Week 7: Sensory Systems

how many “special” senses and “general” senses are recognized?

there are 5 special senses

• sight/vision

• touch/tactile

• hearing/audition

• taste/gustation

• smell/olfaction

and 2 general senses

• balance

• movement

how do the special sense systems relate to CNS?

special sense systems that integrate directly w/ the CNS via cranial nerves

how do general senses relate to PNS?

general senses carry PNS signals to the CNS and include the vestibular system that receives info about balance, gravity, and acceleration, and proprioception that tracks relative position, force and bending moment of body parts during movement

list and define the 3 steps of the sensory receptor cell

1) stimulus = environmental parameter causing a response in a nerve muscle of gland => 2) reception = nerve/epithelial tissue reacts to stimuli by developing an action potential => 3) sensation = perception or awareness of a stimulus

what type of info do photoreceptors provide?

photoreceptors provide more detailed info on near and distant environments regarding distance, color, and direction than any other sense

what info is gained from photoreceptors dealing with distance, color, and direction?

• distance = info is derived from differences in light intensity and contrast

• color = information is derived from differences in light wavelength

• direction = is derived from differences in the plane of polarization light

what sense is required for many animal’s survival?

vision

what is the advantage of light?

major advantage of light is its rapidity of transmission at 300,000 km/sec environmental changes are perceived instantaneously

what are the 5 types of photoreceptors, which phylas do they belong to, and do they form images

• dermal light sense (diffuse photosensitivity) => ALL major phyla => no

• eye spots => Platyhelminthes, Annelida, Arthropoda => no

• ocellus => Arthropoda, Onychophora => no

• convex eye => Arthropoda => yes

• vesicular eye => Cnidaria, Annelida, Arthropoda, Vertebrata => yes

dermal light sense, diffuse photosensitivity (DLS) facts:

• how easy are diffuse photoreceptor cells able to be located?

• what do animals use diffuse photoreceptor cells for?

• how sensitive are DLS cells compared to well-developed eyes?

• can DLS cells enhance light gathering or directional info?

• are the rxn times short/long for DLS cells?

• what can be in addition to DLS?

• what organism’s movement do dermal receptors control?

• diffuse photoreceptor cells are difficult to locate and identify

• animals use diffuse photoreception for tasks that do not require spatial vision

• DLS cells are several 1000x less sensitive than well-developed eyes

• DLS cells can not enhance light gathering, or give directional info

• DLS cells exhibit relatively long rxn times

• animals may exhibit dermal light sense in addition to eyes or eye spots

• Planarians and lower vert movement may be controlled by dermal receptors

what are the 3 uses of DLS

• night/day determinations

• timing of seasonal events by day length

• predators and/or food awareness

what are the visual adaptations?

eye spots

what are the eyespots of flatworms comprised of?

pits containing simple light-sensing nerves but lack structures needed to focus images

what do light sensitive pigment cells contain

opsin

define opsin

a phototransduction protein

what happens when light enters the pit?

light entering the pit initiates a cascade rxn and stimulates neurons that synapse w/ the endom (central ganglion)

recently, what can flatworm eyespots distinguish b/w?

colors

what are compound eyes composed of and what do they send out?

compound eyes are composed of individual ommatidia, each unit sends a signal to the brain where the image is assembled

what type of resolution does the compound eye design provide?

the compound eye provides excellent flicker resolution

what is another term for a compound eye?

multi-faceted

define flicker resolution

highest frequency of flickering light the eye can resolve a discontinuous

what type of eyes do insects, diplopods, and crustaceans have?

simple and compound eyes

describe the ommatidium in simple eyes

simple eyes have few ommatidium that sense light/dark conditions and movement

describe the ommatidium in compound eyes

compound eye have many ommatidia that form a myopic mosaic image

what is the flicker fusion rates of predatory insects

predatory insect flicker fusion rates are 200-300 flashes per second aid in predicting prey flight patterns

what are the morphological differences b/w vert and invert light traps?

Inverts

• Rhabdomeric tubes

• verted retina

Verts

• laminar folds

• inverted retina

describe the evolutionary relationship of invert and vert eyes

invert and vert eyes evolved independently and show major structural differences

how many lenses do vesicular lenses eyes have?

single lens

what are the 10 anatomical features of image forming single lens eyes

1. sclera = tough, fibrous tissue protects the eye and maintains

2. cornea = refracts light and provides 75% of total accommodation

3. pupil = control entering light level via the “pupillary reflex”

4. lens = focuses light on the sensory retina to create clear images

5. iris = controls pupil diameter and light reaching the retina

6. ciliary body = produces aqueous humor and contains ciliary muscles

7. choroid = provides oxygen and nutrients to the retina’s outer layers

8. retina = converts focused light into neural signals sent to the brain

9. fovea = sharpens visual detail needed for key activities

10. optic nerve = sends retinal signals to the brain’s vision centers

what do vert rod and cone photoreceptors show?

vert rod and cone photoreceptors showing photo-transducing outer segments connected to the mitochondria-rich portion of the inner segment via the connecting cilium

how are light-induced changes transmitted in the eye?

light-induced changes in outer segment membrane potential are transmitted though the inner segment resulting in neurotransmitter release at the retinal-neuron synapse

rods vs. cones

rods

• define rods

• how common are rods compared to cones

• what are rods sensitive to and what makes them lose sensitivity

• where are rods concentrated

• describe the relationship of rods and color vision

Cones

• what are cones sensitive to

• what makes cones lose sensitivity

• where are cones concentrated

• describe the relationship of cones and color vision

Rods

• intensity sensors that use rhodopsin pigment

• rods are 20x more common than cones

• rods are sensitive to low light (scotopic vision) and lose sensitivity at high light levels

• rods are concentrated at outer retina edges and are used in peripheral vision

• rods do NOT provide color vision

Cones

• cones are sensitive to wavelength and high light (photopic vision)

• cones lose sensitivity at low light levels

• cones are concentrated in the fovea region of the retina and are used to provide color vision

• only 3 cone colors (red, green, and blue) are needed to make all colors = trichromatic vision theory

what 3 related groups are vesicular eyes found in? what group did they evolve independently in?

jellyfish, annelids, and mollusks

evolved independently in verts

describe the eyes of

• alciopid bristle worms

• box jellyfish

• octopuses

• humans

• alciopid bristle worms have well-developed eyes and excellent vision

• box jellyfish have vesicular eyes that hang from cup-structures on the body

• octopuses have a “camera-type eye” similar to humans

• human eyes are best adapted for diurnal conditions

how are human and octopus eyes similar?

octopus and humans have “camera-type” eyes w/ an iris, lens, vitreous cavity, and photoreceptors that synapse w/ the optic nerve

explain the evolutionary relationship b/w cephalopods and vert eyes?

for 140 yrs, cephalopods have been compared w/ the vert eye as an example of convergent evolution, so it was though they independently evolved the camera-eye trait BUT recent papers suggest that its an example of parallel evolution

what is the usefulness of the cornea underwater and why?

with a refractive index nearly identical to water, the cornea is useless for underwater accomodation

what type of lens can focus underwater?

spherical lenses can focus underwater

list and define the 2 type of aberrations spherical lenses are prone to

• spherical aberration = light focuses at varying distances from lens

• chromatic aberration = failure of a lens to focus all light on the same

what is the accommodation strategy of focusing vesicular eyes of Annelids?

some annelids move the retina, not the lens, but the process is slow and impractical and is known in only a few groups

what is the accommodation strategy of focusing vesicular eyes of Cnidarians and Cephalopods?

jellyfish and cephalopods “squeeze” the eye causing it to bulge which moves the lens

what is the accommodation strategy of focusing vesicular eyes of Vertebrates?

vertebrates accommodate by changing the lens shape, a method that is efficient and fast

• what is the Tapetum Lucidum part of?

• what is the Tapetum Lucidum comprised of?

• what does the Tapetum Lucidum do to photons?

• the Tapetum Lucidum is part of the choroid layer or pigmented epithelium in verts

• its compromised of various reflective materials: guanine crystals, lipids, pteridine, or melanoids

• the tapetum reflects 90% of incoming photons along their original trajectory, thereby amplifying low light signals

what is the function of the parietal/pineal eye

in verts, the pineal gland functions as a photoreceptive neuro-endocrine organ

Pineal eye

• aka

• what is it part of

• what makes the pineal eye associated with, what 2 things make it active, and what role does it play

• aka third eye

• part of the epi-thalamus in some animals

• the eye is associated w/ the pineal gland and is photoreceptive and hormonally active playing a role in regulating circadian rhythmicity and maturation in everything from hagfish to people

describe the parietal eye of iguanas

what covers the eye

• iguanas have a well-developed parietal eye complete w/ a cornea, lens, and retina

• the eye is covered w/ a transparent scale but is not believed to image forming

where is the location of the pineal eyes in reptiles/amphibians/fish compared to mammals

in reptiles/amphibians/fish the pineal eye is on the top of its head (the extinct monitor lizard had 2 pineal eyes) while mammals pineal organ is embedded in the brain and is part of the endocrine system

describe the strange case of the eyeless shrimp

eyeless shrimp feed on sulfide bacteria in hydrothermal vents (>350C) in which newly hatched shrimp lack image-forming optics and have an upper thermal limit of 31C

lacking eyes, how is it possible for shrimp to feed at vents while avoiding lethal temps?

evolutionary answer: a pair of rhodopsin rich organs beneath a transparent carapace => the organs are sensitive to faint sources of black-body radiation emitted by the smokers’ high temp allowing the shrimp to “see” and avoid the vent’s lethal boundary

what is the organ of touch, what is notable about its size?

skin = the organ of touch, the largest sensory system

where are other tactile receptors found?

muscle, bone, heart, and blood vessels

where is tactile simulation processed?

tactile simulation is processed in the brain’s somatosensory cortex

how distorted and disproportionate are touch receptor distributions?

touch receptor distribution is widely distorted and disproportionate

list and define the 6 receptors of the somatosensory system

1. free nerve endings = thermoreceptors, mechano-nociception, polymodal-nociceptors

2. Ruffini’s end-organs = barrow and stretch receptors

3. hair follicle nerve = light touch

4. Pacinian corpuscles = vibration proprioceptors

5. Meissner’s corpuscles = discriminative touch receptors

6. Merkel’s discs = light touch/pressure receptors

what does morphological coding consist of?

modified nerve-endings and thermal sensory input

what do heat receptors increase?

what do cold receptors increase?

at what temp do heat and cold receptors stop working?

• heat receptors increase tonic discharge rate as temp increase and decrease the rate during cooling

• cold receptors increase discharge rate during cooling and decrease the rate during warming

• at temp above 45C or below 32C, heat or cold receptors stop working and pain (nociceptors) take over

describe the thermal receptors in pit vipers.

pit vipers use infrared receptors that are located in the facial pit thermoreceptors that can sense changes of .002C from 4 feet away

what is common among animals when it comes to sound, what is diverse?

sensing sound in air or water is common among animals but hearing adaptations are diverse

what are the hearing adaptations for

• owls

• cats

• moths

• snakes

• spiders

• owls use audition to detect danger or find prey in which the left ear senses sound from below while the right ear hears sound from above which aids in pinpointing prey sounds

• cats have keen hearing and can detect an extremely wide range of frequencies

• moths hear frequencies up to 300 KHz and use their ability to escape predatory bats

• snakes lack an outer ear and eardrum but detect ground and air vibrations using the jaw bones

• spiders sense low-frequency sound up to 5m away using tiny foreleg hairs

what are the 2 components that come with audition in water?

audition in water has a pressure and displacement (particle-motion) component

define near-field sound

water particle displacement

what happens to the statolith and statocyst during near-field sound?

what do hearing generalists detect?

what do all fish detect?

in near-field sound, statoliths are stationary and the statocyst moves

hearing generalists detect low frequency sound 1 or 1.5 kHz

all fish detect near-field sound

what happens to the statolith and statocyst during far-field sound?

who hears far-field sound?

• in far-field sound the statocyst is stationary and the statolith vibrates

• this hearing type is limited to ostariophysan fish (FW species) and hearing specialists that hear sounds >1.5 kHz

how does the swim bladder affect audition?

in rxn to passing sound waves, the swim bladder resonates and the vibration is transmitted to the otoliths resulting in hair cell stimulation

describe the adaptations of

• Webberian ossicles

• sea trout swimbladder

• elasmobranch and fish w/ reduced swim bladders