Module 3D ENT - Lectures Flashcards
What is meant by amplitude and frequency?
- Amplitude (difference between the denser and less dense areas of air molecules) = loudness
- Frequency = the number of waves that pass in one second
–> 1 wave per second = 1 Hertz (Hz)
–> The greater the frequency, the higher the pitch.
What is sound measured in?
decibels (dB)
Ear anatomy
- The pinna is the outer fleshy part of the ear
- Sound waves travel down into the auditory canal until they reach the tympanic membrane
- The tympanic membrane moves in relation to the sound waves hitting it –> this moves the 3 bones within the middle ear –> which in turn moves the oval window which is attached to the cochlear
Middle ear anatomy
- what are the 3 bone structures called
- what holds these bone structures in place?
- The 3 bone structures within the middle ear are called the malleus, incus, and stapes –> held in place by the stabilising ligaments and two muscles (stapedius muscle and tensor tympani muscle)
Do the bones of the middle ear amplify the sound or the force against the oval window + why is this beneficial?
- The bones of the inner ear do no amplify the volume of the sound, they amplify the force
- There is a fluid-filled structure within the cochlear which requires more force as it is fluid not air
What is impedance matching in regards to the middle ear and sound?
Impedance matching allows vibration of the fluid in the inner ear –> sound can be transmitted directly to the cochlear through bone
What is the attenuation reflex in regards to sound and the middle ear?
- this describes the action of the two muscles (stapedius muscle and tensor tympani muscle) in response to a very loud sound
- the muscles help to stabilise the bone structures and in turn protects the cochlear from the loud sound
- it also acts to mask low frequency sounds in loud environments –> reducing background noise making speech easier to hear in noisy enivronments
Describe the travel of sound waves from initial entry to the round window
+ what is the round window?
- The sound waves pass through the aduitory canal, through the middle ear, and through to the cochlear
- They hit the oval window (where the stapes are) –> the waves then pass along through fluid called perilymph which goes all around the cochlear (over the top of the Organ of Corti) to the round window
- The round window is a membranous structure at the other end of the cochlear and basically just allows for the transmission of waves
Where does all of the ‘actual hearing’ take place within the ear + where are low/high frequency sounds heard
- The Organ of Corti
- High frequency sounds –> heard at the base
- Low frequency sounds –> heard near the helicotrema
Organ of Corti
- where does it sit
- what does it do in response to vibrations
- Organ of Corti sits in the middle of these two fluid-filled areas –> gets vibrated as the waves pass either side
- Genereates a nerve impulse in response to vibration of the basilar membrane
- Contains specialised cells called inner and outer hair cells
- Synapses with the spiral ganglion of Corti and then the cochlear nerve
. - Perilymph –> Na+ rich
- Endolymph –> K+ rich
What happens when the oval window is pushed in
- Pushing in of the oval window pushes perilymph into the scala vestibule
- The pressure change travels along the scala vestibule, through the helicotrema along the scala tympani and causes movement at the round window
- Causes non-rigid structures within the cochlear to move –> the basilar membrane moves
Organ of Corti - hair cells
- why are outer hair cells important
- The hair cells (inner and outer) are the structures that actually detect the movement of the basilar membrane
- Movement of the basilar membrane relative to the tectorial membrane –> results in displacement of the hair cells
- Inner hair cells are not attached to the tectorial membrane
- Outer hair cells are important for the amplification of sound
What ion is involved in depolarisation of inner ear hair cells?
Hair cells depolarise with K+, unlike nerve cells
Which inner ear hair cell type innervates the majority of spiral ganglion cells?
Inner hair cell
Outer hair cells are responsible for the amplification of sound –> what is the name of the protein which contracts and elongates to amplify sensitivity to sound waves?
Prestin
Auditory pathway –> which cranial nerve is involved?
Cranial nerve VIII (vestibulocochlear nerve)
Primary auditory cortex
- Primary auditory cortex is like a ‘piano’ –> damage to a part of it can knock out that frequency of sound
The Organ of Corti –> YouTube video
https://www.youtube.com/watch?v=bwCz3Q8y-PM
The vestibular system –> what is it?
- The vestibular system provides information on the spatial orientation and movement of the head and plays an essential role in regulating movement of the trunk and limbs as well as the maintenance of body posture
- In addition, afferent discharges from the vestibular organs influence reflex centres responsible for maintenance of a stable retinal image by controlling neck muscles and extraocular eye muscles
- Rotary movement of the head is detected by hair cells in the semicircular canals, while linear acceleration and the direction of gravity are detected by hair cells in the otolith organs
Inner ear anatomy
- In addition to the cochlear, there is the Otolith organs and the semicircular canals
What is Meniere’s disease?
- A transient condition that can last up to 3hrs
- Symptoms –> dizzy, unsteady, nauseous, ringing in ears, and a drop in hearing
- thought to be due to excessive secretion of endolymph with acute swelling in vestibular and cochlear duct –> self-limiting may be due to minor rupture relieving pressure
- Treatment –> betahistine, diuretics, corticosteroids, surgery
Inner ear –> Otolith organs
Inner ear –> semicircular canals
Vestibular nervous pathway
Vestibular-ocular reflex
The vestibular system endolymph motion –> YouTube video
https://www.youtube.com/watch?v=dSHnGO9qGsE
Benign paroxysmal positional vertigo
- Manoeuvre to diagnose (Dix-Hallpike manoeuvre) –> pt sat on bed, head tilted 45 degrees laterally and eyes facing you for 30 secs, then lower the patient horizontally flat keeping head in 45-degree position –> if pt has nystagmus then +ve test
(perform on both sides)
(video: https://www.youtube.com/watch?v=8RYB2QlO1N4 )
. - Common disorder of the inner ear
- Typically lasts a few seconds to a few minutes
- Thought to be caused by displaced otoconia
- Can be detected using the Dix-Hallpike maneuver
- Head tilting and rotating can reposition otoconia (Epley maneuver)
- Acute severe BPPV can be treated with antivertigo medication
Nystagmus
- Rhythmical, repetitive and involuntary movement of the eyes
- Multiple causes, congenital and acquired
- Semi-circular canals are stimulated while the head is not in motion
- Can be associated with vertigo
.
Video: https://www.youtube.com/watch?v=9LsHp-tgx8w
What is an audiogram?
An audiogram measured by an audiologist using an audiometer converts measured thresholds from absolute sound pressure level to a hearing threshold level relative to the normative population, thereby allowing direct reading of the loss in hearing sensitivity at each frequency relative to the normal population
Anatomy and Physiology of the Auditory system –> YouTube video
https://www.youtube.com/watch?v=A2Ee9VrDHh4
Which of the following best describes the middle ear ossicle attached to the tympanic membrane?
- Incus
- Malleus
- Stapes
Malleus
The cochlea’s 3 chambers are the scala vestibuli, scala media, and scala tympani. The scala vestibuli and scala tympani are filled with _____________ (similar to _____________ fluid).
- Endolymph (similar to intracellular fluid)
- Perilymph (similar to cerebrospinal fluid)
Perilymph (similar to cerebrospinal fluid)
Low-frequency sound causes which portion of the basilar membrane to vibrate to the greatest extent?
- Near oval window
- Middle portion
- Along entire length
- Near helicotrema
Near helicotrema
The otolith organs (utricle and saccule) are primarily involved in detecting which type of movement?
- Rotational movements
- Linear acceleration
- Sound waves
Linear acceleration
Which of the following cranial nerves is involved in transmitting sensory information from the vestibular system to the brain?
- Cranial nerve III (Oculomotor nerve)
- Cranial nerve IV (Trochlear nerve)
- Cranial nerve VI (Abducens nerve)
- Cranial nerve VIII (Vestibulocochlear nerve)
Cranial nerve VIII (Vestibulocochlear nerve)
Carotid sheath –> Axial view
Vagus nerve
- vagus nerve is the 10th cranial nerve –> provides motor supply to the muscles of swallow and speech
- also supplies parasympathetic fibres to all organs except the adrenal glands
- also supplies sensory fibres to the ear, throat, heart, lungs, abdomen, and taste
- one of the main branches is the recurrent laryngeal nerve which supplies all the muscles of the larynx
Facial nerve
- Facial nerve (7th cranial nerve) –> supplies all the muscles of facial expression
- 5 terminal branches –> temporal branch, zygomatic branch, buccal branch, marginal mandibular branch, and the cervical branch
Phrenic nerve?
- at risk during neck surgery
Accessory nerve
- 11th cranial nerve
- motor supply to sternocleidomasteoid and trapezius
- at risk during lymph node excision or neck dissection
Hypoglossal nerve
- 12th cranial nerve
- motor supply for all ipsilateral muscles of the tongue (except the palatoglossus muscle)
Cervical sympathetic trunk
- paired nerve bundle from skull to coccyx
- in neck embedded in posterior wall carotid sheath on prevertebral fascia
- 3 ganglia –> Superior (C2, C3), Middle (C6), and Inferior (1st rib)
- Injury can cause Horner’s syndrome –> ptosis, miosis, and anhidrosis
Thyroid –> arterial blood supply (2) + veins (3)
Arterial supply:
- superior thyroid artery (branch of external carotid artery)
- inferior thyroid artery (branch of thryocervical trunk)
.
Veins:
- Superior thyroid vein
- Middle thyroid vein
- Inferior thyroid vein
History for neck lump
Examination of neck lump
Thyroid examination video
https://www.youtube.com/watch?v=exGgjm55Stw
Why give a glass of water for the pt to swallow during a thyroid examination?
- a thyroid swelling will move up and down on swallowing because the thyroid gland is attached posteriorly to the cricoid and thyroid cartilages by a layer of pre-tracheal fascia called Berry’s ligament
(Note: lymph nodes do not move on swallowing)
Thyroglossal cyst
- most common congenital cyst in neck
- moves up and down on swallowing and tongue protrusion
- can be managed conservatively
Brachial cyst
- typically present with swelling arising deep to upper 1/3 of SCM
- may be infected at initial presentation with erythema/pain/temp.
- Investigate with USS fine needle aspiration and MRI to exclude a deep tract/sinus
- treatment with surgery as they may become recurrently infected
Carotid body tumour (paraganglioma)
- rare
- pulsatille lateral neck swelling at bifurcation of common carotid artery (possible bruit on auscultation)
- typically benign but some are malignant with metastases
- treatment with surgery or radiotherapy
Lyre’s sign
- splaying of the external and internal and external carotid arteries
Schwannomas
Salivary gland tumours
Recurrent salivary gland swellings
Parotid gland swelling
80% of tumours are within parotid gland
Alarming symptoms of a neck/facial lump suggesting malignancy
- Painful mass
- Rapidly increasing mass
- VII nerve weakness
- Lymph nodes
- Paraesthesia
- Trismus
Parotid SCC
Bilateral parotid swelling
Thyroid lumps
Aetiology of thyroid lumps
Alarm bells for thyroid cancer
- Family hx of thyroid cancer
- Hx of exposure to radiaiton
- <20 yrs or >70 yrs
- Male
- Lymph nodes palpable
- Vocal cord palsy
Investigations for thyroid nodules
- TFTs
- Thyroid USS +/- FNA (fine needle aspiration)
When to treat thyroid nodules
- C –> Cosmesis
- C –> Compression
- C –> Cancer
- C –> fear of ‘Cancer’
Sebaceous cyst
Lipoma
Lymphangioma
Main investigation for lymph nodes
USS FNA
- if lymphoma suspected –> USS core biopsy will diagnose and subtype
Reactive lymph nodes
lymph node abscess
Lymph node –> Atypical mycobacteria
TB neck
Other infected lymph node causes
Neck lumps –> Sarcoidosis
How many cranial nerves are there + functions
12 paired cranial nerves (PNS)
- Sensory (general or special)
- Motor
- Parasympathetic
12 cranial nerves names
How do lesions affecting cranial nerves (CN) present?
Most of the time will present with ipsilateral effects –> some may present with contralateral however
- generally cranial nerves do not decussate (cross-over)
What type of nerve fibres carry motor information from the CNS?
- efferent fibres
What type of nerve fibres carry sensory information from the internal and external environment (general and special senses)?
- afferent fibres
- General senses –> pain, pressure, touch, temperature, proprioception
- Special senses –> all carried in cranial nerves –> olfaction, vision, taste and hearing. and vestibular function
Cranial nerves can be organised on the basis of the functional components of each nerve:
1) General Somatic Afferent (GSA)
2) General Visceral Afferent (GVA)
3) General Visceral Efferent (GVE)
4) General Somatic Efferent (GSE)
All modalities of conscious sensation pass through a sequence of ______ neurones from peripheral receptor via the _______ to perception of sensation in the cerebral _______.
Except _____ projections which only consists of ___ neurones between receptor and cerebral cortex and does not primarily project via the _____.
All modalities of conscious sensation pass through a sequence of three neurones from peripheral receptor via the thalamus to perception of sensation in the cerebral cortex.
Except olfactory projections which only consists of two neurones between receptor and cerebral cortex and does not primarily project via the thalamus.
Parasympathetic and sympathetic efferent fibres pass through a sequence of _____ neurones between CNS and innervated structure.
Parasympathetic and sympathetic efferent fibres pass through a sequence of two neurones between CNS and innervated structure.
Where are cell bodies of first order neurone (preganglionic neurone) located?
brain or brainstem
Where are cell bodies of the second order neurone (postganglionic neurone) located?
in the periphery in an autonomic ganglion
What does the brainstem consist of?
- Mid-brain
- Ponjs
- Medulla Oblongata
Where do CN exit brainstem?
- CN III, IV –> Mid-brain
- CN V –> Pons
- CN VI, VII, VIII –> Ponto-medullary junction
- CN IX, X, XI (Cranial part), XII –> Medulla Oblongata
- CN XI (spinal part) –> C1 - 5
Which cranial nerves are from nuclei components of the forebrain and which are from cranial nerve nuclei in the brainstem?
- CN I and II are from nuclei components of the forebrain
- CN III-XII are from cranial nerve nuclei in the brainstem
Functions of the midbrain, pons, and medulla oblongata
Are sensory nerve nuclei usually located medially or laterally in the brainstem?
Laterally
- motor nuclei tend to be located more medially
Olfactory Nerve (CN I) –> function
Purely sensory – olfaction (smell)
What muscle does the trochlear nerve (CN IV) innervate?
Superior oblique muscle
What muscle does the abducens nerve (CN VI) innervate)?
Lateral rectus muscle
What are the 3 sensory divisions of the trigeminal nerve + which division do motor fibres only travel in?
- Ophthalmic
- Maxillary
- Mandibular –> motor fibres travel in the mandibular divison only
Vestibulocochlear Nerve (VIII) –> function
- Vestibular –> carries info regarding position and movement of head
- Cochlear –> carries auditory info
Glossopharyngeal Nerve (CN IX) –> what sensory area is supplied + which muscle is innervated by the motor component?
- Taste from posterior 1/3 of tongue
- Motor component arises from nucleus ambiguous –> innervates one muscle –> stylopharyngeus
Are the Accessory nerve (CN XI) and Hypoglossal nerve (XII) purely sensory or purely motor?
Purely motor
Motor functions of cranial nerves
Sensory functions of cranial nerves
Extradural haematoma
- ‘lemon-shaped’, more localised than subdural haematoma
- located between skull vault and dural layer
Subdural haematoma
- ‘banana shape’
Subarachnoid haemorrhage