Lecture 9 (Auditory System/Communication) Flashcards
What is the unit for sound frequency?
1 Hertz (Hz) = 1 vibration per second
1 KHz = 1000Hz
What is the unit for sound intensity?
Decibels (Db) = loudness
What frequency is the human ear able to detect?
between 20 Hz and 20,000 Hz
What is the frequency BELOW the audible range?
Infrasound (below 20 Hz)
What is the frequency ABOVE the audible range?
Ultrasound (Over 20,000 Hz)
What is the highest frequency a dolphin can hear at?, how many times louder is it than humans?
- 200,000 Hz
- 10x louder
How fast do sound waves travel through the water? How does it compare to sound traveling through air?
- 1.5 km/sec (0.9mi/sec)
- 4.5 x faster in water than air
How does the frequency length of sound affect its ability to travel? Give examples of what animal uses which frequencies.
Lower Frequency (50Hz) = longer wavelength = travels farther
- (used by large whales)
Higher Frequency (1000Hz) = shorter wavelengths - does not travel as far
- (smaller harbor porpoise uses higher freq.)
What is Echolocation?
detection of an object by means of reflected sound
What are the various organs required for echolocation and what frequency does echolocation use?
- Some to produce sound
- some to receive it
- others to decipher meaning
- Frequency = 200,000 Hz (200KHz)
Why is hearing important in Odontocete cetaceans?
- use echolocation to hunt and determine surroundings
Why is sound a double edged sword? (give examples)
- Allows marine mammals to survive in water BUT it also causes mortality
- E.g. Dolphins who suffer from infestation of middle ear nematodes can die of starvation (cannot detect food)
- Loud man made noises can depreive cetaceans of their ‘hearing’ ability causing death through damage to their ears
- Sonar sounds hurt their ears
What are the three parts of the auditory system and what nerve is responsible for it?
- External Ear or External auditory meatus
- Middle Ear
- Inner Ear
(Cranial nerve 8 brings messages to the brain)
What does the external ear consist of and which species have this?
- consists of an outside fleshy part (Pinnae)
- attached to the external auditory Meatus
- Otarids and Ursidae have a Pinnae
- Terminates at tympanic membrane (eardrum)
- Air filled tube on land but fills with water when submerged
What does the middle ear consist of and where is it located?
Consists of:
- Malleus (hammer)
- Incus (anvil)
- Stapes (stirrup)
Middle ear is housed in the tympanic (or ectotympanic) bone
- attached to tympanic membrane and in middle ear cavity (air filled cavity)
What is the inner ear encased in and what two types of fluids are found in the inner ear cavities?
- Housed in the petrosal bone
- Perilymph and endolymph
Which of the three parts of the auditory system is the most critical and what structure is within that part? Describe that structure.
- The inner ear is most critical
- Contains the Cochlea (rolled up organ with 3 ducts)
- Connected to the cochlea is a neural membrane with a long row of neurons –> transmits signals to the vestibulo-cochlear nerve (CN8)
Describe the processing of sound step by step
- Pinnae collects sound
- Sound travels through external auditory canal causing tympanic membrane to oscilate
- Ossicles (3 small bones) move sending signals ot inner ear
- sound waves cause perilymph and endolymph to vibrate
- Fluid vibrations cause tiny hair cells to vibrate sending messages to brain
In the cochlear membrane, which parts register which frequencies?
Apex = low frequencies (20 Hz)
Base = High frequencies (20,000 Hz)
Which two marine mammals have a similar hearing fashion as terrestrial mammals? Are there any unique features about their auditory systems for hearing underwater?
- Polar Bears
- Sea Otters
No obvious specialization for hearing of vocalization underwater
Describe the auditory system of Sirenians
- No external Pinna
- Narrow auditory canal
- structures of middle ear = lack of sensitivity and directionalry
- No ultrasonic capabilities
- Theory: they cannot hear underwater very well so they are suceptable to boat hits
Which Pinnipeds have no exterior Pinnae?
- Auditory anatomy similar to terrestrials with some modifications
- Phocids and Odobenids have NO exterior pinna
What is different about the middle ear in Pinnipeds?
- Tympanic bulla or bone (houses middle ear) is very large, makes middle ear cavity larger than other marine mammals
- In air, this allows for better hearing of LOWER FREQUENCIES
What is unique about the ossicles of phocids compared to other pinnipeds? (how does it help them?)
3 bones are greatly enlarged
- assists in bone conductive hearing
What other feature of the middle ear do pinnipeds have that serves as an adaptation for diving?
- Plexus of arteries and veins
- Plexus inflates, reducing airspace in middle ear which increases pressure, matching the exterior pressure
- Believed that plexus enhances the sound transmission to inner ear
- Assists in hearing HIGHER FREQUENCIES
How are the anatomical features of the cetacean auditory system unique from other marine and terrestrial mammals?
- Odontocetes, external ear has no pinna
- External Auditory Meatus is present as a narrow tube but does not connect to anything
- Major difference is how sound reaches middle ear
In Odontocetes, how is sound conducted to the middle ear? Which bone is involved and what is within that bone?
- conducted through the mandibles or jawbone
- posterior part of jaw called the pan bone
- The pan bone contains tissues called a fat pad or channel
Describe the structure of the fat pad and what bone its attached to.
Describe the composition of that bone
- extends backwards from the pan bone, coming into contact with a thin walled section of the middle ear called the ectotympanic bone
- The ectotympanic bone is composed of 2 separate bones (limited connection to the skull)
What identifies the ear complex as outside or isolated from the skull in odontocetes?
- Ectotympanic bones (limited connection to the skull)
- Sinuses surround ear complex, isolating the complex ‘outside the skull’
How do the ear complexes in Delphinids differ from odontocetes?
- In delphinids only a small cartilage connects the ear complex to the skull
- In Odontocetes this connection is much bigger
How does the mysticete ear complex compare to terrestial mammals? What does this allow for?
- Structure is integrated into the skull similar to terrestrial mammals
- Both ears are independent from each other (acting as separate receivers)
- Allows for better directional localization
How do the ossicles of the middle ear compare to terrestrial mammals
- Different shape and size
- Bones can vary between cetaceans, sirenians, carnivores and vary from species to species within these orders
How do odontocetes hear? What is unique about dolphins?
- Fat pads located at the posterior end of the mandibles act like low density sound conductors directly to the middle ear
- Dolphin lower jaw hearing is 6 times more sensitive than external auditory canal
- Has 2 areas on side of melon for acute hearing
How do Mysticetes hear?
- Hear lower frequency sounds
- Not well understood
- Sound transmitts through a large wax plug
- wax envelopes protrusion of tympanic membrane
how does low frequency hearing come to be in odontocetes?
- Low freq. hearing arises from skull bone vibrations
- creates oscillation of the tympanic bullae creating movement of the ossicles
What is sound in marine mammals used for?
- Communication
- Hunting
- Echolocation
How is sound made by pinnipeds?
- Created by larynx and other structures
- Male walrus -> also use teeth (clacking); throught pouches (bell-like sounds)
- Hooded seals: also use hood and nasal septum for above and below water (breeding, social) sounds
- Above water: moms communicate; breeding males threat calls
What is the purpose of sound for cetceans and what types of sounds are there?
Sound = social
Type
- Whistles (dolphin)
- Language (killer whale)
- Songs (Humpback whale)
How is sound produced in Odontocetes?
- created by nasal sac system just inside blowhole (whistles, ecolocation clicks)
How is sound produced in Mysticetes?
- Sound production thought to come from U-shaped fold in larynx supported by arytenoid cartilage and air from laryngeal sac
How is sound produced and received by Sirenians? (what freq. range do they communicate in?)
- sounds originate from frontal region of head
- Production thought to be similar to whales
- Sounds received by channel filled with oily ‘sponge’ in cheek region of skull
- 2500-5000 Hz, lower sub 500Hz recorded
What does echolocation range depend on and what are the ranges of sperm whales, common dolphins, and harbor porpoises?
- range depends on species
- sperm whales = 6km
- Common dolphins = 100 up to 650 m
- Harbor Porpoise = 25 m
Which marine mammals do not use echolocation?
- Mysticetes
- Pinnipeds
- Sirenians
- Sea Otters
- Polarbears
What organs do odontocetes whales use for echolocation?
- Phonic lips (Monkey lips) break air flow between lips (produces clicks and determines repetition rate
- Sound passes through melon (used to focus and direct sound forward in water to locate objects
- Clicks bounce off objects and return to whale
What are the differences in hunting techniques between Odontocetes and Mysticetes?
Odontocetes - use loud blasts (‘bangs’) temporarily stun or disorientate their prey
Mysticete - whales such as the humpback use bubble netting (which does not use sound)
Within odontocete species what unique ways have bottlenose dolphins and killer whales used to capture prey?
Bottlenose dolphins
- Mud nets in shallow areas
- drive fish on to shore banks
Killerwhales
- have beached themselves to catch unaware seals
