physiology of speech by dr anita teli

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Physiology of Speech:

Physiology of Speech Speaker: Dr Anita Teli PG Chairperson: Dr G.B.Dhanakshirur prof Date & Time : 30 th march 2011 BLDEU’s Shri B.M.Patil Medical College

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Introduction Definition Theories of language Development Mechanism of speech Applied aspect.

Cerebrum :

Cerebrum 2 cerebral hemispheres joined together by corpus callosum. Cerebral hemisphere with well developed language faculties is dominant hemisphere. Left hemisphere – dominant hemisphere (categorical hemisphere) Right hemisphere – representational hemisphere. In 96% of right handed individuals constituting 91% of the population the left hemisphere is dominant. In 4% the right hemisphere is dominant. In 15% of left handed individuals the right hemisphere is dominant. In 15% there is no clear lateralization. In remaining 70% left hemisphere is dominant

Left hemisphere :

Left hemisphere Control of muscles on rt side. Spoken language and written language. Mathematics and scientific skills. Reasoning.

Right hemisphere:

Right hemisphere Control of muscles on left sides. Musical and artistic talents. Insight Visuospatial relation . Sustained attention.

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Communication through language is a unique faculty which places the human beings much above the animals. “Language refers to that faculty of nervous system which enables the humans to understand the spoken & printed words & to express ideas in the form of speech & writing”. There are 2 aspects of communication Language input (sensory aspect) Language output (motor aspect)

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Sensory aspect of language includes visual, auditory & proprioceptive impulses. Motor aspect of language includes mechanisms concerned with expression of spoken & written language.

Wernicke’s theory of language:

Wernicke’s theory of language Wernicke put forward the theory of language which was later modified by Gestiwind . This theory was formulated on the basis of the defects in language observed in patients to lesions of different parts of cortex. According to this theory utterance arises in the Wernicke’s area & is passed on to Broca’s area via the arcuate fasciculus . After sentence is formulated in the Broca’s area, it is transferred to the motor cortex where articulation is programmed by contraction of appropriate muscles in mouth & face etc.

Development of Speech :

Development of Speech Involves coordinated activity of 3 imp areas of cerebral cortex (dominant hemisphere) namely Wernicke’s area Broca’s area Motor area

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Development of speech in a child occurs in 2 stages: First stage : There occurs association of certain words with visual, auditory, tactile & other sensations, aroused by objects in the external world which is stored in memory. Second stage : involves establishment of new neuronal circuits. When definite meaning has been attached to certain words, pathway between auditory area & motor area for muscles of articulation which helps in speech (area 44) is established. Child attempts to formulate & pronounce the words which are learnt.

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The potential for development of language specific mechanisms in the left hemisphere is present at birth. The assignment of language functions to specific brain areas is fairly flexible in the early years of life. The damage to the perisylvian area of the left hemisphere during infancy or early childhood causes temporary minor language impairment.

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But similar damage acquired during adulthood typically causes permanent, devastating language deficits. When a person has learned one language & learns new language, the area in the brain where new language is stored is partly removed from storage area of first language . Both languages are learned simultaneously- are stored together in the same area .

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Speech is of two types: Spoken speech Written speech Spoken speech involves understanding of spoken words as well as expressing the ideas in the form of spoken words. Written speech involves understanding of written words as well as expression of ideas in the form of written words.

Mechanism of Speech :

Mechanism of Speech It involves the coordinated activities of central speech apparatus & peripheral speech apparatus. Central speech apparatus consists of cortical & sub cortical centers. Peripheral speech apparatus includes Larynx, pharynx, mouth, nasal cavities, tongue & lips.

Mechanisms of speech :

Mechanisms of speech Understanding of speech (sensory aspect) Expression of speech (motor aspect)

Understanding of speech :

Understanding of speech Mechanisms involved in the understanding of spoken speech & written speech. Hearing of spoken words Recognition & understanding of spoken words. Interpretation & comprehension of speech ideas.

Hearing of spoken words:

Hearing of spoken words Requires an intact auditory pathway from ears to primary auditory areas. Primary auditory areas : Broadmann’s area 41 & 42 Centre for hearing located in the middle of superior temporal gyrus on the upper margin & on its deep or insular aspect. Function: perceives the nerve impulses as sound i.e. auditory information such as loudness, pitch, source & direction of sound .

Recognition & understanding of spoken words.:

Recognition & understanding of spoken words . Carried out by auditory association areas ( 20 & 21 ) located in the middle & inferior temporal gyrus respectively. Receive impulses from the primary auditory cortex & are concerned with interpretation & integration of auditory impulses .

Interpretation & comprehension of speech ideas – By Wernicke’s area.:

Interpretation & comprehension of speech ideas – By Wernicke’s area . Described by Carl Wernicke 1874 . Broadmann area 22 Located in the temporal gyrus behind areas 41 & 42 in the categorical hemisphere. Interprets the meaning of what is being heard. Comprehension of spoken language & formation of idea that are to be articulated in speech.

Understanding of written speech:

Understanding of written speech Perception of written words Interpretation of written speech Generation of thought/idea.

1.Perception of written words:

1.Perception of written words Requires an intact visual pathway from the eyes to the primary visual cortex. Primary visual cortex (Striate cortex ) Area 17 . Centre for vision lies on the medial surface of occipital lobe in & near the calcarine sulcus occupying parts of lingual gyrus & cuneus.Also extends to the superolateral surface of occipital pole limited by lunate sulcus Functions: Perception of visual impulses.

2. Interpretation of written speech:

2. Interpretation of written speech Visual association areas: area 18 & 19 Located in the wall & in front of lunate sulcus . Function: Recognition & interpretation of written words in light of previous experience.

3. Generation of thoughts/ideas in response to written speech.:

3. Generation of thoughts/ideas in response to written speech. Dejerine area (area 38 ): Located in the angular gyrus behind the Wernicke’s area in the dominant hemisphere. Involved in the activity of generation of thought/ideas in response to written speech. Also called visual speech centre & along with Wernicke’s area forms the sensory speech centre.

Expression of speech :

Expression of speech In the form of Spoken speech Written speech Or both. Involves the activities of motor speech centers- Broca’s area , Exner’s area (expressive or executive areas)

Expression of spoken speech:

Expression of spoken speech Described by Paul Broca 1865. Involves the activities of motor speech centre, Broca’s area . Area 44 . Special area of Premotor cortex located in the inferior frontal gyrus in the left cerebral hemisphere.

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Function: this area processes the information received from sensory speech centers into detailed & coordinated pattern for vocalization which is then projected to the motor cortex for implementation. Movement of the structures which are responsible for production of voice & articulation i.e. activation of vocal cords simultaneously with movement of mouth, tongue during speech.

Vocalization :

Vocalization Voice is produced by the following mechanism (aerodynamic myoelastic theory of voice production) 1.Vocal cords are kept adducted 2. Infraglottic air pressure is generated by the exhaled air from the lungs due to contraction of thoracic & abdominal muscles

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3.The air force opens the cord which releases as small puffs which vibrate the vocal cords and produce sound which is amplified by mouth, pharynx, nose & chest. 4. The sound is converted into speech by the modulatory action of lips, tongue, palate, pharynx & teeth. - Intensity of sound depends on the air pressure produced by the lungs while pitch depends on the frequency with which the vocal cords vibrate.

Expression in the form of written speech:

Expression in the form of written speech Exner’s area (motor writing centre) Location: in the middle frontal gyrus in the dominant hemisphere in the Premotor cortex. Processes the information received from Broca’s area into detailed & coordinated pattern & then along with motor cortex initiates appropriate muscles movements of hand & fingers to produce written speech.

Speech & language disorders:

Speech & language disorders Aphasia Dissociative language syndromes Dysarthria Aphonia

Language disorders:

Language disorders Aphasias : is term applied to disorders of expression in speech, writing & sign language & use of symbols, as well as to disabilities in comprehension of spoken, written & signed language. Lesions causing aphasia are usually in the cerebral cortex & typically are found in cortical association areas. Aphasias are abnormalities of language functions that are not due to defects of vision or hearing or to motor paralysis .

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Cause : lesions in the categorical hemisphere. Most common cause is embolism or thrombosis of a cerebral blood vessel. Classification of aphasia 1.Fluent aphasia 2.Non-fluent aphasia 3.Global aphasia

Fluent aphasia:

Fluent aphasia Sensory aphasia or receptive aphasia Site of lesion: Wernicke’s area Features: 1. Difficulty in understanding the meaning of speech. 2. motor speech is intact & pt talks excessively & fluently. Jargons & neologisms. 3. Impairment in reading & writing. Since the patient cannot comprehend the written words, he/she is unable to read aloud or copy print into writing Cause: occlusion of superior division of middle cerebral artery. Mass lesions including tumor, intra cerebral artery hemorrhage or abscess.

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Speech is associated with Anomia : inability to find appropriate words to express a thought. Neologisms : using or creating new words or new meanings for established words (non-sense words) Paraphasias: production of unintended words or phrases during effort to speak .

Motor aphasia:

Motor aphasia Non fluent aphasia, Broca’s aphasia. Site of lesion: Broca’s motor speech area in the frontal lobe. Cause: embolus to the inferior division of the middle cerebral artery & to the posterior temporal or angular branches is the common cause. Intracerebral hemorrhage, severe head trauma, neoplasm.

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Features: Comprehension of spoken or written speech is good. Difficulty in speaking. The affected individual is able to formulate verbal language in his mind but cannot vocalize the response. Speech is non fluent. Speech is slow & words are hard to come. Pts with severe damage to this area are limited to two or three words with which to express whole range of meaning & emotion. Inability to write ( Agraphia ) Sometimes the words retained are those which are being spoken at the time of injury or vascular accident that caused the aphasia.

Global aphasia:

Global aphasia Refers to total inability to use language communication. Site of lesion: loss of both Wernicke’s & Broca’s area. Features : aphasia is general involving both receptive & expressive functions. Hence speech is scant & non fluent . Cause: stroke involving entire middle cerebral artery distribution in the left hemisphere. Related signs include - rt hemiplegia, hemi sensory loss & homonymous hemianopia

Dissociative language syndromes:

Dissociative language syndromes Refer to language deficit that do not result from lesion of cortical language areas, but from disruption of pathways joining them. Conduction aphasia Pure word deafness Pure word blindness Pure word mutism Anomic aphasia

Conduction aphasia:

Conduction aphasia Another form of fluent aphasia in which pts can speak relatively well & have good auditory comprehension but cannot put parts of words together or conjure up words. It was thought to be due to lesions of arcuate fasciculus connecting Wernicke’s & Broca’s area. However, it now appears to be due to lesions in & around the auditory cortex (areas 40, 41 & 42)

Anomic aphasia:

Anomic aphasia Site of lesion: Angular gyrus in the categorical hemisphere without affecting the Wernicke’s or Broca’s area. Features : there is no difficulty with speech or understanding auditory information, but there is trouble understanding written language or pictures because visual information is not processed & sent to Wernicke’s area.

Pure word deafness:

Pure word deafness Auditory verbal agnosia Impairment of auditory comprehension & repetition, an inability to write following dictation. Spontaneous writing ability & ability to comprehend written language are preserved, that differentiates it from Wernicke’s aphasia . Pts declare that they don’t hear anything but audiometry does not disclose any hearing defect. Site of lesion: bilateral in the superior temporal gyrus

Pure word blindness:

Pure word blindness Visual verbal agnosia Inability to read aloud, understand written script, to name colours Also called visual verbal colour anomia. Understanding of spoken language, repetition of what is heard, writing spontaneously & to dictation & conversation are all intact. Capacity to write fluently is retained, but cannot read what has been written. This is called Alexia without Agraphia. Lesion affects left visual cortex geniculocalcarine tract & the connection of the visual cortex of the dominant hemisphere with language areas.

Pure Word Mutism:

Pure Word Mutism Aphemia or Pure Motor Aphasia of Dejerine. Loss of capacity to speak Ability to write, to understand spoken words, to read silent with comprehension & repeat spoken words is retained. Due to vascular lesion or localized injury to the dominant frontal lobe.

Lesion in the representational hemisphere.:

Lesion in the representational hemisphere. May impair the ability to tell a story or make a joke. May also impair ability to get the point of the joke - A language disorder occurring after a right hemisphere lesion in a right handed person is called Crossed Aphasia.

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Aphasia Comprehension Repetition of spoken language Naming Fluency Wernicke’s impaired impaired impaired Preserved Broca’s preserved impaired Impaired decreased Global impaired impaired impaired Decreased Conduction preserved impaired impaired preserved

Dyslexia :

Dyslexia Broad term applied to impaired ability to read. Inherited abnormality 5% of the population. Word blindness. Its cause is decreased blood flow in the angular gyrus in the categorical hemisphere

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Phonological hypothesis : dyslexics have impairment in the representation, storage, &/or retrieval of speech sounds. The rapid auditory processing theory : primary deficit is the perception of short or rapidly varying sounds Visual theory : defect in the magnocellular portion of the visual system slows processing & also leads to phonemic deficit

Dysarthria :

Dysarthria Impairment of articulation. In pure dysarthria , there is no abnormality of cortical language mechanisms Understanding of whatever is heard & no difficulty in reading & writing. It is commonly due to neuromuscular problems. 4 types of dysarthria .

Causes of dysarthria :

Causes of dysarthria Mechanism Example Weakness of facial & tongue muscles Myasthenia gravis Lesions of lower brain stem Motor neurone disease Bilateral corticospinal tract lesions above the pons Multiple lacunar infarcts Impaired control of phonation & articulation Parkinsonism Imprecise motor control systems Cerebellar lesions Impaired larynx function Reccurent laryngeal nerve palsy

Types of dysarthria:

Types of dysarthria Cerebellar dysarthria : Patient speaks slowly & deliberately, syllable by syllable, as if scanning a line of poetry. The normal flowing, prosodic rhythm of syllable, word & sentence production is lost. When patient is asked to pronounce ‘rhinoceros’ it will be pronounced ‘rhi-noc-er-os’. This scanning or staccato disturbance of speech rhythm is the classical form of severe cerebellar dysarthria.

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Pseudobulbar(spastic) dysarthria : Individual syllables are slurred & the precision of consonant pronunciation is lost. It is due to bilateral lesions in the corticospinal fibres supplying the muscles of the face, larynx, tongue & respiration. It is feature of upper motor neuron lesion. When patient is asked to pronounce ‘British Constitution’ it becomes ‘ Brish Conshishushon’.

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Bulbar dysarthria : It is due to lower motor neurone lesions affecting the speech musculature, resulting in non-specific slurring of speech. It is associated with dysphasia. Cortical dysarthria : There is an irregular hesitancy in word production, associated with difficulties in abstract volitional movements of the lips & tongue. Associated with aphasia due to left frontal & temporal lesions .

Other disorders:

Other disorders Stuttering speech: Has been associated with right cerebral dominance & widespread activity in the cerebral cortex & cerebellum. This includes increased activity in the supplementary activity.

Formal tests for dysarthria :

Formal tests for dysarthria Nonsense syllables that test the lips & jaws – for ex ‘papapapa’ & ‘tatatata’ the tip of the tongue ‘sasasa’ & the body of tongue ‘kakaka’. They can be combined into repetitive tasks as ‘patakapataka’ & ‘fasaxafasaxa’ to evaluate rhythm & prosody more objectively.

Assessment of speech defects:

Assessment of speech defects Speech defects are assessed by disturbances Articulation Fluency Verbal comprehension Naming Repetition Reading Writing

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Disturbances of fluency, verbal comprehension, repetition & writing are all prominent in left anterior temporal lobe lesions. Left frontal lesions affect articulation & fluency. Left parieto-occipital lesions impair reading Left parietal lesions impair writing. Left posterior lesions impair naming & repitition.

Assessment of spoken speech:

Assessment of spoken speech Articulation : tested by words and phrases as ‘British constitution’, ‘West Resgister Street’, ‘biblical criticism’. Fluency is best assessed by spontaneous conversational speech. Naming is assessed by asking the subject to name some common objects like – knife, pen, matchbox etc. Repitition – pt is asked to repeat a simple sentence such as : ‘Today is Wednesday June 4 th , this is the Royal London Hospital ’.

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Look for use of Paraphasias and neologisms. Comprehension of spoken speech : assessed by asking the patient to carry out commands. Staged commands (e.g, ‘ pick up the blue card, fold it in half & put it under the white card’) help bring out subtle defects .

Assessment of written language:

Assessment of written language Reading : reading a loud tests the visual comprehension of language & spoken speech. Reading silently tests comprehension of language through the visual system. Writing : patient is asked to write his or her name, asked to write reply to questions like ‘ what is your address?’ Comprehension of other symbols : some simple calculations are put like 1. 2+2=4 2. 2+2=5 3. 2+2=6 and the patient is asked to point out the correct one - Inability to understand & manipulate mathematical symbols, Acalculia , may occur in posterior parietal lesions affecting dominant hemisphere .

References :

References Indu khurana. Text book of medical physiology. Ganong’s review of Medical Physiology Guyton & Hall. Text book of medical physiology. Text book of physiology – G.K.Pal Hutchison’s Clinical Methods P L Dhingra. Diseases of Ear, Nose & Throat. Macleod’s clinical examination

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