PHYSIOLOGY OF SPEECH

Prof. Vajira WeerasingheDept of Physiology

• Peripheral function– phonation– articulation & resonance

• Central function– cortical control• Broca’s area & Wernicke’s area

Phonation

– Production of speech by the larynx

– Speech is produced during expiration– during• breathing: vocal cords are far apart• phonation: vocal cords are close together, vibrated

– pitch depends on stretch of the folds, how tightly folds are approximated

Phonation

– vocal folds stretch from thyroid cartilage to arytenoid cartilage• vocal folds are stretched by forward rotation of thyroid

crtilage & posterior rotation of arytenoid cartilage

• loosen by thyarytenoid muscles

–muscles controlling arytenoids open or close the glottis

– tension of folds depends on vocalis (intrinsic) muscles & cricothyroid muscles

video

– electrical activity recorded from laryngeal muscles show• even in quiet respiration: there is some activity• during phonation: increased electrical activity in the

adductor muscles– after 0.35 - 0.55 s only sounds onset– this time delay is necessary for pressure to build up

Articulation

• modification of sounds by mouth, throat, nasal cavities, tongue, lips, jaw, soft palate

– vowels are produced by vibration of vocal folds, air stream passes through (voiced)

– consonants are produced by partial obstruction of air stream. Larynx may not be necessary (unvoiced)

• resonance: cavities, sinuses

Articulation

• consonants are classified according to their site of origin– labial (lips, teeth) p,b,w,f,m– dental (teeth, tongue) d,t,s,m– lingual (tongue, soft palate) l– guttural (back of tongue, soft palate) g,k

vagus nerve

– internal laryngeal nerve: sensory to larynx– external laryngeal nerve: cricothyroid muscles– recurrent laryngeal nerve: all other muscles

• frequency range of human voice• 40 - 2000 Hz

– men: 122 - 163 Hz– women 244 - 326 Hz

cortical control of speech

• speech is a mode of communication by means of sounds– receptive aspect – expressive aspect– psychological function

• expressive aspect– production of appropriate movements of lips, tongue,

palate, vocal cords, respiratory muscles

• receptive aspect– auditory discrimination of these sounds

• psychological function–meaning of sounds heard or uttered

Broca’s area

• this is the motor (expressive) area for speech

• it is in the frontal lobe in front of inferior end of the precentral gyrus

• (area 44)

• generally present in the dominant side

Wernicke’s area

• this is the sensory (receptive) area for speech

• it is in the temporal lobe in the posterior end of the superior temporal

• generally present in the dominant side

• comprehension of visual & auditory information

W

B

B Broca’s areaW Wernicke’s area

visual impulses

angulargyrus

auditory impulses

disorders of speech

• dysphonia (aphonia)– difficulty in the production of speech– laryngeal disorder

Video

disorders of speech

• dysarthria– defect in articulation• muscle paralysis• upper motor or lower motor neuron lesion of the

nerves concerned• incoordination of muscles• cerebellar disorders

Video

disorders of speech

• dysphasia (aphasia)– disorders of receptive or expressive aspect of

speech – due to cortical abnormalities– different types of aphasia

Broca’s dysphasia (aphasia)

–motor aphasia, expressive aphasia– nonfluent– disorder of expressive aspect of speech – comprehension is normal, understand written

and spoken word– difficult to initiate speech, few disjointed words,

failure to construct sentences– a lesion in the Broca’s area– spontaneous naming and repetition impaired

Video

Wernicke’s dysphasia (aphasia)

– sensory aphasia, receptive aphasia– fluent– disorder of comprehensive aspect of speech (both written

and spoken word) – expression is normal– incorrect words, errors, unintelligible, structure of

sentences correct but no meaning – jargon aphasia (rubbish)– a lesion in the Wernicke’s area– spontaneous naming and repetition impaired

Video

Global aphasia

– widespread damage– both receptive and expressive aspects affected– nonfluent

Conduction aphasia

– tracts connecting Wernicke’s and Broca’s areas are damaged

– difficulty in repetition of words, reading aloud– fluent– normal comprehension– abnormal meaning– repetition impaired

• word blindness– written word is affected, normal spoken language,

visual comprehension is affected– damage to occipital association areas

• word deafness– spoken word is affected, written word is normal,

auditory comprehension is affected– temporal lobe damage

• dysgraphia (agraphia)– difficult to write, without paralysis of the hand

• dyslexia (alexia)– difficulty to read

• apraxia– inability to carry out a purposive movement nature of which the

person understands– parietal lobe damage

• agnosia– failure of recognition of visual, auditory or tactile objects– lesion in parietooccipital cortical areas

cerebral dominance

• in right handers (90% of the population)– left side is dominant

• in left handers (10% of the population)– in 60% left side is dominant– in 20% right side is dominant– in 20% bilateral

Cerebral asymmetry

• Cerebral hemispheres have shown asymmetry for speech as well as for many other cognitive functions

• Split brain operations performed in 1950-60 to prevent spread of epilepsy has given valuable information about the functional asymmetry

Left side

• Mostly the dominant side

• Verbal

• Temporally sequential in processing

• Mathematical leaning

Right side

• Mostly the non-dominant side• Non-Verbal• Non-Mathematical non-sequential

processing• Visuospatial tasks: reading faces, mental

spatial transformations, perceiving whole from parts

• Musical perception

This functional asymmetry in a structurally symmetrical structure

is a unique human attribute

L R