Nervous Systems and Sense Organs Flashcards
What are neurons (2)?
functional units of nervous systems
cells that are specialized for high-velocity impulse conduction
How is an impulse generated?
impulse is generated (internal or external) within a true nervous system results from a stimulation imposed on the nervous elements
What are neuropils?
dense networks of interwoven nerve fibers and their branches and synapses, usually with glial filaments (brains)
What is a ganglion?
network of cells forming a nerve center
What is a stimulus received by?
receptor/ sense organ
How is a stimulus sent and processed? (3)
organ generates an impulse that is conducted along a sensory nerve/ afferent nerve through a series of adjacent neurons to a coordinating center
information is then processed and a response is made
motor nerve/ efferent nerve conducts an impulse from the center to an effector/ muscle where response occurs
What is common in all nervous system?
depolarization along the length of each neuron and the neurotransmitter between gaps
How is information interpreted within the system for appropriate response? (3)
Each sense receptor has a threshold
nature of receptor
The nervous system is “wired” so that signals coming from a specific type of sense organ are always interpreted in a specific way.
What is the threshold?
the minimum strength a stimulus must have to trigger a signal. Different receptors have different thresholds based on how they’re built or how they work.
ex- low threshold for light will respond to light
How are receptors constructed?
receptors are constructed to permit only certain stimuli to reach impulse-generating cells
ex- light-sensitive cells in eyes are located beneath the eye surface, where stimuli other than light would not reach
Example of the wiring of a nervous system
ex-signals from the eye’s light receptors (photoreceptors) are always understood by the brain as light, no matter what actually caused the signal.
What is taxis (2)?
movement related response in response to a stimuli
positive or negative (moving towards or away from light)
What does the sense organ type and location depend on?
complexity, mode of life, and body plan of an animal
What are mechanoreceptors?
responds to mechanical stimuli like touch, vibrations, and pressure
What are nonmechanical stimuli
chemical, light, temperature
What is magnetic stimuli seen in?
butterflies to migrate using earth’s magnetic field
What are tactile receptors, and what do they depend on?
derived from modified epithelial cells with sensory neurons
depends on structure of body wall
What do tactile receptors depend on? (2)
involve projections from the body surface, such as bristles, spines, setae, and tubercles
objects moves these receptors, deforming them, activating neurons
How is response integrated in tactile receptors, and an example?
often integrated with other sorts of sensory input
can be combined with chemical recognition of kin
What is thigmotaxis?
response to touch
What is vibration sensors common in?
tube-dwellers and crustacean predators/ spiders
What is trichobothria?
tactile setae in spider appendages that sense airborne vibrations of prey (wing beats)
What are georeceptors, and what do they do?
response to pull of gravity
provides orientation to animal
What are statocysts? (2)
fluid-filled chamber containing a statolith (solid granule)
lined with touch-sensitive epithelium with hairs containing neurons
How do open and closed statolith differ?
statolith can be a sand grain from the environment
most are made by the organism itself
How does inertia affect the statolith (2)?
resting inertia of the statolith in the fluid causes movement by the animals to change pattern of stimulation of the sensory epithelium
when stationary, statolith provides information about orientation to gravity
What do georeceptors do in crustaceans?
flow of fluid can provide information about its acceleration relative to its environment
When are georeceptors used, and two examples?
used when sensory reception is inadequate
burrowing inverts must rely on georeceptors when light is unavailable
planktonic animals face orientation issues in deep water or night time
How do aquatic insects detect gravity?
detect gravity by using air bubbles trapped in passageways
What are proprioreceptors (2)?
responds to mechanically induced changes caused by stretching, compression, bending, and tension
gives information about body parts movement and their position
What are proprioreceptors associated with, and two examples?
neurons are associated with parts of the body that is being affected
associated with appendage joints and body extensor muscles in arthropods
specialized muscle cells, elastic connective tissue fibers, joint membranes, that stimulate attached neurons as they are stretched
What are phonoreceptors, and what are they found in?
sensitivity to sound
annelids and arthropods
What are tympanic organs, what do they do, and what groups have them?
tough but flexible layer covering internal air sac that allows it to vibrate when struck by sound
stimulates attached sensory neurons
crickets, grasshoppers, and cicadas
What are slit sense organs?
organs in arachnids that sense sound
What are organs of Tomosvary?
myriapod organs that is sensitive to sound
What are baroreceptors, and what kind of structures are they?
sensitivity to pressure changes
no structures identified
What are baroreceptors seen in, and example?
seen in pelagic invertebrates like medusae, ctenophores, cephalopods, and copepods
migration in response to water pressure changes
What are chemoreceptors, and how do they work (2)?
no sensory structure but irritability of protoplasm itself
chemicals in high concentration can induce response
chemicals stimulate sensory neurons by contact (diffusing in solution across epithelium)
What are aquatic chemoreceptors found in, what do they do (2)?
found in pits or depression where cilia circulates water
leaks amino acid into environment through skin/gills/ excretion
provides body odor to identify one another
What kind of chemoreceptors do arthropods have?
hallow setae/ projections
What are photoreceptors (3)?
sensitivity to light
possesses light-sensitive pigments
absorbs photons to stimulate neurons
What groups have photoreceptors?
cnidaria, molluscs, annelids, arthropods, and chordates have evolved eyes for image formation
How are different photoreceptors similar (2)
all light receptors are similar in structure
photoreceptor protein groups in metazoans
- opsins, cryptochromes, and possibly LITE-1
What groups have well-developed eyes, and how do they differ?
arthropods, molluscs, polychaetes
can range from light perception to image formation
What are eyespots?
simplest photoreceptors of unicellular structure
Types of multicellular photoreceptors
ocelli/ simple eyes
compound eyes
complex eyes
What are direct ocelli, and how do they differ from inverted ones?
light-sensitive cells facing outwards
inverted eyes are common in flatworms and nemerteans
- light enters cups is reflected onto the cells to give info on light direction
What are compound eyes, and how do they work?
arthropod eyes made of units of ommatidia
each ommatidium has its own nerve tract to a large optic nerve and has its own discrete field of vision
visual fields overlap, to detect movement
What are complex eyes, and how are they structured (3)?
cephalopods)- image formation
covered by a cornea
light entering is controlled by the iris
lens is held by ciliated muscles and focuses light on the retina
How do vertebrate and invertebrate complex eyes differ?
vertebrate eyes have inverted retinal layers focus by changing shape of lens
inverts moves lns back and forth and compresses the eyeball
What are ciliary eyes, and what groups have them?
photoreceptor units derived from or with celia (cnidaria, echinoderms, and chordates)
What are rhabdomeric eyes, and what groups have them?
photoreceptor derived from microvilli/ microtubules (flatworms, annelids, arthropods, molluscs)
How did photreceptors evolve?
all photoreceptor is homologous through Pax-6 gene (eye development)
How did blindness evolve (2)?
blindness can evolve through selective advantage (less energy to make eye) or degredation/ reduction
degrades due to disappearing or for photo-stimulation in dark areas
What are thermoreceptors, and examples (2)?
can either be physiological response or organs
insects, crustaceans, and horseshoe crabs can sense thermal variation
leeches can heat-sense to find host
What are independent effectors, and examples?
specialized sensory response structures that receive info from the environment and elicits a response without the nervous system
nematocysts and colloblasts
