9. nervous system and endocrine system

describe the concept of “umwelt”

each species exists within a unique reality constrained by their own nervous system

• it’s why we can’t detect nectar guides or moth pheromones. they don’t impact our survival, so there’s nothing for evolution to act upon

what segments of the body plan make up the brain and esophagus?

segs 1 and 2

what segments of the body plan make up the subesophageal ganglion/zone?

segs 3-6

what segments of the body plan make up the ventral nerve cord?

segs 7-20

what segments of the body plan make up the thoracic ganglia?

segs 7-9

what segments of the body plan make up the abdominal ganglia

segs 10-20

describe what each of these parts of the brain process: optic lobes, antennal lobes, central complex, mushroom bodies, subesophageal zone

optic lobes: vision

antennal lobes: smell

central complex: navigation

mushroom bodies: learning and memory

subesophageal zone: taste, descending motor control

investment in brain regions reflect 2 things

• reliance on specific sensory modalities

• behavioral capabilities

5 insect/mammalian differences in the nervous systems

• CNS position

• cell body position

• neuron morphological type

• myelination

• “identified” neurons

insect/mammalian differences: CNS position

• mammalian CNS is dorsal

  • insect CNS is ventral

insect/mammalian differences: cell body position

• mammalian cell bodies are layered with circuitry above and below

• insect cell bodies surround the neuropil in a “rind”

insect/mammalian differences: neuron morphological type

• most mammalian cell bodies integrate current

• insect cell bodies are “unipolar” → don’t receive synaptic input

insect/mammalian differences: myelination

• most mammalian neurons are “myelinated” → increase conduction velocity

• insect neurons are unmyelinated (shorter axons + space efficient)

insect/mammalian differences: “identified” neurons

• uniquely identified across indivs of the same or different species (i don’t rlly get this slide but wtvr)

5 insect/mammalian similarities in the nervous system

• biochemistry (mostly)

• sensory mapping

• network organization

• neuromodulation

• plasticity

insect/mammalian similarities: biochemistry (mostly)

share many of the same NTs as mammals

• some transmitters differ

  • ex: octopamine vs. epinephrine

• some receptor mechanisms differ

  • ex: insects lack metabotropic histamine receptors and ionotropic serotonin receptors

insect/mammalian similarities: sensory mapping

sensory maps reflect the physical nature of the stimulus and dedicate more real estate to important stimuli

insect/mammalian similarities: network organization

broad principles of organization are either conserved or converged upon

• rhythmic motor output

• sensory mapping

• sparse coding in learning and memory

insect/mammalian similarities: neuromodulation

CNS alters how it operates based on current conditions

• neuromodulators transiently change response properties and synaptic weights of neurons

• ex: low insulin = modulatory receptor expression to increase activity of food-detecting neurons

insect/mammalian similarities: plasticity

insects can learn many associations

• have diff phases of memory consolidation which rely on conserved biochemical pathways

  • ex: cAMP, PKA, MAPK, CREB

• classical vs. operant conditioning

• learn smell, color, patterns, direction, order of events, taste, locations, etc.

3 endocrine structures

• pars intercerebralis

• corpora cardiacum and allatum

• frontal ganglion

pars intercerebralis

• neurosecretory cells in dorsal brain

• regulates metabolism, reproduction, dev, circadian rhythms

• synaptic inputs to endocrine structures

corpora cardiacum and corpora allatum

• attached to the brain

• release hormones into the dorsal aorta and hemolymph

• control heart rate, sugar storage, and dev (molting and metamorphosis)

frontal ganglion

• both neuronal and endocrine signaling

• releases neuropeptides into blood to affect gut motility and molting

adipokinetic hormone

mobilizes fats for fuel

allatotropin and allatostatin

up and downregulate juvenile hormones

cardioactive peptide

increase heart rate

diuretic hormones

increase diuresis

PBAN

induce pheromone production

ecdysis

acts of shedding old cuticle

instar

each juvenile stage

describe the steps of molting (do not factor in hormones)

1. apolysis: epidermis separates from old cuticle

2. new cuticle secreted over epidermis (enzyme resistant) + epidermal cell replication (instar growth)

3. molting fluid fills “exuvial space” w enzyme to break down old cuticle for nutrient recycling

4. ecdysis: insect swallows air or water to split old cuticle (exuvia) along ecdysial structures

5. sclerotization hardens new cuticle

describe molting in terms of the endocrine system

1. based on growth, stretch receptors trigger:

   1. prothoracicotropic hormone (PTTH) from pars intercerebralis

   2. eclosion hormone (EH) and ecdysis triggering hormone (ETH) from corpora cardiacum and bursicon from CNS

2. PTTH stimulates prothoracic glands to produce ecdysone

3. ecdysone converted by fat bodies to 20-hydroxyecdysone → triggers apolysis and synthesis of a new exoskeleton

4. EH, ETH, and bursicon trigger ecdysis

role of juvenile hormone (JH) in molting (high JH + ecdysone, low JH + ecdysone, no JH + ecdysone)

secreted by the corpora allata to repress transition to adulthood

• high JH + ecdysone = nymph/larva-to-nymph/larva molt

• low JH + ecdysone = larve-to-pupa molt

• no JH + ecdysone = nymph/pupa-to-adult molt

sugars are mobilized in 2 phases. describe phase 1

phase 1: octopamine (first 10 minutes)

• released by neurons in CNS motor circuits and into hemolymph by corpora cardiaca upon flight initiation

  • elevates activity in motor pattern circuits in CNS

  • elevates glycolysis in flight muscles (increases twitch velocity)

  • stimulates lipases (convert triacylglyercide to more mobile diacylglyceride) and glycogen phosphorylase (convert DAG to trehalose) in fat bodies → increase circulation of trehalose

describe phase 2 of mobilization of energy stores

phase 2: adipokinetic hormone (after 10 minutes)

• released by corpora cardiaca

• AKH receptor activation lasts longer than octopamine

• stimulates TAG to DAG and glycogen phosphorylase

• shifts muscles to oxidize fatty acids and lipids over sugars

• analogous to vertebrate glucagon in that it mobilizes sugars and fatty acids