lec 19- Animal sensory systems part I Flashcards
what are the steps of transduction of environmental stimuli?
- sensory organs detect change in environment or stimuli
- sensory neurons encode changes in environment as changes in frequency of action potentials
- sensory information is sent to CNS for interpretation
- sensory systems allow animals to have a physiological/biological response
what are sensory receptors categorized by?
by the type of stimulus
are there many types of sensory receptors that transduce the changes in the environment?
yes (mechanoreceptors for pressure, photoreceptors for light, chemoreceptors for molecules, thermoreceptors for temp, nociceptors for harmful stimuli, electroreceptors for electrical fields, and magnetoreceptors for magnetic fields)
what are the three steps for a sensory organ to convey info to the brain?
- transduction- conversion of external stimulus to action potentials
- transmission- transmission of the signal (action potentials) to the CNS
- interpretation- interpretation of the signals by the CNS
what are the two types of receptors in signal transduction?
-specialized sensory neurons that change frequency and send to CNS
-specialized receptor cell that communicates with sensory neuron
what is membrane depolarization?
when ions cause inside to be less negative than resting potential
what is membrane hyperpolarization?
when ions cause inside to be more negative than the resting potential
what is the amount of depolarization or hyperpolarization of the sensory receptor proportional to?
the intensity of the stimulus
what does a change in the sensory receptors membrane potential result in?
change in the firing rate of action potentials sent to the brain
do sensory neurons send their signals to specific parts of the brain?
yes
what are mechanoreception systems used for?
used for a variety of changes in the environment
in mechanoreception, what does direct physical pressure on plasma membrane or distortion of the membrane structure by bending cause?
causes a change in the conformation of ion channels, causing changes in depolarization and hyperpolarization, resulting in the modulation of the frequency of action potentials
in what mediums does sound oscillate?
water and air
what is the speed of sound in air?
343 meters per second
what is the condensed and loose part of a sound wave called?
compressions and rarefactions
what is hearing?
the sensation produced by the wavelike changes in air pressure called sound
what is frequency of sound?
the number of pressure waves that occur in 1 second
what is the differences in sound frequency called?
different pitches
what does the ear do?
the ear transduces sound waves into action potentials that carry info to the brain
what are the three sections of the human ear?
-outer ear
-middle ear
-inner ear
each separated from one another by a membrane
what does the outer ear do?
collects the sound waves and funnels them into the ear canal, where they strike the tympanic membrane (eardrum)
what does the tympanic membrane do once struck?
it vibrates with the same frequency as the sound waves and passes the vibration to three tiny bones that vibrate against one another
what do the three tiny bones (stapes) do?
after vibrating against one another, one of them will vibrate against the oval window (the membrane that separates middle and inner ear)
what does the oval window do?
it oscillates and generates waves in the fluid inside a chamber called the cochlea
what does the cochlea do?
it is where the vibrations are transduced by hair cells into neuronal signals
why is the vibrations enlarged in the ear?
the eardrum is 15 times larger than the oval window, so it increases by a factor of 15 when going to it while the three bones amplify it further, resulting in an overall effect of amplification by a factor of 22 times (this is done so soft sounds can stimulate hair cells of the cochlea)
what is the cochlea and where are the hair cells?
it is a coiled tube with a set of internal membranes that divide it into three chambers, hair cells form rows in the middle chamber effectively sandwiched between membranes
what is the membrane where hair cells are in tissue sitting atop of?
basilar membrane
what part of the hair cells touches the tectorial membrane?
sterocilia
what do hair cells do?
transduce motion of the membranes (caused by soundwaves) to electrical signals
why is the basilar membrane stiff near the oval window and flexible at the other end?
because then different frequencies of sound let it vibrate maximally in specific location along its length, causing vibrations in the membrane
what is the sound of hearing?
when the brain receives action potentials from neurons associating with specific hair cells, it interprets that action potential as a particular pitch (differences in frequency)
what do complex sounds contain?
they contain a wide variety of frequencies and trigger particular combinations of hair cells
what are hair cells and what are they made of?
-mechanoreceptor cells named after their stiff outgrowths called stereocilia
- have a single kinocilium, stereocilia are arranged in order of increasing length with kinocilium being the longest
what are sterocilia reinforced by?
they are microvilli reinforced by actin filaments
what are the 6 steps of signal transduction in hair cells?
- sound waves bend stereocilia towards kinocilium, causing tip links to pull adjacent stereocilia
- mechanotransduction channels (sensitive to stretch, they are K+ channels) open
- influx of K+ occurs causing depolarization
- depolarization triggers release of calcium channels which cause neurotransmitter vesicles to move
- neurotransmitters fuse with plasma membrane
- neurotransmitters are released
if the stereocilia bend the other way, what happens?
hyperpolarization which inhibits action potentials
what has a special composition that causes the Mechanotransduction channel (MET) to do a K+ and Ca influx?
endolymph, extra high in K+
what is the sound range that humans hear?
20Hz to 20 KHz
what is sound below the human range called?
infrasonic
what is sound above the human range called?
ultrasonic
what two things does the brain compare differences in to locate the origin of the sound?
- arrival time (interaural timing)- sound in right, means located to the right
- sound intensity (interaural level)- sound louder in left, means located to the left
what happens when experiencing hearing loss?
-loud sounds cause damage to the cochlea
-prolonged exposure to loud sounds causes hair cells to die
-inner ear damage is permanent
what is the sclera?
the outmost layer of the eye which is tough, and white in color
what is the cornea?
the front of the sclera that is a transparent sheet of connective tissue
what is the iris?
the pigmented round muscle just inside the cornea, can contract and expand to let a certain amount of light in
what is the pupil?
The whole in the center of the iris
what is the lens?
the place where light passes through after it has passed through the cornea then that pupil
what is the retina?
the part of the eye where the light is focused
what is the fovea?
the region of photoreceptors where the light is focused on in the retina
what does the refractive error myopia cause?
the eyeball is too long, causing the light to be focused in front of the retina
what does the refractive error hyperopia cause?
the eyeball is too short, causing the light to be focused behind the retina
what are the three layers of the retina?
- the photoreceptors respond to light and are held in place by the pigmented epithelium
- an intermediate layer of connective neurons called bipolar cells
- ganglion cells from the intermost layer of the retina and their axons project to the brain via the optic nerve
what pathway is signal transduction in the eye done with?
a specialized receptor cell
what do photoreceptors consist of?
-Rods: sensitive to dim light but not to colour
-Cones: less sensitive to light but are stimulated by different wavelengths of light (colour)
what transmembrane protein is in the segment packed membrane rich disks in rods and cones?
opsin
what does each opsin molecule associate with?
with the pigment molecule retinal, the two molecule process in rod cells is called rhodopsin
what happens to retinal when it absorbs light?
-it changes shape, resulting in a conformational change in opsin
-specifically the number 11 carbon in the retinal molecule changes from the cis to the trans conformation (retinal is like a light switch)
what does the retinal conformational change lead to?
-leads to a series of events that climax in a change in frequency of action potentials being sent to the brain
-light closes ion channels and decreases the amount of neurotransmitter being released by the photoreceptor
what happens in rod cells when in the dark?
when in the dark with no light, retinal has not been activated, sodium channels in the membrane are open letting entry of sodium to occur, resulting in depolarization of rod cells
what happens in rod cells when hit by light?
light inhibits the entry of sodium by closing channels and depolarization is stopped by a signal transduction cascade, causing hyperpolarization
what are the 7 steps to rods and cones detecting light?
- rhodopsin is activated when light causes the retinal to change shape
- rhodopsin activates the G protein Transducin, which in turn activates the enzyme phosphodiesterase (PDE)
- PDE breaks down a nucleotide called cyclic guanosine monophosphate (cGMP) to guanosine monophosphate (GMP)
- as cGMP levels decline, cGMP-gated sodium channels in the plasma membrane of the photoreceptor close
- when sodium channels close, sodium entry decreases and the membrane hyperpolarizes
- the resulting decrease in neurotransmitter release from the photoreceptor signals to the postsynaptic bipolar cells that light was absorbed
- as a result, it causes the retinal ganglion cells to send a new pattern of action potentials to the brain
can a single photon cause the closure of 200 ion channels?
yes, one activated rhodopsin can activate 800 transducins
why is colour vision possible?
because different opsins absorb different wavelengths of light
there are three different cone types, each having a different type of opsin, what are the three possible opsins?
-blue (S- short wavelengths, around 420)
-green (M- medium wavelengths, around 530)
-red (L- long wavelengths, around 560)
