L9, 10 and 11 Sensory Systems - Daniel Robert

Question 1

Example of impressive thermal reception

Answer 1

Fire beetles, can detect forest fires 18km away, then be the first ones to escape ad upon return after the fire colonise the area.

Question 2

4 sensory organs on diptera head

Answer 2

• Massive compound eye -can have mecanoreceptory hairs between facets to sense danger to eyes. Maybe give pixllated image, nanostructures on surface of lens to absorb more photons. Fecets in hexagonal arrangement.
• Pheniculus - ‘nose’ olfactory organ, can be sensitive to CO2, humidity, temp…
• Arista - Projection off antennae, sensitive to sound.
• Ocelli - detect light level and direction, horizon.
• Feet also filled with sensory receptors, so can continuously be sensing the ground.

Question 3

What’s special about a Teleopsis dalmanii fly?

Answer 3

Malaysian stalk eyed fly. Antennal eye structures not for producing a 3D vision but for sexual selection/ male competition. Better if further apart so can bash other males out of the way.

Question 4

Why does vision have to be adapted for flight?

Answer 4

Flight is ery fast, need to sense environment much faster. Horse flies are the fastest - 33m/s. They fly faster than our eyes can process.

Question 5

Describe the evolution of eyes

Answer 5

1. ‘Pigment cup’ sphere of cells that produce a pigment layer. Very directional, only if light is from one side. Guanine in cells reflects light to sensitive part of the cell.
   2a. Pinhole - similar to pigment cup but very small entry hole for light.
   3a. Filled cup - Cup filled with oil at a particular refractive index refracts light onto the retina.
   4a. Addition of a lens. ‘Camera lens’ big variation across species in shape of lens.
   2b. multiple pigment tubes - Many of the pigment cups together, at different angles, adds directionality.
   3b, Apposition compound - addition of lenses to each of the pigment tubes. Aperture only over 1 ommatidia as light conducted straight to rhabdom. High resolution.
   4b. Superposition compound - A gap between the lenses and pigment,allows lots of light to be gathered. Aperture covers several ommatidia. Light focuses on one rhabdom gains sensitivity but loses resolution.

Question 6

What types of animals have a compound eye?

Answer 6

insects, crustaceans, some molluscs, some annelids

Question 7

What is the difference between two types of camera eye?

Answer 7

Simple lens - has a lens below the cornea - vertebrates, jellies, molluscs. annelids.
Simple cornea - no lens - arachnids, some vertebrates, larval insects. Can be v large.

Question 8

describe the structure of an ommatidia in a compound eye

Answer 8

Lens
Crystalline cone, surrounded by primary and secondary pigment cells
Rhabdom consists of retinula cells surrounded by secondary pigment cells. Microvilli on the retinula cell facing inwards contain photo pigments.

Question 9

How do ocelli work?

Answer 9

Single lens projects signal onto series of neurones

Measures quantity of light, not image forming.

Question 10

What are Stemma?

Answer 10

Single lens eye in larvae of some insects, on sides of head, aka lateral ocelli.
As larvae develop, they develop into more complex organ.
Corneal lens with a crystalline lens and rhabdom below it.

Question 11

Describe strepsiteran insect eyes

Answer 11

Enormous facets on eye with spaces between them. No more than 50 facets [most insects have 100s]
No retina

Question 12

HEARING ORGANS LECTURE 10

Answer 12

???

Question 13

describe a fly’s balance system

Answer 13

Hind wing modified into halteres, sensory receptors on the bottom of the wing to detect the force caused by turning . Has 1000 information channels, allows accurate manouvering way more agile than bees.

Question 14

What is interesting about St Mark’s fly?

Answer 14

very hairy, long thick hairs even between facets of the eye.

Maybe for electroreception/use in courtship

Question 15

describe a mechanoreceptor of Chironomids

Answer 15

Johnston’s organ at the base of antennae - 16000 cells. Why so many?!
Also measures IR radiation.
Plesiomorphic structure, common among insects.
Old evolutionary trait - many insects developed hearing organs based on antenna oscillating in a sound field.

Question 16

Are tympanal ears common amongst insects?

Answer 16

yes, they have evolved independently 15x in 7 orders.

Question 17

what are 5 functions of hearing in insects

Answer 17

Mate detection
Prey detection
Predator detection
Frequency selectivity
Navigation - sound from wings bounces back off substrates differently.

Question 18

Describe a very simple insect ear

Answer 18

Moth - very very small - 1/10 mm. 
thin membrane (tympanum) on the side of its body. Tympanum nerve is a direct connection from tympanum to the sensory nerve. There is a ligament which can change sensitivity to protect from saturation

Question 19

How and why do locusts detect sound?

Answer 19

hearing organs located along their sides. Very tiny tympanal membrane slightly lower than the cuticle.
Mullers organ connected to the membrane by the Pyriform vesicle and the Folding body. Low frequency sound waves deflect the both the PV and FB, and high frequency sounds deflect just the PV only. Mullers organ has 120 mechanoreceptors in 4 distinct groupings, which transmit signals to the sensory nerve.

Locusts need a system of discriminating between frequencies of the sounds of other locusts wings rubbing within the swarm.

Question 20

Where are cicada ears located and what does it consist of?

Answer 20

on the back of the thorax.
consists of a tympanal ridge which extends under the tympanal membrane through a structure called the tympanal apodeme.
The apodeme is stiff and doesn’t bend, so applies the force to the neurones attached to it. Passive frequency filter which is tuned to the main frequency of cicada’s calling song.

When singing, the tymbal membrane is pulled down by muscles to deactivate it, regulating hearing effectively.

Question 21

describe a parasite with very good hearing

Answer 21

Dipteran fly - Ormia orchracea
Phonotactic parasitoid.
Very good at detecting song of crickets (better than male crickets at detecting females). Ears have 150 mechanoreceptor cells. Placed in front of prothoracic legs, behind head.

Question 22

Describe mosquito mechanoreceptors

Answer 22

For listening for mates, Males have 16000 sensory cells in JO, females have 8000.
At the base of the antenna, 8000/16000 mechanosensory units made of 4 cells.
Attachment cell at centre of JO, joins unit to the non cellular structure.
Mechanoreceptor cell runs longitudinally through the unit, through the scolopale cell [tough, contains globular actin. elongates and compresses with vibrations. Sesitive to nm vibrations]. Support cell links it to edge of JO.

Question 23

In Drosophila, where does most mechanoreception occur?

Answer 23

In the pedicel of the antenna, this is where the JO is. 100-200 neurones. The funiculus also packed with olfactory receptors which use these neuones.

Question 24

What is a mechanosensory touch receptor?

Answer 24

Trichoid sensilla.
Seta [hair] protrudes out of cuticle and attached to bipolar sensory neurone dendrite (400nm thick) underneath cuticle.
Bipolar sensory neurone cell body is surrounded by Trichogen cell, which secretes the seat, and a tormogen cell.

Question 25

How can a trichoid sensilla be used as a proprioceptor?

Answer 25

If positioned next to a joint, the bending joint deflects the hair.

Question 26

What is a scolopedia?

Which organs are they found in?

Answer 26

Mechanoreceptor placed below intersegmental cuticle which detects tension on cuticle.
Cilium connects neurone and non cellular scolopale structure attached to microtubules connecting to the cuticle. Stretching of the cilium is detected.
Long scoloped units detect low freq, and high freq detected by short scoloped units.
Perhaps derived from campaniform sensilla - v oldin arthropods.

Found in : Chordotonal system, Subgenual system, Auditory organs and Thermosensory organs

Question 27

What is a proprioceptor found in joints?

Answer 27

Campaniform sensilla
Small bump in flexible cuticle, contains tubular body and connected to dendrite.
Used in limb positioning and strain measurement.
In joints of legs, wings, halteres and pedicel/flagella

Question 28

What is a slit organ in spiders?

Answer 28

Lyriform organ
measures strain/bending on small slits in the exoskeleton, not present in insects.
Needed because spiders don’t cope with breaks in the cuticle as they use hydrostatic pressure not extensor muscles so all pressure would be lost.

Question 29

How do spiders measure vibration?

Answer 29

small pads sensitive to shocks in joints of spider legs, btw tarsus and metatarsus.