Transcript Sensory Receptors

Sensory Receptors
8th ed 50.1 to 50.4
7th ed 49.1 to 49.4
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Physiological basis for all animal activity:
processing sensory information and
generating motor output in response to that
information
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This is a continuous cycle
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Sensory information can be from external or
internal environment.
Sensory pathway:
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Sensory reception
Transduction
Transmission
Perception
Amplification and adaptation
Sensory pathway:
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Sensory reception
Transduction
Transmission
Perception
Amplification and adaptation
Sensory reception
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1st step of sensory pathway
Sensory receptors: Specialized neurons or
epithelial cells; Single cells or a collection of
cells in organs
Very sensitive
Sensory pathway:
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Sensory reception
Transduction
Transmission
Perception
Amplification and adaptation
Sensory transduction:
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Conversion of physical, chemical and other
stimuli to change in membrane potential
Receptor potential:
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change in membrane potential itself
Sensory pathway:
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Sensory reception
Transduction
Transmission
Perception
Amplification and adaptation
Transmission:
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Sensory information is transmitted through the
nervous system as nerve impulses or action
potential to the Central Nervous System (CNS).
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Some axons can extend directly into the CNS and
some form synapses with dendrites of other neurons
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Sensory neurons spontaneously generate action
potential without stimulus at a low rate
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Magnitude of receptor potential controls the
rate at which action potentials are generated
(larger receptor potential results in more
frequent action potentials)
Weak
muscle stretch
Muscle
Stretch
receptor
Membrane
potential (mV)
Dendrites
Strong
muscle stretch
–50 Receptor potential
–50
–70
–70
Action potentials
0
0
–70
–70
Axon
0 1 2 3 4 5 6 7
Time (sec)
0 1 2 3 4 5 6 7
Time (sec)
Sensory pathway:
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Sensory reception
Transduction
Transmission
Perception
Amplification and adaptation
Perception:
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Action potential reach the brain via sensory neurons, generating
perception of a stimulus
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All action potentials have the same property, what makes the
perceptions different are the part of the brain they link to.
Sensory pathway:
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Sensory reception
Transduction
Transmission
Perception
Amplification and adaptation
Amplification and adaptation:
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Strengthening of stimulus energy during
transduction (involves second messengers)
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Continued adaptation: decrease in
responsiveness upon prolonged stimulation
Types of sensory receptors:
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Mechanoreceptors
Chemoreceptors
Electromagnetic receptors
Thermoreceptors
Pain receptors
Mechanoreceptors:
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sense physical deformation caused by
pressure, touch, stretch, motion, sound
Stretch receptors are mechanoreceptors are
dendrites that spiral around small skeletal
muscle fibers
Weak
muscle stretch
Muscle
Dendrites
Stretch
receptor
Membrane
potential (mV)
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Strong
muscle stretch
–50 Receptor potential
–50
–70
–70
Action potentials
0
0
–70
–70
Axon
0 1 2 3 4 5 6 7
Time (sec)
Crayfish stretch receptors have
dendrites embedded in abdominal
muscles. When the abdomen bends,
muscles and dendrites stretch, producing a
receptor potential in the stretch receptor. The
receptor potential triggers action potentials
0 1 2 3 4 5 6 7
Time (sec)
in the axon of the stretch receptor. A stronger
stretch produces a larger receptor potential
and higher frequency of action potentials.
Light
touch
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Touch
receptors
(light and
deep touch)
are
embedded in
connective
tissue
Strong
pressure
Epidermis
Dermis
Hypodermis
Nerve
Connective
tissue
Hair
Chemoreceptors:
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General receptors: respond to total solute
concentrations
Specific receptors: respond to concentrations
of specific molecules
Electromagnetic
receptors:
 Detect various forms
of electromagnetic
energy like visible
light, electricity,
magnetism
 Snakes can have very
sensitive infrared
receptors – detect
body heat of prey
 Animals can use
earth’s magnetic field
lines to orient
themselves during
migration (magnetite
in body) – orientation
mechanism
Eye
Infrared
receptor
This rattlesnake and other pit vipers have a pair of infrared
receptors, one between each eye and nostril. The organs
are sensitive enough to detect the infrared radiation
emitted by a warm mouse a meter away.
Some migrating animals, such as these beluga whales,
apparently sense Earth’s magnetic field and use the
information, along with other cues, for orientation.
Heat
Cold
Thermoreceptors:
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Detect heat and cold
Located in skin and
anterior hypothalamus
Mammals have many
thermoreceptors each
for a specific
temperature range
Nerve
Connective
tissue
Hair
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Capsaicin triggers the same thermoreceptors
as high temperature
Menthol triggers the same receptors as cold
(<28oC)
Pain
Pain receptors
(nociceptors):
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Stimulated by
things that are
harmful – high
temperature, high
pressure, noxious
chemicals,
inflammations
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Defensive function
Nerve
Connective
tissue
Hair
Sensing gravity and sound in invertebrates:
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Hair of different stiffness and length vibrate at
different frequencies and pick up sound
waves and vibrations
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Statocyts:
organ with
ciliated receptor
cells surrounding
a chamber
containing
statoliths in
invertebrates –
sense gravity
Ciliated
receptor cells
Cilia
Statolith
Sensory
nerve fibers
Tympanic
membrane
1 mm
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Tympanic membrane stretched over their
“ear” help sense vibrations
Sensing gravity and sound in humans:
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Human ear: sensory organ for hearing and
equilibrium
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Our organ for hearing “hair cells” are
mechanoreceptors because they respond to
vibrations
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Moving air pressure is converted to fluid
pressure
Ear structure:
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Outer ear:
pinna, auditory
canal, tympanic
membrane
(separates
outer and
middle ear)
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Middle ear: three small
bones malleus (hammer),
incus (anvil) and stapes
(stirrup) transmit
vibrations from tympanic
membrane to the oval
window.
Eustachian tube connects
middle ear to the pharynx
and equalizes pressure
Inner ear: consists of
fluid filled chambers
including semicircular
canals (equilibrium) and
cochlea (hearing)
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Moving air travels through the air canal and causes
the tympanic membrane to vibrate
Three bones of the middle ear transmit the
vibrations to the oval window, a membrane on the
cochlear surface
That causes pressure waves in the fluid inside the
cochlea
The cochlea:
 Upper vestibular canal and inner tympanic
canal filled with perilymph; middle cochlear
duct filled with endolymph
Organ of Corti:
 Floor of the cochlear duct is the
basilar membrane
 Organ of corti is located on the
basilar membrane, with hair cells
which has hair projecting into the
cochlear duct.
 Many of the hairs are attached to the
overhanging tectorial membrane.
 Sound waves cause the basilar
membrane to vibrate. This results in
displacement and bending of the
hair cells within the bundle.
 This activates the
mechanoreceptors, changes the hair
cell membrane potential (sensory
transduction) which generates action
potential in the sensory neuron.
Cochlea
Stapes
Vestibular
canal
Oval
window
Perilymph
Apex
Base
Round
window
Tympanic
canal
Axons of
sensory
neurons
Basilar
membrane
Equilibrium:
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In the vestibule behind the oval window are
urticle, saccule and three semicircular canals
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Three semicircular canals arranged in three spatial
planes detect angular movements of the head
The hair cells form a cluster. They have a
gelatinous capula.
Fluid in the semicircular canals pushes against the
capula deflecting the hairs, stimulates the neurons
Semicircular canals
Ampulla
Flow
of endolymph
Flow
of endolymph
Vestibular nerve
Cupula
Hairs
Hair
cell
Vestibule
Nerve fibers
Utricle
Saccule
Body movement
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Utricle (oriented horizontally),
saccule (oriented vertically) tell
the brian which way is up and the
position of the body and
acceleration
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Sheet of hair cells project into a
gelatinous capula embedded with
otoliths (ear stones). Movement
of the head causes otoliths to in
different directions against the
hair protruding from the hair cells.
This movement is detected by
the sensory neurons
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Dizziness: false sensation of
angular motion
http://www.dizziness-andbalance.com/disorders/bppv/otoliths.html
Hearing and equilibrium in fish:
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Vibrations in the water – conducted by
skeleton to inner ear canals, move otoliths
which stimulate hair cells
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Swim bladder: air filled, responds to sound
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Lateral line sense organ
Lateral line sense
organ:
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Water flows through
the system
Bends hair cells;
generates receptor
potential
Nerve carries action
potential to the brain
Helps them sense
water currents,
moving objects, low
frequency sounds
Lateral line
Lateral line canal
Scale
Neuromast
Epidermis
Segmental muscles of body wall
Opening of
lateral line canal
Lateral nerve
Cupula
Sensory
hairs
Supporting
cell
Nerve fiber
Hair cell
Vision
Light
Photoreceptors
 Planarians: Ocelli or eye
spots in the head region
 Light stimulates
photoreceptors
 Brain compares rate of
action potential coming
form the two ocelli
Photoreceptor
 Brain directs the body to
turn until sensation form
both ocelli are equal and
minimal
Visual pigment
 Animal can move to
shade, under a rock away
Ocellus
from predators
Light shining from
the front is detected
Nerve to
brain
Screening
pigment
Light shining from
behind is blocked
by the screening pigment
Compound eyes:
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Very good at detecting movement
Very good at detecting flickering light (6 times
faster than human eye)
Some bees can see in the ultraviolet range of
light
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Several thousand omatidia (facets) in every eye
Cornea and crystalline cone form the lens which
focuses light on the rhabdom
Light stimulates the photoreceptors to generate
receptor potential which generates action potential
Cornea
Crystalline Lens
cone
Rhabdom
Axons
Photoreceptor
Ommatidium
Vertebrate eye
 Single lens system (very different from
invertebrate single eyes)
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Sclera
Eyeball or globe
consists of
Choroid
Iris
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Sclera: tough
white outer
Cornea
connective tissue
Cornea: clear part
of sclera in the
front of the eye –
lets light into the
eye, acts as a
fixed lens
Choroid:
pigmented inner
layer: forms iris
(doughnut shaped)
– can change size
to regulate the
amount of light
Pupil
coming in
Optic
nerve
Central artery and
vein of the retina
Optic disk
(blind spot)
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Retina: innermost
layer with neurons
and
photoreceptors
Aqueous humor:
fluid that fills the
anterior cavity
(blockage of ducts
increases
pressure and
causes glaucoma)
Vitreous humor:
jellylike, fills the
posterior chamber
Retina
Fovea (center
of visual field)
Aqueous
humor
Vitreous humor
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Ciliary body
Suspensory
ligament
Lens
Lens: clear disk
of protein
Humans and other
mammals
Front view of lens
and ciliary muscle
Choroid
Lens (rounder)
Retina
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spherical ( ciliary
muscles contract,
sensory ligaments relax
– near objects)
Ciliary
muscle
Near vision (accommodation)
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flatter (ciliary muscles
relax, edge of choroid
moves away from lens,
suspensory ligaments
contract and pull the
lens – distant objects)
Suspensory
ligaments
Lens (flatter)
Distance vision
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Fishes, squids and octopuses focus by
moving lens forward and backward
Photoreceptors
 Rods: sensitive to light, do not distinguish
colors
 Cones: detect color, not very sensitive to
light
 Nocturnal animals have a higher proportion of
rods
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Rods and cones
have stacks of
disks
rhodopsin
(retinal - vitamin
A derivative +
opsin) in the
membrane
get activated
and cause
sensory
transduction
Rod
Outer
segment
Disks
Inside
of disk
Cell body
Synaptic
terminal
Cytosol
Retinal
Rhodopsin
Opsin
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Information from the each
eye is carried by the optic
nerve (each with about a
million axons)
Optic nerves meet cross at
the optic chiasm
Information from right visual
field of both eyes goes to the
left side of the brain
Information from the left
visual field of both eyes goes
to the right side of the brain Optic nerve
Synapse with interneurons
which take the information to
the primary visual cortex
Lateral
geniculate
nucleus
Primary
visual cortex
Left
visual
field
Left
eye
Right
visual
field
Right
eye
Optic chiasm
Perception of gustation (taste) and olfaction
(smell)
Insects
 In insects taste sensation is located within sensory
hairs called sensilla (on feet and mouthparts)
 Olfactory odorants are detected by olfactory hairs
Sensillum
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Mammals
In mammals specialized epithelial cells form taste
buds
Tastants detect five perceptions of taste: sweet,
sour, salty, bitter and savory (MSG)
Chemoreceptors generate receptor potential by
triggering a chain of reactions involving different
proteins for different tastes in the receptor cells
Taste pore
Taste
bud
Tongue
Sugar
molecule
Sensory
receptor
cells
Sensory
neuron
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Sensory neurons lining the nasal cavity and
extending into the mucus layer get stimulated
by odorants. The stimulus is transmitted
directly to the olfactory bulb of the brain
Brain
Olfactory bulb
Nasal cavity
Bone
Odorant
Epithelial cell
Odorant
receptors
Chemoreceptor
Plasma
membrane
Odorant
Cilia
Mucus