sensory systems Flashcards
receptors
stimuli are transduced by receptors grouped together to form a sensory surface
- photoreceptors = responsive to light
- mechanoreceptors = sensitive to mechanical energy i.e. pressure (skin), stretch (muscles), sound waves (bending of hair cells), barometer (BP)
- thermoreceptors = sensitive to temp
- osmoreceptors detect changes in [solute] in ECF
- chemoreceptors = sensitive to chemicals (i.e. taste, smell)
- nociceptors (pain) = sensitive to tissue damage i.e. cuts, burns
transduction pathway
conversion of stimulus energy to neuronal signal
- receptor: axon/dendrite can transduce in a sensory modality (sensory input i.e. taste, temp, pressure, smell)
- relay nuclei: groups of neurons located in the CNS that process signals from receptor neurons & transmit to thalamus
- thalamus: groups of neurons organized into nuclei that process signal from relay nuclei & transmit to cerebral
- 1º cerebral cortex: process signals from thalamus & transmit to 2º cerebral cortex
- 2º cerebral cortex: process signals from 1º sensory cortex & transmit to association cortex, motor cortex, & subcortical structures
receptor ➞ relay nuclei ➞ thalamus ➞ primary cerebral cortex ➞ secondary cerebral cortex
visual
- light signal goes through lens until hits retina
- photoreceptor transduces light info to electrical signals that go through optic nerves to thalamus & then to to occipital lobe for processing
- large monocular field w/ larger binocular overlap
optic anatomy
- cornea
- optic nerve
-
optic disc = blind spot
- no photoreceptors
- no light hits
- no images transmitted
- no processing
-
retina contains photoreceptors
-
rods
- sensitive to low light levels (scotopic)
- cannot distinguish btwn wavelengths
- ↓ acuity & peripheral field
-
cones
- sensitive to bright light (photopic)
- can distinguish between diff wavelengths
- 3 types: blue, green & red ➞ color vision
- white = all cones activated
- dark = no light, no cone activated
-
fovea = high acuity
- aka macula lutea
- most distinct & distinguished vision
- center of retina in “dip”
- bipolar cells & ganglion cells pulled aside
- no cells above photoreceptors ➞ light hits directly
- no rods, cones only
- macular degeneration: loss of photoreceptors in fovea
-
rods
phototransduction
- Light activates rhodopsin (opsin + retinal)
- activated rhodopsin activates cGMP phosphodiesterase &
- rhodopsin activation decreases cGMP & closes cGMP-gated Na+
- cell membrane hyperpolarizes & decreases neurotransmitter release
* light passes through neural circuitry of retina before making contact with photoreceptors in back of eye
* rhodopsin = visual pigment in rods- inactivated in dark (depolarized)
- activated in light (hyperpolarized)
- in light: retinal changes to all trans-retinal ➞ active form
- retinal conformational changes
auditory
auditory receptors: location where sound information is transduced to electrical pathways to temporal lobes
- hair cells located in cochlea
- cochlea changes sound info to electrical passage through auditory nerve to temporal lobe
external & middle ear
external ear:
- pinna = outer ear
- external acoustic meatus = passageway from outside to tympanic membrane = ear drum ➞ separates external & middle ear
middle ear:
- auditory ossicles (bones) vibrate & transmit sound waves
- malleus
- incus
- stapes ➞ connected to oval window = entrance to fluid-filled cochlea
- round window seals scala tympani from middle ear
inner ear
-
cochlea: structure of sound transduction
- helicotrema: where scala tympani meets scala vestibuli (after tip of cochlear duct)
- scala tympani & scala vestibuli filled with perilymph fluid
- endolymph fluid fills cochlear duct
- basilar membrane forms floor of cochlear duct ➞ holds inner hair cells
-
organ of corti (spiral organ): sense organ for hearing
- contains inner hair cells with stereocilia (hairs) on each cell
- tectorial membrane: stationary membrane connected to stereocilia on inner hair cells
- vestibular apparatus: semicircular canals & utricle & saccule
- auditory nerve relays receptor potential signals through thalamus to auditory cortex in temporal lobe) ➞ sound transduction
sound transduction
- mechanoreceptors: stretch receptor ➞ respond to mechanical pressure of distortion
- movement of endolymph fluid in cochlear duct causes deflection of basilar membrane
- stereocilia bend back & forth
- bending opens mechanically gated channels ➞ ion movements ➞ receptor potential
- when cells stretch ➞ receptors open ➞ depolarize
- when cells loosen/bend ➞ receptors close ➞ hyperpolarizes
- inner hair cells do not undergo AP, communicate via chemical synapse with auditory (cochlear) nerve
- auditory nerve relays receptor potential signals through thalamus to auditory cortex in temporal lobe
inner hair cells
transform mechanical forces of sound from endolymph vibration to AP propagating auditory messages to cerebral cortex (temporal lobe)
sound transduction pathway
sound waves
↓
vibration of tympanic membrane
↓
vibration of auditory ossicles
↓
vibration of oval window
↓
endolymph fluid movement
↓
vibration of basilar membrane
↓
bending of inner hair cells
↓
graded receptor potential
↓
AP generated in auditory nerve
↓
propagation to auditory cortex (in temporal lobe)
differences in sound come from
pitch: discrimination depends on where the basilar membrane vibrates
-
high frequency sound vibrations begin at narrow stiff end close to oval window
- waves = many short oscillations
-
low frequency sound travels to helicotrema near **wide flexible end **
- waves = few, wider oscillations
volume discriminates based on how much ➞ amplitude of vibration
- loud = stronger & larger vibrations
- too loud damages hair cells ➞ normally grow back after a few hours but chronic loud noise ↓ regeneration time until does not grow back
somatosensory
- mechanoreceptors
- proprioception: body’s ability to sense movement, action, & location ➞ awareness of body in space in relation to other things
-
touch
-
tonic receptors: feeling stimuli constantly until stimuli stops
- do not adapt or adapt slowly
- sustain pressure & stretch of skin (i.e. massage)
-
phasic receptors ➞ on/off during constant stimuli ➞ only on again when stimuli changes
- adapt rapidly
- off response
- signal changes in pressure on skin surface
- i.e. wear/take off watch/rings
-
tonic receptors: feeling stimuli constantly until stimuli stops
acuity
discriminative ability: ability to sense/distinguish 2 separate points
* somatic acuity varies between body parts/areas
* fingers, toes, face > arms, legs, torso
* avg 2-point discrimination threshold: finger < palm < belly < thigh
* inflluenced by:
1. receptor density: more receptors = higher acuity
2. receptive field size: each sensory neuron responds to stimuli info only within a restrictive specific area
3. lateral inhibition: inhibition of adjacent neurons in a map ➞ facilitates localization of stimuli & sharpens contrast
