Craniofacial Muscles

178 C.L. Ludlow
wall are powerful stimuli for inducing fi ctive swallowing in the rat (Kitagawa et al.
2002, 2009 ) . This has recently been used clinically for inducing the return of swallowing
in stroke patients by use of electrical stimulation to the pharyngeal wall
(Jayasekeran et al. 2010 ) . The powerful effects of sensory triggers to the brainstem
centers controlling the laryngeal and pharyngeal muscles for swallowing are an
attractive mechanism for enhancing re fl exogenic swallowing in patients who have
lost volitional control.
10.7 Central Neural Control of the Laryngeal
and Pharyngeal Muscles
Some neural substrates controlling this automatic motor patterning for voice and
speech are located in the cortex. Brain lesions or disease affecting the basal ganglia,
cerebellum, and thalamus often produce a slowing or a loss of the normal rhythm of
speech, producing disorders referred to as dysarthrias but the pattern of muscle
activation for the production of speech sounds is retained. Only when damage
involves cortical regions or interactions of other brain regions with the cortex is the
motor pattern for speech articulation disturbed, resulting in the loss, distortion, or
errors in speech articulation programming accuracy resulting in a disorder referred
to as apraxia of speech (Kent 2000 ) .
Vocalization which is not based on speech or singing is present at birth (the birth cry)
and depends upon mammalian vocalization systems which are contained in the brain
stem, pons, and periaqueductal gray and have a similar bases in humans as in other
mammals (Jurgens 2000 ) . In contrast, voice production for speech is cortically based
and unique to human species (Jurgens 2002 ) . As a result, studies of the neural control
of voice and speech in humans are limited to the study of the effects of brain lesions
or more recently to functional brain imaging and transcranial magnetic stimulation.
The neural substrates for swallowing involve subcortical brain mechanisms that
are similar in humans and other mammals and involve patterning of the laryngeal
and pharyngeal muscles. Cortical control for the volitional elicitation of swallowing
on command is also present in the human and has more recently been studied using
functional brain imaging showing cortical control is present similarly for volitional
and automatic swallowing (Martin et al. 2001, 2007 ) while brainstem control centers
are also active (Komisaruk et al. 2002 ) .
10.8 Effects of Neurological Diseases on Laryngeal
and Pharyngeal Muscle Control
Motor control for speech and swallowing are affected by a multitude of neurological
diseases. Peripheral neuropathies that are length dependent and impacted by the
RLN, the longest nerve innervating craniofacial muscles, are often affected by