Bio 367 - sensory systems, internal anatomy

dendrites

Attach in or on sensory neurons, under seta. Sensory input triggers action potential on neuron membrane

axon

Path following nerve cell from which signal travels to brain

mechanoreceptor

receptor that must be moved

tactile mechanoreceptor

detect touch or air current

proprioceptors

detect position of body components relative to one another

tactile receptors

must be touched

stretch receptors

on inside of the body

auditory receptors

detect sound-producing air waves

Types of tactile receptors

tactile seta, hair row/plate, campaniform sensillum

Traits of tactile receptors

Seta hollow w/no pores, most soft and flexible (stiff=bristles). Detect air, water, & solid vibrations

Traits of hair row or plate

Found on cuticle between two adjacent sclerites, when sclerites touch/deflect hairs proprioceptors are stimulated

Traits of campaniform sensillum

Seta modified into dome, proprioceptors on cuticle must be pushed to detect pressure. On insect wings too

Types of non-touch proprioceptors

stretch organs

Example of internal stretch organ

Ventriculus lining in the gut detects being full of food

Example of subdermal stretch organ

Inside body wall, detects growth

Traits of stretch organs

Composed of cells, neural dendrites spread out & terminate at epithelial or cuticle layer

Types of auditory receptors

Tympanum, Johnston’s organ

Traits of tympanum

Contain chamber in exoskeleton oftentimes covered w/tympanic membrane & lined w/sensory neurons. On tibia & abdomen

Traits of Johnston’s organ

Open or closed chamber in antennae containing thousands of radially arranged mechanosensory units. Used to pick up wing beats/determine sex or species in mosquitos.

infrared organs

Pit in cuticular surface containing several infrared sensilli

Example of thermoregulation in fire beetles

Have an especially large array of IR sensilli so they can detect distant fires to lay eggs in trees

Gustatory chemoreceptors

liquid chemicals, taste

Olfactory chemoreceptors

gas chemicals, smell

Traits of Gustatory chemoreceptors

Hollow seta with a single terminal pore that liquid enters. Chemicals picked up by sensory neuron receptors on dendrite.

Traits of Olfactory chemoreceptors

Hollow seta w/multiple pores that gas enters, then diffuses into ECM and is picked up by receptors on sensory neuron dendrites inside seta

photoreceptors

visual receptors that pick up light

Apposition eye

Typical compound eye. High resolution, low light sensitivity because small lenses are separated by pigments, panoramic view due to array of ommatidia

Role of ommatidia

Each resolves its own image and brain stitches them together to make a high resolution image. More ommatidia=better color, more 3D, clearer

Structure of Apposition eye

Each ommatidia has: 1 cuticular lens, 8 retinula cells, rhabdomeres

Apposition compound eye

cuticular lens

cornea, directs light into eye

retinula cells

light directed here, arranged like petals of a flower

rhabdomeres

8 rhabdomeres=rhabdom, microtubules on retinula cells w/rhodopsin.

What’s the difference of rhabdoms in a nocturnal vs diurnal bee?

Nocturnal bees have larger rhabdoms with more SA to better absorb light. Pigments surround retinula cells to cut of light between ommatidium and deters it from bouncing out, which helps with light absorption

Light into vision steps

Light enters lens, stimulates optical pigments in rhabdomeres, changes pigment shape from cis to trans, excitation in retinula cell membrane travels along axons of neurons of retinula cells

Color vision (most have rhodopsin) 

Absorb a wide range of electromagnetic frequencies on UV spectrum, some are biochromatic & cannot see many colors

trichromatic

bees & butterflies, can see wider ranges of colors due to three visual pigments

Optical superposition eye

Modified compound eye for changing light conditions and lower resolution, in nocturnal insects

Sensing polarized light

Longitudinally twisted ommatidia descatter light waves. Rhabdoms rotate through length of ommatidium to catch scattered light coming at different angles

Structure of Optical Superposition Eye

Visual pigments missing from some pigment cell clusters so light can pass through ommatidium

Modified Optical Superposition eye

High light absorption and sensitivity when light is needed, or vice versa to change with insect needs. In insects active at crepuscular hours or ones that go into dark environments

Structure of Modified Optical Superposition eye

Mobile pigments of certain pigment cells can block light between ommatidium to increase resolution, OR migrate back to allow light between ommatidium increasing light capture

Stemma

Group of simple eyes that work collectively, on side of head of holometabolous larvae, structurally the same as one ommatidium. High light sensitivity w/low resolving power

Structure of Stemma

Lens (cornea), one rhabdom, pigment cells surrounding retinula cells

Stemma

Optical Superposition eye

Structure of Ocellus

Lens (cornea), many rhabdoms, pigment cells surrounding 8 retinula cells, 1 lens for all rhabdoms

Ocellus

Group of simple eyes that work collectively in addition to compound eyes, sensitive in low-light & subtle changes, very low resolution. Horizon detectors & register changes in intensity that effect diurnal behavioral rhythms

ocellus

dermal photoreceptors

Respond to light only-not an optical system & may be present in those that lack eyes. Determine day/night, position relative to shade, circadian rhythms. 

Insect circulatory system

Open with a series of hearts and open-ended blood vessels. When heart contracts blood is pushed toward vessel openings

hemocoel

body cavity containing bulk of hemolymph and few vessels, has muscles that push food in foregut but not for nutrient digestion in midgut

Coelomate

In humans, muscles surround all areas of body responsible for food intake, digestion, and excretion

Where does circulation start?

Hemolymph is pulled through ostia (openings) of dorsal blood vessels. Hearts push blood anterior from heart to heart, then out of vessel into head

What happens when hemolymph leaves the head?

Blood flows into antennae, eyes, & thorax. Diaphragm pushes blood posterior through wings, antennae, legs, and back into hemocoel, to re-enter ostia of hearts.

Hemolymph makeup

Water, ions, hormones, ventriculus digestive products, trehalose (blood sugar), hemocytes (blood cells)

prohemocytes

hemocyte stem cells, low abundance

granulocytes

initial detection of foreign invaders, encapsulation (proteins block invaders signals)

plasmatocytes

phagocytosis of invasive pathogens, parasitic eggs, multicellular organisms

adipohemocytes

store lipids

What is circulated?

Hormones, digestive nutrients, hemocytes, ions, water, not respiratory gasses

What is stored?

Water, ions, allelochemicals and other toxins

allelochemicals

Chemicals stored in plants for defense, example of reflexive bleeding in lady bugs

Tracheal system

for gas exchange (respiration)

Tracheal system organization

spiracle, atrium, tracheae, tracheoles, aeriferous tracheae

Spiracle

can close and open similar to stomata, may be able to filter

atrium

pocket for air to enter inside spiracle, filter and valve to prevent water loss, invasion, etc. 

trachea(e)

tracheal tubes w/taenidia, molted

tracheoles

cellular, fluid filled, no taenidia, not molted

aeriferous tracheae

spirals into hemolymph around ovaries, is the exception to gas being transported to a part of the hemocoel

Pre-oral cavity consists of…

Buccal cavity (food mixes w/saliva), mouthparts (manipulation), saliva, pharynx

role of saliva

Has enzymes for carb breakdown, mucus, anesthetic in some

role of pharynx

swallowing organ, pushes food into esophagus

Foregut consists of…

esophagus, crop, proventriculus

Esophagus

transfers food from pharynx

crop

stores food, vestigial or absent in fluid feeders

proventriculus

grinding, vestigial or absent in fluid feeders

Midgut consists of…

gastric caecae, ventriculus, endoperitrophic space, ectoperitrophic space, endothelium, malpighian tubules

gastric caecae

produce & circulate digestive enzymes

ventriculus

absorption & digestion, lined by endothelium cells, much longer in fluid feeders

peritrophic membrane

divides endo & ectoperitrophic space to protect from invaders, slightly sclerotized

endoperitrophic space

enzyme digestion

ectoperitrophic space

digested nutrients enter this space

endothelium

absorb digested nutrients

malpighian tubules

osmoregulation while ions, water, and vitamins flow past

Hindgut consists of…

ileum, rectum, colon

ileum

contains beneficial microbes, final absorption of water, salts, vitamins & microbe produced fatty-acids

rectum

final compaction of frass and excretion

colon

where frass compaction starts

Cryptorephretic system for excretion

In insects with dry diets, very efficient water conservation and drying of feces. Distal ends of malpighian tubules attach to rectal pads

Filter chamber

Efficient water and sugar elimination in Hemiptera, midgut attaches to itself at junction of hindgut

Glowing malpighian tubules - glow worms

Produce light via chemical reaction to attract insects. Sticky, high protein saliva traps flying insects

Fat bodies

Organs composed of adipocytes (fat)

Fat bodies function

Carb, lipids, nitrogenous compound metabolism. Stores glycogen, lipids, proteins. Synthesis and regulation of blood sugar. Stores uric acid and sequesters allelochemicals for defense.

apophyses

flexible joint and striated muscle attachment sites that contain resilin

resilin

molecule that gives spring of wings and jump to insects

apodemes

rigid apophyses

tentorium

apophyses in head

visceral muscle

Surround tubes & ducts, dorsal & ventral diaphragm, peristalsis (moved food through digestive tract)

segmental muscle

Telescoping of body, molting and locomotion in larval insects