Special Senses

Question 1

What is olfaction - What is used to detect

Answer 1

detection of odorants dissolved in the air

odorants are volatile molecules, dissovlved in mucus, detected by chemoreceptors?

Question 2

What is the olfactory epithelium? What are the 3 cell types?

Answer 2

It is a sensory receptor organ that involves

1. located in superior region of nasal cavity, rejuvenation and sensitivty of recepotrs decline with aging; has three types of cells
   
   1. olfactory receptor cells - detect odors
   2. supporting cells - sustain receptors
   3. basal cells - replace olfactory receptor cells every 40-60 days
2. Lamina propria
   
   1. areolar connective tissue layer in the internal to olfactory epithelium
   2. houses blood vessels, nerves, olfactory glands
3. olfactory glands
   
   1. helps form mucous covering olfactory epithelium.

Question 3

What is the function of olfactory receptor cells?

Answer 3

Olfactory receptor cells are the primary neurons in the sensory pathway for smell

They are bipolar structured neurons: single dendrite and unmyelinated axon

Contain olfactory hairs and olfactory nerves

• olfactory hairs: cilia projecting from receptor cell dendrite
  
  • house chemoreceptors for a specific odorant
    
    • perceived smells depend on which cells are stimulated!
• olfactory nerves
  
  • bundles of olfactory cell axons
  • project through the skull’s cribiform plate and enter olfactory bulbs

Question 4

What is the olfactory bulb? what does it have connections with?

Answer 4

Olfactory bulb is a pair of the end of olfactory tracts located under the brains frontal lobes

Olfactory nerve fibers synapse here with mitral cells and tufted cells

Connections form the olfactory glomeruli

Question 5

What is the process of detecting smells?

Answer 5

1. Mucus contains odorant-binding proteins
   
   1. olfactory sensations begin when odorant binds to protein and protein stimulates receptor cell (rapidly adapting receptor)
      
      1. G protein in receptor cell activates adeylate cyclaes, converts ATP to cAMP
      2. cAMp leads to opening of ion channels for sodium and calcium to depolarize
      3. action potential is triggered on axon, conducted to glomerulus
2. Secondary neuron conducts signals to various CNS areas
   
   1. cerebral cortex (percive, identify smell) hypothalamus (visceral reaction to smell), amygdala (smell recognition, emotional reaction.

Question 6

where are gustatory cells located?

Answer 6

gustatory cells are chemoreceptors within taste buds

Question 7

What are the papillae of the tongue?

Answer 7

• Filiform papillae: short and spiked
  
  • no taste buds ( no role in gustatino) help manipulate food
  • located on the anterior two thirds of the tongue
• fungiform papillae: mushroom shaped
  
  • each contain a few taste buds
  • location on tip and sides of tongue
• Vallate (circumvallate papillae)
  
  • largest, least numerous
  • located in a row of 10-12 along the posterior dorsal tongue surface
• foliate papillae: leaflike ridges
  
  • not well developed
  • house a few taste buds in early childhood
  • located on posterior lateral tongue.

Question 8

What are the three cells that taste buds house?

Answer 8

1. Gustatory cells : neuroepithelial cehmoreceptive receptor cells of the taste buds (live-7-9 days)
   
   1. gustatory microvillus (taste hair) forms dendritic ending
   2. microvillus often extends through taste pore to tongue surface
2. supporting cells: sustain gustatory cells
3. Basal cells: neural stem cells that replace gustatory cells

Question 9

What are the five basic taste sensations?

Answer 9

Sweet -

salt

sour

bitter - alkaloids

unami - amino acid

Question 10

Transduction in gustatory cells. (sweet, bitter, umami) vs (salty, sour)

Answer 10

1. For sweet, bitter, and umami the tastants are molecules
   
   1. tastant binds to specific cell membrane recepotr
   2. g protein is activated causing formation of 2nd messenger
   3. results in cell depolarizatoin
2. for salt and sour the tastants are ions
   
   1. tastants depolarize cell directly
3. depolarized gustatory cells release neurotransmitter stimulating primary neuron in CN VII, or CN IX

Question 11

What happens in hyperopia (farsightedness)

Answer 11

The image is focused beyond the back of the retina, related to the shape of the eyeball and the lens

Convex lens is required to fix

Question 12

What happens in myopia?

Answer 12

the image is focused before it reaches the retina,

concave lens is required to fix

Question 13

Describe the refractoin of light

Answer 13

Sharp vision requires light rays to be bent (refracted) as they pass through the retina

• Refraction results when light passes
  
  • between media of different densities as air and cornea
  • through curved surfaces such as the lens
• Refractive index: a number that represents its comparative density

Question 14

What is the near response?

Answer 14

• Near resposne is for objects closer than 20 feet: eyes converge, lens accomodates, pupils constrict
  
  • convergence of the eyes: extrinsic muscles pull medially
    
    • directs image of interests onto both foveas
    • weak extrinsic eye muscles may cause diplopia (double vision)
  • Accomodatoin of the lens - ciliary muscle contraction thickens lens
    
    • slackened suspensory ligaments allow lens to thicken
    • refraction increases
  • constriction of pupils
    
    • sphincter pupillae contraction shrinks hole
    • light passes through the center of the lens, avoids blurriness at thin edges

Question 15

What is the far response?

Answer 15

Response of eyes for objects 20 feet or further away: no

no convergence

eyes face forward (not converged)

lens is flattened, ciliary muscle relaxes (suspensory ligaments taut)

pupil is relatively dilated - allows more light into the eye.

Question 16

What are the photoreceptors?

Answer 16

• Rods and cones
• Rods
  
  • rods are longer and narrower than cones; more numerous
  • each rod is highly sensitive: activated by even dim light
  • The periphery of the retina contains many rods
    
    • many rods converge on fewer bipolar cells, which converge on fewer ganglion cells
    • results in sensitivity to dim light but a blurry image
• cones
  
  • highly concentrated at the fovea centralis
    
    • activated by high intensity light, allows color vision
  • cones have a 1 to 1 relationship with bipolar cells and ganglion cells
    
    • this results in a sharp image but only possible in bright light

Question 17

What are photopigments? where are they found? What are they made of?

Answer 17

• These are light absorbing molecules
  
  • they are found within the membranes of the outer segments of rods and cones
  • they are made of opsin protein and light absorbing retinal (made from Vitamin A)
  • Different pigment types have different opsins transducing different wavelengths (colors) of light
    
    • each photoreceptor has only one photopigment type
    • rods contain rhodopsin
    • Three types of cones each containing a type of photopsin with a different sensitivity
      
      • blue cones detect short wavelengths, green cones absorb intermediate wavelengths, and red cones best detect long wavelengths

Question 18

Absorption wavelengths

Answer 18

short wavelength: blue cones `420

intermediate: green

long wavelength: red cones~560

Question 19

Describe phototrasnduction in terms of rhodopsin

Answer 19

• Light triggers electrical events
  
  • in the dark, rhodopsin contains cis-retinal
  • light causes reconfiguration to trans-restinal, which dissociates with opsin (bleaching)
• After bleaching, rhodpsin must be rebuilt for rod to function
  
  • trans-retinal transported to pigemented layer and actively converted to cis-retinal
  • cis-retinal transported back into rod and combined with opsin
  • process is slow for rhodopsin- rods don’t function in bright light
• Process is similar for cone photopsins, but quicker
  
  • more intense light needed for bleaching
  • photopsin regenerates rapdily.

Question 20

Bleaching and regeneration of rhodopsin

Answer 20

1. Rhodopsin (opsin + cis-retinal) absorbs light rays
2. Cis-retinal is transformed to trans-retinal via light rays
3. Transretinal dissasocitates from

Question 21

What is dark adaptation and what is light adaptation

Answer 21

1. Dark adaptation
   
   1. return of sensitivity to low light levels after bright light.
   2. bleached rods must regenerate rhodopsin –> transretinal to cis retinal
   3. May take 20 to 30 minues to see well
2. light adaptation
   
   1. process of adjusting from low to bright conditions
   2. pupils constrict, but cones initially overstimulated
   3. takes about 5-10 minutes for full adjustment.

Question 22

Phototransduction initiating nerve signals

Answer 22

• In the dark, rodsa are depolarized (membrane is -40mV)
  
  • cyclic guanosine monophosphate (cGMP) is produced
  • cGMP binds with cations channels and keeps them open
  • Sodium and calcium enter the cell “dark current”
  • Voltage gatd caclcium channels in rods synaptic terminal stay open
• Glutamate transmitter is continously released by rod
• glutamate hyperpolarizes bipolar cells preveting them from exciting ganglion cells.

In the light

• Light hyperpolarizes rods
  
  • light splits rhodopsin and a g protein 2nd messenger system is activated
  • phosphodiesterase is activated and breaks down cGMP
  • cGMP gated cation channels close
  • sodium and calcium stop entering the cell and the cell becomes more negative.
  • Voltage gated caclium in the rods synaptic terminals close
• rods stop releasing glutamate
• bipolar cells are no longer inhibited, now releasing glutmate to the ganglion cell
• ganglion cell excitation leads to impulses being sent along the axon to the brain.

Question 23

Sound wave pathway through the ear

Answer 23

1. sound waves are directed by the auricle to the tympanic membrane causing it to vibrate
2. tympanic membrane vibration moves the ossicles, and causes the stapes to push into the oval window
3. the stapes at the oval window generates pressure waves in the perilymph within the scala vestibuli
4. Pressure waves cause the vestibular membrane to move, resulting in pressure wave formatin in the endolymph within the cochlear duct and displacement of a specific region of the basilar membrane. Hair cells in the piral organ are distorted and initiate nerve signals to the cochlear branch of the vestibulococchlear nerve.
5. remianing pressure waves are trasnferred to the perilymph within the scala vestibuli and absorbed by the round window.

Question 24

Cochlear hair cell stimulation

Answer 24

1. inner hari cells contian ion channels at their tips and tip link proteins that connect them
2. Hair cells are bathed in K+ endolymph that is far more positive than the fluid inside the cell
3. when the basilar membrane moves, hair cells are pushed into the tectorial membrane and their tips are tilted, pulling tip links
4. Tip links pull open ion channels allowing K+ to diffuse into the hair cell and depolarize it
5. Hair cells release more neurotransmitter form its base, exciting the sensory neuron which can fire action potentials
6. When basilar mmebrnae moves down, the process quickly reverses.

Question 25

What is pitch? where are high frequency sounds excited in the basilar membrane? Where are low frequency sounds excited?

Answer 25

Pitch depends on the frequency of the vibrating object. Frequnecy is the rate of virbation in hertz

Variatoins in ptich are detectable due to variations in the stifness of basilar membrane from the ovla window to the cochlear apex

High frequency - stiff membrane, near oval window

low frequency - flexible membrane - near apex