Sensory systems

• SMELL

  • smell (olfactory)
  • starts with olfactory neurons and project endings to the flomeruli (found in the antennal lobe or the olfactory bulb) --> convey olfactory information to olfactory centers or the mushroom body/lateral horn
  • same neurons converge together 

  1. cilia on the olfactory receptor endings will be activated by different odants
• SMELL cont.

  • human olfactory receptors are gpcrs --> odarants binding leads to opening of a cyclic nucleotide gated channels 

  1. depolarizes olfactory receptor neurons --> action potential firing 
  2. odorants bind to the gpcrs, exchanges gdp for gtp --> activates adenylate cyclase --> changes atp to camp -->camp binds to cyclic nucleotide gated channels--> sodium enters the cell and causes depolarization
• COMBINATIONAL CODING- SMELL

  • odorants have diverse chemical structure  can’t predict how anything smells based on the structure
  • each ordorant binds to various receptors and activates many neurons --> each neurons is activated by many orodrant 
  •  pheromones --> detected by the vomeronasal oragn

  1. located in nasal cavity 
  2. respond to non-voltaile chemicals 
  3.  detects a wide range of signals 
  4. sends signals to the hypothalamus  influences reproduction system and production of adrnal setroids
• TASTE

  • 5 basic tastes related to survival:

  1. bitter --> avoid poisons
  2. sweet --> sugar and carbohydrates
  3. umami --> I-amino acids (monosodium glutamate)
  4. salty --> sodium 
  5. sour --> acids/H+

  • receptors are found on the tounge
  • bind to the tip of taste receptor cells  cluster around taste pore

  1. can regenerate
  2.  each taste bus contains cells that can detects chemicals

  • taste cells release neurotransmitters --> activate terminal branches of gustratory nerve
• TASTE cont.

  • 3 different types of structure --> papillae

  1. found on different parts of the tongue
  2. back --> circumvallate
  3. side region --> foliate
  4. front --> fungiform

  • taste receptors can be found on legs and wings of other species 
  • sweet/umami/bitter --> all gpcrs

  1. umami == t1r1 + t1r/ sweet == t1r2 + t1r3/ bitter == 30 of t2rs/  

  • sour --> trp channels

  1. pkd2l1 + pdk1l3

  • salty  sodium channels 

  1. sensitive to low and high salt concentrations 
  2. in mammals --> low slat concs are detected in epithelial sodium channels  (not foundin humans)

  • receptor for fat is not isolated
• HEARING AND VESTIBULAR SYSTEM

  • we detect sound as vibrations in air pressure
  • range --> 20hz to 20000 hz
  • lower frequency == lower pitch
  • insects detect speed of moving particles 

  1. can only detect within close proximities

  
• AUDITORY SYSTEM

  • external ear 
  • middle ear (bones, mallelus, incusm stapes)
  • inner ear (cochlea)
• VESTIBULAR SYSTEM

  • semicircular canals (posterior, horizontal, anterior)
  • otolith organs (utricle and saccule
• COCHLEA

  • spiral shaped and fluid filled
  •  3 fluid filled chambers
  • scala vesetibuli, scala media and scala tympania
  • activated or moved and transmit motion information
  • hair cells transduce sounds into electrical signals
  • outer hair cells provide active amplification
  • inner hair cells sends signal to the brain
  • hair cells are connected to basilar membrane  movment is detected by basilar membrane as it vibrates
  • sterocilium arranged like a staircase and connected by tip link
• COCHLEA cont.

  • when movement of hair cells  mechanical force which pulls the channel and causes it to open 
  • channels == potassium channels
  • potassium moves into the cell  causes depolarization causes opening of voltage-gated calcium channels --> vesocilar release of glutamate
• TONOTOPY

  • representation of sound due to the properties of basilar membranes
  • hair cells are tuned from being ssensitive to higher frequencies --> found at the base of the coclear
  • lower frequencies found at the apex
  • membrane is wider and less stiff at the apex of the cochlea --> can resolnate at lower frequency 
  • neurons project to intermediate center (spiral ganglion)
  • neurons of similar types converge
  • sound localization in space

  1. position of sound source is detected by comparing the time of the sound arrival to both ears (interaural time difference)
• VESTIBULAR SYSTEM

  • detects balance and movement
  • two organs that are important : otholith organs+ semicicualr canals
  • otolith organs (saccule and utricle)

  1. Uses calcium carbonate crystals to detect foce of gracity and acceleracy
  2. hair cells are found between two cell bodies and stick into crystals (otoliths) which moves with gravity

  •  semicircular canals

  1. detect head rotation
• TOUCH AND SENSORY CORTEX AREA

  • nerve terminates in the boundary layer but some are found in the dermis layer
  • neruons respond to different ways

  1. steady pressure --> merkle cells and ruffini ending
  2. vibration --> meissner and pacinian corpuscles 

  • piezo in merkel cells 
  • different parts of our brain detects different senses

  1. olfactory cortext --> in the temporal lobe
  2. autidory cortex --> temporal lobe
  3. vestibular cortex --> partietal lobe
  4. somatosensory cortex --> parietal lobe
  5. gustatory cortex --> insular and frontal lobe
  6. visual cortex --> occipital lobe