Animal Sensory Systems: Mechanoreception

touch, orientation and sound

mechanoreception

involves physical movement

sensilla function

both mechanoreceptions and chemosensory

* movement of the hair stretches the transient receptor potential ion channel and opens its
* depolarization

vertebrate skin and touch: how does it work?

nerve endings and corpuscles detect pressure from prolonged contact and release

how does mechanosignaling in hair cells work?

apical steteocilia are organized like a stair-case and directional movement of the hair opens TMC K+ channels

* pulling towards the longest hair opens the channel and depolarizes cell
* this releases NTM and triggers and action potential

taut

* pulling longest hair
* depolarization
* excitory

slack

* pushing the tallest hair
* repolarizes/hyperpolarization
* inhibitory
* closes potassium channels

kinocilium

tallest hair-like projection

does the endolymph have a high or low concentration of potassium?

high concentration

detecting changes in water pressure in fish

the lateral line contains neuromasts (clusters of hair cells) in a cupula (gel bubble)

* when the gel vibrates from touch it moves the hair cells which stimulates an action potential

purpose of the cupula

protection of the hair cells

concept of distant touch

you dont need to make direct contact with the organisms

* banging on the glass of a fish tank

describe the shark lateral line

denticles and surface pores that all sea water to enter and tickle neuromasts in lateral line canal

C start

when pressure disturbances are heard or felt by the lateral line it startles the fish into a reflexive C start

* faces away from the stimulus

how to tentacled snakes detect motion of prey?

mechanosensory protrusions below the nostrils

C start and predator arms race example

snakes predictively striking to where the fishes head will be once its startles it

middle ear consists of

tympanic membrane and auditory ossicles (malleus, incus and stapes)

tympanic membrane

thick tight drum that creates vibrations

purpose of the auditory ossicles

relay information to the cochlea

parts of the inner ear

semicircular canals, maculae and cochlea

semicircular canals include

ampullae

* spatial orientation

maculae includes

utricle

* linear acceleration

saccule

* gravity

cochlea includes

lagena

* important for hearing
* non-human vertebrate name for the cochlea

why is bilateralism important with ears?

important for homing - detecting where the sound is coming from

what is the maculae?

beds of hair cells

how do we sense 3D spatial equilibrum and motion?

X Y and Z planes

* rotational acceleration of the endolymph pushes the cupula of the neuromast, hits the ampulla and is sensed by the hair cells

evolution of the semicircular canals

* hagfish have 1
* lampreys have 2
* bony fish and so on have 3

turning your chin to the left does what?

pressure from endolymph goes to the right which pulls the tallest have and excites the action potential

turning your chin to the left does what?

pressure from the endolymph does to the left which pushes the tallest hair and inhibits an action potential

purpose of ear stones

provide sensation of gravity and spatial orientation

* balancing

what were to happen if we had magnetic ear stones?

we would have a ability to sense magnetic fields

what is a macula (not macuale)

bed of hair cells underlying ear stones called otoliths with a gel matrix on top to protect hair cells

* movement of otoliths vibrates gel and activates hair cells
* due to inertia

utricle

located above the saccule and detects linear acceleration forces due to movement of otoliths

saccule

located below the utricle and detects gravity

difference in ear stones in vertebrates and invertebrates

vertebrates

* otoliths

invertebrates

* statoliths that are surrounded by sensory neurons (make up a statocyst)
* analogous to hair cells

where did ear bones evolve from?

jaws in fish

what freed the articular and quadrate?

a dentary-squamosal jaw joint

that quadrate turned into what?

the incus

the articular turned into what?

the malleus

where did the stapes come from?

dermal ear bone in fish

reptiles have how many ear bones?

one

mammals have how many ear bones? whats the advantage

three

* great sound amplification

how does mammalian hearing work with the cochlea?

* sound hits the tympanic membrane
* ear drum and middle ear bones amplify the sound the oval window
* this vibrates perilymph passes into the cochlear and bends hair cells according the loudness and frequency
* sound causes the basilar membrane to resonate and shear to distinguish pitch
* the round window prevents reverberation
* stimulation of the hair cells sends APs down cochlear nerve to brain

describe the basilar membrane

stiff but not uniform and detects frequencies

* higher frequencies are stiff and lower frequencies are flexible to the membrane

how does the round window work?

shock absorber so sound doesnt linger

the cochlea is also called

the organ of corti

how many orders of magnitude does vertebrate hearing vary by?

four

humans hear approximately what range of frequencies?

20-20,000

* no infrasonic or ultrasonic

what are the only animals that can hear infrasonic frequencies?

elephants

what animals can hear ultrasonic frequencies?

mouse, bat, belgua whales and dolphins

why do herptiles hear less than other animals?

shorter cochlea and less ear bones

how do animals decide to vocalize?

within their hearing range

insect hearing is special because?

evolved dozens of times

how do flies and bees hear?

detect sound vibrations by ciliated cells at the base of their antennal ears

where are tympanal membranes located in insects?

on any part of the cuticle

where do crickets and katydids have their tympana?

on their tibias

* this is where they hear
* same principle as our ears just in their legs

but they have modified breathing tubes called acoustic trachea to carry the sound

echolocation is

navigating through the dark

two examples of echolocation we discussed

big brown bat

* use acoustic mapping to hunt in the dark

toothed whales

* air passed through phonic lips produced clicking noises for acoustic mapping and melon contorts that sound to adjust it
* melon processes

acoustic mapping

phonic lips make loud and rapid chirps that bounce off items and are bounced back to the organisms to give them a sense of direction

* bilaterialism is important

compare sound travel in and out of water

5x faster in water

how is the dolphin cranial anatomy specialized for echolocation?

* air sacs trigger phonic lips in blow hole and send sound out into environment
* sound passes through melon and jiggles is
* sound bounces on things in environment
* then it its the fatty pads and is recognized by the brain which is where it is processed

where are the fatty pads located?

the lower jaw

the blowhole is a homologous evolution of what?

the nostrils

what are hearing aids for bony fish?

swim bladders

* gas-filled balloon reacts to sound waves because when the air sac vibrates
* webarian ossicles sense the movement of the swim bladder and relay information to the inner ear

otocephalans include

herring, minnows, catfish and piranha

* they all have connection from the bladder to the inner ears

benefit of weberian ossicles

they increase hearing sensitivity

examples of specialized acoustic communication

ultra-rapid contractions of sonic muscle fibers produce sound

* tail of rattlesnake
* tymbal of cicada
* swim bladder of toadfish