Module 5

Sensory systems

allow organisms to detect changes (external and internal) and respond as needed

Stimulus

internal change or change to the extenal environment

Receptors

what organisms have to detect stimuli; often a part of a larger organ/system

Response

when triggered, receptors will generate a signal → internal communication

Types of Sensory Systems

chemoreception, mechanoreception, photoreception, thermoreception, electroreception, magnetoreception

Chemoreception stimulus

chemicals

chemoreception in prokaryotes

chemicals binding to trans-membrane receptors activate certain protein pathways to trigger a reaction

Chemoreception in fungi

use outside chemical signals for growth, mating, and symbiotic relationships with plants

Chemotropism

outside chemical signal directs growth

Fungi symbiotic relationships with plants

hyphae sense chemical gradients coming from roots and grow to intercept

Chemoreception in plants

Volatile Organic Compounds to communicate danger/response to predators

Volatile Organic Compounds (VOCs)

can warn other plants or other parts of the same plant → primed to produce chemical defenses, like toxins in leaves

Green Leaf Volatiles (GLVs)

attract herbivore-specific predators

Plants that receive VOC signals do what?

increase Ca²⁺ in guard cells → triggers defenses

“Acacia” trees response to herbivory

leaves fill with toxin and release gas to warn other trees

2 main modes of chemoreception in animals 

olfaction and gustation

Olfaction

sense of smell; no direct contact with source; monitor environment/detect threats, find food, find mates and conspecifics (pheromones)

Gustation

sense of taste; requires direct contact with source; monitor environment and determine if something is good to eat

Both olfaction and gustation use

receptions that bind to proteins → action potential → central nervous system

Olfactory Receptor Neurons

neurons have modified cilia that houses receptors and axon that goes directly to the CNS; very diverse (bind to one odor or multiple); respond to a diverse set of signals; air/water

Olfactory Receptor Neurons signal contexts

searching for food or a mate; exploring the environment; detecting threats

Cephalization

concentrates sensory structures towards anterior end of bilaterally symmetrical animals

Gustatory Receptor Neurons

collection of diverse cell types, including non-neural cell types and neurons with modified sensory cilia; detect signals related to food; control behaviors tied to feeding

Why do gustatory receptors neurons detect signals related to food?

presence/absence of macronutrients or micronutrients; taste sensors lost in animals with specialized diets

Sense of taste likely evolved

independently in different lineages, but convergently to detect similar signals

Taste buds

taste sensors in mammals; clusters of cells embedded in epithelium (confined to mouth); contain multiple receptor types, each sensitive to categories (sweet, salty, sour, bitter)

Taste sensors in insects

modified hairs with a pore at the end; mouthparts and appendages

Tastants

chemical molecules; bind to receptors on taste; receptors cells → depolarization → neurotransmitter release

Mechanoreception stimulus

physical pressure or shape change

Mechanoreception in Plants

deformation of structure → deforms cell walls → mechanosensitive ion channels in cell membrane open → change ion concentration → AP; protects photosynthetic tissue & not as easy to eat

Mechanoreception in Prokarytoes

touch certain protein pathways → reaction

Mechanoreception in Fungi

touch provides information about environment and can induce differentiation in symbiotic or pathogenic fungi; mechanosensitive ion channels in fungal cell membrane open in response to touch → change ion concentrations → response

Mechanoreception in Animals

deformation of cell membrane → mechanosensitive ion channels in cell membrane open → change ion concentrations → AP

Simple Mechanoreceptors in Animals

sense of touch (external); sense posture and muscle/connective tissue stretch (internal)

Complex Mechanoreceptors in Animals

use of deflection of modified cilia; sense gravity, acceleration, and hearing

Statocysts are _______ mechanoreceptors

complex

What animals use statocysts?

invertebrates

Statocysts

sense body orientation; spheres or cups lined with ciliated cells containing small solid objects (statolith); movement of statolith bends cilia → opens ion channel → AP

Lateral Line System and Neuromasts are ______ mechanoreceptors

complex

Lateral Line System in Fish

lined with neuromasts to detect changes in the currents around them; changes in water pressure deflect modified cilia → opens ion channel → AP

Modified Neuromasts in inner ear

deflect in response to vibrations in environment → hearing; deflect in response to changing flow of inner ear fluid → sense motion and body orientation

Neuromasts

specialized sensory organs found in fish and amphibians that detect water movement and vibration

sound waves

pressure changes traveling through water; fast, long-range, and for hearing

water movement/velocity

actual flow of water; slow, local, detected by lateral line system

Hearing in water ____ hearing in air

does not equal

Tetrapods have additional structures in middle ear to

transmit and translate vibrations in air

Tympanic membrane

eardrum; thin, flexible membrane that separates the outer ear from the middle ear in vertebrates

Middle ear structures

tympanic membrane, columella

Middle Ear mechanoreception

tympanic membrane → columella → vibration reaches inner ear → deflect modified cilia → opens ion channel → AP

Mammals further modify middle ear for

more acute hearing

Insects in mechanoreception

independently evolved ears at least 20 times so very different

Mycorrhiza fungi

symbiotic fungi that associates with plant roots; get photosynthesis products and provides water and mineral nutrients to plants

Photoreception stimulus

light

photoreception

biological ability to sense light

phototaxis

move away (-) or towards (+) light

Prokaryotes in photoreception

light activates certain protein pathways → reactions

Fungi- light signaling can regulate

growth & development, reproduction (asexual & sexual), pigment production, metabolic production

Fungi photoreceptors

blue light (short wavelengths), green light (mid-wavelengths), red light (long wavelengths)

Phototropism

growth of plants in response to light stimulus

What does plants have to sense light?

phototropins

Plant in photoreception

light senses by phototropins; auxin is moved to shady plant side, away from light and causes cell expansion by making cell wall acidic and breaking bonds between cellulose fibers; plant bends towards light

Animal photoreceptors

opsins

Simple Eyes

rhodopsin to sense light/dark; cups of light/dark receptors under layer pigment cells; many invertebrates

Radial Symmetry Scyphozoan jellyfish in photoreception

8 rhopalia (sensory organs) that include simple light-sensing organs arranged around a bell

Radial Symmetry Corals and Anemones in Photoreception

no eye spots; have opsins to help regulate circadian rhythm (important for spawning and photosynthetic symbionts)

Bilateral Symmetry with invertebrates in photoreception

have simple eye spots at anterior end

Image forming eyes

use lens to focus light; evolved multiple times independently

Radial symmetry Cubozoan jellyfish in photoreception

4 rhopalia (sensory organs) arranged around a bell; both simple and image forming eyes

bilateral Symmetry with Arthropods in photoreception

have ommatidia (multiple units) to produce low-resolution pixelated image

Ommatidia

compounds eyes; collection of multiple units, each with narrow visual range

Bilateral Symmetry mollusca in photoreception

have image forming eyes; no blind spots since retina (photoreceptors) are in from of optic nerve

Bilateral symmetry with vertebrates in photoreception

image forming eyes; have a blind spot because retina (photoreceptors) are behind optic nerve

Retina

photoreceptors

thermoreception stimulus

heat

prokaryotes in thermoreception

change in temperature → activates certain protein pathways → reaction

Fungi with thermoreception

largely unstudied; response to change in temperatue depends on species and interactions with co-occurring species

Plants thermoreception

many mechanisms- membrane-bound proteins, photoreceptors, metabolite accumulation

Animals thermoreception

sensory neurons with action potentials that change firing rate with temperature

Electroreception

detect prey, navigate and orientation, communication, sensing predators

Electroreception stimulus

change in charge

prokaryotes in electroreception

change in change activates certain protein pathways → reaction

fungi in electroreception

difficult to study; signals appear to be generated by active fungal growth

Plants for electroreception

flowers may detect electrical stimuli via induction and transmit to neighboring plants via soil as they use environmental negative charge to interact with positive charge on animal pollinators to facilitate pollen transfer

Invertebrates in electroreception

animals accumulate positive charge by moving and interreacting with air molecules; positive charge on mechanosensory antenna hairs deflect towards negative charge → AP

Vertebrates electroreception

possible ancestral trait; passive & active

passive electroreception

ability to detect external electric fields, such as those surrounding living organisms

active electroreception

ability to produce electric fields via electric organ and detect perturbations in generated electric field; evolved independently; typically modified muscle tissue; mechanism of charge generation variable; electrolocation, electrocommunication, & locate/stun prey

Ampullae of Lorenzini eletroreception

ancestral electroreceptors in fish, lost some in lineages; some groups evolve analogous structures; very only to magnify voltage differences

Monotremes (Platypus & Echidna) electroreception

secondarily evolved electroreception; free nerve endings associated with mucus glands in snouth

Dolphins electroreception

secondarily evolved electroreception; pits on snout, modified from ancestral whiskers observed in the Guiana dolphin

Electrolocation

interpret objects in environment based on electrical properties

Electrocommunication

recognition of conspecific or help keep groups of individuals together

Magnetoreception stimulus

Earth’s magnetic field

Magnetoreception in Prokaryotes

have some response to change in magnetic field, purpose unclear

Magnetoreception in fungi

have some response to change in magnetic field, purpose unclear

Magnetoreception in Plants

have some response to change in magnetic field, purpose unclear

Magnetoreception in animals

typically found in migrating species, or species that travel long distances

2 proposed mechanisms for magnetoreception

iron-based & cryptochrome

Iron-Based magnetorecpeiton mechanism

iron deposits in tissues near nerve clusters respond to magnetic field

Cryptochrome magnetoreception mechanism

sense quantum entanglement of electron produced by eye pigment protein