Special Senses Flashcards
What is sound?
A pressure wave that spreads out from a source, using a medium whose particles vibrate.
What is frequency?
Pitch
The number of vibrations per second in Hertz
What is a typical range of hearing for a young human?
20-20,000Hz
What is loudness?
Intensity
Strength of the vibrations
What is the loudest sound we can hear?
100 trillion times the energy of the quietest sound we can hear.
Use log scale called decibels
What would differ in a 10dB increase in terms of perception and energy?
Perceived as twice as loud
Has 10 times the amount of energy
Why do we have two ears?
So we can localize sounds on a horizontal plane.
Time difference is cue
What is the pinna
External portion of ear
Amplifies, shapes, and filters sound to give directionality
Filters out high frequency sound from behind
Helps distinguish front from back, and up from down (due to shape)
What is the ear canal?
A tube
Sounds at central frequencies are amplified (by about 10dB) in here because of resonance.
What structures make up the outer ear?
Pinna and ear canal
What structures make up the middle ear?
Tympanic membrane Ossicles (malleus, incus, stapes) Eustachian tube Stapedius Muscle Tensor Tympani
What structures make up the inner ear?
Cochlea
Vestibule
Semi-circular canals
Oval window
What amplifies sound?
- The area ratio of tympanic membrane and the oval window causing a 25dB increase in loudness
- The lever action of the ossicles
What embryological structures give rise to the ossicles?
First branchial arch turns into mandible and gives rise to malleus and incus
Second branchial arch gives rise to stapes
What structures are found within the middle ear that help protect from load noises?
Stapedius Reflex- connects to stapes and contracts when ear is exposed to loud sound to protect the cochlea
Tensor Tympani- Large muscle running up eustachian tube joining onto back of malleus. Stop you from blowing out tympanic membrane when coughing and sneezing. Protects from loud sound
What is the eustachian tube?
Cartilage and bone lined in mucosa moving from nasopharynx to middle ear.
Allow air into middle ear to equalize pressure, allowing tympanic membrane to vibrate appropriately
What are conductive hearing loss problems?
Inner ear works fine, but sound is appropriately conducted to the cochlea
Can correct by vibrating the skull
What are some causes of hearing loss in the outer and middle ear?
Ear canal- wax, foreign body, congenital atresia
Tympanic Membrane Perforation
Ossicles- congenital fusion, damage from infection
Middle ear space- fluid instead of air
What structures sit on either end of the ossicles?
Tympanic membrane sits by malleus, and oval window (fenestra ovalis) sits beside the stapes and is much smaller
What is the vestibular apparatus for and what structures are apart of it?
For balance
Utricle & Saccule - linear acceleration
Semi-circular canal- rotatory motion in 3 planes
Contain sensory epithelial
What is the Cochlea and what is it used for?
Forms part of the inner ear, used for converting physical vibrations into electrical impulses
Joined to utricles/saccule, and semi-circular canal
How does sound move from the oval window through the inner ear?
Vibrations passed to oval window -> vestibule -> scala vestibuli -> helicotrema -> back through scala tympani (lower cochlear duct) -> waves terminate at round window
What is found within the Scala Media?
Contains the Organ of Corti (sensory epithelium containing auditory hair cells) Stria Vascularis (regulates electrolyte composition within endolymph so it optimal for hair cell function)
What is contained within the organ of corti?
Tectorial membrane superior
Spiral ganglion
Auditory nerve fibers
Basilar membrane
How do we pick up frequency within the cochlea?
As the sound moves through the scala vestibuli/tympani, certain frequencies are optimally picked up by certain portions of the basilar membrane.
Base- high frequency
Apex- low frequency (hairs at helicotrema are more stiff)
What are the different hairs within the inner ear?
Outer hairs- efferent, help amplify sound. We have more of these
Inner Hairs- afferent, carry sound stimuli to brain using vestibulocochlear nerve
What does the tectorial membrane touch?
Hairs rub against it
What do the nasal concha do?
Increase turbulence to help circulate air so we can smell it all.
What nerves supply the tongue?
Anterior 2/3 is supplied by the facial (taste) and the lingual nerve, a sub-branch of the trigeminal nerve (general sensation)
Posterior 1/3- glossopharyngeal nerve
Hypoglossal nerve supplies the tongue muscle
What is the tallest stereocilia called and why is it relevant to membrane potential?
Kinocilium- pushing of hairs towards kinocilium causes depolarization (K influx), where as movement of the kinocilium towards the other shorter hair causes hyperpolarization
Does increased frequency cause hyperpolarization or depolarization?
Depolarization
What is the function of the inner hair cell?
Transducer
It works as a receptor that picks up basilar membrane vibrations and changes that form of energy into another
Afferent
What are the roles of outer hair cells?
Cochlear Amplification - contract in response to sound actively, which feeds energy into basilar membrane (reverse transduction) helping it to move more
Make frequency response more selective by reducing vibration besides them on the basilar membrane, helping with localization of sound
How could you test to see if an infant has hearing problems?
Otoacoustic emissions test.
Placed over babies ears, and can pick up on the sound of the movement of outer hair cells
What happens with hair loss within the cochlea?
Inner- complete hearing loss
Outer- loss of sound (50db) and loss of sound discrimination
How does reception of high vs low pitch in terms of frequency change?
You can hear low pitches moving at a high frequencies more than high pitches at high frequencies because refractory period isn’t as long for low pitches
How does sound move through the central pathways?
First order neuron axons project through cochlear nerve (CN8) in internal acoustic meatus -> cerebello-pontine angle -> synapse in cochlear nuclei (medulla-pons junction) and may move contralaterally now -> Move through olive and trapezoid body in pons to midbrain (inferior colliculus) -> thalamus (medial geniculate body) -> cortex (superior temporal gyrus)
How long is pitch maintained when moving from the cochlea to the brain?
All the way to the temporal lobe
What is the Occipital Somite?
What most of the tongue muscles develop from- somites are from the paraxial mesoderm
Describe the embryology of the tongue and corresponding nerves.
1st Brachial Arch Endoderm- Forms mucosal surface of anterior 2/3 of tongue. Trigeminal nerve 5 for touch and pain, and facial nerve 7 for taste
3rd Brachial Arch Endoderm- forms epithelial lining of posterior 3rd of tongue. Glossopharyngeal nerve 9
Mesoderm of upper neck- intrinsic/extrinsic muscles. Hypoglossal nerve 12
What bones is the tongue suspended by?
Mandible, hyoid, and styloid process
What extrinsic muscles aid in the movement of the tongue and the suspension from the bones?
Styloglossus
Hyoglossus
Genioglossus
Palatoglossus - more movement, not suspension
What structures make up the tongue?
Palatine tonsils
Lingual tonsils (small aggregations of lymphoid tissue, blobby surface appearance)
Foramen caecum (where thyroid gland develops in embryo)
Epiglottis
Circumvallate papillae (large bumps, demarcation differentiating anterior 2/3 from posterior 3rd)
Fungiform papillae (carry taste buds)
Filiform papillae (add roughness to help move food)
What chemicals do taste buds detect?
Sour- acid, hydrogen ions Sodium- stimulate salty ones Sweet- glucose/fructose Bitter- quinine. Coffee, beer, blue cheese, olives (most sensitive, protects from poison) Savoury/umami- glutamate
How many taste buds does a typical human have?
2000-8000
How is taste mediated on a neurological bases in the anterior and posterior tongue?
Anterior 2/3- Lingual nerve (trigeminal CN 5- for pain, touch, temp.)
Taste initially carries by chordae tympani (which runs through tympanic membrane), then moves to run with facial nerve (CN7)
Lingual and Chordae meet, but then divide
Posterior 3rd- Pain, temperature, touch, and taste through Glossopharyngeal CN 9
How does taste travel through the brain?
Taste fibers synapse in nucleus tractus solitaries of the medulla, then up brainstem, past thalamus, to gustatory cortex on under-surface of frontal lobe.
What are other sensory inputs involved in eating?
Pungency (capsaicin in chilli- pain/temp receptors)
Coolness (menthol via temp receptors)
Fattiness
Temperature (enhances odorants and improves texture)
Texture (crunchy/creamy)
How can different surgeries impact taste?
Ear- damage to chordae tympani can leave metallic taste
Sublingual/mandibular salivary glands- damage chordae tympani/ lingual nerves causing loss of taste/sensation in floor (anterior 2/3) of mouth
Dry mouth- need saliva to dissolve chemicals (radiation/chemo, autoimmune diseases)
How is flavour interpreted?
Smell
This is how you enjoy flavour, especially during mastication
What are turbinates?
Projections within the nose that increase turbulence, surface area, and warm/humidify air
AKA Conchae
Where is smell picked up?
By Olfactory bulbs sitting superior to the cribriform plate, which is superior to olfactory mucosa at the roof of the nasopharynx
How does smell travel from olfactory receptors to the brain?
Pick up odorant molecules by dendrites of olfactory receptor cells, signal then travels up through nasal epithelium and cribriform and is relayed to glomeruli within olfactory bulb.
Then synapses from glomeruli to mitral cells and tuft cells which carries signal to brain
How many genes are used in human smelling?
1000 genes, about 400 are active
Can identify about 10,000 to a trillion smells
What determines response to smell?
The combination receptor response and odour stimulation.
What is the central pathway of smell?
Does not relay through thalamus
Olfactory nerve projects to limbic system- the amygdala, hippocampus, and para-hippocampal
What is the name for inability to smell, and some examples of clinical disorders which may cause this?
Anosmia
-typically acquired in adults, rhinosinusitis, neurological disorder (Alzheimer’s, Parkinson’s, MS), base of skull fracture, tumour (meningioma), Covid
-Kallmann syndrome (delayed puberty association, rare, congenital anosmia)
How is action potential met within the villi of taste receptors?
The taste opens ion-gated channels (salty/sour) or binds G-Protein Coupled Receptors (sweet/bitter) activating a second messenger.
The changes caused by the binding to receptors elicits changes in the taste cell, causing depolarization and firing of an action potential
Do the senses of smell and taste involve any cilia or villi?
Taste- villi
Smell- cilia
What secretes mucous onto the olfactory membrane?
Bowman’s gland- helps dissolve odorants (therefore odorants must be partially water-soluble)
How is action potential met within the cilia of olfactory receptor cells?
Odorant binds G-protein on cilia of olfactory -> intra-cellular activation (G protein activates adenylyl cyclase which activates cAMP, which opens gated sodium channels) -> Gated sodium channels open, allowing influx of sodium -> depolarization -> Action potential reached and fired
What is found within the organ of corti?
Tectorial membrane superior
Stereocilia with tips in the tectorial membrane, and anchored by reticular lamina
Reticular lamina held up by rods of Corti
Rods of Corti held by basement membrane
Basement membrane held by Modiolus
Spiral ganglion extending towards inner/outer hair cells
Cochlear Nerve within spiral ganglion
What is the iris?
Smooth muscle, between pupil and sclera (white portion) which control diameter of pupil via sphincter pupillae and dilator pupillae.
What is the cornea?
Clear portion on surface of eye that helps to refract light.
Common in transplants, avascular so less likely to be rejected
What is jaundice of the eye?
Yellowing, typically of the sclera (white portion) which is covered by the bulbar conjunctiva.
Can indicate liver/blood pathologies
What is keratoconus?
Thinning of the cornea, resulting in coning of eye, can cause blurring of eyes and may require surgery
What fluids are found in the anterior and posterior chambers of the eyes?
Aqueous humour is produced by ciliary bodies. It circulates from anterior to posterior to maintain pressure within the eye.
Anterior is between cornea and iris, posterior sits just behind the iris
What is the lens?
Helps focus light onto the retina.
Located between iris, posterior to pupil
What is contained between the lens of the eye and the retina?
Vitreous chamber, which has vitreous humour that is largely composed of water, as well as phagocytes.
What is the retina?
Back of eye
Where you get interpretation of black and white (rods) and colour (cones).
Describe the movement of light from the cornea to the occipital lobe.
Light hits cornea, passes through anterior chamber, pupil, and lens (iris and posterior chamber on sides), through vitreous chamber/humous to hit the retina (containing rods and cones) to cranial nerve 2, optic nerve.
Moves along optic nerve to optic chiasm, some impulses will cross contralaterally, then moves along optic tract to optic radiation, along to project into occipital lobe.
Where is the lacrimal gland and what is its purpose? Include movement of its products.
Lateral, superior side of eye.
Produces tears.
Tears will be produced in lateral, superior corner of eye to remove debris, lubricate eye, and will travel to medial corners to drain through superior/inferior lacrimal canals into the nasal cavity.
What sinuses are found within the skull and what is their purpose?
Maxillary - under eye, blow fractures result in eye falling into here (herniation)
Frontal- forehead
Ethmoid
Sphenoid
Purpose: weight reduction, circulation of mucous, resonance of sound
What nerves are involved in moving the eye?
Cranial Nerves 3, 4, 6
Oculomotor, Trochlear, Abducens.
note, not directly involved in special senses, but rather movement of eye
What are the 7 extraocular muscles and their associated movements?
Levator palpebrae superioris (lifts eyelid)
Superior rectus- elevation, slight medial rotation
Inferior rectus - depression of eye, slight medial rotation
Medial rectus- adduction
Lateral rectus - abduction
Superior obliques-depresses eye, abduction, lateral rotation
Inferior obliques- elevation, abduction, lateral rotation
What muscle(s) do each nerve innervating movement of the eye control?
Oculomotor- inferior oblique, superior rectus, inferior rectus, medial rectus
Trochlea- superior oblique
Abducent- lateral rectus
LR6 SO4
What glands are found within the skull?
Sublingual Gland- below tongue
Parotid Gland- largest, posterior
Submandibular gland- 2nd largest, in submandibular triangle
What are the primary surfaces found within the mouth?
Buccal- side of mouth, where cheeks are. Space between cheeks and teeth
Lingual Surface- facing tongue from teeth.
Mylohyoid Space- within the mandible, where the tongue sits
What papillae are found on the tongue?
Fungiform- Anterior 2/3s of tongue, carry taste buds
Filiform- very small, anterior 2/3
Foliate- on sides of tongue
Vallate- large, distinguish anterior 2/3 from posterior 1/3. Some taste buds, and minor salivary glands
What is the foramen caecum?
Where thyroid developed in utero
What nerves pass through the internal acoustic meatus?
Facial
Vestibulocochlear
What is the petrous and squamous temporal bone?
Petrous in internal aspect of temporal, squamous is external
What nerve does NOT pass through the thymus?
Olfactory
What structures form the lateral and medial walls of the tympanic cavity?
Lateral- tympanic membrane
Medial- Vestibular window (oval) and Cochlear window (round)
What structures form the lateral and medial walls of the tympanic cavity?
Lateral- tympanic membrane
Medial- Vestibular window (oval) and Cochlear window (round)
What sinus sits inferior to the orbit?
Maxillary
Which cranial nerve supplies the lateral rectus?
Abducens (CN5)
Which cranial nerve supplies the superior oblique muscle?
Trochlear
Which cranial nerve carries taste fibres from the posterior one-third of the tongue?
Glossopharyngeal
Which cranial nerve carries taste fibres from the anterior two-thirds of the tongue?
Chordae Tympani (Facial Nerve CN7)
What may cause palsy of the cranial nerves?
Stretching due to increased cranial pressure i.e. haemorrhage, tumour, or trauma (skull fracture)
What is the pterion?
The point on the lateral surface of the skull where the temporal, parietal, frontal, and sphenoid bones meet
Where do the salivary glands open in the mouth and how much saliva is typically produced per day?
Parotid salivary gland opens opposite the second upper molar tooth
Both the submandibular and sublingual glands open either side of the lingual frenulum.
500ml-1500ml
What types of secretions does each salivary gland produce?
Parotid salivary gland- Serous secretions
Sublingual salivary gland- Mucous secretions (more viscous)
Submandibular salivary gland- Mixed seromucous secretions
What are the intrinsic muscles of the tongue?
Superior longitudinal, Vertical, Horizontal (transverse), and Inferior longitudinal
What are the genioglossus and geniohyoid muscles of the tongue?
Genioglossus- fan shaped extrinsic muscle within tongue
Geniohyoid- Attaches tongue to hyoid bone
What is the artery supply to the tongue?
Lingual artery (branch of the external carotid artery) and also the tonsillar artery from the facial artery for collateral circulation
What fibres are carried in the olfactory nerve and where does the olfactory nerve enter the cranial cavity, through which bone, and what foramina?
Special visceral afferent nerve carrying information related to smell
Foramen of the Cribriform plate of the ethmoid bone
What is trigeminal neuralgia?
Chronic condition impacting trigeminal nerve in which mild stimulations can cause excruciating pain.
Where does the trigeminal nerve exit the cranial cavity?
Ophthalmic – superior orbital fissure
Maxillary – foramen rotundum
Mandibular – foramen ovale
Where does the facial nerve exit the cranial cavity?
Stylomastoid foramen
Where does the hypoglossal nerve originate from and where does it exit the skull?
Origin- Medulla oblongata (i.e. brainstem)
Exit- Hypoglossal canal
What is responsible for production of endolymph?
Stria Vascularis
