Lecture 24: Sensing the Environment Flashcards
importance of sensing the environment
- survival
- finding mates
- finding food
star- nose mole
- animals have a lot more senses that humans
- unique nose with lots of sensory neurons
- can use nose to sense its environment
nervous system’s flow of information
- sensory input is detected by sensory receptors
- this input is sent to the CNS for processing
- the CNS analyzes information and sends out motor output to effectors
- the peripheral nervous system connects sensory receptors and effectors to the CNS
sensory receptor
- light, sound, touch, smell
- structures or cells that detect environmental stimuli, like light (eyes) or sound (ears)
- they send signals to the nervous system
sensory receptors code four aspects of stimulus
- modality or type = the kind of stimulus
- intensity = the strength of the stimulus
- location = where the stimulus is located
- duration = how long the stimulus lasts
propagation of action potential (demonstrating how electrical signals travel along axons)
- sodium ions (Na+) enter the axon, initiating depolarization
- depolarization spreads downstream across the axon membrane
- voltage-gated channels open as they detect changes in the membrane potential
vision
- species perceive environments differently
- light and color
- some species can view UV wavelengths
rods
photoreceptor cells in the retina that are sensitive to dim light but not color
cones
photoreceptor cells that detect color and fine detail in bright light
sense of smell (journey of odorant molecules from the nasal cavity to the brain)
- odorant molecules dissolve in mucus and are detected by odorant receptors on chemoreceptors in the nasal cavity
- action potentials are generated by chemoreceptors, traveling through the olfactory nerve to the olfactory bulb and eventually reaching the brain
hearing
- animals was diverse ears unique to their needs
what is sound
- sound waves propagating
- regions of compression and regions of refraction
regions of compression
areas of high pressure where air molecules are densely packed
regions of refractions
areas of low pressure where air molecules are spread apart
how we hear: the auditory process
- outer ear: sound waves enter and travel through the ear canal to the eardrum
- middle ear: three tiny bones amplify the vibrations caused by the eardrum
- inner ear (cochlea): activated hair cells release neurochemical signal
- auditory nerve: transmits these electrical signals to the brain from interpretation
anatomy of frog’s ear
- they use external and internal structures
- key parts are the tympanum and stapes
tympanum
a membrane acting as an eardrum, capturing sound vibrations and transmitting them to the inner ear
stapes
a bone that further amplifies and transmits vibrations within the ear
three main characteristics of the measurement of sound
wavelength, frequency, intensity
wavelength
the distance between two consecutive points in a sound wave that are in the same phase
frequency
the number of cycles a wave completes per second, determining its pitch, measured in Hertz or kilohertz
intensity
commonly associated with loudness, measured in decibels
looking at table 6.6 - relative magnitude of common sounds
highlights how sound intensity is measured on a logarithmic scale
- the logarithmic progression emphasized the dramatic increase in intensity as decibel levels rise
loss of intensity graph (how sound attenuation changes with distance and frequency)
- high frequency sounds attenuate faster over distance than low frequency sounds
long distance communication through
low frequency sounds
example of long-distance communication through low frequency sounds
elephants use low frequency infrasound (below 20Hz) to communicate over long distance
- high pitched sounds are reflected and reduced by obstacles like trees
- low pitched sounds penetrate through forests, allowing uninterrupted transmission over long distances, even as upper frequencies diminished
echolocation
a biological sonar mechanism in which animals emit sound waves and analyze the echoes to interpret their surroundings
echolocation frequency range
between 11Hz and to over 200kHz depending on the species
echolocation functions
the process involves sending auditory information to oneself
- produce a spatial map of the surrounding area
- navigate through obstacles
- locate objects efficiently
who echolocates?
- 18% of all mammals echolocate
- ex: chiropterans (bats), cetaceans (whales and dolphins), shrews, tenrecs, otter shrews, flying lemurs
where is sound produced by echolocators?
- larynx: bats (micro chiropterans) and shrews
- clicks from the tongue: bats (mega chiropterans)
- clicks in the nasal passages (cetaceans)
constant frequency
- a sound wave maintaining the same frequency over time, often used in echolocation to identify stationary or moving objects
- useful for detecting motion in echolocation systems
doppler effect
the change in frequency or wavelength of a wave in relation to an observer moving relative to the wave source
concept of the doppler effect
- send out CF (constant frequency): refers to transmitting a steady sound frequency
- use changes in frequency to detect motion: variations in frequency indicate movement or speed of objects
sound waves in the doppler effect
- pushed together: when the source moves closer to the observer, leading to a higher frequency (compression)
= stretched apart: when the source moves away from the observer, creating a lower frequency (rarefaction)
frequency modulated (FM)
- a sound wave whose frequency varies over time; used by echolocating animals to extract detailed information about objects
- used to detect finer details of target (size, shape, texture)
shallow FM
the frequency starts high and gradually decreases over time
steep FM
the frequency decreases more sharply over time, providing higher precision in detecting details
harmonics
- frequencies that are multiples of a base frequency, used to add detail or richness to sounds
- increases scanning and detection ability
fundamental
the base frequency of the sound wave
third harmonic
a higher frequency wave that is a multiple of the fundamental
how do bats echolocate?
- emission of high frequency sounds (20-100 kHz from their nose or open mouth
- constant frequency (CF) signals: these are used to locate prey initially
- frequency modulated (FM) sweeps: once the prey is detected, FM sweeps are employed at a rate of 10 cycles per second for detailed tracking
- increased call frequency: as bats approach their prey, they call more frequently to refine their attack
hunting sequence (in the Rhinolophus)
search phase, approach phase, and terminal phase
search phase
bat emits high frequency sounds (70-90 kHz) as it scans for prey
approach phase
frequency begins to drop as the bat locks on to a detected target
terminal phase
the bat lowers its sound frequency even further (30-40 kHz) to close in on its prey
high frequency sounds advantages/pros
- provide fine details about targets
- enable detection of very small objects (wire or human hair = 0.08mm)
high frequency sounds disadvantages/cons
- more energy intensive, requiring faster vibrations of vocal cords = more expensive
- attenuate faster over distance compared to lower frequencies
screaming-hearing conflict
- airplane (150 dB): represents an extremely loud sound
- whispering (15 dB): demonstrates a very soft sound
- standing next to a loud noise like an airplane taking off, and then trying to hear a whisper, is near impossible as you just experience such a loud noise
how do bats solve the issue of screaming-hearing conflict?
the tensor tympani and stapedius muscles are pivotal in protecting ears from overwhelming sounds
tensor tympani muscle
contracts to dampen vibrations from loud sounds, reducing potential damage to the inner ear
stapedius muscle
the smallest muscle in the human body, it controls vibrations of the stapes bone to protect against sound-induced harm
echolocation in water
- sound travels about 4 times faster in water
- sound loses intensity at a slower rate in water, enabling long-distance echolocation
echolocation in sperm whales
sperm whales can detect prey at distances of approximately 1/2 mile away
