PBL 10 Flashcards
What are the two systems that the ear can be split into functionally?
Auditory and vestibular
What is the auditory system responsible for?
hearing
When does the auditory system begin?
As soon as sound waves enter the ear
What does the auditory system consist of?
The external, middle and inner ear
What is the external ear made up of?
The auricle (pinna) and the external acoustic meatus (auditory canal)
What are the auricles/pinnae made of?
They are composed of and shaped by elastic cartilage that is covered with skin
What is the function of the auricles/pinnae?
To direct sound into the external acoustic meatus
What are the three parts of the auricles/pinnae?
The helix, tragus and lobule
What is the external acoustic meatus?
An S-shaped passage that begins as an opening in the auricle
Where does the external acoustic media travel?
about 4 cm through the tympanic portion of the temporal bone to terminate at the tympanic membrane
What is The external acoustic meatus lined with?
mucous membrane containing sebaceous glands and modified sweat glands known as ceruminous glands
How is earwax (cerumen) formed?
when the secretions of ceruminous and the sebaceous glands combine
What is the function of earwax?
prevents the entrance of foreign particles into the ear and reduces the risk of bacterial and fungal infection
Where does the external acoustic meatus direct the sound waves to?
The tympanic membrane
what is contained in the middle ear?
The structures that amplify sound. these include the ossicles and auditory muscles
What is the tympanic membrane?
A thin, semi-transparent concave sheet.
What is the function of the tympanic membrane?
- separates the external and middle ear
- transmits vibrations from sound to the ossicles (malleus)
What is the tympanic cavity?
The cavity of the middle ear that contains the three ossicles
What is the tympanic cavity connected to?
The nasopharynx by the eustachian tube
What is the tensor tympani
a small muscle in the middle ear
Where is the tensor tympani?
it originates from the eustachian tube and sphenoid bone and inserts into the malleus
What is the function of the tensor tympani muscle?
To tense the tympanic membrane in response to abrupt noise and in anticipation to loud vocalization
What is the stapedius?
A small muscle in the middle ear
Where is the stapedius?
Attached to the temporal bone and the neck of the neck of the stapes
What is the function of the stapedius?
To dampen the vibrations of the ossicles by contracting in response to high intensity sound
What are the ossicles?
Three tiny bones found in the middle ear
What are the three ossicles?
The malleus, the incus and the stapes
What is the function of the ossicles?
They transmit and magnify sound from the tympanic membrane and across the tympanic cavity
What is the malleus?
largest and most lateral of the ossicles, It is attached to the tympanic membrane and articulates with the incus
What is the incus?
the middle ossicle and is located in the epitympanic recess of the tympanic cavity (middle ear) and it articulates with the stapes
What is the stapes?
the smallest and most medial ossicle of the middle ear. it articulates with the oval window of the inner ear
What is the function of the Eustachian tube?
- Connects the middle ear to the nasopharynx
- Allows the pressure within the cavity to remain equal to local barometric pressure
What is the oval window?
an opening between the middle and inner ear that articulates with the footplate of the stapes
What is the function of the oval window?
Allows the footplate of the stapes to transmit the sound vibrations from the middle ear to the inner ear
What is contained in the inner ear?
The sensory structures for both hearing and balance
What does the inner ear consist of?
A network of bony canals contained deep within the temporal bone
What are the parts of the bony labyrinth?
The cochlea and the semi-circular canals
How are the cochlea and semi-circular canals connected?
A centrally placed vestibule
What is the bony labyrinth?
a tube of bone that coils around a central pillar called the modiolus. It resembles a snail shell. Between the bony labyrinth and membranous labyrinth, sit two fluid-filled spaces: the scala vestibuli and scala tympani
What is the scala vestibuli?
A fluid filled space that passes the entire length of the cochlea.
What is the scala tympani?
A fluid filled space that passes through the entire length of the cochlea.
What is the fluid in the scala vestibuli and the scala tympani known as?
perilymph
What is perilymph maintained by?
The secretory epithelial cells that line the canals
What does the scala vestibuli connect to?
The oval window sits at the base of the canal, where it connects to the tympanic cavity.
What is the scala tympani connected to?
At its base sits the round window, which connects it to the tympanic cavity, and at its apex the helicotrema joins it to the scala vestibuli
What is the membranous labyrinth?
A coiled tube that contains the cochlear duct
What is the cochlear duct (scala media)?
The middle triangular canal that contains the organ of corti
What forms the roof and floor of the cochlear duct?
Roof - vestibular membrane
Floor - basilar membrane
What fluid does the cochlear duct contain?
Endolymph
What is the vestibule?
The central part of the bony labyrinth
What does the vestibule do?
connects the inner ear with the middle ear and has a supportive role
what does the vestibular membrane do?
Separates the cochlear duct from the scala vestibuli
What is the vestibular membrane?
a thin transparent membrane that stretches obliquely from the inner membrane of the modiolus
How does the vestibular membrane contribute to hearing?
When vibrations of the tympanic membrane are felt in response to sound waves, the pressure waves created are transmitted through the vestibular membrane to the basilar membrane
what does the basilar membrane do?
Supports the organ of corti and separates the cochlear duct (scala media) from the scala tympani
What is the structure of the basilar membrane like?
It is not uniform in width or thickness, as it is wider, thinner, and more pliant at the apex than at the base
What is the spiral ganglion?
The group of nerve cells that serve the sense of hearing by sending a representation of sound from the cochlea to the brain
Where is the spiral ganglion found?
The modiolus. Fewer ganglion cells are found in the middle turn compared with the apical and basal turns
What is found within the spiral ganglion?
the cell bodies of the cochlear branch of the vestibulocochlear nerve (VIII)
What is the cochlear nerve?
A branch of the vestibulocochlear nerve (VIII)
Where do the nerve fibres of the cochlear nerve pass?
from the hair cells of the organ of Corti and through the modiolus as the spiral ganglia, before continuing onto the internal auditory meatus
What is the function of the hair cells on the organ of corti?
They act as sensor transducers
Where are the hair cells of the organ of corti found?
They rest on the basilar membrane with their stereocilia (hairs) embedded in the underside of the tectorial membrane.
What types of hair cell are there?
There are three or four rows of outer hair cells but only a single row of inner hair cells
What are stereocilia?
Membrane bound cellular projections of inner and outer hair cells
What is the role of the stereocilia?
they create a streaming movement in the surrounding fluid
where are the stereocilia found?
protrude from hair cells through the reticular membrane and point towards the tectorial membrane that lies above
How do the stereocilia contribute to hearing?
The bending movement causes them to depolarize and send information to the rest of the hair cell, turning the mechanical energy of a sound wave into a neural signal
What is the tectorial membrane?
a semi-transparent, fibro gelatinous structure that overlies the hair cells of the organ of Corti
What is the function of the tectorial membrane?
it withstands the mechanical stresses associated with cochlear fluid vibrations
What are the supporting cells of the organ of corti?
a series of specialized epithelial cells that provide mechanical support to the sensory cells that they surround.
what are sound waves?
oscillations of pressure in a medium, such as air or liquid
Where do external sound waves travel?
Through the external and middle ear to the auditory receptors in the cochlea
What is the pathway of sound in the external ear?
sound waves are directed by the auricle through the external acoustic meatus, to the tympanic membrane
What do the sound waves do to the tympanic membrane?
They cause it to vibrate
What does the tympanic membrane articulate with?
The ossicles
What happens when the tympanic membrane vibrates?
The ossicles transmit these vibrations to the cochlea
Where do the vibrations travel in the perilymph?
up the scala vestibuli and down the scala tympani
What happens when the vibrations arrive back at the round window?
it bulges out into the middle ear
Where is the cochlear duct?
Between the scala vestibuli and scala tympani
What are the two branches of the vestibulocochlear nerve?
The vestibular and cochlear
What parts of the ear are involved in balance?
The vestibule and semi-circular canals
What does the vestibule contain that helps with balance?
Mechanoreceptors called maculae that detect static equilibrium
What is static equilibrium?
The movements of the body relative to the forces of gravity
What do the semi-circular canals contain that helps with balance?
mechanoreceptors called crista ampullaris that detect dynamic equilibrium
What is dynamic equilibrium?
The angular movements of the body
What is Acute otitis media?
A painful infection of the Middle ear
What happens in Acute otitis media?
The middle ear becomes inflamed and infected
What can cause Acute otitis media?
a primary or secondary bacterial infection or a virus
What is a secondary bacterial infection?
Occurs after or because of a primary infection
What happens if the swelling in the ear is too great?
the blood vessels in the ear drum are compressed, local tissue necrosis and the ear drum bursts, letting out pus and relieving the pain
What is the standard treatment of Acute otitis media?
The prescription of an antibiotic even though 80%of all acute otitis media resolve spontaneously without treatment
What happens if the inflammatory exudate causes the tympanic membrane to rupture?
The inflammatory exudate may spread to the mastoid air cells, causing acute mastoiditis
What is serous otitis media?
When fluid accumulates in the middle ear as a consequence of eustachian tube obstruction
What is another cause of serous otitis media?
It can also occur following otitis media, when the fluid in the ear, formed by the infection, does not drain spontaneously
What does serous mean?
of, resembling, or producing serum
What are the possible complications of serous otitis media?
risk for further infection and worsens hearing by about 30 dB
How can serous otitis media be resolved?
by removing the obstruction e.g. in patients with tonsillar hyperplasia
What is chronic otitis media?
persistent or repeated acute bacterial infections
Why is there hearing loss if the tympanic membrane is perforated?
there is not enough area of the tympanic membrane to catch sound
What are 4 common complications of chronic otitis media?
- Tympanic perforation and discharge
- Aural polyps: granulation tissue in the middle ear
- Disarticulation and resorption of ossicles, with conductive hearing loss
- Cholesteatoma
What is Cholesteatoma?
accumulation of keratin derived from squamous epithelium spreading in from the external auditory canal following tympanic perforation
What is labyrinthitis?
An infection of the inner ear/labyrinth
What is the usual cause of labyrinthitis?
Virus
Why are children more likely to get ear infections than adults?
- their eustachian tubes are smaller and more level
- Childrens immune systems aren’t as well developed as adults
- Sometimes bacteria get trapped in the adenoids causing chronic infection that can pass to the ear
What does the structure of children’s eustachian tube have to do with the increased likelihood of them getting an ear infection?
smaller and more level, which makes it difficult for fluid to drain out of the ear.
What is thermoregulation?
a process that allows your body to maintain its core internal temperature
What is the aim of all thermoregulation mechanisms?
to return your body to homeostasis
How can muscles increase metabolic heat production?
They contract e.g. shivering
What is non-shivering thermogenesis?
The breakdown of brown fat / brown adipose tissue
Who has the most brown fat?
Babies - its prevalence decreases as humans age but there is still a small amount in adults
What is vasoconstriction?
Shrinking the diameter of blood vessels that supply the skin
What is vasodilation?
blood vessels get wider, or dilate, increasing blood flow to the skin
What is counter-current heat exchange?
a circulatory adaptation that allows heat to be transferred from blood vessels containing warmer blood to those containing cooler blood
How does counter-current heat exchange work?
As warm blood passes down the arteries, the blood gives up some of its heat to the colder blood returning from the extremities in these veins.
What are the four ways heat can be lost?
convection, conduction, radiation, and evaporation
What happens in hot conditions?
- Eccrine sweat glands under the skin secrete sweat
- The hair on the skin lie flat, preventing heat from being trapped by the layer of still air between the hair
- Arteriolar vasodilation, redirecting blood into the superficial capillaries in the skin increasing heat loss by convection and conduction
What happens in cold conditions?
- Sweat production is decreased
- hair erector muscles contract causing a layer of air to be trapped, insulating the skin
- arteriolar vasoconstriction
- shivering and muscle contraction to generate heat
- non-shivering heat production through brown adipose tissue
What is thermogenin?
The uncoupling protein used to generate heat by non-shivering thermogenesis
Where is thermogenin found?
The mitochondria of brown adipose tissue
What is a fever?
having a temperature above the normal range
What are pyrogens?
Chemicals in the bloodstream that cause fevers
What are fevers caused by?
Pyrogens
What are the two types of pyrogens?
Endogenous and exogenous
What is an endogenous pyrogen?
Internal
What is an exogenous pyrogen?
external
What is a common example of a pyrogen?
Interleukin-1 (IL-1)
What are most endogenous pyrogens?
Cytokines
How is IL-1 produced?
By macrophages when they come into contact with certain bacteria and viruses
What do pyrogens cause the release of?
Prostaglandin E2 (PGE2)
What does PGE2 do?
acts on the hypothalamus, which creates a systemic response in the body causing heat-generation effects to match a new higher temperature set point.
What is the ultimate mediator of the fever?
PGE2. The set point temperature of the body will remain elevated until PGE2 is no longer present.
What does the hypothalamus act as?
A thermostat
What causes the hypothalamus to change set point?
Prostaglandins
What is thought to be the purpose of a fever?
to raise the body’s temperature enough to kill off certain bacteria and viruses sensitive to temperature changes
What does the increase in set point trigger?
increased muscle contractions and a feeling of cold
Why does paracetamol not work as an anti-inflammatory?
It does not appear to inhibit the function of any cyclooxygenase (COX) enzyme which is what NSAIDs such as aspirin do
How does paracetamol work?
It appears to inhibit COX in the brain selectively
How does paracetamol inhibit COX?
This does not appear to be by direct inhibition (by blocking an active site), but by reducing COX which must be oxidised in order to function.
How is paracetamol thought to relieve pain?
by reducing the production of prostaglandins in the brain and spinal cord, increasing our pain threshold
When are prostaglandins produced?
by the body in response to injury and certain diseases
What is one of prostaglandins actions?
to sensitise nerve endings, so that when the injury is stimulated it causes pain
How does paracetamol work on a fever?
It acts as an antipyretic and reduces fever by promoting heat loss and thus helps reset the hypothalamic thermostat
