olfaction Flashcards
chapter 14
odor
any smell sensation
odorant
a chemical compound that we can smell
- it must be volatile, small and hydrophobic
nose function
- filter and hummidify air
- smell
olfactory cleft
part at the back of the nose where the main olfactory epithelium is located
olfactory epithelium
patch of tissue in the upper nose that contains ORNs and is covered in a layer of mucus
cribiform plate
a bony tructure riddled with tiny holes that separates the nose from the brain
- axons of the ORNs pass through it
anosmia
the total inability to smell often resulting from illness or head injuries
- loss of taste
supporting cells
metabolic and physcial support to the olfactory receptors
cells in the olfactory epithelium
- supporting cells
- basal cells
- olfactory receptor neurons
basal cells
precursor cells to olfactory receptor neurons
- help replace them when they die
olfactory receptor neurons
the main cell type that contains receptors on its ilia
- located under the watery mucous layer
olfactory bulb
bulbous end of the olfactory tract containing mitral, tufted and glomeruli cells
mitral cells
the main projective output neurons in the olfactory bulbs
- relay
tufted cells
sencodary output neurons in the olfactory bulbs
- their axons form the olfactory tract which go to the brain
glomeruli
spherical conglomerates containing the incoming axons of the ORNS
- each receptor cells converge onto two glomureli and then synapse onto the mitral and tufted cells
cilia
hair like prootrusions on the dendrites of ORNs that contain receptors for oderants
olfactory receptors
region on the cilia that oderant molecules bind to
ORN adaptation
the nose adapts to oderants so if ypu give a burst then another immediately after, they will respond less to the second one
- if you wait 5 seconds it will be recovered
- cortical adaptations happens too
psuedogenes
we have about 1000 different genes but about 60-70% dont work.
- so we have about 300-400 receptors
neural coding for odors
the receptors each bind to one specific molecule but they work together in a population code to to account for the whole variety of smells we perceive
piriform cortex
the primary olfactory cortex which receives signals directly from the olfactory bulb
- dedicated solely to olfaction
entorhinal cortex
receives direct input from olfactory regions and provides the major association input into the hippocampus
amygdala-hippocampus complex
critical for the unique emotional associative properties of olfactory cognition
limbic system
the encompassing group of neural structures that include the olfactory cortex, amygdala, hippocampus, piriform cortex and entorhinal cortex
- olfaction is very connected to this system which gives it unique emotional associations
tip of the nose phenomenon
- when you know a smell but cat name it
- olfaxtion is disconnected from language and does not fo through the thalamus so it does not integrate with the other senses
cross adaptation of smell
the reduction in detection of an oderant following exposure to another oderant
cognitive habituation
psychologucal process by which, after a long term exposure to an odorant, one is no longer able to detect that odorant or has very diminished ability
why do we have cognitive habituation of smell
- receptors may be hindered after continuous exposure and may take longer to recycle
- odorant molecules may be absorbed into bloodstream
- cognitive-emotional factors
attention and smell
we need some level of attention to smell
- looking for smell helps us detect it
