E104 -MT 2

Dendrite

Receive info

• from sensory structure, tissue, or another neuron

Axons

Send info away from neuron

• can send to another neuron

• glandular structure

• effector

Synapses

• where axons & dendrites meet

• neurotransmitters trigger the next neuron to fire

• neurotransmitters change the likelihood of the neuron firing

• simple: one to one

• complex: many to many

Effector

Receives input & does something

• muscle or gland that changes function in response to a signla from a brain center

Simplest behaviors are

walking, jumping, flying, etc.

Simple insect gait

classic tripod gait

• first & third on one side & middle leg on the other move while other tripod provides stability

Complex insect gait

• roaches can sprint on their hind

• roaches can gallop like a horse

  • all legs are off the ground at the same time

• when legs are surgically removed a new stereotyped pattern suitable for the remaining legs is immediately used

Other stereotyped behaviors are…

• flight

• digging

• eating

• reproduction

• anti-predation

• signaling

In some sense…

nearly all insect behavior is stereotyped

• either cyclical or

• one time in response to cues

Nerves are…

organized into fixed circuits that control stereotyped periodic behavior like walking

• can function independent of sensory inputs

• circuit repeats with the period of the behavior to create a rhythm

Models are often

theoretical

• mathematical

• computer simulation

Models can also be

physical however,

• physical models can highlight real world problems difficult to imagine with a theoretical model

Responses to external stimuli: Reflexes

• a sensory structure receives info

• info is relayed by neurons to a ganglion (or spinal cord in vertebrates)

• CNS sends signal to effector such as a muscle to jump or run (connections are fixed)

• response time is the time the signal takes to propagate along path from sensory structure to effector

Insect have

much less consolidation of nervous system

Info is received via sensory structure

sometimes many structure at once

info is filtered

• most useful info is kept

• can happen in the peripheral nervous system

signal is sent to the brain (afferent)

• info is again filtered & integrated

  • in brain centers of interneurons

• animal status is factored in

  • hunger, reproductive status, etc.

signal is sent out to

one or more effectors to change behavior (efferent)

• corpora allata

• mucles

• fat body

Neuroethology

• it works by comparing the smell to a template in the brain & make a decision

  • central nervous system

• habituation to the odors of nestmates

  • don’t smell nestmates

  • peripheral nervous sytem

Sensory systems are…

• mechanical stimuli

• thermal stimuli

• chemical stimuli

• visual stimuli

Basic insect tactile structure

trichoid sensilla

• hair connected to a sensory neuron

Movement of the hair…

squeezes the dendrite of the sensory neuron causing it to fire

• sensory transduction

trichoid sensilla

are very sensitive to air

• air currents

• touch

Proprioceptors

structures that measure position of one body segment relative to another

• important for balance, etc.

Forms of proprioceptors

• hairs

  • continuous signal of degree of postion

• cuticule structures

  • campaniform sensilla

Chordotonal organ

insects have highly modified proprioceptors in several joints across their body

• serve a variety of sensory functions

Sound receptors

substrate vibrations are sensed with the subgenual organ

• sensory structure sits at joint on legs

• as legs go up & down sensory neurons fires

Ears are…

just modified proprioceptors

Hearing

some sounds can be heard with the Johnson’s organ on the antenna

• also used to sense air speed by deflection of antennas insect flies

• has hundreds of neurons & complex

Hearing most sounds requires…

a tympanic organ

• ear drum

  • thin membrane connected to an air sac that vibrates when sound hits it

  • can be anywhere on insect body depending on order

  • moths & insects that sing to find mates in particular have elaborate ears

Moths & Bats

• Bats = echolocation

  • high frequency sounds to hunt prey

• Moths = ears evolved to hear when being tracked

  • they are very sensitive just to the frequencies used by bats that hunt them

Reception of echolocation sounds…

triggers evasive action

• irregular flight pattern

• dropping to ground & holding still

• jamming

Thermosensing

is poorly understood but the receptor is on the antenna in most insects

Because insects are so small…

they have a high surface area to volume ration

• they lose hear fast

• 1 degree every second in a bee

Insects can…

heat themselves up with floght muscles, but they do it immediately before taking off

Honey bees…

thermoregulation in the winter is an important exception

Bees & heat

• bees create warm clusters that they keep up the while winter

• hot bees are in the cneter & work hard to make heat

• eventually get tired & go to the edge to act as insulation utnil they get too cold

• go back to the center

• done for the whole winter by the same bees

Bees can…

• create colony fever to try to kill fungus in their combs

Bees can also…

use their heating & ball overwintering technique to kill giant wasps

• only Asian bees can do it

• a few giant hornets can kill a whole European honey bee hive

Chemoreception

• insects both taste & smell

• molecules to be sensed are trapped in a viscous substance

• odorant binding proteins carry molecules to odorant receptor proteins on sensory neurons which trigger firing of the neuron

• mechanisms by which odors trigger impulses are either simple or very complex

Insects sense chemicals with

• antennae

  • smell & taste

• mouthparts

  • taste

• feet, ovipositor, etc

  • taste

chemosensory structures can be…

many places depending on the speices & what they need to sense

Larva insect vision…

have a few stemmata

• good at detecting light/poor at resolving

Adult insect vision…

have

• ocelli

  • 3 on top of head

  • very sensitive to light/poor resolving power

  • may be horizon detectors used in flight

• compound eyes

Insect…

• have poor resolution relative to us

• have good ability to sense movement

• can see into ultraviolet & can see polarized light

• can see color

• cannot see in the dark