Chapter 7 Flashcards
Nonvisual Sensation and Perception: Audition Touch Smell Taste
Audition
Sound processed by auditory system.
Audition is synonym for hearing.
Like vision, acoustic information uniquely perceived by humans relative to other species.
Sound waves must travel through medium
Sound can’t travel through a vacuum.
Mediums include air and water.
Sound Frequency
- Frequency refers to the cycles per unit of time, or wavelength of a sound
- Frequency is measured in Hertz (Hz)
- Pitch is our perception of the frequency of a sound
Sound Intensity
- Intensity (loudness) is a function of sound wave amplitude
- Intensity is measured in decibels (dB)
- Loudness is our experience of sound energy
Amplitude
Sound Intensity, i.e., Loudness.
Amplitude measures the height of a wave.
High amplitude translates to loud sounds.
Frequency
Sound Wavelength, i.e., Pitch.
Frequency measures the number of wave cycles per unit of time.
High frequency translates to high pitch sounds.
Timbre
Sound Complexity
The distinct uniqueness of a sound.
Timbre describes the specific combination of fundamental frequency and harmonic frequencies in a given sound.
Allows us to distinguish which instrument produced a note.
Pure tones have a single frequency.
Complex tones are made up of several frequencies.
Eardrum
In human anatomy, the eardrum, or tympanic membrane, is a thin, cone-shaped membrane that separates the external ear from the middle ear in humans and other tetrapods. Its function is to transmit sound from the air to the ossicles inside the middle ear, and then to the oval window in the fluid-filled cochlea. Hence, it ultimately converts and amplifies vibration in air to vibration in fluid. The malleus bone bridges the gap between the eardrum and the other ossicles.
There are 2 general regions of the tympanic membrane: the pars flaccida (upper region, see picture on right) and the pars tensa. The pars flaccida consists of two layers, is relatively fragile, and is associated with eustachian tube dysfunction and cholesteatomas. The larger pars tensa region consists of three layers: skin, fibrous tissue, and mucosa. It is comparatively robust, and is the region most commonly associated with perforations.
Rupture or perforation of the eardrum can lead to conductive hearing loss. Collapse or retraction of the eardrum can also cause conductive hearing loss or even cholesteatoma.
Ear Canal
The ear canal (external auditory meatus, external acoustic meatus, EAM) (Latin: meatus acusticus externus), is a tube running from the outer ear to the middle ear. The adult human ear canal extends from the pinna to the eardrum and is about 2.5 centimetres (1 in) in length and 0.7 centimetres (0.3 in) in diameter.
Structure
The human ear canal is divided into two parts. The elastic cartilage part forms the outer third of the canal, Its anterior and lower wall are cartilaginous, whereas its superior and back wall are fibrous. The cartilage is the continuation of the cartilage framework of pinna. The bony part forms the inner two thirds. The bony part is much shorter in children and is only a ring (annulus tympanicus) in the newborn.
Size and shape of the canal vary among individuals. The canal is approximately 2.5 centimetres (1 in) long and 0.7 centimetres (0.28 in) in diameter. It has a sigmoid form and runs from behind and above downward and forward. On the cross-section, it is of oval shape. These are important factors to consider when fitting earplugs.
Disorders
Due to its relative exposure to the outside world, the ear canal is susceptible to diseases and other disorders. Some disorders include:
Atresia of the ear canal Bone exposure, caused by the wearing away of skin in the canal Cholesteatoma Contact dermatitis of the ear canal Ear fungus Ear mites in animals Ear myiasis, an extremely rare infestation of maggots Foreign body in ear Granuloma, a scar usually caused by tympanostomy tubes Otitis externa (swimmer's ear), bacteria-caused inflammation of the ear canal Stenosis, a gradual closing of the canal
Earwax
Earwax, also known as cerumen, is a yellowish, waxy substance secreted in the ear canals. It plays an important role in the human ear canal, assisting in cleaning and lubrication, and also provides some protection from bacteria, fungi, and insects. Excess or impacted cerumen can press against the eardrum and/or occlude the external auditory canal and impair hearing.
Pinna
The outer part of the ear.
–Collects, focuses, and localizes sound
–Acts like funnel
–Emotional states
Vestibule
The vestibule of the ear is the central part of the inner ear labyrinth, as used in the vestibular system.
Semicircular Canal
A semicircular canal is one of three semicircular, interconnected tubes located inside each ear. The three canals are:
the horizontal semicircular canal (also known as the lateral semicircular canal),
superior semicircular canal (also known as the anterior semicircular canal),
and the posterior semicircular canal.
Structure
The anterior and posterior semicircular ducts are oriented vertically at right angles to each other. The lateral semicircular duct is about 30-degree angle from the horizontal plane. The orientations of the ducts cause a different duct to be stimulated by rotation of the head in different planes. Thus, the horizontal canal detects horizontal head movements (such as when you spin in a rotating chair), while the superior and posterior canals detect vertical head movements (such as when you bend forward to pick something up from the floor).[1]
The semicircular canals are a component of the bony labyrinth. Among species of mammals, the size of the semicircular canals is correlated with their type of locomotion. Specifically, species that are agile and have fast, jerky locomotion have larger canals relative to their body size than those that move more cautiously.[2]
Cochlear Nerve
The cochlear nerve (also auditory or acoustic nerve) is one of two parts of the vestibulocochlear nerve, a cranial nerve present in higher vertebrates. The cochlear nerve carries sound waves from the cochlea of the inner ear directly to the brain. The other portion of the vestibulocochlear nerve is the vestibular nerve, which carries spatial orientation information to the brain from the semicircular canals.
Anatomy and connections
In terms of their anatomy, auditory nerve fibers are bipolar, with the most distal portion being called the peripheral process and the central projection being called the axon; these two projections are also known as the “peripheral axon” and the “central axon”. The peripheral process is sometimes referred to as a dendrite, although that term is somewhat inaccurate. Unlike the typical dendrite, the peripheral process generates and conducts action potentials, which then “jump” across the cell body (or somata) and continue to propagate along the central axon. In this respect, auditory nerve fibers are somewhat unique bipolar cells in that action potentials pass through the soma. Both the peripheral process and the axon are myelinated.
In humans, the number of nerve fibers within the cochlear nerve averages around 30,000.[1] The number of fibers varies significantly across species for example; the domestic cat has some 50,000 fibers. Auditory nerve fibers provide synaptic connections between the hair cells of the cochlea and the cochlear nucleus within the brain-stem. The cell bodies of the cochlear nerve lie within the central aspect of the cochlea and are collectively known as the spiral ganglion. This name reflects the fact that the cell bodies, considered as a unit, have a spiral (or perhaps more accurately, a helical) shape, reflecting the shape of the cochlea. The terms “cochlear nerve fiber” and “spiral ganglion cell” are used, to some degree, interchangeably, although the former may be used to more specifically refer to the central axons of the cochlear nerve. These central axons exit the cochlea at its base, where it forms a nerve trunk. In humans, this aspect of the nerve is roughly one inch in length. It projects centrally to the brain-stem, where its fibers synapse with the cell bodies of the cochlear nucleus. A good anatomical description of human auditory nerve fibers is provided by Spoendlin and Schrott (1985). Important earlier work was done by Schuknecht.
It was once believed that most of the cochlear nerve fibers were directed to the outer hair cells, but it is now understood that at least 90% of the cochlear ganglion cells terminate on inner hair cells, the rest terminating on the outer hair cells.
The transmission between the inner hair cells and the neurons is chemical, using glutamate as a neurotransmitter.
Cochlea
–Responds to vibrations from middle ear
–The oval window initiates liquid pressure wave
–The round window relieves pressure
–3 parallel chambers
•Vestibular Canal
•Cohlear Duct (contains Organ of Corti)
•Tympanic Canal
–2 membranes
•Reissner’s membrane
•Basilar membrane
Eustachian Tube
The Eustachian tube, also auditory tube or pharyngotympanic tube, is a tube that links the nasopharynx to the middle ear. It is a part of the middle ear. In adult humans the Eustachian tube is approximately 35 mm (1.4 in) long. It is named after the sixteenth-century anatomist Bartolomeo Eustachi. Some modern medical books call this the pharyngotympanic tube.
Structure
The Eustachian tube extends from the anterior wall of the middle ear to the lateral wall of the nasopharynx, approximately at the level of the inferior nasal concha. A portion of the tube proximal to the middle ear is made of bone; the rest is composed of cartilage and raises a tubal elevation, the torus tubarius, in the nasopharynx where it opens.
In the equids (horses) and some rodent-like species such as the desert hyrax, an evagination of the eustachian tube is known as the guttural pouch and is divided into medial and lateral compartments by the stylohyoid bone of the hyoid apparatus. This is of great importance in equine medicine as the pouches are prone to infections, and, due to their intimate relationship to the cranial nerves (VII, IX, X, XI) and the internal and external carotid artery, various syndromes may arise relating to which is damaged. Epistaxis (nosebleed) is a very common presentation to veterinary surgeons and this may often be fatal unless a balloon catheter can be placed in time to suppress bleeding.
Muscles
There are four muscles associated with the function of the Eustachian tube:
Levator veli palatini (innervated by the vagus nerve) Salpingopharyngeus (innervated by the vagus nerve) Tensor tympani (innervated by the mandibular nerve of CN V) Tensor veli palatini (innervated by the mandibular nerve of CN V)
Development
The Eustachian tube is derived from the first pharyngeal pouch, which during embryogenesis forms the tubotympanic recess. The distal part of the tubotympanic sulcus gives rise to the tympanic cavity, while the proximal tubular structure becomes the Eustachian tube.it helps transformation of sound waves.
Function
Pressure equalization
Under normal circumstances, the human Eustachian tube is closed, but it can open to let a small amount of air through to prevent damage by equalizing pressure between the middle ear and the atmosphere. Pressure differences cause temporary conductive hearing loss by decreased motion of the tympanic membrane and ossicles of the ear.[4] Various methods of ear clearing such as yawning, swallowing, or chewing gum, may be used intentionally to open the tube and equalize pressures. When this happens, humans hear a small popping sound, an event familiar to aircraft passengers, scuba divers, or drivers in mountainous regions. Devices assisting in pressure equalization include an ad hoc balloon applied to the nose, creating inflation by positive air pressure.[5] Some people learn to voluntarily ‘click’ their ears, together or separately, when deliberating doing a pressure equalizing routine by opening their Eustachian tubes where pressure changes are experienced (as in ascending/descending in aircraft flight, mountain driving, elevator lift/drops, etc.). Some even are able to deliberately keep their Eustachian tubes open for a brief period, and even increase or decrease air pressure in the middle ear. The ‘clicking your ears’ can actually be heard audibly if one puts one’s ear to another person’s ear for them to hear the clicking sound. Those that are borderline on learning this voluntary control first discover this via yawning or swallowing or other means (above); which later on discover can be done deliberately without force even when there are no pressure issues involved, by ‘clicking one’s ears’. When the Eustachian Tubes are deliberately held open voluntarily, one’s voice sounds louder in one’s head than when they are closed.
Mucus drainage
The Eustachian tube also drains mucus from the middle ear. Upper respiratory tract infections or allergies can cause the Eustachian tube, or the membranes surrounding its opening to become swollen, trapping fluid, which serves as a growth medium for bacteria, causing ear infections. This swelling can be reduced through the use of systemic pseudoephedrine or topical oxymetazoline.[citation needed]. Ear infections are more common in children because the tube is horizontal and shorter, making bacterial entry easier, and it also has a smaller diameter, making the movement of fluid more difficult. In addition, children’s developing immune systems and poor hygiene habits make them more prone to upper respiratory infections.
Clinical significance
Otitis media, or inflammation of the middle ear, commonly affects the Eustachian tube. Children under 7 are more susceptible to this condition and one theory is that this is because the Eustachian tube is shorter and at more of a horizontal angle than in the adult ear. Others argue that susceptibility in this age group is related to immunological factors and not Eustachian tube anatomy.
Barotitis, a form of barotrauma, may occur when there is a substantial difference in air or water pressure between the outer inner and the inner ear, for example in a rapid ascent while scuba diving, or a sudden decompression of an aircraft at high altitude.
Some people are born with a dysfunctional Eustachian tube,[6] which is much slimmer than the usual human Eustachian tube. This may be genetic, but it has also been suggested to be a condition in which the patient did not fully recover from the effects of pressure on the middle ear during birth (retained birth compression).[7] It is suggested that Eustachian tube dysfunction can result in a large amount of mucus accumulating in the middle ear, often impairing hearing to a degree. This condition is known as otitis media with effusion, and may result in the mucus becoming very thick and glue-like, a condition known as glue ear.
A patulous Eustachian tube is a rare condition, in which the Eustachian tube remains intermittently open, causing an echoing sound of the person’s own heartbeat, breathing, and speech. This may be temporarily relieved by moving into a position where the head is upside down.
Smoking can also cause damage to the cilia that protect the Eustachian tube from mucus, which can result in the clogging of the tube and a buildup of bacteria in the ear, leading to a middle ear infection in some cases.[8]
Eustachian tube dysfunction can be caused by recurring and chronic cases of sinus infection. This results from excessive mucus production which causes obstruction to the openings of the Eustachian tubes.
The Middle Ear
Boundaries of middle ear are formed by 2 membranes:
–Tympanic membrane (eardrum)
–Oval window
Ossicles
The 3 bones in the middle ear that are among the smallest bones in the human body. They transfer sound from air to fluid:
–Malleus (Hammer)
–Incus (Anvil)
–Stapes (Stirrup)
The 3 Parallel Chambers of the Cochlea
- Vestibular Canal (Contains Perilymph)
- Cohlear Duct. Located in the middle. (contains Organ of Corti and Endolymph)
- Tympanic Canal (Contains Perilymph)
Perilymph: like Cerebrospinal fluid
Endolymph: high K+, low Na+
Vestibular Canal
?
Perilymph
perilymph resembles extracellular fluid in composition (sodium salts are the predominate positive electrolyte) and, via the perilymphatic duct, is in continuity with cerebrospinal fluid.
Endolymph
high K+, low Na+
Endolymph is the fluid contained within the membranous labyrinth of the inner ear; endolymph resembles intracellular fluid in composition (potassium is the main positively-charged ion).
Reissner’s membrane
?
Basilar membrane
?
Organ of Corti
•Contains hair cells:
– inner hair cells act as receptor for auditory transduction
•Sits on the basilar membrane
•Inner hair cells are attached to the tectorial membrane via cilia
•Vibration of the basilar membrane bends and activates hair cells
tectorial membrane
The tectorial membrane (TM) is one of two acellular gels in the cochlea of the inner ear, the other being the basilar membrane (BM).
The TM is located above the sulcus spiralis internus and the spiral organ of Corti and extends along the longitudinal length of the cochlea parallel to the BM. Radially the TM is divided into three zones, the limbal, middle and marginal zones. It overlies the sensory inner hair cells and electrically-motile outer hair cells of the organ of Corti and during acoustic stimulation stimulates the inner hair cells through fluid coupling, and the outer hair cells via direct connection to their tallest stereocilia.
The TM is a gel-like structure containing 97% water. Its dry weight is composed of collagen (50%), non-collagenous glycoproteins (25%) and proteoglycans (25%). Three inner-ear specific glycoproteins. Due to the increased structural complexity of the TM relative to other acullular gels (such as the otolithic membranes), its mechanical properties are consequently significantly more complex.[4] They have been experimentally shown to be radially and longitudinally anisotropic[5][6] and to exhibit viscoelastic[7][8] properties.
The mechanical role of the tectorial membrane in hearing is yet to be fully understood, and traditionally was neglected or downplayed in many models of the cochlea. However, recent genetic[9][10][11] , mechanical[7][8][12] and mathematical[13] studies have highlighted the importance of the TM for healthy auditory function in mammals. Mice that lack expression of individual glycoproteins exhibit hearing abnormalities, including, most notably, enhanced frequency selectivity in Tecb-/- mice,[11] which lack expression of β-tectorin. In vitro investigations of the mechanical properties of the TM have demonstrated the ability of isolated sections of TM to support travelling waves at acoustically relevant frequencies. This raises the possibility that the TM may be involved in the longitudinal propagation of energy in the intact cochlea.[13]
Sound Transduction
- Ossicles transfer vibrations from the tympanic membrane to the oval window.
- Movement of the oval window creates waves in the perilymph within the vestibular canal.
- The waves of perilymph push the basilar membrane up and down.
- The waves travel back along the tympanic canal from the apex to the round window.
- The waves push the round window in and out.
