Physiology of speech

Speech It is the ability to express thoughts in the form of words in response to visual and auditory stimuli. Words may be spoken or written. Speech is human-specific

Physiology of speech

The dominant hemishere (for language)�The left hemisphere is dominant in 95% of right-handed people 70% of left-handed people,   �The Rh hemisphere is dominant in 5% of right-handed people 15% of left-handed people

1.Types of speech Spoken speech : understanding spoken words & expressing ideas in speech  Written speech :understanding written words and expressing ideas in writing 

2.Mechanism of Speech :  Needs sensory input information (visual or auditory) Which become processed in the CNS (thoughts) To give expression (motor output as spoken (articulation) or written (writing) words).  

3.Steps of Speech auditory & visual stimuli auditory & visual associatin areas brain perception & intergration ---> brains areas associated with speech (understanding & formulation) motor execution ---> motor area controlling muscle of phonation & articulation

4.Location of languange areasare arranged along lateral cerebral sulcus (sylvian fissure) of left (dominant) hemsiphere1) Wernicke's                 4)Arcuate fasciculus2)Broca's                         5)Motor cortex3)Angular gyrus

A)Repeating a spoken word primary auditory cortex wernicke's area  arcuate fasciculus broca's area motor cortex B)Reading a word out loud primary visual cortex angular gyrus wernicke's area arcuate fasciculus broca's area motor cortex

Wernicke's area Posterior end of superior temporal gyrus essential for languange comprehension

Broca's area in front of lower end of motor area  essential for articulation (mechanical production of speech)

Angular gyruscentre of integration of auditory and visual information

Arcuate fasciculusTo speak inteligibly , words originating  in wernicke's area must be sent to broca's area

Motor output of SpeechBroca’s area (motor speech area)in the lower part of premotor area (area 6Receive impulses from Wernick’s areaForm the program for muscles of articulation (lips, tongue, and larynx) to produce the words chosen by Wernick’s areaSends the pattern to face region in the primary motor area which initiates the appropriate movements of muscles of articulation.  2.  Exener's area (motor writing area)in the upper part of premotor area (area 6)Form the program for muscles of the hand to write the words chosen by Wernick’s areaSends the pattern to the hand area in primary motor area which initiates  the appropriate movements of muscles of the hand.

* Broca's area contains memories of the sequences of muscular movement that are needed to articulate words

Visual stimuli 1. Primary visual area (area 17 in the occipital lobe)2. Visual association area(area 18 & 19 in occipital lobe)

Auditory stimuli 1. Primary auditory area(area 41 & 42 in temporal lobe)2. Auditory association area(area 22 in temporal lobe)

Wernicke's area (sensory speech area) send to Broca's area via arcuate fasciculus comprehension of visual & auditory information  choice of words to be used in expression of thoughts

* Wernicke's area contains neural circuits responsible for understanding the meaning of spoken or written words.

Articulation  means the muscular movement of the tongue, lips, and larynx for the actual emission of sound. it needs the normal function of motor cortex, cerebellum & basal ganglia

Mechanism of articulation speech initiated  descending corticobulbar pathway from left hemisphere to nuclei X and XII  connection through corpus callosum to motor cortex of right hemisphere descending corticobulbar pathway from right hemisphere to nuclei 10 and 12

AphasiaAcquired loss of production or comprehension of spoken and/or written words 2ry to brain damagenot due to defects of vision, hearing or motor systemTypes: Sensory (fluent) aphasia. Motor (non fluent) aphasia. General (global) aphasia  

1. Sensory (Fluent) Aphasia�Lesion in Wernicke’s area�Defective understanding (inability to find an appropriate word to express a thought)�The patient  can not understand the meaning of spoken (Auditory aphasia; word deafness) or written words (visual aphasia; word blindness)�But Motor Speech is normal and sometimes the patients talk excessively�Meaningless words (word Salad; full of neologisms that make little sense)

2- Motor (non Fluent) AphasiaA) Broca’s Aphasia (expressive aphasia)Lesion in Broca’s areaSpeech is slow (words hard to come) he patient is limited to few common simple words But understanding is normal

B) Exener’s AphasiaLesion in Exener’s areaCan not express by writing (agraphia)Normal Understanding of written & spoken words 

3- Global Aphasia�Combination of sensory (Wernicke’s lesion) & motor aphasia (Broca’s lesion)�Loss of expressive (motor) & sensory (understanding of meaning of words)�The patient can not speak or understand language�Due to Wide spread lesion (the commonest aphasia after a severe left hemisphere infarct. )

�Anomic AphasiaSubtype of sensory aphasia Due to Lesion in angular gyrus Causing failure of processing visual information and transmitting it from visual cortex to Wernicke’s areaPatient finds Trouble in understanding written words or picturesNormal interpretation of auditory information

Conduction Aphasia A subtype of fluent AphasiaDue to lesion in auditory areas Patient can speak relatively well with good auditory understanding BUT can not put words togetherTermed conduction because it was thought that it is due to lesion in arcuate fasiculus connecting Wernicke’s & Broca’s areas

Dysarthria�Disorder of Articulation due to lesion in muscles of articulation leading to speech abnormality (defective vocalization)�Language is intact�Many aphasic patients are somewhat dysarthric

Causes of dysartheria Paralysis affecting muscles of articulation : UMNL &LMNL Neocerebellar lesion : staccato speech  Parkinsonism : 1.Lesion in basal ganglia                                                2.slow monotonous speech

Dyslexia �A broad term describes impaired ability to read �Causes:Reduced ability to recall speech sounds, so there is trouble translating them mentally into sound units. a defect in the magnocellular portion of the visual system that slows processing.

�*There is decreased blood flow in angular gyrus in categorical hemisphere in both cases.

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