Special Senses Concepts Flashcards
Describe the structure of the olfactory receptors and other cells involved in olfaction.
Olfactory receptor cells= Bipolar, first order, ciliated neurons that act as chemoreceptors to bind odorant molecules at the apical surface of the olfactory epithelium and transduce stimulation (binding) into receptor potentials - and then into action potentials sent along the axons of the neurons, through the olfactory foramina of the cribriform plate of the ethmoid bone to synapse on second order neurons of the olfactory bulb
Supporting cells= pseudostratified, ciliated columnar cells of the olfactory epithelium that provide structural and metabolic support to the olfactory receptor cells. Also, mimic myelin sheaths by “insulating” the nerve olfactory receptor cells
Basal cells= mitotically active (stem cells) at the basal end of the olfactory epithelium. They divide to replace worn-out olfactory receptors every month or so.
Describe the sensation of olfaction in terms of the type of sensory receptor and steps needed to transduce odorants. Describe the location of the olfactory epithelium and some nearby structures.
- Air inhaled through the nostrils
- Air humidified, cleansed, and connected among the nasal conchae
- Odorant molecules in air bind to the olfactory receptors
- Stimulation (chemoreception) transduced to receptor potential
- Action potential sent along the bipolar olfactory receptor
- Axons of olfactory receptor synapse (EPSP) on the neurons of the olfactory bulb
- CN I runs to the primary olfactory area, then on to the olfactory association area (oribitalfronal area) with lots of collaterals to the limbic system and hypothalamus
Outline the neural pathway for olfaction.
First-order olfactory receptor synapses on the dendrites or cell bodies of second-order olfactory neurons in the olfactory bulb. Olfactory bulbs sit superior to the cribriform plate of the ethmoid bone and lateral to the crista galli. Then to the primary olfactory area, then on to the olfactory association area. Lots of collaterals along the way are sent to the limbic system and hypothalamus.
Explain how only a couple hundred odorants can account for tens of thousands of smells.
You get tens of thousands of smells through combinations of odorant molecules
Discuss the rate of adaptation of olfactory receptors and compare it to that of other fast and slow-adapting receptors.
The rate of adaptation of olfactory receptors is fast adapting. About 50% adaptation in the first second after stimulation and eventually enough of a continued slow adaptation become completely insensitive and you become nose blind to certain strong odors within a minute or so.
Name the 5 primary tastes and be able to link gustation to olfaction, conceptually.
Sweet, sour, bitter, salty, umami
- 80% of taste is actually olfactory
- Taste is completely wrapped up in olfaction with 1000s of “flavors” steeming from combinations of the 5 tastes plus olfaction
Contrast the structure, function, and location of the 4 different papillae of the tongue.
Vallate papilla= about 12 very big, taste, posterior 1/3 of tongue
Fungiform papilla= spread all over the tongue (mushroom-shaped), taste, anterior ⅔ of tongue
Filiform papilla= no taste, increased friction, good for licking, bumpy, center of the tongue
Foliate papilla= very lateral aspects of the tongue, but degenerate early in childhood
Describe the structure and function of gustatory receptors, focusing on which type of cell they are.
Epithelial cells with hairs push through the taste pore and out into the oral cavity. Chemoreceptors bind sweet, bitter, and umami tastants to trigger secondary messenger paths to depolarize the cell with Ca influx to trigger NT release from synaptic vesicles and the synaptic cleft
Compare the structure and function of the other types of cells in the gustatory epithelium to those of the olfactory epithelium.
Taste buds are oval-shaped bodies found within the papillae and connected to the outside world via a taste pore. These taste buds hold the gustatory receptor cells. Inside the taste bud is a “mini-epithelium” with 3 cell types: gustatory receptor, supporting cells, and basal cells. So, same concept as olfactory cells, mitotically active and replacing.
Describe the basics of the neural pathway for gustation.
- two-step process
- Gustatory receptor cells transduce binding of tastant molecules, but the real 1st order neuron is a “sensory” neuron found on the basal side of the taste bud
- The receptor creates a “receptor” potential and needs to synapse on the 1st-order neuron to generate an AP
Explain how Na, as a tastant, can be both a ligand and a transported cation.
The molecule that binds to the metabotropic receptor is sodium as salty food is high in sodium, also causing sodium to rush in when the receptor is activated.
Compare gustatory adaptation to that of other sensory modalities.
The threshold is lowest for bitter tastants…poisons
Sweet and salty have a much higher threshold
Adaptation is complete within 1-5 minutes of continuous stimulation (take small bites and savor)
Describe the location and function of accessory structures of the eye.
Eyebrows: above eyes, protection
Eyelashes: protect eyes from foreign substances
Eyelids: upper and lower structures anterior to the eyeball that open and close to expose, or protect the eyeball
7 extrinsic eye muscles:
Lateral, medial, superior, and inferior rectus= mostly moving the eye linearly. Up, down, over, and out
Inferior and superior oblique= aid in “rolling” the eyes
Levator palpebrae= opens the eye by lifting the upper palpebra (eyelid)
Lacrimal apparatus= lubricate eyes
Review the 7 extrinsic muscles of the eye, including insertions, roles, and CN innervation
Lateral, medial, superior, and inferior rectus= Cranial nerve 6 (abducens), moving the eye linearly. Up, down, over, and out
Inferior and superior oblique= Cranial nerve 4 (trochlear), aid in “rolling” the eyes
Levator palpebrae= Cranial nerve 3 (oculomotor), opens the eye by lifting the upper palpebra (eyelid)
originate on the temporal or lacrimal bone and inserts on the sclera of the eys
Trace the path of lacrimation, including the relevant structures.
The lacrimal gland secretes tears into excretory lacrimal ducts, which distribute tears over the surface of the eyeball. The superior or inferior lacrimal canaliculi drain tears into the lacrimal sac, which drains tears into the nasolacrimal duct, which drains tears into the nasal cavity.
Review 2 small ANS adjustments to vision
Accommodation: viewing near and distant objects differently
Pupi diameter to match the amount of available light
Discuss the fluids of the eye, using an anterior/posterior cavity analysis
anterior cavity= aqueous humor, liquid-like substance
posterior cavity= vitreous humor, gel-like substance
Discuss the importance of the fovea centralis in image formation.
The fovea centralis is a small indentation in the center of the macula lutea, which is the dead center of the posterior retina receiving the projected image. This area only has cones, so it’s the area of highest visual activity and why we always orient to and look directly at things we want to see the clearest, having the image landing on the fovea centralis.
Discuss the roles of the two primary layers of the retina and the associated cells and structures found in each.
Pigmented layer= melanin granules, pigment epithelial cell
Neural layer (inner segment and outer segment) = rod and cones, mitochondrion, Golgi complex, nucleus, synaptic terminal, synaptic vesicles, discs
Describe phototransduction in detail, starting with light passing through the neural layer and ending with depolarization of bipolar sensory neurons.
- When light hits the opsin and trans-retinal is briefly set free, trans-retinal sets off a molecular chain reaction that shuts down the influx of Na into the photoreceptor
- This hyperpolarizes the photoreceptor and stops the flow of glutamate, an inhibitory NT of the eye, onto the bipolar cells
- This stops the inhibition of bipolar cells
- This means in the light, the bipolar cells are actively depolarizing and signaling the CNa (transduction is occurring)
Contrast rods and cones, structurally and functionally
Rods: rod-shaped
- rhodopsin
- Night vision
- Fuzzy vision
- Peripheral vision
- Active only in low light
Cones: cone-shaped
- 3 different Opsins
- Color vision
- Edge detection
- Central vision
- Only in bright light
Discuss, briefly, how amacrine and horizontal cells can modify phototransduction.
If you’re in bright light, they’re quieting now the stimulation and if you’re in a dark room they amplify what little signal is there so you can create more signal
Describe the neural pathway for vision.
- Ganglion cells synapse onto CN II axons that coalesce at the optic disc to pass through the retina and onto the CNS
- Via the optic chasm, immediately to the lateral geniculate nuclei of the thalamus then onto the primary visual area with collaterals to:
- Superior colliculi of the midbrain
- Other nuclei of the midbrain coordinate pupil size, accommodation, and head movement
- The suprachiasmatic nucleus of the hypothalamus (sleep & circadian rhythms)
Discuss the role of tensor tympani and stapedius in modifying sound transduction.
The tensor tympani is a small skeletal muscle under ANS control that contracts to stiffen the malleus against the tympani membrane to dampen excess vibration from loud noises
The stapedius is a small muscle in the body under ANS control that contracts to dampen the vibration of stapes on the oval window in “loud” environments
