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Home , Chemoreceptor, Photoreceptor cell, Sensory neuron

Sensors & Transducers

SENSES Sensory Receptors (Sensors) • Transducer: a structure that converts a into a graded . • Physiological transducers are derived from specialized , often associated with modified epithelia. 1. Exteroceptors: external stimuli a) passive — sense environmental stimuli b) active — sense self-generated stimuli ÿ bat sonar, flashlight fish, knife fish electric fields. 2. Interoceptors: sense internal body condition

Types of Sensory Receptors: Types of Sensory Receptors: Mechanisms of Transduction Mechanisms of Transduction 1. 1. Chemoreceptors: chemical stimulus binds to 2. specific binding protein on surface ‡ open ion gates ‡ depolarization. 3. • Interoceptors 4. Photoreceptors – glucose, fatty acids, pH 5. Other Electromagnetic Receptors – Nocioceptors — chemicals released by damaged cells () • Exteroceptors (special ) – Olfaction (smell) – Gustation ()

Types of Sensory Receptors: Types of Sensory Receptors: Mechanisms of Transduction Mechanisms of Transduction

1. 1. 2. 2. Mechanoreceptors: physical distortion of cell 3. Thermoreceptors: -induced change membrane ‡ open ion gates ‡ depolarization. of membrane protein ‡ open ion gates ‡ • Interoceptors depolarization. – Propioceptors — muscles, tendons, joints • Interoceptors – Visceral stretch receptors – Body temperature [BT] — hypothalamus – Blood , osmotic pressure • Exteroceptors (cutaneous senses) • Exteroceptors (cutaneous senses) – Hot & cold sensations – Touch & pressure (“Cold” is a , not a real physical entity.) • Exteroceptors (special senses) – Auditory “hair cells” – Equillibrium “hair cells”

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Types of Sensory Receptors: Types of Sensory Receptors: Mechanisms of Transduction Mechanisms of Transduction

1. 1. 2. 2. 3. 3. 4. 4. Photoreceptors: absorbed by pigment- 5. Other Electromagnetic Receptors: EM energy protein ‡ close ion gates ‡ hyperpolarization. absorbed by special metallo-protein complexes • Exteroceptors (special senses) ‡ transduction mechanism unclear – Vision — rods & cones • Electromagnetic fields • radiation

Generator Potentials afferent transmission of stimulus intensity Gentle pressure • In response to stimulus, sensory endings 1. Frequency modulation produce a local graded • Stronger stimuli result in Sensory change in membrane Low frequency of action potentials More pressure more frequent . potentials • Potential changes are called – Amplitude not changed! receptor or generator (a) Single sensory . activated High frequency of action potentials • Must be cummulative to Gentle threshhold before decay pressure 2. Receptor recruitment nPhasic response: Fewer receptors activated • Stronger stimuli may n Generator potential increases with increased Sensory stimulus, then as stimulus continues, generator receptors result in transduction by potential size diminishes. More pressure more sensors nTonic response: – More sensory send n Generator potential proportional to intensity More receptors signals of stimulus. (b) Multiple receptors activated activated

Receptive Sensory Convergence Receptive Sensory Convergence Stimuli fields Sensors neurons Stimuli fields Sensors neurons Low convergence: few Low convergence: more sensory receptors converge on a single neurons from a given area connect sensory . to more cells of the sensory High acuity: many small cortex: High acuity. receptive fields per given area distinguish among individual stimuli. But low sensitivity. High convergence: many receptors converge on a single . High sensitivity: many stimuli summed within a single

. Sensory But low acuity. cortex

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Perception of Senses Sensations • Law of Specific Nerve Energies: “Any stimulation of a — sensory neuron is perceived according to that nerve’s • Somatesthetic senses (“body ”) adequate stimulus.” vertebrates, via spinal • Adequate stimulus: the normal type and intensity of stimulus – Cutaneous senses that would cause stimulation of that neuron’s sensory receptor. – Visceral senses • I.e., “it’s all in your head!” Anything that stimulates the sensor, – Proprioceptors sensory neuron, or will be interpreted by the to be the sensation normally transduced or transmitted by those • Special senses — via structures. • Examples of misinterpretation: – Gustatory (taste) – “Seeing stars” from trauma – Olfactory (smell) – : “ringing in your ” – Auditory () – in amputees – Equilibrium – Referred pain from visceral trauma – Vision – “Hot” spices

Somatesthetic Sensory Neurons Ascending Somatesthetic Spinal Tracts Spinothalamic tracts: the three-sensory-neuron trail 1. First order sensory neuron travels from cutaneous receptors, proprioceptors • Spinal sensory neurons: pseudounipolar neurons or visceral receptors to the with cell bodies located in dorsal root ganglia. CNS via spinal dorsal root. Axon either terminates at or ascends ipsilateral tract to medulla. 2. Second order sensory neuron crosses to contralateral side and ascends to . 3. Third order sensory neuron ascends from thalamus to sensory cortex. (Remaining on contralateral side.)

Cutaneous Sensations Cutaneous-like Sensations through a cuticle Heat Gentle Pain Cold Hair touch • Mediated by dendritic nerve endings of different sensory Arthropods neurons. • Mechanoreceptors — dendritic nerve endings of • Mostly in the . But some in sensory neurons attached to articulating bristles basal stratum of epidermis.

• Thermoreceptors: heat and cold – More receptors respond to cold Dermis than warm. • (pain) • Mechanoreceptors — free – Touch

Hypodermis – Slow adapting (tonic) • Mechanoreceptors — encapsulated – Touch & pressure Nerve Connective Hair Strong – Rapidly adapting (phasic) tissue movement pressure

Fig. 50-3

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Antenna sensilla Proprioceptors

Proprioceptors: body positioning sensors • Spindles within muscles Magnified view of – Maintain muscle tension The seven types of sensory one of the pore structures on the antennae: plates on the • Golgi organs in tendons a. Small thick-walled hair worker bee’s b. Thick-walled peg – Inhibitory reflex; prevents c. Slender thin-walled peg overexertion of muscle d. Large thin-walled peg e. Pore plate • Ligament stretch receptors f. Pit organ g. Pit organ – Detect degree of joint extension/flexion

Transduction in stretch receptors Chemoreception • Taste & smell food — primal importance – A stretch receptor in a crayfish abdominal muscle – palatibility

Weak Strong Muscle – hunting muscle stretch muscle stretch Dendrites –50 Receptor potential –50 • Smell conspecifics –70 –70 Stretch (mV) receptor Action potentials – sexual

Membrane 0 0 Axon potential • elephants & use (Z)-7-dodecen-1-yl acetate) –70 –70 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 Time (sec) Time (sec) – kin recognition (a)Crayfish stretch receptors have dendrites stretch, producing a receptor potential in the stretch receptor. A stronger stretch produces embedded in abdominal muscles. When the receptor. The receptor potential triggers action a larger receptor potential and higher • wasp nestmates abdomen bends, muscles and dendrites potentials in the axon of the stretch requency of action potentials. • trails Figure 49.2a

Gustation: Sensation of taste. Taste Taste Myth • Epithelial cell receptors clustered in barrel-shaped taste buds. – Apical microvilli (taste hairs) increase surface area for chemoreception. – Stimulated taste cells release NTs to stimulate sensory neuron. • Each has taste cells only responding to one class of dissolved chemical stimulus.

• 1° sensory neuron from taste bud via cranial nerves to . 2° neuron to thalamus. Illustration reproduced and artistically enhanced over many 3° neuron to sensory cortex. generations of textbooks. But never actually verified!

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Gustatory Sensilla • Bipolar sensory neuron extends Olfaction (Smell) ciliated dendrites into nasal taste chemoreception via hollow epithelium, exposing tips to nasal sensory hairs (sensilla) primarily on legs To brain . • Odorant molecules (odorogens) and mouth-parts. Chemo- receptors Sensillum dissolve in mucus and bind to dendritic receptor proteins. Microelectrode EXPERIMENT Insects taste using gustatory sensilla (hairs) on their feet To voltage • Intracellular amplification: and mouthparts. Each sensillum contains four chemoreceptors with recorder dendrites that extend to a pore at the tip of the sensillum. To study the odorogen bound to a single receptor sensitivity of each , researchers immobilized a blowfly protein may open many ion gates. (Phormia regina) by attaching it to a rod with wax. They then inserted the tip of a microelectrode into one sensillum to record action potentials in the Pore at tip Very sensitive response! chemoreceptors, while they used a pipette to touch the pore with various Pipette containing test substances. test substance • Very large variety of chemoreceptors. can detect RESULTS Each chemoreceptor is especially sensitive to a Chemoreceptors >10,000 different ! particular class of substance, but this specificity is relative; each cell can respond to some extent to a broad range of different chemical stimuli. • First order sensory neuron extends across nasal plate of skull to the CONCLUSION Any natural food probably stimulates multiple chemoreceptors. 50 . By integrating sensations, the insect’s brain can apparently distinguish a very large number of . 30 0.5 M Meat 0.5 M Honey • Second order sensory neurons travel NaCl Sucrose • Olfactory tract branches also to limbic Stimulus via the olfactory tract (Cr-I) directly 10 system — odorant arousal of memories 0 to the olfactory cortex in the frontal in first second of response Number of action potentials and base emotions! Figure 49.13 & temporal lobes. — Bypass thalamic filter!

Olfactory Chemoreception Directional olfaction in in Invertebrates hammerhead • Chemoreceptor organs in antennae, tentacles, mouthparts, ovipositor, legs, everywhere! • Two of the most sensitive and specific nares chemoreceptors known are present in the antennae of the male silkworm moth

Figure 49.4 0.1 mm

Special Mechanoreceptors: Hair Cells Special Mechanoreceptors: Hair Cells

• NOT associated with hair!!! • receptors: – Stereocilia and • Special sensory epithelium kinocilium: – Rigid stereocilia look “hairy”. • When stereocilia bend – Deflection of stereocilia cause toward kinocilium; membrane depolarizes depolarization of associated and stimulates dendrites. sensory dendrites. • When bend away from kinocilium; • Used as the principle hyperpolarization occurs components of a variety of and inhibits dendrites. sensory structures. – Frequency of APs carries information about movement.

Hair cell from a vertebrate vestibular apparatus

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Pressure & Waves Communication Sound Sources

• Pressure waves move through water & air. • w/ vocal chords in larynx • Reveal location of food or other individuals. • Song w/ muscular syrinx • May be used to communicate. • Arthropod stridulation w/ legs or wings

Sound Ears and Hearing • Sound waves travel in all directions from their source. conduction • Waves are characterized by frequency and intensity. in the – Frequency: mammalian • Measured in hertz (cycles per second). • Pitch is directly related to frequency. – Greater the frequency the higher the pitch. Outer Ear Middle Ear – Intensity (loudness): • Directly related to amplitude of sound waves. • Sound waves are funneled by • Cavity between tympanic membrane • Measured in decibels. the pinna (auricle) into the and oval window of the . external auditory meatus. • Vibrations transferred through 3 • External auditory meatus bones: malleus to incus to stapes a channels sound waves to the – Provides protection and prevents nerve tympanic membrane. damage. Muscle can pull stapes from l – Increases sound wave intensity. oval window to dampen vibrations.

Sound Transduction in the Effects of Different Frequencies — Cochlea • Vibrations by stapes on the oval window • Displacement of produces pressure waves that displace basilar membrane is perilymph fluid within the cochlea. central to pitch discrimination. • Pressure wave corresponding in Cochlea frequency and amplitude to the vibrations • Waves in basilar Stapes of membrane reach a travel through the perilymph, down the sensory neurons scala vestibuli on one side and back up Oval peak at different window Vestibular the scala tympani on other the side. canal Perilymph Apex regions depending upon pitch of sound. • The pressure waves traveling up and back squeeze the cochlear duct between the • The location of specific sets of hair cell stimulated scalae. Base correlates to the pitch of • “Hair cell” mechnoreceptors of the Organ the vibration. Round Tympanic window of Corti in the cochlear duct are canal Basilar membrane Figure 49.9 • The degree of stimulated by the compression. compression on the hair cells correlates with the amplitude of the vibration. The cochlea “unwound” for clarity of illustration The cochlea “unwound” for clarity of illustration

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Binaural Snake hearing Localization ß Snakes lack external ears & middle ear bones. ß They do have a cochlea & hair cells. • Azimuth (right/left): – Interaural time difference (ITD) ß They hear airborne through skin; Substrate-borne vibrations through jaw. – Big head —“head shadowing” • Front/back: – Asymmetrical pinnae • Elevation (up/down): – Cock head

– Asymmetrical ears Barn Owl (Tyto alba) – Uneven ear height

• The asymmetrical design of the Barn Owl's ears is essential for pinpointing its prey in the dark. (From: Biological Anomalies: )

Vibration sensors in Arthropods Insects Ears • Sounds vibrate body hairs or tympanum (membrane) • chordotonal organs — analogous to hair cells on front or rear legs, or on abdomen. • Esp. in legs and antennae. But may be anywhere. – Abdominal tympani pressed against tracheal air sacs • Sensed by chordotonal organs . • Sensory cilia vibrate like strings of piano. – Chitin granule in dilation increases momentum.

Tympanic membrane

Figure 49.7 1 mm

ECHOLOCATION ECHOLOCATION — Active hearing — Active hearing • Rudimentary in seals, shrews & oilbirds. • Sophisticated in bats & whales – for prey location, navigation, Infrared film communication. shows muzzle is warm, keeping nerves sensitive – low pulse rate and skin supple for vibrissae for navigation. movement. – high pulse rate for detail of objects.

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Active vs. Passive Hearing Bats & Moths Chordotonal organ

• Active hearing — bats echolocate flying moths. – Detect moth-size prey w/in ~3m • Passive hearing — moths listen for bat clicks. – flee if low pulse rate – drop when high pulse rate

Odontocetes Odontocetes

• clicks & whistles are focused by melon • Returning echo is transmitted through jaw

Odontocetes & Fish Pressure & Baroreception

• Echo reflects off prey’s swim bladder. • Not well understood • Herring & shad detect ultrasound: • Aquatic – with their swim bladder – Plankton & fish sense and adjust for depth. – take evasive action – Distension of swim bladder or pneumocyst? • Land – Bats sense air pressure & emerge from caves only when conditions good for insect prey.

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Neuromasts & Facial extensions of the lateral line the Lateral Line System system in sharks Sense vibrations and pressure waves through dense aquatic medium. • Locate prey • Avoid predators • Coordinate schooling • Navigate currents • Feel barriers & obstacles

Vestibular Apparatus and Utricle and Equilibrium • Utricle and saccule provide information about linear acceleration. • Sensory structures of the • Chambers lined with hair cells covered in a gelatinous membrane. vestibular apparatus is • This otolithic (“ear rocks”) membrane is impregnated with calcium located within the carbonate crystals to increase its mass and therefore its inertia and membranous labyrinth. gravitational drag. – Filled with endolymph. • Equilibrium and • Utricle: More sensitive to acceleration (including horizontal acceleration. orientation with respect to – During forward acceleration, gravity) is due to vestibular otolithic membrane lags behind apparatus. hair cells, so stereocilia are pushed backward. • Vestibular apparatus consists of 2 parts: • Saccule: More sensitive to vertical acceleration. – organs: – Stereocilia are pushed upward • Utricle and saccule. when person descends. – Semicircular canals.

Semicircular Canals Semicircular Canal Variations • Provide information about ß More agile animals (arboreal or aerial) have bigger rotational acceleration. semicircular canals. – Project in 3 different planes. ß Sedentary or buoyant animals have smaller. • Each canal contains a semicircular duct. • At the base is the crista ampullaris, where sensory hair cells are located. – Hair cell processes are embedded in the cupula. Dolphin • Endolymph provides inertia so that the sensory Bush baby processes will bend in direction opposite to the angular acceleration.

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Vision Invertebrate Statocysts • Rods & cones in the retina transduce energy in the electromagnetic spectrum. • Statocysts have hair cells depressed by – Only wavelengths of 400–700 nm constitute visible light to humans. statoliths.

• work the same way as vertebrate saccule & utricle

Vision Types Functions: » Prey detection. Rod Predator detection. Outer Segment Rhabdomere Mate detection. » Location positioning & navigation. Orientation & maneuvering. » Photokinesis — increased activity in the presence of light. Ciliary type: Microvillar type: [vertebrates [most invertebrates] — movement toward or away from light source. & cnidarians] Visual pigment in » Photoperiod & biological rhythms. Visual pigment in membrane of membrane of numerous parallel – Diurnal numerous parallel discs microvilli (rhabdomere) within outer segment of – Seasonal expanded

Vertebrate Ciliary Photoreceptors Rods & Cones Vertebrate Retina • Consists of single-cell- thick pigmented epithelium, layers of other neurons, and photoreceptor neurons (rods and cones). – Neural layers are forward extension of the brain. – Neural layers face outward, toward the incoming light. • Light must pass through several neural layers before striking the rods and cones.

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Effect of Light on Visual Pigment • Rods and cones are activated when light produces chemical change in visual pigment. Visual pigment in rods is . – Bleaching reaction: • Changes shape when it absorbs light. • Initiates changes in ionic permeability to produce APs in ganglionic cells.

Rod

Outer segment H H C O H CH 3 C C CH 3 H3C H H2C C H H C H C C C C C Disks 2 C C C C H

CH 3 H CH 3 H cis isomer Cell body Inside of disk

Light

Synaptic terminal H H CH 3 C CH 3 H2C C H H H H

H2C C C C C C O C C C C C C H Cytosol CH 3 H CH 3 CH 3 CH 3 Physiol Rev. 85(3) Figure 49.20a, b trans isomer Rhodopsin

Electrical Activity of Retinal Cells Electrical Activity of Retinal Cells (continued) • cells and amacrine cells are only neurons that • Na+ channels rapidly close in response to light. produce action potentials (neural impulses). – Absorption of single of light can block Na+ entry: – Rods and cones; bipolar cells, horizontal cells secrete excitatory or inhibitory • Hyperpolarizes and release less inhibiting NT. • In dark, photoreceptors release inhibitory NT that – Light can be Dark Responses Light Responses hyperpolarizes bipolar neurons. transduced & Rhodopsin inactive Rhodopsin active

perceived. Na+ channels open Na+ channels closed • Light inhibits photoreceptors from releasing inhibitory NT. • Releases bipolar cells to produce EPSPs in ganglion cells to transmit APs. • Dark current: Rod depolarized Rod hyperpolarized + Glutamate No glutamate – Rods and cones contain many Na channels that are open in the released released dark. Bipolar cell either Bipolar cell either depolarized or hyperpolarized or hyperpolarized, depolarized, depending on • Causes slight membrane depolarization in dark, depending on glutamate receptors causing release of inhibitory NT . glutamate receptors Figure 49.22

Light Sensors: Light Sensors: Ocelli Cup-shaped

ß The deeper the cup, the more directional the vision. ß Pinhole eyes, lenses, and focusing allow for improved image forming.

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Light Sensors: Light Sensors: Camera Eye Camera Eye http://library.thinkquest.org/28030/eyeevo.htm • Vertebrates, cephalopods, cubozoan cnidarians, Function Camera Eye Similarities & some . 1. opening for light to enter aperture 2. control the amount of light diaphragm control muscles control size of • Pupil surrounded by light-regulating iris entering camera/eye size of aperture pupil 3. refract light glass biconvex lens mainly ; lens, aqueous & vitreous humor 4. object of light action to form photosensitive Photoreceptors (rods & cones) image chemicals on film in retina 5. absorb excessive light to prevent dark internal pigmented, dark multiple images formation surface Difference 1. focusing mechanism change distance change shape/focal length of between lens & film lens

Light Sensors: Camera Eye Compound Eyes mm 2 eyes • Major eye type in arthropods Cornea • Also in some Crystalline Lens annelids & cone bivalve molluscs (convergence?) Photoreceptor •8 per

Rhabdom [light path] Axons •converged rhabdomeres of the 8 photoreceptors

e, concave-mirror eye: Ommatidium [unit eye] bivalve molluscs

http://astro.berkeley.edu/~jrg/CELT/ay250_012403.html Fig. 50-17

Eyes of cnidarian medusas

Box jelly • Four rhopalia — each with six eyes – Pair of pit eyes; pair of slit eyes, pair of camera eyes

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Refraction • Light that passes from a medium of one density into a medium of another density (bends). • Ability of the eyes • Refractive index (degree of to keep the image refraction) depends upon: focused on the – Comparative density of the 2 media. retina as the • Refractive index of air = 1.00. • Refractive index of cornea = 1.38. distance between – Curvature of interface between the the eyes and object 2 media. • Image is inverted on retina. varies.

“Camera eye” – pupil surrounded by light- regulating iris

Visual Acuity

• Sharpness of vision. Deer’s Eye View of Tiger • Depends upon resolving power: – Ability of the to resolve 2 closely spaced dots. – Myopia (nearsightedness): • Image brought to focus in front of retina. – Hyperopia (farsightedness): • Image brought to focus behind the retina. – Astigmatism:

n Asymmetry of the cornea and/or lens. n Images of lines of circle Whereas most other vertebrates, and many appear blurred. invertebrates, have good vision, most have poor (nocturnal).

Exceptional Mammals: “Old World” Primates Cones and Color Vision High-precision Color vision • Cones have much less convergence than do rods. • Therefore, cones are less sensitive than rods to light. • And thus cones provide greater . • Cones also provide color vision. • High light intensity bleaches out the rods, and color vision with high acuity is provided by cones. • Trichromatic theory of color vision: – 3 types of cones: red, green, and blue [RGB]. • According to the region of visual spectrum absorbed. blue scrotum changes w/ • All other detected as a blend of these three. breeding state

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Visual Acuity and Sensitivity

Cones and Color Vision (continued) • Each eye oriented so that image falls within . – Fovea only contain cones. • Each type of cone • Degree of convergence of cones in fovea is 1:1 (no convergence - highest acuity). contains – Peripheral regions contain both rods and cones. • Degree of convergence of rods is much higher (high convergence - higher sensitivity). associated with – Visual acuity greatest and sensitivity lowest when light falls on fovea. . – protein is unique for each of the 3 cone pigment. • Each cone absorbs different wavelengths of light.

Dichromatic vs. Trichromatic Cones Dichromatic vs. Trichromatic Cones

Color vision Acuity

(Similar to “red-green colorblindness.”) < 12 cycles/degree* (*Equivalent to ~20/80 myopia.)

• Cats respond to the colors purple, blue, green and (weakly) to yellow. > 30 cycles/degree – Red, orange and brown colors appear to fall outside cats color range, and are most likely seen as dark to mid shades of gray. • Humans also see more color saturation, meaning we not only see more colors, but we see colors more intensely or vibrantly than do most mammals.

Color Vision – Extended Spectrum Color Vision – Extended Spectrum birds, bees, & butterflies light light

” ” visible visible “ “

blackeyed susan Cleopatra butterfly light light ultra-violet ultra-violet

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Color Vision inferred from cone types in retina ANIMAL THE COLORS THEY SEE SPIDERS (jumping spiders) AND GREEN INSECTS (bees) ULTRAVIOLET, BLUE, YELLOW CRUSTACEANS (crayfish) BLUE AND RED • Up to 16 CEPHALOPODS (octopi and ) BLUE ONLY different FISH MOST SEE JUST TWO COLORS AMPHIBIANS (frogs) MOST SEE SOME COLOR receptor REPTILES (snakes) SOME COLOR AND INFRARED types! BIRDS FIVE TO SEVEN COLORS • Can sense MAMMALS (cats) TWO COLORS BUT WEAKLY polarized light MAMMALS (dogs) TWO COLORS BUT WEAKLY MAMMALS (squirrel) BLUES AND YELLOWS • Stereo vision MAMMALS (primates-apes and chimps) SAME AS HUMANS in each eye! MAMMALS (African monkeys) SAME AS HUMANS MAMMALS (South American monkeys) CAN'T SEE RED WELL

Visual Field Eye Specializations

• Image projected onto • Predators have forward eyes for stereovision retina is reversed in each eye. • Cornea and lens focus the right part of the visual field on left half of retina. • Left half of visual field focus on right half of each retina.

Extreme stereovision & peripheral vision — jumping spiders Eye Specializations • 4 pairs of eyes • Prey have eyes on side of head for wide field. – AME: high resolution – ALE: stereovision – PME & PLE: peripheral vision • tetrachromatic color (including UV)

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Tapetum lucidum Eye Specializations • Reflective layer behind retina • Present in most vertebrate • Raptors have two fovea eyes except in primates – one at top of 8X eye for good downward vision. and diurnal squirrels & birds. • Provides “second chance” for photoreceptors to encounter light signal • Increases sensitivity >6x • Sacrifices acuity

The combination of the and elliptical In a pig’s eye! permit cats to see extremely well in near (identical illumination) • In human:

• In cat:

Reflections of an odd-eyed cat

• Different amounts of melanin in the iris absorb/scatter different Active Sensing w/ Light wavelengths of light on the way in, and the way out. • Flashlight fish illuminate prey.

ambient light flash light

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Bioluminescent Bacteria Photoreception & Light Weirdos • Insects, dinoflagellates, & deep sea • Cephalopod retina is fish/ lure prey & signal mates. inverted – rods & cones face light.

lanternfish http://astro.berkeley.edu/~jrg/CELT/ay250_012403.html

Different eyes / Different tissues Incredible Analogy

vertebrate arthropod cephalopod

Photoreception Weirdos Photoreception Weirdos • The tarsier of Southeast • Wrinkled Asia has the largest eyes – Fruit bats have small relative to body size of folds in their retinas any living creature. – Increases surface area – The eyes are so enormous that they cannot be moved in their for photoreceptors sockets. – To compensate, tarsiers can swivel their necks 180 degrees in either direction. – has the vision, speed and reflexes to catch small prey in pitch darkness.

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Spookfish — primary & secondary eyes Spookfish — primary & secondary eyes

lens 2° mirror eye 1° eye retina

Focusing mirror in the 2° Light reflecting from the Light reflecting from the eye 1° dorsal-oriented retinas 2° ventral-oriented retinas retina

http://www.wired.com/wiredscience/2009/01/mirroreyes/ http://www.wired.com/wiredscience/2009/01/mirroreyes/

Photoreception Weirdos Photoreception Weirdos Extraocular Photoreceptors Extraocular Photoreceptors • Butterfly genitals • Backs of eyeless deep-sea vent shrimp – Japanese Papilio swallowtails – Originally thought to sense IR from vents – get parts aligned – But sensitive to green/blue light

• Left side view of the abdominal tip of both sexes. Location of two pairs of genital photoreceptors, P1 and P2, is indicated by arrows; (a) male and (b) female • BioScience 51(3):219-225. 2001 “Naked retina” of dorsal organ contains 2-8x more visual pigment than a normal shrimp eye.

Photoreception Weirdos Photoreception Weirdos Extraocular Photoreceptors Extraocular Photoreceptors

the "black brittlestar” Ophiocoma wendtii • Calcite plates form precise micro-lenses • Focus light onto photoreceptors Tube foot expression of r-opsin in S. purpuratus. • Much of aboral surface a giant ! Ullrich-Lüter E M et al. PNAS 2011;108:8367-8372 • Photoreceptors shielded by iris-like chromatophores in daylight ©2011 by National Academy of Sciences

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Pit Organs Sense Infrared (Heat) Pit Organs of Vampire Bats • “pit vipers” (rattlesnakes), boas & pythons. • Only known mammal w/ IR sensors • Like a pinhole camera: infrared image focused on • 3 leaf-pits surrounding nares sensory surface. • Detect cutaneous vessels by “hot-spots” on warm-blooded prey.

Electrical Sensing Electrical Prey Detection • Monotremes (egg-laying mammals): • Electroreceptor cells response to fluctuations in – platypus bill environmental electric fields. – echidna snout • Used in: – Prey Detection • Sense electric fields created by muscle activity of hidden prey. – Navigation • Sense distortions in a self-generated field. • Map patterns of saltwater currents. – Communication – Detect crustacean prey during nocturnal aquatic foraging. • Signaling mates, territoriality, identity. – Eyes, nostrils and ears are all closed when underwater! – May consume half its weight in prey!

Ampullae of Lorenzini Relative importance of Sharks & rays. electroception & olfaction in lungfish

nanovolt sensitivity!

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Active Electro-reception Active Electro-reception • Elephant-nose fish (African rivers).

The field generated by the fish is distorted by nearby objects. • Objects less conductive than water (e.g., rocks) spread the lines of force out.

q Electrical “bright spot” • Objects more conductive (other animals) draw the lines together. ß Electrical “dark spot” • Electric organ (modified muscle) — generates pulses. • Electroreceptors — three types 1. mormyromasts — detect the electric organ discharge. – navigate and detect movement in murky water. 2. knollen organs — detect the electric organ discharge of other elephant nose fish. – communication and finding mates. 3. ampullary receptors — detect the low frequency electric fields emitted by other aquatic animal to probe for prey.

Electroreception Electrocommunication Imaging (* EOD: electric organ discharge)

Knifefish (South American rivers)

Electrogeneration & Predation • Better known electric eels and electric rays create Magnetic Fields & Migration more powerful (10–1000V) electric organ • Magnetite (iron oxide) for navigation in: discharges to stun prey. — Not sensory. – bacteria – bees – migratory birds – sea turtles – cetaceans

Electric eel Electrophorus electricus

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