Esophagus A. Empty tube approx. 20 cm in length (See Figure 2-4, page 15 in Kahrilas)
Esophagus (cont.) B. Two muscle layers 1. Inner circular layer 2. Outer longitudinal layer
Esophagus (cont.) C. Muscle Type 1. Upper 1/4 striated (similar to pharyngeal muscles) 2. Middle 1/4 mixed striated & smooth 3. Lower 1/2 smooth (similar to gastric muscles)
Esophagus (cont.) D. Innervation -Vagus Nerve 1. Meissner's plexus - "submucosal" between muscularis mucosa and circular muscle layer
Esophagus (cont.) D. Innervation -Vagus Nerve (cont.) 2. Auerbach's plexus - "myenteric" between circular and longitudinal muscle layers
Esophagus (cont.) E. Esophageal Peristalsis 1. Onset with bolus entry through Upper Esophageal Segment 2. Moves from striated to smooth
A. Sensory Input 1. Anterior 2/3 of tongue (cont.) a) General Sensation - Trigeminal (V) (Lingual nerve) b) Taste - Facial nerve (VII) (chorda tympani)
A. Sensory Input (cont.) 2. Posterior 1/3 of tongue (cont.) a) Glossopharyngeal (IX) for Gen. Sensation & Taste
A. Sensory Input (cont.) 3. Pharynx (gen sens.) a) Vagus (X) (via SLN & Pharyngeal Branch) b) Glossopharyngeal(IX)
Primary Afferent input controlling the swallowing response is from the Superior Laryngeal Nerve. (Kahrilas Figure 2-5, page 17)
B. MotorInnervation 1. Glossopharyngeal (IX) 2. Vagus (X) 3. Hypoglossal (XII).
C. CENTRAL SWALLOW CENTER? 1. Medullary Reticular Formation - most ventral (toward belly) part of the reticular formation extending rostrally through the pons and midbrain
C. CENTRAL SWALLOW CENTER? 1. Medullary Reticular Formation a. Receives sensory input for swallowing from Vagus (primarily superior laryngeal nerve) and Glossopharyngeal nerves.
C. CENTRAL SWALLOW CENTER? 1. Medullary Reticular Formation b. Receives excitatory motor input from structures involved in motor control including the motor and premotor cerebral cortex via cortico reticular pathway
C. CENTRAL SWALLOW CENTER? 1. Medullary Reticular Formation c. Sends excitatory motor output via anterior and lateral reticulospinal tract
Schematic of Theoretical Model of Neural Control of Swallowing Cerebral Cortex Corticoreticular Pathway Dorsal and Ventral Trigeminal Lemniscus MOTOR PATHWAYS SENSORY PATHWAYS Medullary Reticular Formation Reticulospinal Pathway Spinal Trigeminal Neucleus and Tract CN Motor Nuclei V, IX, X, XII Spinal Motor Neurons CN Sensory Nuclei VI, VII, X
C. CENTRAL SWALLOW CENTER? 1. Medullary Reticular Formation d. Only one side of the medullary swallowing center is necessary to coordinate a swallow response.
NOTE: CORTICAL INPUT IS NOT NECESSARY FOR NORMAL SWALLOW RESPONSE (HOWEVER, DAMAGE TO PRECENTRAL GYRUS HAS BEEN ASSOCIATED WITH ORAL PHASE IMPAIRMENT)
C. Sequence of events from CNS to cranial nerves 1 . Appropriate sensory stimulation activates the swallow center 2. "...the entire behavior of swallowing results from activation of the center." (p. 17)
C. Sequence of events from CNS to cranial nerves (cont.) 3. A bilateral sequence of excitation and inhibition occurs involving approximately 2 dozen motoneuron pools scattered throughout the brainstem.
C. Sequence of events from CNS to cranial nerves (cont.) 4. Efferent signal activates portions of the nucleus ambiguous and nuclei of cranial nerves V, VII, and XII (associated with oral phase)
C. Sequence of events from CNS to cranial nerves (cont.) 5. Once stimulated, the entire pharyngeal swallowing response is generated (CN X)
C. Sequence of events from CNS to cranial nerves (cont.) 6. An apneic pause of .5 to 3.5 sec. accompanies swallowing. The swallow center inhibitory influence overrides respiratory centers competing for access to the same motoneurons.
Swallow Response Neurophysiology (cont.) D. Sequence of muscle contraction events (observed experimentally, Doty & Bosma, 1956)
D. Sequence of muscle contraction events 1. Mylohyoid contraction (first detectible action, precedes other muscular contraction by 30-40 ms)
D. Sequence of muscle contraction events 2. "Leading complex" activation
2. "Leading complex" activation a) Posterior tongue b) Superior constrictor c) Palatopharyngeus d) Stylohyoid e) Geniohyoid
D. Sequence of muscle contraction events 3. Pharyngeal constrictors fire in overlapping order 4. Cricopharyngeal dilation 5. Esophageal peristalsis (velocity between 2-4 cm sec)