Chapters 4 & 5 - Orienting movements & Active orientation and localization

Question 1

Taxis

Answer 1

• Orienting reaction or movement in freely moving organisms directed in relation to a stimulus
• Prefix: defines nature of the stimulus
• Modifiers:
  – positive: orienting movement toward the stimulus
  – negative: orienting movement away from the stimulus
• Taxis responses occur even in organisms without a nervous system

Question 2

Herbert Spencer Jennings (1868-1947)

Answer 2

• Introduced behavior of paramecium (unicellular protist)
• Instrumental in taxis

Question 3

Gyration

Answer 3

Revolution around longitudinal axis

Question 4

Paramecium and CO2

Answer 4

They stay within a certain pH range (cannot survive if pH is too low – acidic), which is why they stay at a certain distance of the CO2 (CO2 dissolved in water makes a weak acid, lowering the pH)

Question 5

pH

Answer 5

Method to qualitatively express the concentration of H3O+ ions in a solution. The pH is defined as the negative logarithm to the base 10 of the hydrogen ion concentration. Pure water is neutral and has a pH of 7. A pH of less than 7 indicates an acidic solution, a pH of greater than 7 indicates a basic (alkaline) solution.

Question 6

Cilia/cilium

Answer 6

Hairlike appendages of many kinds of cells with a bundle of microtubules at their core. The microtubules are arranged such that nine doublet microtubules are located in a ring around a pair of single microtubules. This arrangement gives them the distinctive appearance of a ‘9+2’ array in electron micrographs of cross-sections.

Question 7

Cathode

Answer 7

Negative pole of a voltage source (where the cations move towards)

Question 8

Anode

Answer 8

Positive pole of a voltage source (where the anions move towards)

Question 9

Cations move towards the…

Answer 9

Cathode

Question 10

Phobotaxis in paramecium

Answer 10

• Avoidance response controlled by depolarization and hyperpolarization
• If paramecium gets touched, it propels either forward or backward to avoid it
  – For the paramecium to swim forward, the K+ channels open, resulting in K+ leaving the cell and the cell becoming more negative, meaning the cell gets hyperpolarized, triggering forward movement
  – For the paramecium to swim backward, the Ca2+ channels open, resulting in Ca2+ entering the cell and the cell becoming less negative, meaning the cell gets depolarized, triggering backward movement

Question 11

Parallel plate capacitor

Answer 11

Composed of two parallel metal plates isolated against each other. They have equal, but opposite, charges. By definition, the electric field lines arise from the positively charged plate (anode) and run, perpendicular to the plates, to the negatively charged plate (cathode)

Question 12

In an electric field, a paramecium swims towards the…

Answer 12

• Cathode with their anterior pole first
• This behavior is triggered by a differential polarization of those parts of the cell that are closer to the cathode and the anode, respectively, and, thus, by the generation of a differential beat pattern of the cilia in different parts of the cell

Question 13

Hyperpolarizing movement of cilia make a paramecium swim…

Answer 13

Forward

Question 14

Depolarizing movement of cilia make a paramecium swim…

Answer 14

Backward

Question 15

Cilia stroke pattern in paramecium is determined by…

Answer 15

The intraciliary Ca2+ concentration

Question 16

The inner ear is made up of the…

Answer 16

The labyrinth

Question 17

The vestibular organ is made up of the…

Answer 17

Otolith organs and the semicircular canals

Question 18

The labyrinth is made up of the…

Answer 18

Vestibular organ and the cochlea

Question 19

The ossicles are made up of the…

Answer 19

Incus, malleus, and stapes

Question 20

In the cochlea, further from the center (apex) are the ________ frequencies and closer to the center (apex) are the ________ frequencies.

Answer 20

• Higher
• Lower

Question 21

Place theory of hearing

Answer 21

• Perceived pitch (frequency) of a tone depends on the position or place on the basilar membrane
• High frequency sounds selectively lead to vibrations of the basilar membrane of the inner ear near the entrance port (the oval window)
• Lower frequencies travel further along the membrane before causing appreciable excitation of the membrane
• The frequency-determining mechanism is based on the location along the membrane where the hair cells are stimulated

Question 22

A lower pitch (frequency) results in ________ vibration of the hair cells.

Answer 22

Slower

Question 23

A lower volume sound results in ________ vibration of the hair cells.

Answer 23

Smaller

Question 24

The inner ear hair cells are arranged…

Answer 24

In groups with the shortest hairs (stereocilia) in the front and the longest in the back, with one kinocilium in the very back of the group

Question 25

Kinocilia

Answer 25

• 9+2 microtubule structure
• True cilia (stereocilia are not because they do not have the proper microtubule structure)

Question 26

Hair cell

Answer 26

• Array of stereocilia at apical end
• Possibly one true cilium (kinocilium) at one flank of the array of sterocilia
• Cilia bathed in potassium-rich endolymph (normally, extracellular fluid poor in potassium)
• Synaptic connections at basal end: afferent (sensory) and efferent (motor; presumably to control sensory function)

Question 27

Tip link

Answer 27

• Protein fiber linking one stereocilia to another, connecting the Ca2+ and K+ channels together
• The stereocilia move from one side to the other, opening and closing the channels
  – When the stereocilia moves in one direction and the channel opens, Ca2+ and K+ enter the stereocilia, depolarizing the membrane of the hair cell, due to the abundance of Ca2+ and K+ in the extracellular area
  – When the channel closes, the Ca2+ and K+ are removed from the stereocilia via pump, hyperpolarizing the membrane of the hair cell

Question 28

Mechanically sensitive channels

Answer 28

• Transduction mediated by mechanically sensitive channels
• Extremely fast: delay between deflection of hair bundle and onset of receptor current as short as 10 µsec
• Enormously sensitive: deflection of the tip of the stereocilia by as little as +/- 0.3 nm may be sufficient to trigger a response

Question 29

Hearing: mechanism of transduction

Answer 29

• The transduction of the mechanical stimulation of the stereocilia into an electric response is mediated by mechanically sensitive transduction channels concentrated near the tip of the stereocilia
• During displacement of the stereocilium toward the adjacent taller stereocilium, the tip link provides the tension to open the transduction channel, leading to an influx of cations, and thus to a depolarization of the membrane of the hair cells, which is followed by an increase in firing in the afferent fiber (sensory information to brain)
• Conversely, deflection of the stereocilia toward the shorter edge of the hair bundle closes the transduction channels open at rest, leading to a reduced influx of cations into the cell, and thus, to a hyperpolarization, which is then followed by a decrease in firing in the afferent fiber

Question 30

Effect of aminoglycoside antibiotics

Answer 30

• The cation-selective channels in hair cells are blocked by amino-glycoside antibiotics, e.g., streptomycin
• Higher doses of such antibiotics have toxic effects on hair cells, damaging the stereocilial bundles and eventually killing the cells

Question 31

Transduction is mediated by…

Answer 31

Mechanically sensitive channels in hair cells

Question 32

Carlsbad Caverns National Park (New Mexico)

Answer 32

Known for the abundance of bats

Question 33

Lazaro Spallanzani (1729-1799)

Answer 33

Believed bats oriented by hearing

Question 34

Donald R. Griffin (1915-2003)

Answer 34

Demonstrated that bats use ultrasound

Question 35

Ultrasound

Answer 35

Sound in the frequency range above that of human hearing, above approximately 20 kHz

Question 36

Simmons’ bat behavioral experiments

Answer 36

• Big brown bat (Eptesicus fuscus)
  – Trained bats to discriminate targets placed at different distances
  – Then replaced natural echo by electronically controlled ‘phantom echoes’
• Threshold at which the bats can still discriminate two targets based on signal-to-echo delays: 60 µsec (corresponding to difference in target distance of 10-15mm)

Question 37

Doppler shifts

Answer 37

• Discovered by Austria physicist Christian Johann Doppler (1803-1853) in 1842
• They involve a shift in frequency and occur whenever the source of any kind of propagating energy, such as light or sound, moves relative to the receiver of this energy
• E.g., the siren of an ambulance, which is perceived as a constant pitch by a listener as long as both ambulance and listener are stationary, changes in pitch (frequency) when the ambulance goes by
  – As the ambulance approaches, the frequency is increased, since sound waves from the siren are compressed toward the observer
  – As the ambulance moves away, the frequency is decreased, since the sound waves are stretched relative to the listener
• Lower frequency echo –> receding object
• Higher frequency echo –> approaching object

Question 38

Bats and acoustic orientation via hair cells

Answer 38

Based on the frequency spectrum, the ultrasound produced by bats can be divided into frequency modulated (FM) signals, quasi-constant-frequency (QCF) signals, and signals consisting of a rather long constant-frequency (CF) component, followed by a downward frequency-modulated sweep (CF-FM signals)

Question 39

Hair cells play a critical role in…

Answer 39

Processing auditory information (including information used for acoustic orientation)

Question 40

Frequency modulated (FM) signals

Answer 40

• FM signals are used to estimate the distance of the bat from an object
  – This is achieved by measuring the time delay between the emitted signal and the returning echo
  –In the inferior colliculus of bats, neurons have been identified that serve as time markers by encoding for the time interval between the emitted pulse and the returning echo; in the auditory cortex, neurons exist that respond best to a particular pulse-echo-delay time

Question 41

Constant frequency (CF) component in signals

Answer 41

• The CF component of bat ultrasound is well-suited for the so-called Doppler shift analysis, which is performed during flight and when localizing flying insects
  – During flight movements of the bat, this analysis forms the basis for Doppler shift compensation to keep the frequency of the returning echo in the range of maximal sensitivity of the auditory system
  – During prey hunting, Doppler shift analysis is used to detect the fluttering of wings of the flying insects
  – Both sensory structures in the ear and neural structures in the brain of the bat are specialized to maximize sensitivity to frequencies in the range of the CF component of the returning echo (this includes an over-representation of such frequencies in the cochlea and the auditory cortex)

Question 42

Noctuid moths

Answer 42

• To counteract bat echolocation, noctuid moths have developed a number of adaptations
  – They include the development of ears sensitive in the ultrasound range, and, in some species, the production of high-frequency clicks