Anatomy & Physiology of the Speech Mechanism II

COMSDIS 210: Survey of Communication Disorders

SummaryHow is speech produced?

1. A person inhales and then exhales air. The exhaled air is sent upward through the larynx, where it passes through the vocal folds.

2. As the air passes through the vocal folds, they are set into rapid vibration, which transforms the air into sound. (Sounds like a “buzz”.)

3. The sound is modified by the shape and configuration of an individual’s vocal tract. (particularly the oral and nasal cavities)

4. The sound is shaped into specific speech sounds created by manipulations of the speech articulators.

Modification of the sound• The vocal tract is an acoustic resonator. It modifies the

quality of sound produced by the larynx.

• Each sound has a fundamental frequency and harmonics. – FF = lowest frequency component directly related to speech at which vf are opening and closing)– Harmonics (whole number multiples of the FF)

• Depending upon the physical characteristics of the resonator (vocal tract) some frequencies will be attenuated (reduced) and some will be enhanced.

Resonance

• Resonation: modification of the glottal tone, through the attenuation and enhancement of its frequencies, as the sound moves through the pharyngeal tract (laryngopharynx, oropharynx, nasopharynx).

• Every persons pharyngeal tract is shaped differently which creates individual variation.

• Adds to the “fullness” and “richness” of the sound

Shaping of speech sounds• The sound is further shaped by modifications of the

articulators.

• Articulators include: lips, tongue, teeth, hard palate and soft palate (velum).

• Movements of the mandible (lower jaw) and maxilla (upper jaw) aid in shaping of individual speech sounds (the process of articulation).

• Figure 3.6, p. 93

• The larynx is also an articulator.

– Responsible for “voiced” versus “voiceless sounds”.

– Cognates: two sounds that are produced exactly the same way and differ only by voicing.

Speech and language activity is controlled by brain

• Neuroanatomy: structures associated with the human nervous system.

• Neurophysiology: function of the structures associated with the human nervous system.

The 2 major nervous systems of the human body

• Central Nervous System (CNS)– Brain– Spinal cord

• Peripheral Nervous System (PNS)– The nerves that emerge from the brain and spinal

cord to innervate the rest of the body.

Peripheral nerves• Carry info back and forth between the brain, spinal cord

and rest of body

• Cranial nerves (emerge from the brain)– 12 pairs of cranial nerves– Run between brain stem and face/neck– Impt. For speech, language, hearing & swallowing

• Spinal nerves (emerge from the spinal cord)– 31 pairs of spinal nerves– Run between spinal cord and peripheral areas of body– Impt. For reflexes and voluntary sensory, motor activity

P. 93 (List of cranial nerves)

• I (Olfactory) VII (Facial)• II (Optic) VIII (Acoustic)• III (Oculomotor) IX (Glossopharyngeal)• IV (Trochlear) X (Vagus)• V (Trigeminal) XI (Accessory)• VI (Abducens) XII (Hypoglossal)

Neurons and neurotransmission

• Neuron: the cells making up the nervous system that also carry the sensory and motor information.– Most covered in myelin (sheath of coating)

• Protects the neuron• Contributes to the rapid relay of nerve impulses

• Myelination: growth of the myelin sheath (begins in utero but not complete until late childhood)

• Demyleination: loss of myelin; results in malfunctioning of the nerve cells; many different symptoms

• Neurons composed of a cell body and two extensions.

• The extensions receive and transmit information to and from the cell body in the form of electrical-chemical nerve impulses

• Axons: take nerve impulses away from the cell body (efferent extensions)

• Dendrites: take nerve impulses into the cell body (afferent extensions)

Figure 3.2, p. 84

• Impulses move from one neuron to another by traveling down one’s dendrite and into its cell body and then along the axon to another neuron’s dendrite.

• Synapse: space where two neurons meet. (Impulse must cross the synapse)

• Neurotransmitters (chemical agents helping to carry info across the synaptic cleft).

3 major divisions of the brain

• Brain stem

• Cerebellum

• Cerebrum (cerebral cortex)

Brain stem• Sits on top of the spinal cord. Is the conduit

between the rest of the brain and the spinal cord.

• Includes 3 major reflex centers: cardiac (heart), vasomotor center (blood vessels) and respiratory center (breathing). Regulates breathing and blood circulation; affects level of consciousness.

• Also controls visual and auditory reflexes via nerves supplying the face and head.

Cerebellum

• Sits posterior to the brain stem.

• Regulates motor and muscular activity.– Coordination of movements– Muscle tone– Strength and range of motion– Posture and equilibrium

• Linked to higher-order cognitive functions.

Cerebrum (Cerebral cortex)

• Largest of the 3 major divisions

• Controls thinking, problem solving, planning, creating and rationalizing

• Consists of 2 hemispheres (left and right) separated by a long crevice (longitudinal fissure).

• The 2 hemispheres need to communicate with each other. The corpus callosum (band of fibers connecting the hemispheres) enables communication between the 2 hemispheres.

– Figure 3.3, p. 86

The cerebrum’s 4 lobesFigure 3.4, p. 87

• Each represented in both hemispheres

• Frontal lobe

• Temporal lobe

• Parietal lobe

• Occipital lobe

Frontal lobe• Largest lobe; sits in the most anterior part of the

brain.

• 2 primary functions:– Activates/controls fine and complex motor activities

including speech

– Controls executive functions (problem solving, organizing, planning, creating, reasoning, decision making, social awareness and rationalizing)• In prefrontal cortex

Frontal lobe (continued)

• Houses “Broca’s area”Important region for speech and languageLeft hemisphere onlyResponsible for fine coordination of speech

• Broca’s aphasia – Acquired language disorder characterized by short,

aggrammatical sentences, difficulty with word retrieval, slow labored speech and writing, speech sound errors and difficulty with speech imitation.

Parietal lobe

• Sits above the ears on the left and right sides behind the frontal lobe.

• Functions:– Perceive and integrate sensory and perceptual

information– Comprehension oral and written language and

calculation for math.

Temporal lobe

• Sits behind (posterior to) the frontal lobe, but below (inferior to) the parietal lobe.

• Contains auditory cortex (Heschl’s gyrus) and Wernicke’s area. Both very important to communication.

Auditory cortex/Heschl’s gyrus

• Controls fined-tuned analysis of the physical properties (physics) of sound, auditory perception and sensation.

• Located in both hemispheres; each hemisphere responsible for particular tasks

– Left auditory cortex: temporal processing– Right auditory cortex: melody, prosody, pitch (musical)

Temporal lobe• “Wernicke’s area”– Highly specialized area for processing and

comprehension of oral and written language– In left hemisphere; it is where meaning is attributed

to the stimuli sent forth from Heschl’s gyrus.

• Wernicke’s aphasia– Acquired language disorder characterized by very fast

strings of sentences with little pause for acknowledgment or turn taking.• Content may be incoherent/incomprehensible but fluent

and well-articulated.

Occipital lobe

• Sits in front of and above the cerebellum and behind the cerebrum.

• Receives and processes visual information