Senses
Terms
Sensory Receptors: specialized cells
Sensory transductions: conversion of stimuli to nerve
impulses.
Perception: stimuli any organism become concious
Chemoreceptor: food, mate, danger, environmental
changes…
Photoreceptors: light
Thermo receptors: heat/ temperature
Mechanoreceptors: any mechanical change such as pressure
…
Electromagnetic receptors: light, electromagnetic force
Figure 50.3
(a) Receptor is afferent neuron.
(b) Receptor regulates afferent neuron.
To CNS
To CNS
Afferent
neuron
Afferent
neuron
Receptor
protein
Neurotransmitter
Sensory
receptor
Stimulus
Sensory
receptor
cell
Stimulus
leads to
neurotransmitter
release.
Stimulus
Figure 50.4
(a) Single sensory receptor activated
Gentle pressure
Low frequency of
action potentials per receptor
Sensory receptor
More pressure
High frequency of
action potentials per receptor
(b) Multiple receptors activated
Sensory receptor
Gentle pressure
Fewer
receptors
activated
More pressure
More
receptors
activated
Electromagnetic Receptors
• Electromagnetic receptors detect electromagnetic
energy such as light, electricity, and magnetism
• Some snakes have very sensitive infrared receptors that
detect body heat of prey against a colder background
• Many animals apparently migrate using the Earth’s
magnetic field to orient themselves
Figure 50.7
Eye
Infrared
receptor
(a) Rattlesnake
(b) Beluga whales
Chemical Senses
Taste
Olfactory
on tongue
olfactory epithelium,
roof of nasal cavity
Sweet, sour, salty, bitter,
Sense of taste and smell
and umami (savory)
Interpreted by the cerebral
Interpreted by??????
cortex
6
Chemical Senses
• Sense of Taste in Humans
– In humans, taste buds are located primarily on the
tongue
• Taste buds open at a taste pore
• Taste buds have supporting cells and elongated taste
cells that end in microvilli
• Five primary tastes
– Sweet, sour, salty, bitter, and umami (savory)
– Taste buds for each are located throughout the tongue,
although certain regions may be more sensitive to particular
tastes
7
Taste Buds in Humans
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tonsils
epiglottis
sensory nerve fiber
papillae
b. Papillae
taste pore
10 µm
taste bud
a. Tongue
supporting cell
c. Taste buds
connective tissue
taste cell
microvilli
d. One taste bud
b(All): © Omikron/SPL/Photo Researchers, Inc.
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Olfactory Cell Location and Anatomy
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olfactory bulb
neuron
olfactory tract
frontal lobe of
cerebral hemisphere
olfactory bulb
olfactory epithelium
nasal cavity
odor
molecules
sensory
nerve fibers
olfactory
epithelium
a.
supporting
cell
b.
olfactory
cell
olfactory cilia of
olfactory cell
odor molecules
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Hearing and
Equilibrium in Mammals
• In most terrestrial vertebrates, sensory organs for
hearing and equilibrium are closely associated in
the ear.
Human Ear
Middle
ear
Outer ear
Skull
bone
Inner ear
Stapes
Incus
Malleus
Semicircular
canals
Auditory nerve
to brain
Bone
Cochlear
duct
Auditory
nerve
Vestibular
canal
Tympanic
canal
Cochlea
Pinna
Auditory
canal
Oval
window
Tympanic
membrane
Round
window
Eustachian
tube
Organ of Corti
Hair cells
Hair cell bundle from
a bullfrog; the longest
cilia shown are
about 8 µm (SEM).
Basilar
membrane
Tectorial
membrane
Axons of
sensory neurons
To auditory
nerve
Hearing
• Vibrating objects create percussion waves in the air
that cause the tympanic membrane to vibrate.
• Hearing is the perception of sound in the brain
from the vibration of air waves.
• The three bones of the middle ear transmit the
vibrations of moving air to the oval window on the
cochlea.
• These vibrations create pressure waves in the fluid
in the cochlea that travel through the vestibular
canal.
• Pressure waves in the canal cause the basilar
membrane to vibrate, bending its hair cells.
• This bending of hair cells depolarizes the
membranes of mechanoreceptors and sends action
potentials to the brain via the auditory nerve.
Sensory reception by hair cells.
“Hairs” of
hair cell
–50 Receptor potential
Action potentials
Signal
0
–70
0 1 2 3 4 5 6 7
Time (sec)
(a) No bending of hairs
Less
neurotransmitter
–70
0
Signal
–70
Membrane
potential (mV)
–50
Membrane
potential (mV)
Signal
Sensory
neuron
More
neurotransmitter
–70
0 1 2 3 4 5 6 7
Time (sec)
(b) Bending of hairs in one direction
–50
Membrane
potential (mV)
Neurotransmitter at
synapse
–70
0
–70
0 1 2 3 4 5 6 7
Time (sec)
(c) Bending of hairs in other direction
The lateral line system in a fish has mechanorecptors that sense water movement
Lateral line
Surrounding water
Scale Lateral line canal
Epidermis
Opening of
lateral line canal
Cupula
Sensory
hairs
Hair cell
Supporting
cell
Segmental muscles
Fish body wall
Lateral nerve
Axon
Vision
• Photoreceptors:
Compound eyes: Arthropods
• Many independent units ( ommatidia )
• Insects: limited color vision
• Camera-Type eye: vertebrates and certain
mollusks as Octopus
2 mm
Figure 50.16
(a) Fly eyes
Cornea
Crystalline
cone
Rhabdom
Photoreceptor
Axons
(b) Ommatidia
Ommatidium
Lens
Camera Type( Vertebrates and certain
Molluscus)
• Single lens focuses an image of the visual field on closely-packed
photoreceptors
– Stereoscopic vision
• Found in animals with two eyes facing forward
• Common in predators: Chameleon: chameleons are able to hunt
with a high degree of accuracy while remaining protected from
other predators.
– Panoramic vision
• Wide visual field
• Common in prey animals: Goats….it helps them to find the
predators
Sense of Vision
 The Human Eye: Reacts with light and pressure
 Three Layers
 Sclera - Opaque outer layer
 Fibrous layer covering most of the eye
 In front of the eye, the sclera becomes the transparent cornea:
window of eye
 Conjunctiva – : Thin layers of epithelial cells to covers surface
of the sclera and keeps the eyes moist
 Retina - Inner layer


20
Contains photoreceptors called rod cells and cone cells
Contains the fovea centralis
o Region of densely packed cone cells where light is focused
Sense of Vision
 The Human Eye
 Three Layers
 Choroid - Thin middle layer





21
Contains blood vessels and brown pigment which absorb light
In front of the eye, the choroid thickens to form the ciliary body and the
iris: Colored portion of eyes
The iris regulates the size of the pupil
The lens helps form images
Pupil: Like aperture of Camera lens,, Controls light entering the eye.
Anatomy of the Human Eye
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sclera
choroid
retina
ciliary body
retinal blood
vessels
lens
iris
optic nerve
pupil
fovea centralis
cornea
posterior compartment
filled with vitreous humor
anterior
compartment
filled with
aqueous humor
retina
choroid
sclera
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suspensory
ligament
Sense of Vision
 Focusing of the Eye
 Light rays pass through the pupil and are focused on the retina
 Focusing starts at the cornea and continues as rays pass through
the lens, which provides visual accommodation
 Shape of lens is controlled by the ciliary muscle


23
Distant object – ciliary muscle is relaxed
Near object – ciliary muscle is contracted
Focusing of the Human Eye
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ciliary muscle relaxed
lens flattened
light rays
suspensory ligament taut
a. Focusing on
distant object
ciliary body
ciliary muscle contracted
lens rounded
b. Focusing on
near object
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suspensory ligament relaxed
Somatic Senses
 Somatic senses
 Senses whose receptors are associated with the skin, muscles,
joints, and viscera
 Proprioceptors
Mechanoreceptors involved in reflex actions that maintain muscle tone
Muscle spindles, Golgi tendon organs
 Cutaneous receptors



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Make the skin sensitive to touch, pressure, pain, and temperature
Muscle Spindles and Golgi Tendon
Organs
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1
muscle spindle
2
muscle fiber
2
1
quadriceps
muscle
3
bundle of
muscle fibers
sensory neuron
to spinal cord
Golgi tendon organ
tendon
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