Whale of a Dilemma
 Whales communicate and sense the world
around them using sound – a problem when
ships and defense-systems testing flood the
seas with noise
34.1 Overview of Sensory Pathways
 Sensory receptors determine what stimuli an
animal can detect and respond to
 Different kinds of sensory receptors produce
action potentials in response to different types of
stimuli
Sensory Receptor Diversity
 Mechanoreceptors: mechanical energy
• Body position or acceleration
• Touch or stretching
• Pressure waves (hearing)
 Pain receptors (nociceptors): tissue damage
• Some reflexes
 Osmoreceptors: change in solute concentration
Sensory Receptor Diversity
 Thermoreceptors: specific temperature or
temperature change
 Chemoreceptors: specific solutes dissolved in
fluid (also function in smell)
 Photoreceptors: light energy
• Including UV receptors in insects
Sensory Receptors
 Mechanoreceptors in bat hearing,
thermoreceptors in snakes
Photoreceptors and UV Light
From Sensing to Sensation
 In animals with a brain, input from sensory
neurons can give rise to sensation
 The brain determines stimulus location and
strength by which axons respond, how many
respond, and frequency of action potentials
 In sensory adaptation, sensory neurons cease
firing under continued stimulation
Sensory Information in Action
34.1 Key Concepts
How Sensory Pathways Work
 Sensory receptors detect specific stimuli
 Different animals have receptors for different
stimuli
 Information from sensory receptors becomes
encoded in the number and frequency of action
potentials sent to the brain along particular
nerve pathways
34.2 Somatic and Visceral Sensations
 Somatic sensations are signals from receptors in
the skin, joints, and skeletal muscles
• They travel along sensory neuron axons, to the
spinal cord, to the somatosensory cortex
 Visceral sensations are signals from sensory
neurons in walls of internal organs
• Relayed to the spinal cord and the brain
The Somatosensory Cortex
 Somatosensory cortex
• Part of the cerebral cortex
• Like the motor cortex, neurons are mapped to a
plan of the body
 Example: Skin receptors
• Free nerve endings around roots of hairs,
Meissner’s corpuscles (touch), Pacinian capsules
(pressure), Ruffini endings, bulb of Krause
Body Regions in
the Somatosensory Cortex
Sensory Receptors in Human Skin
hair shaft inside follicle
epidermis
dermis
free nerve
endings
Pacinian
corpuscle
Ruffini
endings
bulb of Meissner’s
Krause corpuscle
Fig. 34-6, p. 581
Animation: Sensory receptors in the
human skin
Pain
 Pain
• Perception of a somatic or visceral tissue injury
• Injured cells release chemicals that stimulate pain
receptors, affected by neuromodulators
 Referred pain
• Because pain signals usually originate with
somatic sources, the brain sometimes
misinterprets visceral pain as coming from the
skin or joints
Referred Pain
lungs,
diaphragm
heart
stomach
liver, gallbladder
pancreas
small intestine
ovaries
colon
appendix
urinary bladder
kidney
ureter
Fig. 34-7, p. 581
Animation: Referred pain
34.2 Key Concepts
Somatic and Visceral Senses
 Somatic sensations such as touch are easily
localized and stem from receptors in the skin,
muscles, or near joints
 Visceral sensations, such as a feeling of fullness
in your stomach, are less easily pinpointed; they
arise from receptors in the walls of internal
organs
34.3 Sampling the Chemical World
 Both smell and taste begin when chemoreceptors
are stimulated by the binding of specific dissolved
molecules
Sense of Smell
 Olfaction (sense of smell)
• Olfactory receptors detect water-soluble or
volatile chemicals, send signals to olfactory bulbs
• Olfactory nerves send signals to cerebral cortex
 Pheromone
• A type of signaling molecule secreted by an
individual that affects others of the same species
• Detected by a vomeronasal organ
Sense of Smell
olfactory tract
from receptors
to the brain
olfactory
bulb
bony
plate
ciliated
endings of
olfactory
receptor
that project
into mucus
inside nose
Fig. 34-8, p. 582
Sense of Taste
 Taste receptors detect chemicals dissolved in
fluid, and have different structures and locations
in different animals
 Humans have taste buds (in epithelial papillae
on the tongue) that detect five main sensations:
sweet, sour, salty, bitter, and umami
Sense of Taste
34.3 Key Concepts
Chemical Senses
 The senses of smell and taste require
chemoreceptors, which bind molecules of
specific substances dissolved in the fluid bathing
them
34.4 Sense of Balance
 Organs inside your inner ear are essential to
maintaining posture and a sense of balance
 Somatic sensory receptors also contribute to
balance
Organs of Equilibrium
 Organs of equilibrium
• Parts of sensory systems that monitor the body’s
positions and motions
 Vestibular apparatus
• Contains organs of equilibrium in vertebrates
• Semicircular canals, sacs, saccule and utricle
 Hair cells
• Mechanoreceptors with modified cilia
Organs of Equilibrium in the Inner Ear
semicircular canals
vestibular
nerve
A Vestibular apparatus
inside a human inner
ear. The organs of
equilibrium in its fluidfilled sacs and canals
contribute to a sense of
balance.
saccule
utricle
gelatinous membrane
in a semicircular canal
hair cells with their cilia
embedded in membrane
sensory neurons
B Components of
one of the organs
inside a semicircular
canal. Shifts in the
position of the head
bend hair cells and
alter their frequency
of action potentials.
Fig. 34-10, p. 583
Animation: Dynamic equilibrium
34.5 Sense of Hearing
 Hearing
• Perception of sound (mechanical energy)
 Sound waves
• Human ears collect, amplify, and sort out sound
waves (pressure waves traveling through air)
• Wave amplitude determines loudness
• Wave frequency determines pitch
Wave Properties
Amplitude
one cycle
Frequency per
unit time
Soft
Loud
Same frequency,
different amplitude
Low
note
High
note
Same amplitude,
different frequency
Fig. 34-11, p. 584
Animation: Properties of sound
The Vertebrate Ear
 Outer ear gathers sound
 Middle ear amplifies and transmits air waves
• Vibrations are transmitted from eardrum
(tympanic membrane), to hammer, anvil and
stirrup bones, to oval window
 Inner ear (vestibular apparatus and cochlea)
• Cochlea contains organs of Corti with hairs cells
that generate action potentials
How Humans Hear
Fig. 34-12a, p. 584
INNER EAR
vestibular
apparatus,
cochlea
OUTER EAR
pinna, auditory
canal
MIDDLE EAR
eardrum, ear
bones
A The outer ear’s flap and
canal collect sound waves.
Fig. 34-12a, p. 584
Fig. 34-12b, p. 584
oval window
(behind stirrup)
MIDDLE EAR BONES:
stirrup
anvil
auditory nerve
hammer
auditory
canal
EARDRUM
round
window
COCHLEA
B The eardrum and middle ear bones amplify sound.
Fig. 34-12b, p. 584
Fig. 34-12 (c-e), p. 585
Fig. 34-12c, p. 585
the cochlea, “uncoiled” for clarity
waves
of air
pressure
oval window
vestibular duct
waves
of fluid
pressure
eardrum
cochlear duct
tympanic duct
round window
C Pressure waves are transferred to
fluid inside the ducts of the cochlea
(shown here uncoiled).
Fig. 34-12c, p. 585
Fig. 34-12d, p. 585
vestibular duct
cochlear duct
organ of Corti
sensory
neurons (to
the auditory
nerve)
tympanic duct
D Pressure waves are detected by the organ of Corti in the cochlear duct.
Fig. 34-12d, p. 585
Fig. 34-12e, p. 585
hair cells of organ of Corti
tectorial membrane
basilar membrane
E Movement of the basilar membrane (the floor of the cochlear
duct) bends hair cells against the organ of Corti’s tectorial
membrane. This bending causes hair cells to fire. The action
potentials travel along the auditory nerve to the brain.
Fig. 34-12e, p. 585
Animation: Ear structure and function
Animation: Action potentials
Animation: Olfactory pathway
Animation: Somatosensory cortex
Animation: Taste receptors