Sensory Physiology - Arthropods Flashcards
How is the stimuli disadvantage of cuticle overcome?
The cuticle can be modified structurally and chemically for numerous functions
What are sensilla?
Specialized cuticular structures that transmit stimuli such as: mechanical forces temperature humidity various chemicals electromagnetic radiation light
How can sensilla be identified?
all types develop from a mother cell
The modality deduced from cuticular apparatus
How much does cuticular density vary?
Over 7 orders of magnitude-
from butterfly larvae, up to an armored rhinoceros beetle
How many classes of sense organs in drosophila
Four
Type 1-ciliated
type2 - nonciliated (non cuticular apparatus)
How do locusts beat their wing?
Single synaptic feedback- btwn stretch receptor and motor neuron
motor neuron inhibited -wing up
motor neuron excited - wing down
What are the 4 types of cuticular mechanoreceptor?
bristle- touch
filiform-air currents and sound
campaniform sensillum-cuticular deformation
scolopidia - stretch
How sensitive are mechanoreceptors in insects?
4x10-21J
displacement of 0.1-0.3nm
Can detect mechanical stimuli of atomic dimensions
Describe campaniform sensilla
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
Describe sensillium development (microchaeta)
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
Describe macrocaheta development
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
When caterpillars molt - what happens to hair sensillium?
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
Which channels mediate sensitive mechanosensation
TRP channels
What are chordotonal organs
organs consisting of scolopidia
What is Scolopale?
Fibrous material with actin arranged in a ring or a series of rods
What are proprioceptive chordotonal organs?
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
What is a subgenual organ?
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
Where can insect ears be found?
Almost in any body part
How many times have insect ears been developed?
Independently perhaps 19 times in 9 insect orders
How did propioceptive stretch receptor organs transform into hearing organs?
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
What are tympanal organs?
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
What is mullers organ?
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
What is Johnstons organ?
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
What does johnstons organ do?
- Air speed indicator
- Particle movement detector- perceiving near-field sound
some males detect females by their flight tone
