larynx Flashcards
what is the larynx commonly known as and why
voice box
- structure that makes the fundamental sounds of speech
how does the larynx play a key role in phonation
- by pressing together the right and left vocal cords as air is forced between them
- resulting vibration of the cords induces vibrations in the air that we ultimately detect as sound
what is important to note about the phonation produced by the larynx
- key role but NOT the only role
- only generates the basic sounds (fundamental vibrations = greatly modified before emerging as spoken words ie by the tongue, palate, lips, teeth, nasal cavity)
what is the other role of the larynx
protects deeper parts of airways (trachea and its branches) from inhaling solid materials
how does the larynx protect the deeper parts
- vocal chords play a role in it (probably why they originally evolved)
- the EPIGLOTTIS = 1st + most important line of protection - flap which covers entrance to the airways when we swallow food
how is the function of the larynx a mammalian response
all mammals use larynx to produce sound other animals (ie bird) use completely different structure
what is the larynx is composed of
series of
cartilages
membranes
ligaments
muscles
- has a cartilaginous skeleton connected by membranes + muscles
- muscles move the various components around
what supplies motor and sensory nerve supplies to the larynx
- branches of cranial nerve X
= vagus nerve
what structure does the larynx lay immediately anterior to
laryngopharynx (most inferior part of pharynx)
what structure is attached to
a) inferior end of the larynx (hangs from its final cartilaginous element )
b) inferior end of the pharynx
what does this result in
a) trachea
b) oesophagus
air in through mouth and nose
directed down into the larynx through the vocal cords
then down through trachea (takes air to lungs) which lies immediately anterior to part of the oesophagus which takes swallowed materials to the stomach, (oesophagus longer as needs to reach into abdomen)
where does the larynx lie
midline of anterior neck
hangs from hyoid bone
which gland wraps partially around the inferior part of larynx and upper part of trachea
thyroid
what are the two major cartilages of the larynx
- thyroid (attached to hyoid bone by thyrohyoid membrane )
- cricoid (most inferior cartilage in larynx )
what are the two important membranes of the larynx
- thyrohyoid
- cricothyroid (runs between the 2 cartilages)
what hangs from the larynx
trachea
which 5 cartilages of the larynx must we consider (not including the smaller cartilages which appear like dots / small pieces)
EPIGLOTTIC (forms core of epiglottis + attaches to inside of thyroid cartilage)
THYROID (large ‘shield’ of cartilage easily felt in neck)
ARYTENOID (2 cartilages - key functions in speech)
CRICOID (most inferior - arytenoid and thyroid cartilages articulate with it)
what is the thyroid cartilage characterised by
- largest cartilage of the larynx
- by two sheets of cartilage that join in the midline anteriorly (its laminae)
how does the thyroid cartilage form the adams apple (laryngeal prominence)
where the 2 laminae fuse there is a region which projects out anteriorly
this most anterior part forms it
why is the laryngeal prominence (adams apple) more prominent in men
bc of effects testosterone has on the larynx at puberty
it causes the throid cartilage to grow in the anterioposterior direction so it sticks out more
(also reason men’s voices tend to be lower pitched than women’s)
what other main feature exists in the thyroid cartilage
HORNS
- superior stick up
- inferior ones stick down (THESE MAKE A JOINT W THE CRICOID CARTILAGE)
what is the shape of the cricoid cartilage (2nd largest) likened to and why
reversed signet ring
its the only complete ring of cartilage in entire respiratory tree
what is the cricoid cartilage characterised by
single lamina placed posteriorly
anterior to the lamina is the arch of the cricoid cartilage
what does the cricoid cartilage articulate with and how
thyroid cartilage and both arytenoid cartilages
contains 2 facets for articulation (1 = for articulation w inferior horn of thyroid cartilage
2= for arytenoid)
what is the significance of the 2 depressions on the posterior surface of the cricoid cartilage
where the right and left posterior cricothyroid muscles originate
why are the posterior cricothyroid muscles most important ones of the larynx
only muscles we have to move vocal cords apart
if they both fail, vocal cords can snap together, making it difficult or impossible to breathe in)
how does the thyroid cartilage articulate with the cricoid cartilage
- inferior horns form right and left cricothyroid joints with facets on the posterolateral aspect of the cricoid
- thyroid cartilage can rotate / pivot around the cricothyroid joints so the cartilage thus laryngeal prominence moves up and down (movement central to determining pitch of the sound larynx produces (determines pitch of the voice)
where do the arytenoid cartilages sit
on top of cricoid (articulate with its facets to form the cricoarytenoid joints - where the arytenoids can rotate / slide closer or further apart)
what are the 3 processes of each arytenoid
1) superior (points upwards + attaches a muscle)
2) muscular (points laterally)
3) vocal (points anteriorly - attaches the posterior end of the vocal cord to arytenoid on each side)
how are the tips of the right and left vocal processes moved
what are these movements called
- when arytenoids rotate around cricothyroid joints
can be - ADDUCTED (moved closer together - towards midline of body)
- ABDUCTED (moved further apart - further away from midline)
which muscle attaches to the arytenoid from the back and rotates the arytenoids in the opposite direction to abducted the vocal cords
posterior cricoarytenoid muscle
why are rotatory and sliding movements of the arytenoids vitally important
vocal cords attach to vocal processes so rotating or sliding can
1) press the cords together (for speech)
2) open up a space between them (for breathing)
what is the epiglottic cartilage and where does it lie
flap-like cartilage
attaches to the inner surface of the thyroid cartilage by a small very elastic ligament (allows epiglottis to flap down + form a lid over entrance to larynx)
what is mainly responsible for moving the epiglottis over the opening of the larynx
the bolus of food being swallowed itself
what are the vocal cords (aka vocal folds)
key structures for generating sound in larynx
what does each vocal cord have
a core called the vocal ligament (its the thickened upper edge / superior aspect of the cricothyroid ligament/membrane)
where does the cricothroid ligament run
starts at cricoid cartilage
upwards
part inserts into thyroid cartilage
why cant we see the vocal ligament using a laryngoscope
see the vocal cords but w the soft tissue overlying them
what does rotating the arytenoid cartilages closer together or further apart also move
the vocal cords
what is the opening between the vocal cords called
the glottis
the vocal cords are
a) abducted to facilitate
d) adducted to facilitate
a) breathing
b) sound production
which muscles adduct the vocal cords and how
INTERARYTENOID MUSCLES (pull arytenoids closer together)
LATERAL CRICOARYTENOID (run between the cricoid cartilage and the muscular process of arytenoid SO When they contract, they rotate the arytenoid they’re attached to so vocal processes move closer together, thus adducting the vocal cords)
which muscle abducts the vocal cords
POSTERIOR CRICOARYTENOID (left one rotates left arytenoid anticlockwise, right one rotates right arytenoid clockwise)
where does the posterior cricoarytenoid run
arises from depressions on the posterior surface of the cricoid cartilage
run up + laterally to insert into muscular process of arytenoid cartilage
why may the posterior cricoarytenoid muscle fail
nerve injury (nerve supplying it damaged)
many types of surgery (esp to thyroid gland) that can cause this damage - some patients end up on mechanical ventilators bc nerve damage has affected both sides @ same time
what happens if 1 posterior cricoarytenoid muscle fails
- vocal cord controlled by the affected muscle becomes adducted (adductors not opposed by an abducting muscle)
- adbucting effect is lost
- adducting effect has nothing working against it so cord lies nearer the midline than usual
marked effect on patients voice (SOUND HOARSE)
what happens if BOTH posterior cricoarytenoid muscle fails
- patient in serious, potentially life-threatening situation
- cords will be pressed together by the unopposed adductor muscles
- difficult or impossible to breathe in
what determines the tone of voice
length and tension of the vocal cords (controlled by the larynx)
- shorter = pitch increase
- longer = pitch decreases
where do vocal cords attach to
inner surface of the thyroid cartilage anteriorly + vocal processes of the arytenoid cartilages posteriorly
how can length and tension of the cords be changed
- thyroid cartilage can rotate around the cricothyroid joints
- cricothyroid muscle rotates it so laryngeal prominence moves downwards (ELONGATES)
- returned to resting position by thryroarytenoid (SHORTENS)
- by rotating thyroid cartilage, these 2 muscles can change both the length and tension of the vocal cords
(part of thyroarytenoid also acts directly on adjacent cord to change its tension in a complex manner)
where does the cricothyroid muscle run
between cricoid cartilage and inserts into lower border of thyroid cartilage
where does the thryroarytenoid muscle run
between inner aspect of thyroid cartilage and anterior aspect of arytenoid cartilage
lies inside vocal cord just lateral to vocal ligament
what do the thyroarytenoid muscles do
run adjacent to the vocal cords
act on them DIRECTLY
what nerve do (all but the cricothryroid muscle) all muscles of the larynx receive their motor supply branch from
- recurrent laryngeal nerve (branch of vagus nerve - cranial nerve X)
why is the recurrent laryngeal nerve called ‘recurrent’
passes downwards well beyond its target
before turning back on itself and travelling back up to the larynx
where does the RIGHT recurrent laryngeal nerve arise and run
- given off by right vagus nerve
- quite short
- wraps around the subclavian OR brachiocephalic artery
- then comes back up into larynx
where does the LEFT recurrent laryngeal nerve arise and run (true for ALL mammals)
- left vagus nerve goes right down into the chest / thorax before giving it off
- loops round arch of aorta
- then comes coming back up alongside the trachea + behind the oesophagus to get to larynx
what is the clinical significance of the left recurrent laryngeal nerve
sits close to root of left lung
can be affected by left-sided lung cancers (interfere with action of the nerve)
presenting symptom = hoarse voice
how can surgical removal of the thyroid gland result in changes to the voice
recurrent laryngeal nerve passes v close to main artery supplying thyroid gland (inferior thyroid artery)
surgical removal can damage the nerve
results in changes to voice
sometimes right and left nerves are both damaged = ventilator
why do surgeons go into thyroid surgery “blind”
- inferior thyroid artery breaks up into a variable no of branches before entering the thyroid glands (3 or 4 - surgeon not know)
- recurrent laryngeal nerves intertwine (VARIABLY) with the branches
- arteries have to be ligated before the thyroid glands removed to prevent bleeding to death SO there risk they may also tie off the recurrent laryngeal nerve
how can nerves be moved simply by moving them around
if moved slightly too far
can stretch the fibres in it which can inhibit its function
what would happen if the surgeon tied off the right recurrent laryngeal nerve
PARALYSE all muscles of the larynx on rhs EXCEPT the cricothyroid (only one NOT supplied by recurrent laryngeal nerve)
fibres supplying which muscle are most susceptible to damage if nerve is moved
posterior cricoarytenoid muscle
fibres to other muscles less effected
what happens to the vocal cords if fibres supplying the abductor muscle are inhibited
vocal cord on the affected side of the head positioned MORE towards the midline
what happens if the surgeon damages the recurrent laryngeal nerve on BOTH sides of the neck when taking the thyroid gland out
vocal cords will adduct together
patient will struggle to breathe
mechanical ventilator
what happens when the epiglottis fails
material inhaled past it + into the larynx
becomes lodged just above the vocal cords
airway can be completely occluded and person unable to breathe if food piece large enough
why are humans more susceptible to epiglottis failure than most animals
larynx lies lower in the neck
how do dogs drink and breathe at the same time
connect their epiglottis to their soft palate
what is the 1st way to deal with choking
Heimlich manoeuvre
what is the 2nd way to deal with choking - emergency procedure to save a life
cricothyrotomy / larygotomy / cricothyroidotomy / cricothyroidostomy (all the same thing)
what is a cricothyrotomy /laryngotomy
incise the middle part of the cricothyroid membrane
insert a small tube to establish an emergency airway (ie using a biro)
why does a cricothyrotomy /laryngotomy work
the cricothyroid membrane is located below the level of the vocal cords, so the emergency airway isn’t affected by the inhaled material lying just above them
why must you be qualified to perform this
real dangers
big blood vessels just next to the larynx ie common carotid artery, internal jugular vein
could end up causing the person to bleed to death rather than choke
what is the surgical procedure for opening the airways
tracheostomy
- incision into the trachea cartilage
- inserting a port to connect a breathing tube
- tube then connected to a mechanical ventilator
- patient can be maintained on the ventilator for long periods (years)
