ELM 15 Hearing, chemical senses and touch

Question 1

How does smell perception vary across species?

Answer 1

Smell perception is similar across species, with neurons converging based on their response to specific odorants, often at glomeruli.

Question 2

What is the role of glomeruli in the olfactory system?

Answer 2

Glomeruli play a role in olfaction by serving as sites where neurons with similar odorant responses converge.

Question 3

Describe the signaling pathway involved in human olfactory receptors.

Answer 3

Human olfactory receptors are G-protein coupled receptors (GPCRs) that, upon odorant binding, trigger the opening of cyclic nucleotide-gated channels and depolarization of olfactory receptor neurons.

Question 4

How does odorant binding affect the membrane potential of olfactory receptor neurons?

Answer 4

Odorant binding leads to depolarization of olfactory receptor neurons, unlike in vision where light causes hyperpolarization.

Question 5

What is combinatorial coding in the olfactory system?

Answer 5

Combinatorial coding in olfaction refers to the diverse chemical structures of odorants and the unpredictable nature of smell based on structure. Each odorant binds to various receptors, activating many neurons, and each neuron can be activated by multiple odorants.

Question 6

What makes predicting the smell of a substance challenging based on its chemical structure?

Answer 6

The diverse chemical structure of odorants makes predicting smell based on structure challenging, as different odorants can activate the same receptors and vice versa.

Question 7

How does olfaction differ from vision in terms of neural processing?

Answer 7

Unlike vision, where light passes through retinal cell types before activating photoreceptors, olfaction involves direct synaptic interaction between odorants and GPCRs.

Question 8

What is the primary difference in the origin and direction of the stimulus between olfaction and vision?

Answer 8

The primary difference between olfaction and vision lies in the origin and direction of the stimulus: in olfaction, the stimulus is an odorant that directly synapses with GPCRs, while in vision, light stimuli come from the bottom up, passing through retinal cell types before reaching photoreceptors.

Question 9

Explain the direct synaptic interaction between odorants and receptors in olfaction.

Answer 9

n olfaction, odorants directly synapse with GPCRs on olfactory receptor neurons, triggering a cascade of events leading to neural activation.

Question 10

Contrast the pathway of stimulus in olfaction with that in vision.

Answer 10

Olfaction involves direct synaptic interaction between odorants and receptors, while vision requires light to pass through all retinal cell types before activating photoreceptors.

Question 11

What are the five tastes crucial for survival, and what are their functions?

Answer 11

he five tastes essential for survival are bitter (to avoid poisons), sweet (indicating sugar/carbs), umami (associated with amino acids), salty (related to Na+), and sour (signifying acids/H+).

Question 12

What is the suggested potential sixth taste based on evidence, and what does it relate to?

Answer 12

vidence suggests a potential sixth taste related to fat, based on the presence of fat receptors in the tongue.

Question 13

define taste receptor cells (TRCs), and what is their regenerative capability?

Answer 13

Taste receptor cells (TRCs) are neuroepithelial cells capable of regeneration. They form taste buds and play a role in taste perception.

Question 14

Explain the composition and function of taste buds.

Answer 14

Taste buds contain cells that detect tastants and release neurotransmitters when activated, which then activate gustatory nerves.

Question 15

What are the three main structures of taste buds/papillae?

Answer 15

Taste buds are found in three main structures: circumvallate, foliate, and fungiform papillae.

Question 16

Where are taste/gustatory receptors primarily found in humans, and how does this compare to Drosophila?

Answer 16

In humans, taste/gustatory receptors are primarily located on the tongue, while in Drosophila, similar receptors are found in various locations such as legs and wings, serving different functions.

Question 17

How do gustatory neurons in Drosophila differ in distribution and function from those in humans?

Answer 17

Gustatory neurons in Drosophila are not specific to the tongue and are found in various places, unlike in humans where they are primarily on the tongue and dedicated to taste perception.

Question 18

What are the molecular mechanisms underlying gustatory receptor function?

Answer 18

Gustatory receptors utilize diverse molecular mechanisms. Some are G-protein coupled receptors (GPCRs), while others involve transient receptor potential (TRP) channels and epithelial sodium channels.

Question 19

Which taste receptors are currently best understood in terms of their molecular structure and signaling pathways?

Answer 19

The molecular structure and signaling pathways of bitter, sweet, and umami taste receptors, which are GPCRs, are currently best understood.

Question 20

Which receptors are involved in detecting sour and sodium tastes?

Answer 20

Sour taste is detected by TRP channels, while sodium taste involves epithelial sodium channels, though the latter are not present in humans.

Question 21

What is the vomeronasal organ (VNO), and where is it located?

Answer 21

The vomeronasal organ (VNO) is an additional olfactory organ located in the nasal cavity, above the roof of the mouth.

Question 22

What types of chemical cues does the vomeronasal organ respond to?

Answer 22

The VNO responds to non-volatile chemical cues in the environment.

Question 23

How do snakes use tongue flicking behavior in relation to the VNO?

Answer 23

Snakes exhibit tongue flicking behavior to sample scents from the environment and deliver them to the VNO.

Question 24

How do elephants utilize their trunk and behavior to deliver scents to the VNO?

Answer 24

Elephants use their trunk, often with a prehensile “finger” at the tip, to deliver scents to the VNO. They can also direct inhaled air onto it.

Question 25

Describe the role of facial grimaces in relation to the VNO in many mammals.

Answer 25

Many mammals have distinct facial grimaces that help direct scents to the VNO.

Question 26

What kinds of signals does the vomeronasal organ respond to, and what information do they provide?

Answer 26

The VNO responds to a wide range of signals, some of which provide information about prey and the status of members of the same species.

Question 27

What are pheromones, and how do they function in intraspecies communication?

Answer 27

Pheromones are intraspecies signals that can produce profound changes in behavior.

Question 28

What profound changes in behavior can pheromones induce, and what signaling pathway does the VNO use?

Answer 28

Pheromones can induce significant changes in behavior, and the signaling pathway the VNO uses sends signals to the hypothalamus.

Question 29

How does the hypothalamus respond to signals from the VNO, and what physiological systems does it influence?

Answer 29

Signals from the VNO influence the hypothalamus, which in turn influences the reproductive system and the production of adrenal steroids.

Question 30

Is the existence of the vomeronasal organ in humans confirmed?

Answer 30

The existence of the vomeronasal organ in humans is not yet definitively confirmed.

Question 31

How are sound waves detected by the human auditory system, and what is the typical range of human hearing?

Answer 31

Sound waves are detected as variations in air pressure, with the typical human hearing range being 20-20,000 Hz.

Question 32

How do lower frequency waves and lower intensity waves affect pitch and volume, respectively?

Answer 32

Lower frequency waves result in lower pitch, while lower intensity waves produce quieter sounds.

Question 33

Why is the human auditory system more effective for detecting sounds from a distance?

Answer 33

The human auditory system is optimized for detecting sounds from a distance because air pressure waves can travel further without dissipating.

Question 34

What is the role of the vestibular system in hearing, and what additional contributions does it provide?

Answer 34

The vestibular system in the ear contributes to balance and spatial orientation, detecting forces of gravity, acceleration, and head rotation.

Question 35

Describe the structure and function of the cochlea in the auditory system.

Answer 35

The cochlea is a spiral-shaped structure where fluid movement transmits motion information from sound waves into electrical signals.

Question 36

How do hair cells in the cochlea transduce sound into electrical signals?

Answer 36

Hair cells in the cochlea transduce sound into electrical signals by converting movement of fluid into mechanical forces that open ion channels, leading to depolarization.

Question 37

What is the role of glutamate in the transmission of auditory signals to the brain?

Answer 37

Glutamate serves as a neurotransmitter that activates terminals on spiral ganglion neurons, transmitting auditory signals to the brain.

Question 38

How does the basilar membrane contribute to frequency tuning in the cochlea?

Answer 38

The basilar membrane in the cochlea contributes to frequency tuning by being wider and less stiff at the apex, resonating at lower frequencies, while the base is attuned to higher frequencies.

Question 39

Explain the mechanism by which sound localization in space occurs.

Answer 39

Sound localization in space occurs by comparing the time of sound arrival at both ears, with barn owls and other animals having specialized brain machinery for this task.

Question 40

What functions do the otolith organs and semicircular canals serve in the vestibular system, and how do they detect motion and balance?

Answer 40

The otolith organs use calcium carbonate crystals to detect gravity and acceleration, while the semicircular canals detect head rotation and balance through hair cells that respond to fluid movement. Disorders in the vestibular system can lead to seasickness or dizziness when there’s a mismatch between vestibular and visual inputs.

Question 41

What types of receptors are involved in detecting steady pressure, and how do they adapt to stimuli?

Answer 41

Merkel cells and Ruffini endings are involved in detecting steady pressure, with slowly adapting properties that allow them to continue discharging action potentials throughout the duration of the stimulus.

Question 42

Which receptors are responsible for sensing vibrations, and how do they adapt to stimuli?

Answer 42

Meissner’s corpuscles and Pacinian corpuscles are responsible for sensing vibrations, with rapidly adapting properties that fire only at the onset and offset of the stimulus.

Question 43

How do neurons respond differently to various types of tactile stimuli?

Answer 43

Neurons respond differently to tactile stimuli based on the type of receptor and the adaptation properties involved.

Question 44

What are nociceptors, and what type of stimuli do they respond to?

Answer 44

Nociceptors are high-threshold receptors responsible for sensing potentially harmful stimuli.

Question 45

Describe an experiment used to study touch sensation at the cellular level.

Answer 45

In an experiment studying touch sensation at the cellular level, isolated neurons are recorded intracellularly using a patch electrode while a stimulus probe deforms or manipulates the membrane of the cell to recreate mechanical touch stimuli.

Question 46

What is the role of Piezo2 in touch sensation, and how does its absence affect neuronal response to pressure stimuli?

Answer 46

Piezo2 is a gene involved in touch sensation, and its absence results in altered neuronal responses to pressure stimuli, with reduced initial depolarization and shorter firing duration.

Question 47

How have genetics contributed to our understanding of touch receptors?

Answer 47

Genetics have contributed to our understanding of touch receptors by identifying genes such as Piezo2 that play important roles in touch sensation.

Question 48

What sensory cortex areas are involved in processing touch sensation?

Answer 48

Sensory cortex areas, including the somatosensory cortex, are involved in processing touch sensation.

Question 49

How has our understanding of touch sensation been influenced by studies of brain injuries?

Answer 49

Our understanding of touch sensation has been influenced by studies of brain injuries, which have helped identify specific areas of the brain involved in processing tactile information.