Sensory Physiology - Arthropods

Question 1

How is the stimuli disadvantage of cuticle overcome?

Answer 1

The cuticle can be modified structurally and chemically for numerous functions

Question 2

What are sensilla?

Answer 2

Specialized cuticular structures 
that transmit stimuli such as:
mechanical forces 
temperature
humidity 
various chemicals
electromagnetic radiation
light

Question 3

How can sensilla be identified?

Answer 3

all types develop from a mother cell

The modality deduced from cuticular apparatus

Question 4

How much does cuticular density vary?

Answer 4

Over 7 orders of magnitude-

from butterfly larvae, up to an armored rhinoceros beetle

Question 5

How many classes of sense organs in drosophila

Answer 5

Four
Type 1-ciliated
type2 - nonciliated (non cuticular apparatus)

Question 6

How do locusts beat their wing?

Answer 6

Single synaptic feedback- btwn stretch receptor and motor neuron
motor neuron inhibited -wing up

motor neuron excited - wing down

Question 7

What are the 4 types of cuticular mechanoreceptor?

Answer 7

bristle- touch
filiform-air currents and sound
campaniform sensillum-cuticular deformation
scolopidia - stretch

Question 8

How sensitive are mechanoreceptors in insects?

Answer 8

4x10-21J
displacement of 0.1-0.3nm
Can detect mechanical stimuli of atomic dimensions

Question 9

Describe campaniform sensilla

Answer 9

Oval shape -
situated close to cuticular areas of stress (e.g. joints)
mouthparts,
basal segment of antennae
veins close to wing base
ovipositor
Structure varies according to the position of the sensillum even within species

Question 10

Describe sensillium development (microchaeta)

Answer 10

development starts when an epidermal cell is committed to a sensillogenic fate
cell becomes a bristle mother cell then divides twice
1st- smc (basal position), and tmc (apical position)
2nd- scm yields sensory neuron and thecogen
and tmc yields trichogen and tormogen

Question 11

Describe macrocaheta development

Answer 11

Trichogen cell produces shaft of bristle
Trichogen cell reduced
Tormogen cell starts formation of outer receptor lymph cavity
Final- tricho and tormo retract from the cuticle forming outer receptor lymph cavity

Question 12

When caterpillars molt - what happens to hair sensillium?

Answer 12

Dendritic sheath protects dendrite from enzymes
sound-sensitive hair non-functional for 30 min before ecdysis and the new hair is functional a few minutes after cuticle is shed

Question 13

Which channels mediate sensitive mechanosensation

Answer 13

TRP channels

Question 14

What are chordotonal organs

Answer 14

organs consisting of scolopidia

Question 15

What is Scolopale?

Answer 15

Fibrous material with actin arranged in a ring or a series of rods

Question 16

What are proprioceptive chordotonal organs?

Answer 16

They monitor relative movements.
can be made up of one or more chordotonal sensilla each consisting of 1 to 3 mechanosensory neurons and 3 supporting cells

Question 17

What is a subgenual organ?

Answer 17

Its a chordotonal organ in the proximal part of the tibia
not associated with a joint
they respond to vibrations of the substratum
In cockroach- periplaneta
responds to a displlacement of 0.2nm at frequency of 1.5Hz
up to vibration of 8kHz

Question 18

Where can insect ears be found?

Answer 18

Almost in any body part

Question 19

How many times have insect ears been developed?

Answer 19

Independently perhaps 19 times in 9 insect orders

Question 20

How did propioceptive stretch receptor organs transform into hearing organs?

Answer 20

Tympanal –CO connects to a thinned tympanal membrane backed by a tracheal air sac - so it vibrated in response to sound

Antennal –
Distal part of the antenna acts as a sound receiver that follows air particle displacements-vibrations are picked up by johnston’s organ in the 2nd antennal segment

Question 21

What are tympanal organs?

Answer 21

Specialized CO for sound reception
Consists of area of thin cuticle, backed by air sacs free to vibrate
behind is CO which contains a varied number of scolopidia

Question 22

What is mullers organ?

Answer 22

A tympannal CO in Locusta with 80 neurons with cell body aggregated into a ganglion
4 groups of sensilla are attached to the membrane by auxilliary cells

Question 23

What is Johnstons organ?

Answer 23

An antennal CO
in the antennal pedicel
occurs in adult insects and in a simplified way, in larvae
Single mass of several groups of scollopidia that respond to movements of the flagellum with respect to the pedicel

Question 24

What does johnstons organ do?

Answer 24

1. Air speed indicator
2. Particle movement detector- perceiving near-field sound
   some males detect females by their flight tone

Question 25

Which organ is an insects nose?

Answer 25

The antennae

Question 26

Chemoreception in insects : types

Answer 26

Sense of smell
sense of taste
located in many parts of the body-can detect chemicals on dry surfaces as well as solutions

Question 27

How do insects process chemoreceptors?

Answer 27

Axons from all olfactory receptor terminate in the antennal lobes in the brain

Axons from contact chemoreceptors terminate within the ganglion of the body segment on which the receptor occurs

Question 28

How does olfaction happen in insects?

Answer 28

Odor molecules (lipophillic) dissolve in the epicuticular lipid covering the sensillum
Odor-binding proteins solubilize odor molecules
3 types:
pheromone
2 types of general odor binding proteins

Question 29

How are olfactory sensilla distributed?

Answer 29

multiporous probably present on antennae of all insects
Some may occur in the maxillary and labial palps
physiological classes different than anatomical ones- because neurons may respond to different ranges of compounds

Question 30

How are olfactory molecules transduced?

Answer 30

Not entirely clear

Genes encode for olfactory receptor proteins 7TM similar to GPCR
Species differ in the number of OR genes- massive numbers in ants

or and orco form ion channel complex

cAMP messenger increases

IP3 might be involved in pheromone-sensitive cells

Question 31

What are IRs

Answer 31

ionotropic odor receptors

closely related to ionotropic glutamate-sensitive ion channels

not very diverse
might predate insect olfactory receptors and terrestrial lifestyle

Question 32

What do antennal lobes do?

Answer 32

Process olfactory information

comparable to the vertebrate olfactory bulb

All axons expressing the same receptor gene converge into a single glomerulus

spatial separation match different receptor types on the antenna

Question 33

What is the combinatorial benefit of glomeruli?

Answer 33

greatly enhance coding capacity of the system

50 glomeruli can code for 125000 odorants

Question 34

What role do mushroom bodies play in olfaction

Answer 34

olfactory and visual input- allowing them to learn that an odor in a particular visual context has a different meaning from the same odor in a different visual context

Question 35

What role do kenyon cells play?

Answer 35

allow the insect to distinguish a very high number of odors

Question 36

What do projection neurons do?

Answer 36

Process olfactory information

leave the antennal lobe and innervate brain structures
in the mushroom body and lateral horn