L4: Neural Control of Swallowing

Question 1

neural control of swallow is…

at a minimum it involves…

but also incorporates…

Answer 1

multidimensional

brainstem “swallow centre” in medulla;

sensory inputs from pharynx, larynx, esophagus;

motor outputs via motor nuclei and motorneurons to muscles

also incorporates descending cortical and subcortical inputs

Question 2

medullary swallow centre is…

Answer 2

a central pattern generator

functional neural circuit = groups of neurons generate motor pattern without reliance on peripheral sensory feedback

bilateral

Question 3

medullary swallow centre has two groups:

Answer 3

dorsal swallowing group

ventral swallowing group

Question 4

dorsal swallowing group involves

Answer 4

nucleus tractus solitarius (NTS) and adjacent reticular formation (RF)

programming component (active early in swallow)

Question 5

ventral swallowing group involves

Answer 5

nucleus ambiguous and adjacent RF

motor execution component (active later in swallow)

Question 6

the dorsal swallowing group receives what inputs?

Answer 6

palatal, pharyngeal, laryngeal

neurons can be excited by electrical stimulation of CN IX and X (phX and iSLN)

Question 7

synapses in the dorsal swallowing group can be ….

also called…

Answer 7

excitatory or inhibtitory

trigger neurons = stimulation results in a swallow

Question 8

describe the initiation of the pharyngeal swallow

Answer 8

most complex ‘reflex’ initiated by CNS

afferent info from IX and phX is necessary to trigger pharyngeal swallow response but also must be sufficient

sensory threshold = affected by level of arousal and by sensory capacity

best when it comes from a larger number of receptive fields, dynamic and multimodal

Question 9

ventral swallowing group: activity of neurons above NA occurs…

Answer 9

during leading phase of swallowing - “motor control”

active following firing in the DSG; damage to DSG neurons eliminates VSG responses

activity of neurons w/i NA - “motor execution”

Question 10

what are the 4 sensory inputs involved in swallow behaviour?

Answer 10

cephalic phase of control

oral preparatory and oral phase

initiation of pharyngeal swallow

modulation of pharyngeal swallow

Question 11

describe the cephalic phase

Answer 11

settling the gastrointestinal tract context

visual, auditory, olfactory (inc salivation, which aids in triggering the swallow)

Question 12

sensory (afferent) inputs include what CNs?

what do they do?

Answer 12

IX, X, VII, V

sensory input triggers the pharyngeal swallow

sensory input also modifies the swallowing pattern that is programmed w/i the brainstem swallow centre

Question 13

describe how the afferent sys works in the oral prep and oral phase

Answer 13

inputs to the trigeminal sensory nuclei (touch, pressure, temp)

info shared bw tongue and palate (bolus prep, guide tongue shape/position/pressure generation)

gustatory inputs to rostral nucleus tractus solitarius

Question 14

two regions in upper aerodigestive tract that are densely innervated are…

Answer 14

oropharynx

laryngopharynx

Question 15

oropharynx contains areas known to be

Answer 15

reflexogenic - triggering the swallow

found in behavioural studies and histochemical studies (area of dense dual innervation –> pharyngeal plexus supplied by pharyngeal branch of IX and X)

Question 16

laryngopharynx contains…

what do behavioural and histochemical studies show us?

Answer 16

areas known to be reflexogenic - laryngeal closure

behavioural studies –> laryngeal adductor reflex (LAR) elicited when air puffs are delivered to the periarytenoid region

histochemical studies –>area of dense innervation - iSLN supplies the laryngeal epi, aryepiglottic folds, postcricoid, periarytenoid regions

Question 17

efferent system includes 3 components

Answer 17

motor nuclei

motor neurons

swallowing musculature (activated in a stereotyped seq during swallowing) - patterned motor seq

Question 18

what are the 6 motor nuclei involved? and where are they located?

Answer 18

trigeminal nucleus (pons)

facial nucleus (pons)

nucleus ambiguus (medulla)

dorsal motor nucleus of X (medulla)

hypo nucleus (medulla)

spinal nuclei (C1-C3)

Question 19

spinal nuclei (C1-C3) involves…

Answer 19

fixed seq of muscle recruitment

duration and amp of contraction modifiable

Question 20

what 7 CN/motor neurons are involved?

Answer 20

trigeminal (V)

Facial (VII)

Glossopharyngeal (IX)

Vagus (X)

accessory (XI)

hypoglossal (XII)

spinal nerves C1-C3

Question 21

what does the “leading complex” involve?

Answer 21

suprahyoid muscles (mylohyoid, stylohyoid, geniohyoid)

posterior tongue muscles (hyoglossus, styloglossus)

posterior pharyngeal wall

intrinsic tongue muscles

Question 22

response sets: closure of velopharyngeal port + ……

Answer 22

cessation of resp (glottal closure)

Question 23

response sets: pharyngeal shortening + ……

Answer 23

anterior-superior excursion of hyolaryngeal complex

Question 24

response sets: bolus propulsion from oral cavity + ……

Answer 24

to pharynx

Question 25

after leading complex, the pharyngeal constrictors...

Answer 25

propel bolus thru pharynx

Question 26

clinical, neurophysiological and neuroimaging studies show....

Answer 26

infarcts in primary sensorimotor and supplementary motor areas, basal ganglia, and internal capsule inc risk of dysphagia stimulation of anterolateral frontal, lateral pericental, and insular cortex --> evoke swallowing and induce activity in medullary CPG neurons primary sensorimotor cortex and insula are activated during swallowing

Question 27

how can the efferent system be modulated?

Answer 27

type of material to be swallowed (solid vs liquid, alimentary vs non alimentary) properties of bolus to be swallowed (cold vs warm, chemical vs inert) swallowing task (first vs subsequent swallow, command vs naive swallow)

Question 28

cortical regions implicated in swallowing include (3)...

Answer 28

lateral pericentral cortex (primary motor and primary somatosensory) premotor cortex anterior insula

Question 29

subcortical circuits include (3)...

Answer 29

hypothalamus, midvrain ventral tegmental field - facilitate reflexive swallowing basal ganglia - dysphagia in PD internal capsule - stroke in this region inc odds of experiencing dysphagia

Question 30

what are the two functions of the cortex in swallowing?

Answer 30

modulation of phases of swallowing integration w other complex oral functions

Question 31

describe how the primary sensorimotor cortex modulates swallowing

Answer 31

M1 - control of movements in/around mouth; receives sensory info from S1; projects directly to CN motor nuclei --> important to facial movements, tongue movements, jaw opening --> stimulation of M1 does not elicit swallowing S1 - receives input from face and mouth; extensive synpatic connections w M1 --> implicated in control of vol movement interacts w motor nuclei involved in fine controls plastic system capable of adapting thru learning

Question 32

describe the integration w other complex oral functions: supplementary regions

Answer 32

premotor cortex (ex. BA 6) - anterolateral region immediately in front of M1 --> evokes pharyngeal swallowing often w chewing like movements (even in M1 destroyed) anterior insula - associated w coordinating interaction of oral musculature, taste, and autonomic functions ; CVA of anterior insula results in dysphagia may determine seq of complex oral responses (chewing, swallowing) by descending sequential signals to central pattern generators in brainstem

Question 33

cortical and subcortical regions are...

Answer 33

NOT essential for the automatic sequential activation of muscles in the pharyngeal and esophageal phases of swallowing seq activation of muscles continues after cortical and subcortical inputs to the brainstem are interrupted BUT the cortex exercises sig control over initiation of swallowing and level of neuromuscular activity