sensory receptors 8 th ed 50.1 to 50.4 7 th ed 49.1 to 49.4
TRANSCRIPT
Sensory Receptors8th ed 50.1 to 50.4
7th ed 49.1 to 49.4
Physiological basis for all animal activity: processing sensory information and generating motor output in response to that information
This is a continuous cycle
Sensory information can be from external or internal environment.
Sensory pathway:
Sensory reception Transduction Transmission Perception Amplification and adaptation
Sensory pathway:
Sensory reception Transduction Transmission Perception Amplification and adaptation
Sensory reception
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:
Sensory reception Transduction Transmission Perception Amplification and adaptation
Sensory transduction: Conversion of physical, chemical and other
stimuli to change in membrane potential
Receptor potential: change in membrane potential itself
Sensory pathway:
Sensory reception Transduction Transmission Perception Amplification and adaptation
Transmission:
Sensory information is transmitted through the nervous system as nerve impulses or action potential to the Central Nervous System (CNS).
Some axons can extend directly into the CNS and some form synapses with dendrites of other neurons
Sensory neurons spontaneously generate action potential without stimulus at a low rate
Magnitude of receptor potential controls the rate at which action potentials are generated (larger receptor potential results in more frequent action potentials)
MuscleWeakmuscle stretch
Receptor potential
Action potentials
Mem
bra
ne
po
ten
tial
(m
V)
Time (sec)0 1 2 3 4 5 6 7
–70
–70
–50
0
Stretchreceptor
Dendrites
Axon
Strongmuscle stretch
Time (sec)0 1 2 3 4 5 6 7
–70
–70
–50
0
Sensory pathway:
Sensory reception Transduction Transmission Perception Amplification and adaptation
Perception:
Action potential reach the brain via sensory neurons, generating perception of a stimulus
All action potentials have the same property, what makes the perceptions different are the part of the brain they link to.
Sensory pathway:
Sensory reception Transduction Transmission Perception Amplification and adaptation
Amplification and adaptation:
Strengthening of stimulus energy during transduction (involves second messengers)
Continued adaptation: decrease in responsiveness upon prolonged stimulation
Types of sensory receptors:
Mechanoreceptors Chemoreceptors Electromagnetic receptors Thermoreceptors Pain receptors
Mechanoreceptors:
sense physical deformation caused by pressure, touch, stretch, motion, sound
Stretch receptors are mechanoreceptors are dendrites that spiral around small skeletal muscle fibers
MuscleWeakmuscle stretch
Receptor potential
Action potentials
Mem
bra
ne
po
ten
tial
(m
V)
Time (sec)0 1 2 3 4 5 6 7
–70
–70
–50
0
Stretchreceptor
Dendrites
Axon
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
in the axon of the stretch receptor. A stronger stretch produces a larger receptor potential and higher frequency of action potentials.
Strongmuscle stretch
Time (sec)0 1 2 3 4 5 6 7
–70
–70
–50
0
Lighttouch
HairStrongpressure
Hypodermis
Nerve Connectivetissue
Dermis
Epidermis
Touch receptors (light and deep touch) are embedded in connective tissue
Chemoreceptors:
General receptors: respond to total solute concentrations
Specific receptors: respond to concentrations of specific molecules
LE 49-4
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
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.
Eye
Infraredreceptor
Some migrating animals, such as these beluga whales, apparently sense Earth’s magnetic field and use the information, along with other cues, for orientation.
Cold HairHeat
Nerve Connectivetissue
Thermoreceptors:
Detect heat and cold Located in skin and
anterior hypothalamus Mammals have many
thermoreceptors each for a specific temperature range
Capsaicin triggers the same thermoreceptors as high temperature
Menthol triggers the same receptors as cold (<28oC)
Pain Hair
Nerve Connectivetissue
Pain receptors (nociceptors):
Stimulated by things that are harmful – high temperature, high pressure, noxious chemicals, inflammations
Defensive function
Sensing gravity and sound in invertebrates:
Hair of different stiffness and length vibrate at different frequencies and pick up sound waves and vibrations
Statolith
Sensorynerve fibers
Ciliatedreceptor cells
Cilia
Statocyts: organ with
ciliated receptor cells surrounding a chamber containing statoliths in invertebrates – sense gravity
Tympanic membrane stretched over their “ear” help sense vibrations
1 mm
Tympanicmembrane
Sensing gravity and sound in humans:
Human ear: sensory organ for hearing and equilibrium
Our organ for hearing “hair cells” are mechanoreceptors because they respond to vibrations
Moving air pressure is converted to fluid pressure
Ear structure:
Outer ear: pinna, auditory canal, tympanic membrane (separates outer and middle ear)
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)
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.
Ovalwindow
Cochlea
Tympaniccanal
Basilarmembrane
Vestibularcanal
Perilymph
Stapes Axons ofsensoryneurons
Apex
Base
Roundwindow
Equilibrium:
In the vestibule behind the oval window are urticle, saccule and three semicircular canals
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
Flowof endolymph
Vestibular nerve
Nerve fibersVestibule
Utricle
Saccule
Ampulla
Flowof endolymph
Cupula
Body movement
Hairs
Haircell
Utricle (oriented horizontally), saccule (oriented vertically) tell the brian which way is up and the position of the body and acceleration
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
Dizziness: false sensation of angular motion
http://www.dizziness-and-balance.com/disorders/bppv/otoliths.html
Hearing and equilibrium in fish:
Vibrations in the water – conducted by skeleton to inner ear canals, move otoliths which stimulate hair cells
Swim bladder: air filled, responds to sound
Lateral line sense organ
Lateral line sense organ:
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
Epidermis NeuromastOpening oflateral line canal
Scale
Lateral nerveSegmental muscles of body wall
Cupula
Supportingcell
Nerve fiber
Sensoryhairs
Hair cell
Nerve tobrain
Screeningpigment
Ocellus
Visual pigment
Photoreceptor
Light
Light shining frombehind is blockedby the screening pigment
Light shining fromthe front is detected
VisionPhotoreceptors Planarians: Ocelli or eye
spots in the head region Light stimulates
photoreceptors Brain compares rate of
action potential coming form the two ocelli
Brain directs the body to turn until sensation form both ocelli are equal and minimal
Animal can move to shade, under a rock away from predators
Compound eyes:
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
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
2 m
m
Ommatidium
Rhabdom
PhotoreceptorAxons
Cornea
Crystallinecone
Lens
Vertebrate eye Single lens system (very different from
invertebrate single eyes)
Central artery andvein of the retina
Optic disk(blind spot)
Opticnerve
ChoroidSclera Eyeball or globe consists of
Sclera: tough white outer 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 coming in
Iris
Cornea
Pupil
Aqueoushumor
Vitreous humor
Fovea (centerof visual field)
Retina 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
Ciliary body
Suspensoryligament
Lens
Lens: clear disk of protein
Retina
Choroid
Suspensoryligaments
Front view of lensand ciliary muscle
Ciliarymuscle
Lens (rounder)
Lens (flatter)
Near vision (accommodation)
Distance vision
Humans and other mammals
spherical ( ciliary muscles contract, sensory ligaments relax – near objects)
flatter (ciliary muscles relax, edge of choroid moves away from lens, suspensory ligaments contract and pull the lens – distant objects)
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
Rods and cones have stacks of disks
rhodopsin (retinal - vitamin A derivative + opsin) in the membrane
get activated and cause sensory transduction
Outersegment
Disks
Rod
Insideof disk
Cell body
Synapticterminal
Rhodopsin
Cytosol
Retinal
Opsin
Leftvisualfield
Rightvisualfield
Lefteye
Righteye
Primaryvisual cortex
Lateralgeniculatenucleus
Optic nerve
Optic chiasm
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
Synapse with interneurons which take the information to the primary visual cortex
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
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
Tongue
Taste pore Sugarmolecule
Tastebud
Sensoryneuron
Sensoryreceptorcells
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
Nasal cavity
Brain
Odorant
Odorantreceptors
Odorant
Plasmamembrane
Mucus
Olfactory bulb
Action potentials
Bone
Epithelial cell
Cilia
Chemoreceptor