a natomy and physiology of the l arynx february 3, 2014
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ANATOMY AND PHYSIOLOGY OF THE LARYNXFebruary 3, 2014
WHY DO WE NEED TO KNOW THE ANATOMY AND PHYSIOLOGY OF THE LARYNX
A solid understanding of normal structure and function of the larynx basis for Evaluating larynx and phonatory function Impact of specific pathologies Interpretation of evaluation findings Development of appropriate voice treatment
plans
LARYNX
Larynx (http://www.youtube.com/watch?v=Or5vGSLvoiE&feature=fvsr), (http://www.youtube.com/watch?v=DfN5J0-WbzM&feature=relmfu) http://www.youtube.com/watch?v=jlgUbA2ozNY
http://www.youtube.com/watch?v=TiCgex4dBH4
LARYNX
Cartilaginous tube Connects to the respiratory system (trachea and lungs)
inferiorly Superiorly to the vocal tract and oral cavity Position important because of its relationship and
integration between three subsystems Pulmonary power house Laryngeal valve Supraglottic vocal tract resonator
Lungs are the power supply for aerodynamic (subglottic tracheal) pressure that blows vocal cords apart – sets them into vibration
Vocal cords oscillate in a series of compressions and rarefactions
Modulate the subglottic pressure or transglottal pressure of short pulses of sound energy to produce human voice
LARYNGEAL VALVE Complex arrangement of muscles, mucous
membrane, and connective tissue Soft tissues responsible for airway
preservation Cartilage serves as a protective shield Muscles and cartilages create three levels of
folds or sphincters for communication and vegetative body functionsEpiglottis folds posteriorly and inferiorly
over the laryngeal vestibule – separates the pharynx from the larynx – first line of defense for preserving the airway
LARYNGEAL VALVE
Second sphincter is formed by the ventricular folds (not active during phonation) become active during hyper function or effortful speech production and extreme vegetative closureCause increase in intra-thoracic pressure by blocking outflow of air from lungs
Tight compression with rapid contraction of the thoracic muscles during sneezing and coughing
Longer durations to stabilize the thorax during physical tasks (e.g., lifting, childbirth, defecation, etc.)
LARYNGEAL VALVE
Third and final layer is the true vocal cords Vibration for speech productionClose tightly for non-speech and vegetative tasks such as coughing, throat clearing and grunting
Angles of closure are multidimensional Horizontal (lateral to medial)Vertical
STRUCTURAL SUPPORT FOR THE LARYNX
Larynx is suspended from a single bone – hyoid or superior border
Six laryngeal cartilages Three unpaired (epiglottis, thyroid and cricoid) Three paired (arytenoid, corniculate, cuneiform)
Hyoid bone articulates with the superior cornu of the thyroid cartilage via the thyrohyoid membrane
Epiglottis cartilage – leaf shaped- attached to the inner portion of the anterior rim of the thyroid cartilage
Made up of elastic cartilage - does not ossify or harden with age – remains flexible to allow a pliable free edge to assist in closing airway and diverting foods and liquids towards the esophagus
STRUCTURAL SUPPORT FOR THE LARYNX Thyroid cartilage – three sided, saddle shaped curve Anterior attachment of the true vocal cords at the
internal rim of the anterior curve Posteriorly are two cornu or horns that extend
upward to articulate with the hyoid bone and inferiorly to articulate with cricoid cartilage
Made up of hyaline cartilage that ossifies – limits flexibility with age
Lateral walls form quadrilateral plates or laminae – meet in the midline in a thyroid notch or prominence
In newborns, the laminae form a curve of 130 degrees – angle becomes more acute with age
A fully matured thyroid cartilage is 90 degrees in males (Adam’s apple) and 110 degrees in females
STRUCTURAL SUPPORT FOR THE LARYNX Cricoid cartilage – hyaline cartilage – below the thyroid Signet ring shaped – narrow anterior curve and broad
posterior back Two sets of paired facets (flat surfaces) that articulate with
adjacent thyroid and arytenoid cartilages The cricothyroid joint connects the lateral edges of the
cricoid to the inferior cornu of the thyroid Cricothyroid joints are positioned on the top of the
posterior cricoid rim Both joints are lined with a synovial membrane (or
connective tissue cushion for the joint, supplies secretions for lubrication, blood supply, adipose cells and lymph tissue)
Do not display age related deterioration and gender differences
Inferior to the cricoid cartilage are the tracheal rings
STRUCTURAL SUPPORT FOR THE LARYNX Arytenoid cartilages are pyramidal in shape Four surfaces – anterior, lateral, medial and a base Anterior angle projects forward at the base forming the
vocal process Hyaline cartilage except for vocal process which is made
up of elastin Vocal process is the cartilaginous portion of the vocal
folds Lateral arytenoid angle is the muscular process – intrinsic
muscles for abducting and adducting the vocal folds Medial angle faces its arytenoid pair forms an even
surface for midline glottic closure Base is concave to allow smooth articulation with the
humped (convex) surface of the posterior cricoid cartilage (half cylinder over a bar)
STRUCTURAL SUPPORT FOR THE LARYNX
Cricoarytenoid joint – two basic motions Rocks anteriorly and posteriorly over the cricoid
surface It also slides laterally Causes adduction, abduction and stabilizes the
vocal folds Vocal process tips can be pulled medially or
laterally to determine the size and shape of the glottis
Tips directed medially causes the vocal folds to meet in midline and close or adduct
When the vocal process tips are pointed laterally the vocal folds are drawn open and abduction occurs
STRUCTURAL SUPPORT FOR THE LARYNX
Corniculate cartilages (cartilages of Santorini) are attached by a synovial joint to the superior tip of the arytenoids
The cuneiform cartilages (cartilages of Wrisberg) are embedded in the muscular complex superior to the corniculates
Hyaline cartilages Add structure and stability to preserve the
airway
EXTRINSIC AND INTRINSIC MUSCLES Extrinsic laryngeal muscles - attached to a site on the
larynx and an external point (hyoid bone, sternum, mandible or skull base)
Major function – to change the height and tension as a gross unit (swallowing, lifting, phonating and other vegetative acts)
Also alter the shape and filtering characteristic of the supraglottic vocal tract – modifies vocal pitch, loudness and quality
Intrinsic muscles – both ends attached within the larynx Primary function – alter shape and configuration of the glottis
to modify the position, tension and edge of the vocal folds Adduction (closing), abduction (opening) and modifying vocal
fold length, tension and thickness Both sets of muscles also help with ventilation, airway
protection, communication and laryngeal valving
EXTRINSIC LARYNGEAL MUSCLES Suprahyoid (above the hyoid bone) and infrahyoid (below the
hyoid bone) Identified based on their names which describe their anatomical
attachments Knowing the attachments one can predict the effect of the
individual muscle contraction (shortening) between the sites Stylohyoid (styloid process of the temporal bone to the hyoid bone) -
raises the hyoid bone posteriorly Mylohyoid (mandible to the hyoid bone) – raises the hyoid bone
anteriorly Digastric anterior belly (mandible to the hyoid) – raises the hyoid bone
anteriorly Digastric posterior belly (mastoid process of the temporal bone to the
hyoid) – raises the hyoid bone posteriorly Geniohyoid (mandible to the hyoid) – raises the hyoid bone anteriorly
Raises the larynx during swallowing to protect airway Laryngeal elevation during phonation is a sign of excessive
extrinsic laryngeal muscle tension and a sign of hyperfunctional voice use
EXTRINSIC MUSCLES OF THE LARYNX
Infrahyoid muscles Sternohyoid (sternum to hyoid bone) – lowers the
hyoid bone Sternothyroid (sternum to thyroid cartilage) –
lowers the thyroid cartilage Omohyoid (scapula to the hyoid cartilage) –
lowers the hyoid bone Thyrohyoid (thyroid cartilage to the hyoid bone)
– shortens the distance between the thyroid and hyoid bone
Sternocleidomastoid (forms a sheath between the mastoid process and the sternum)
Lower the larynx in the neck
EXTRINSIC LARYNGEAL MUSCLES
INTRINSIC LARYNGEAL MUSCLES
5 intrinsic muscles attaches to cartilages to modify the cricothyroid and cricoarytenoid joint relationships Affect the position, length and tension of the
vocal folds Changing the position of the cartilage framework
that house the vocal folds Altering the shape and configuration of the
glottis, the opening between the vocal folds
INTRINSIC LARYNGEAL MUSCLES
Cricothyroid – broad, fan-shaped muscle – inferiorly to the cricoid cartilage and superiorly to the thyroid cartilage – decreases the distance between the two cartilages – lengthening the vocal cords Pars recta (vertical belly) Pars oblique (angled belly)
Reduces the vibrating mass of the vocal folds by increasing the longitudinal tension, limits the vibrations to the thinnest portion of the vocal fold located at the medial edge
Greatest contributor to the fundamental frequency control – higher tones
INTRINSIC LARYNGEAL MUSCLES
INTRINSIC LARYNGEAL MUSCLES Thyroarytenoid – attached anteriorly to the internal
angle of the thyroid cartilage and posteriorly to the vocal process of the arytenoid
Two compartments Thyromuscularis lateral component – adduction of the vocal
cords – fast acting muscle fibers Thyrovocalis (vocalis) medial component – greater control
over phonation – slow acting muscle fibers Body of the vocal fold – contraction shortens the fold
length by pulling the arytenoid cartilages anteriorly and thickens the vocal cords by increasing the mass of the vibrating medial edge
Lowers the fundamental frequency, increases loudness and tightens the glottic closure
Control over the vocal fold shape and edge and glottic closure patterns
INTRINSIC LARYNGEAL MUSCLES
INTRINSIC LARYNGEAL MUSCLES Lateral cricoarytenoid muscle – broad fan-shaped
muscle – lateral side of the cricoid to the arytenoid muscular process Rocks the arytenoids anteriorly and slides them laterally Redirects the vocal process medially brings the
membranous vocal folds to midline or adduction Strongest vocal fold adductors
Interarytenoid muscles – two bellies Transverse portion (only unpaired intrinsic laryngeal
muscle) attaches to the posterior plane of each arytenoid Oblique portion (crossed bellies) attached at a 45 degree
angle from the inferior border of one arytenoid to the superior border of its contralateral pair
Shortens the distance between the arytenoid cartilages causing adduction – forceful closure of the posterior glottis
INTRINSIC LARYNGEAL MUSCLES
Posterior cricoarytenoid – sole abductor of the vocal folds
Posterior lamina of the cricoid and the muscular (lateral) arytenoid cartilage
Contraction causes abduction (opens) the vocal folds
When the arytenoids rock posteriorly to redirect the vocal processes laterally and separate the membranous portions of the vocal folds
Abducts for respiration and quick glottal opening gestures during unvoiced sound productions
INTRINSIC LARYNGEAL MUSCLES
INTRINSIC LARYNGEAL MUSCLES
Exceptional rules All muscles are paired (right with a left) except
for the transverse interarytenoid which functions as one unit, bringing the arytenoid cartilages together
All intrinsic muscles server as adductors except for posterior cricoidarytenoid muscles or the sole abductor
All muscles are innervated by the recurrent laryngeal nerve except the cricothyroid which is innervated by the external branch of the superior laryngeal nerve
INTRINSIC LARYNGEAL MUSCLES
VOCAL CORD MICROSTRUCTURE
Membranous portion of the vocal folds – 5 histologically discrete layers – vary in composition and mechanical properties
Membrane oscillates to create sound Integrity of the vibration pattern for
phonation relies on the pliable elastic structure
Different layers provide variable amounts of flexibility and stability
VOCAL CORD MICROSTRUCTURE
5 layers are epithelium, 3 layers of the lamina propria (superficial, intermediate and deep) layers, and the vocalis muscleEpithelium – mucosal covering of
stratified squamous cells that wraps over the internal contents, thinnest layer, consists of 6-8 cell layers, described as a pliable capsule – needs a thin layer of slippery mucous lubrication to oscillate
VOCAL CORD MICROSTRUCTURE Next 3 layers form the lamina propria
Loose extracellular tissue (extracellular matrix) composed of lipids, carbohydrates and specialized proteins
The lamina is slightly more dense than the epithelium but still flexible and loose
Superficial layer or Reinke’s space is a gelatinlike soft, slippery substance which allows it to vibrate significantly during phonation which is violated by vocal cord pathology, forceful abduction
Intermediate layer is composed principally of elastic fibers which can stretch to twice its length
VOCAL CORD MICROSTRUCTURE
Deep layer of the lamina propria is still denser and composed of collagen fibers
Tissues of the third and fourth layers form the vocal ligament-not present in the new born – appears between 1-4 years and continues to develop until maturity at puberty
Deep layer is interspersed by muscle fibers to join vocalis muscle and the deep layers together
VOCAL CORD MICROSTRUCTURE
The fifth layer or the vocalis muscle forms main body of the vocal fold Provides tonicity, stability and massIt is the only true “active” tissue and is the only portion of the vocal cord that can contract and relax in response to neurologic control
The lamina propria and epithelium layers vibrate passively in response to aerodynamic breath support
VOCAL CORD MICROSTRUCTURE
Extracellular matrix of the lamina propriaComposed of fibrous proteins,
interstitial proteins, carbohydrates and lipids
Fibrous proteins consists of elastin and collagen found in different concentration in different layers of the lamina and contributes to the vibratory properties of the vocal fold cover
VOCAL CORD MICROSTRUCTURE
Elastin fibers predominate in the superficial and intermediate layers, collagen in the deep layer
Elastin lets the layers stretch and then return to its original shape
Collagen does not stretch easily but tolerates stress but offers strength to the extracellular matrix
VOCAL CORD MICROSTRUCTURE
Interstitial proteins Consists of proteoglycens and glycoproteins
Role in vocal cord vibration is related to control of tissue viscosity, layer thickness and internal fluid content
Hyaluronic acid appears in greater concentration in the intermediate layer
Attracts water to form large, space filling molecules that creates a gel – acts as a cushion and resists compressive and shearing forces during vibration
VOCAL CORD MICROSTRUCTURE
Also protects cells from deterioration, assists in tissue repair and clotting
Exceeds in males to females (3:1) Glycoproteins, lipids and
carbohydrates Consists of fibronectin found in normal and injured vocal cords – plays a role in wound healing
VOCAL CORD MICROSTRUCTURE
Body cover theory of vocal fold vibration (Hirano)Three vibratory divisions
Cover (epithelium and superficial layer of the lamina propria)
Transition (intermediate and deep layer of the lamina propria)
Body (vocalis muscle)
VOCAL CORD MICROSTRUCTURE
The vibrating cover forms the compliant, fluid oscillation seen in the vocal vibratory patterns while the body provides stiffer underlying stability of the vocal fold mass and tonus
The transition serves as coupling between the superficial mucosa and the deep muscle tissue of the vocal folds during vibration
Undulation or oscillation of the superficial vocal fold layers creates a ripple of tissue deformation and recoil
VOCAL CORD MICROSTRUCTURE
Three vibratory phases of wave motion seen in endoscopyHorizontal (medial to lateral movements) as seen in the open and closing patterns of vibration – 1-2 mm
Longitudinal (anterior and posterior – zipperlike wave) seen in front-to-back travelling wave 3-5 mm
Vertical phase (inferior to superior opening and closing of the vocal folds) as seen in an upper versus lower lip differences – mostly unseen
FOLDS AND CAVITIES OF THE LARYNX
Major folds are true vocal folds Superior and lateral to the true folds are the
false or ventricular folds Do not actually vibrate in normal voice
production except at very low fundamental frequency (below 50 Hz)
Few muscle fibers – very difficult to regulate their tension, mass and length
Aryepiglottic folds form a sphincter enclosing the entrance to the larynx
During swallowing and protective acts these folds contract to reduce the diameter of the laryngeal entrance to protect the airway
FOLDS AND CAVITIES OF THE LARYNX
Supraglottal cavity Lies above the vocal folds Superior border is the aryepiglottic sphincter Acts as a resonator of the sound produced by the
vocal cords Subglottal cavity
Lies beneath the vocal folds Lower boundary is the first tracheal ring Pressure increases beneath the closed vocal
folds until it becomes sufficient to force the folds open and begin phonation
FOLDS AND CAVITIES OF THE LARYNX
Ventricles Paired cavities lying above and
slightly lateral to the true vocal cords
Opening is very small and little effect on the sound produced
However in some conditions of singing the opening is sufficient to permit meaningful resonance adding to the glottal tone
DEVELOPMENTAL CHANGES
Newborns the larynx is situated high in the neck – cricoid positioned at the level of C3 to C4
Newborns breathe only through nasal passages in the first few months of life allowing them to breathe and swallow simultaneously
During the first year the larynx begins its descent in the neck as the pharynx lengthens and widens
By puberty the larynx is at the level of C6 or C7 Accompanied by skeletal facial growth and
development, creates an expanded vocal tract which contributes a drop in fundamental frequency
DEVELOPMENTAL CHANGES Intrinsic larynx also undergoes dramatic changes from
birth through puberty Vocal fold length of boys and girls is similar until 10
years Gradual and consistent gender development changes
vocal cord length and ratio between membranous to cartilaginous portions of the vocal cords
In males with the rise in testosterone at puberty stimulates the anterior growth of the thyroid notch and wide growth of the pharynx
In newborns have no vocal ligament (intermediate and deep layers of the lamina propria) and therefore little stability, the greater ratio of cartilage to membrane length provides protection of the airway (vocal ligament emerges between 1-4 years)
DEVELOPMENTAL CHANGES
GERIATRIC VOCAL FOLD
Deterioration in voice quality, pitch and loudness range and endurance among geriatric speakers
Common appearance of thinned (bowed) vocal folds in elderly patients with no other pathology except advanced chronological age
Described by the term “presbylaryngeus” Intermediate layer of the geriatric vocal folds
was observed to be looser and thinner causing loss of tissue bulk, resulting in bowed appearance
Studies confirm that the lamina propria decreases in flexibility and elasticity with age due to increased cross-linking of fibers
PHYSIOLOGY OF PHONATION Theory of vibration
Based on physical process of flow-induced oscillation A consistent stream of air flows past the tissues creating a
repeated pattern of opening and closing Van den Berg’s aerodynamic myoelastic theory
At the onset of phonation, subglottal pressure rises as expiratory forces are met by resistance from the adducted vocal folds
When the pressure rises to overcome the resistance the folds are blown and subglottal pressure diminishes creating an increase in flow through the glottis
Because air pressure and flow are inversely proportional, when flow increases, air pressure decreases between the vocal folds (Bernoulli Principle)
The elastic tissue recoil pulls the vocal cords back toward midline completing the cycle of vibration
PHYSIOLOGY OF PHONATION Self oscillating system by Titze
Respiration is the driving force that sets the vocal folds in motion and kept in motion as follows: In the subglottal region the leading edge of the
vocal folds are blown apart and set into motion by subglottic pressure and translaryngeal (glottal flow) is positive
Intraglottal space or the small space directly between the vocal folds – intraglottal pressure keeps the vocal folds oscillating by alternating exchange of airflow and pressure peaks – when the vocal cords close the pressure is negative but rises as the air flow is cut off by the closing glottis
PHYSIOLOGY OF PHONATION
Supraglottal air column located at the outlet of the glottis immediately above the vocal folds – air molecules are compressed or rarified in a delayed response to the alternate pressure and flow puffs modulated by the vibrating vocal folds (molecules are pushed and released in response to the sound energy pulses released from the oscillating vocal folds) causing transfer of energy from the fluid or air pressure to the tissue or upper lip of the vocal folds and assists in sustaining the oscillation
MECHANISM OF VOCAL FREQUENCY CHANGE
The physical properties that determine the frequency of a vibrating string also determine the vibrating frequency of the vocal cords
Determined by length, tension and mass Total mass is not important but the mass
vibrating is more important Amount of mass set into vibration depends
upon fundamental frequency, intensity and mode of vibration and length of the vocal cord
As the band is stretched, the thickness of the band decreases
VOCAL FOLD LENGTH AND FUNDAMENTAL FREQUENCY Three voice register with respect to pitch
Pulse register or glottal fry Modal register Falsetto
In the pulse register vocal folds are closed 90% of the cycle (60Hz)
In the modal register, as the vocal length increases, frequency increases
Vocal cords are closed 50% of the time In the falsetto or upper register the fundamental frequency
appears to decrease as vocal fold length is increased Opposite to that predicted by that of a vibrating string The vocal cords also do not seem to adduct completely
during phonation Length is not the sole mechanism of fundamental
frequency
VOCAL FOLD TENSION AND FUNDAMENTAL FREQUENCY As tension increases the frequency increases (similar to
that of a string) Difficult to measure tension Indirect evidence must be obtained Largest variations occur in the upper frequencies or in
the falsetto register Very little variation in the frequencies heard in speech Tension is not the only determinant but mass per unit
length has a pronounced influence on the fundamental frequency of vibration
In the modal register the mass is an important factor however, in the falsetto register, tension is a determinant factor
Mass per unit length more important than just tension or mass
VOCAL FOLD MASS AND FUNDAMENTAL FREQUENCY
Vocal frequency decreases as mass increases (similarly to the vibrating string)
FREQUENCY AND AIR FLOW
Airflow is another contributing factor – sign of an inefficient system
The speed of the airflow also causes variations in frequencies in voice production
However excessive airflow makes the system inefficient resulting in breathiness
All three factors important in voice production Mass Tension Air flow
MECHANISM OF LOUDNESS CHANGE
Wide range of vocal intensities (exceeding 60 dB) Additional changes of intensity result from
variation in the size and shape of the vocal tract which acts as a resonator
Combination of airflows and pressure Increased pressures below the vocal folds when
released by the folds would produce a greater intensity
Controlling mechanism of vocal intensity is not subglottal air pressure rather it is degree and time of closure of the vocal folds
Maintaining closure of the vocal folds there is more time to build up pressure beneath them
MECHANISM OF LOUDNESS CHANGE More intense sound results when the subglottal air
pressure is sufficient to overcome the resistance of the vocal folds
The more vocal fold resistance there is to opening the greater the pressure disturbance when the resistance is overcome and folds are forced to open
Intensity is often controlled by the vocal folds through variation of glottal resistance (which is ratio of the pressure divided by the airflow)
Glottal resistance is a major controlling factor in the lower frequencies
At higher frequencies (in the falsetto range) airflow becomes a major variable
Very little variation of intensity in the falsetto range
MECHANISM OF LOUDNESS CHANGE
Intensity is also dependent upon velocity of closure of the vocal folds
Glottal power is directly related to the rate of change of the airflow pulse at the moment of the closure
This rate of change of airflow is called airflow closing slope (page 395)
Steeper the slope the greater the increase in frequency
Intensity control therefore depends upon two factors – glottal resistance and rate of airflow change at the moment of closure
MECHANISM OF LOUDNESS CHANGE
In an attempt to speak at a normal vocal intensity, patients increase air pressure by increasing the expiratory force from the thorax-abdomen system
The patient may attempt to increase glottal closure in an effort to increase glottal resistance and to maintain an adequate level of tension in the vocal folds
These increase in muscle activity causes vocal fatigue as well as excessive air rushing across the vocal folds (causing an increase in noise levels)
Vicious cycle ensues, vocal fatigue results in poorer vocal fold adduction and the greater need for even greater effort on the patient’s part leading to poorer voice
MECHANISMS OF LOUDNESS CHANGE
Variation of the frequency composition of a tone also varies its intensity
Adding frequencies or varying the amplitude of the components of the tone affects the intensity of the complex tone
Spectrum of the vocal folds can be varied (within limits) and thus alter the overall intensity of the vocal fold tone
Speed of closure affects the spectral features of the glottal tone
Number of frequency components in the pathological voice is smaller than in the normal voice
MECHANISMS OF LOUDNESS CHANGE
Lower intensities are used to compensate for the different spectral characteristics and their effect on intensity
A patient may also try to increase subglottal pressues or adductory forces – results in an increase in strain and abuse to the vocal folds
Loudness is the perceptual correlate of intensity but intensity is not the only factor that affects loudness Pitch of the voice and its spectral composition also
affects perceived loudness Other factors include distance from the speaker,
room acoustics, interference at may affect the loudness of a voice as perceived by a listener
MECHANISM OF QUALITY VARIATION Identifies an individual and sets him or her apart
from another Spectrum determines voice quality It refers to number and amplitude of the frequencies
present in a complex tone (vocal fold tone) Vocal fold produces many different vocal qualities
each with its own spectral characteristics Shape and configuration of the vocal tract (length,
cross-sectional area, ratio of oral to pharyngeal cavity size, etc.) determine the voice quality
Physiological changes in laryngeal and vocal tract configuration produce different voice qualities
Change in voice quality can signal benign or a life threatening condition
NEUROANATOMY OF THE VOCAL MECHANISM
Volitional control rests in the brain Many points in the cortex, subcortical areas,
midbrain, and medulla play an important role in the ultimate control of phonation
Cerebral cortex responsible for conceptualization, planning and execution of speech act including phonation
3 major areas of cortex responsible for vocalization Precentral and postcentral gyrus (Rolandic area) Anterior (Broca’s) area Supplementary motor area
NEUROANATOMY OF THE VOCAL MECHANISM
Speech can be initiated, stopped, slurred or distorted
Result of stimulation in the dominant or non-dominant hemisphere
Control of the motor acts occur in the cortex, individual muscle control occurs at a much lower level
NEUROANATOMY OF THE VOCAL MECHANISM
Subcortical mechanismsMotor cortex has numerous
connections to the thalamus, metathalamus, hypothalamus, epithalamus, and subthalamus
Thalamus has numerous connections to the cerebellum and midbrain
Ventral lateral nucleus of the thalamus was responsible for initiating speech movements, control of loudness, pitch, rate and articulation
NEUROANATOMY OF THE VOCAL MECHANISM
Thalamus acts as not only a relay station but is also involved in maintenance of consciousness, alertness, attention and integration of emotion into the speech act
Thalamus also integrates sensory information, coordinating outgoing information from the cortex and other areas of the brain and adding the emotionality to speech and voice
NEUROANATOMY OF THE VOCAL MECHANISM
Midbrain structures Structures that connect the cerebrum with the
brainstem and spinal cord Four rounded areas called colliculi on the
posterior surface Superior colliculi assoicated with vision Inferior colliculi concerned with audition Stimulation of the cavity or cerebral aqueduct of
Sylvius and grey matter dorsal to the aqueduct or periaqueductal gray (PAG) produces activity in the laryngeal muscles
Lesions in this area also causes mutism Control muscles of respiration, vocalization and
orofacial region
NEUROANATOMY OF THE VOCAL MECHANISM
Brainstem Nucleus ambiguus, nucleus tractus solitarii,
reticular formation have connections to the motor roots of the vagus and the PAG area
Neurons in this area responsible for control of respiration
Cerebellum Control and planning stages of a movement Without this control the cerebral cortex could not
function and would be ineffective Acts to regulate motor movement continuously
and regularly Coordinates muscles of the larynx
PERIPHERAL CONNECTIONS: THE VAGUS NERVE
Vagus provides sensory and motor fibers Start in the caudal portions of the nucleus
ambiguus Vagus emerges from the surface of the
medulla between the cerebellar penduncle and the inferior olives in the midbrain and exist the skull through the jugular foramen
After exiting the skull, the vagus divides into many branches that serves the head, neck, thorax and abdomen
PERIPHERAL CONNECTIONS: THE VAGUS NERVE
After exiting a small filament or the meningeal filament exits the nerve to serve the Dura mater on the posterior fossa of the base of the skull
The auricular branch provides sensory fibers to the skin behind the pina and to the posterior par of the external auditory meatus
The pharyngeal branch provides motor fibers to the muscles of the pharynx and the soft palate
PERIPHERAL CONNECTIONS: THE VAGUS NERVE
The major portions of the vagus serving the larynx are the superior laryngeal and recurrent laryngeal nerves
Superior laryngeal – primary sensory nerve – arises from the inferior ganglion of the vagus and descends along the side of the pharynx behind the internal carotid artery where it sends off two branches
The external branch descends along the side of the larynx to serve the cricothyroid muscle
The internal branch descends to an opening in the thyrohyoid membrane and enters the larynx to serve the mucous membrane of the larynx down to the true vocal folds, big SENSORY
PERIPHERAL CONNECTIONS: THE VAGUS NERVE
The recurrent laryngeal nerve follows a different course on either side of the body
On the right side the recurrent descends in the neck to loop around the subclavian artery (just below the clavicle) and then ascends alongside the trachea to serve the remaining intrinsic muscles of the larynx
On the left side the recurrent laryngeal nerve takes a more circuitous route
Descends into the thorax, loops around the aorta and then ascends alongside the trachea until it reaches the larynx
It provides motor fibers to the remaining intrinsic laryngeal muscles
PERIPHERAL CONNECTIONS
The extrinsic muscles of the larynx are innervated by several nerves Anterior belly of the digastric – mylohoid branch
of the inferior alveolar nerve Posterior belly of the digastric – 7th cranial nerve
(facial) Mylohyoid muscle – mylohyoid branch of the
inferior alveolar nerve Geniohyoid, sternohyoid, sternothyroid, and
omohyoid by the ansa cerivcalis
PERIPHERAL CONNECTIONS
Protective reflexes of the larynx used to protect the airway and sustain life Sensory endings collect information from larynx
and respiratory system Transmit this information through reflexes arcs
and directly to the CNS Responds to changes in mechanical forces and
air pressure Send information to the CNS as well as to the
joints of cartilages that discharge Affect the electrical activity of some intrinsic
laryngeal muscles Stretch receptors in the muscles also discharge
when the muscle is stretched or contracts
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