DEVELOPMENTAL INFLUENCES ACROSS THE LIFESPAN Part 2.

DEVELOPMENTAL INFLUENCES ACROSS THE

LIFESPANPart 2

Anatomical Differences Between Infants & Adults

At birth, the neurocranium and orbits have reached a much larger proportion of their adult dimensions than have the mandible and maxilla.

The nasal floor lies in close proximity to the floor of the orbits.

Upper face width is nearly 2/3s of its adult size.

In contrast, face height and mandibular length are 1/3 their adult dimensions.

Because the maxilla is diminutive, the mandibular angle is more obtuse.

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The neonate oropharynx lies at the level of the adult nasopharynx due to small midface.

The hyoid is at the level of the atlas rather than at cervical vertebrae 3-4 as seen in adult.

Descent of the pharynx is incomplete at birth and it is much shorter in the infant than the adult.

The neonate’s larynx also occupies a higher position in the neck.

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• The laryngeal aditus lies at C2, rather than at C5, as in adults and the laryngeal vestibule is more horizontally directed.• The thyroid cartilage is contiguous with the hyoid bone, so the entire larynx elevates to a much lesser degree in infants than adults. •Between the upper and lower esophageal sphincters, the esophagus measures 7 to 14 cm (adult measures approximately 25 cm), with a diameter of 5-6 mm.•During the postnatal period, there are significant changes in the size and location of components of the oropharyngeal cavities.


In general, the central mobile elements of the oropharynx in the infant are large in comparison to their containing chambers.

Because the mandible is still retruded relative to the maxilla, and the midface small, the tongue almost entirely fills the oral cavity, frequently occupying the space between the alveolar processes.

The extrinsic muscles are oriented to move the tongue primarily on a horizontal plane.

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Because the intrinsic muscles of the tongue are poorly developed at birth, the extrinsic muscles are the principal determinant of tongue movement.

The suspensory system of the infant tongue also differs markedly from that of a mature person.

The lingual system is basically a dual reciprocating structure with the mandible as the anterior hub and the hyoid-styloid complex as the posterior hub.

This system provides a highly stabilized space in which the tongue functions in the whole-organ activity of suckle-swallow.


• The infant’s epiglottis is bulky at this stage when see superiorly.• The arytenoid mass is nearly mature in size compared to the small-sized vestibule and ventricle of the larynx. •Also, because of the proximity of laryngeal and nasopharyngeal structures, the infant’s epiglottis may contact the soft palate.• Together with the aryepiglottic folds, the omega-shaped epiglottis lies over the dorsum of the tongue. • This anatomic arrangement provides the neonate with an additional valve to keep food in the mouth until the pharyngeal swallow is initiated.


• It also enables the airway between nose and lungs to be maintained even while liquids to be swallowed are channeled laterally around the interlocked larynx. • The higher position in the neck and the posterior tilt of the larynx in the infant result in more efficient respiration than in the adult.• Therefore breathing and swallowing can proceed simultaneously and poor closure of the airway or even a partial paralysis of the vocal folds may not be as evident.


04/19/23

As maturation progresses, the face vertically elongates and the chambers of the oral cavity and oropharynx enlarge.

By 4 to 6 months of life, the larynx and associated structures have begun to descend, drawing away from the nasopharynx.

Coincident with this anatomical development, the tongue elongates and acquires a variety of discrete lever and probe functions within the expanding oral space.

As the teeth emerge, the tongue retreats from between the arches to lie in contact with the teeth and the palate.

The cheeks and lips contact the buccal and labial surfaces of the teeth and the alveolar processes.

Anatomical Differences Between Toddlers & Adults

Anatomical Differences Between Children & Adults

The upper pharynx enlarges and the constrictor portions of the pharyngeal wall become more stable.

The soft palate has greater spatial range available and becomes more mobile.

By the age of 6 years, the mandibular and maxillary structures have reached 80% of their ultimate growth so their adolescent growth spurt is moderate compared to other long bones of the body.

Also by 6 years of age, the upper respiratory system has essentially the adult configuration.

By approximately 9 years of age, the posterior third of the tongue is located vertically in the neck.

Anatomical Differences Between Adolescents & Adults

During adolescents, the most notable growth occurs in the ramus of the mandible.

Consequently, the profile of the face becomes less convex and the structures more aligned.

The maxillary and mandibular incisors upright themselves and the dentition takes a less prominent position in relation to the rest of the face.

Because of vertical increase in the height of the lips, the teeth are better covered by the lips.

While this growth spurt is clearly present in boys, it is not always demonstrable in girls.


•While many 15- and 16-year-old girls show little further facial change, boys between 15 and 20 years usually show quite marked changes and achieve their adult facial form at a much later age than do girls.•Also, at the end of adolescence, the composition of the soft tissue of the face is different for girls than boys.•Adult males have a straighter profile, a more dominant chin, nose and eyebrow ridges, more upright anterior teeth, and a less visible dentition than adult women. •Adult women have more smoothly curved and flowing facial contours than men.


•During puberty, the larynx of both the male and female begin to enlarge.•However, the male larynx outdistances the female larynx, especially in its growth on the antero-posterior plane.• From their length of about 4 mm in infancy, male vocal folds grow to measure 12-15 mm in adolescents, while female vocal folds grow to be 7-8 mm.•By adulthood, the membranous portions of the male vocal folds from 16-18 mm, whereas female membranous vocal folds increase to only 12 mm in length.

Anatomical Changes in Adulthood

•The thyroid cartilage, followed by the cricoid cartilage, begin to ossify between the ages of 20 and 23 years. •At the same time, the laryngeal mucosa begins to lose its transparency and becomes stronger.•The epiglottis flattens, increases in size, and elevates. • The tonsils and adenoids partially atrophy.• In the late 30s, the arytenoid cartilages ossify.• By age 65 years, all the laryngeal cartilages except the cuneiforms and corniculates have ossified.

Swallowing Characteristics

• The young infant, to a great extent, interprets the world with her mouth.• The mouth, at birth, is a very active perceptual system. • Tactile acuity is much more highly developed in the lips and the front part of the tongue than it is in the fingers. • The infant uses her mouth and face for perceptual functions even more than she does her hands. •She carries objects to her mouth to aid in perception of size and texture long before she inserts them into her mouth as a part of teething.


• The neonate slobbers, drools, chews her toes, sucks her thumb, and discovers that gurgling sound can be made with her mouth. • The perceptual functions of the mouth and face are combined with the sensory functions of taste, smell, and jaw position. • These sensory inputs are compounded by many dual contacting surfaces, such as the tongue and lips, soft palate and posterior pharyngeal wall, and the strcutures of temporomandibular articulation.


•Reflexes, the innate and automatic responses to sensory input, form the basic language of the motor program, underlying all or most voluntary movements. • The oral pharyngeal reflexes present at birth are the underpinnings for future feeding and swallowing maturation. •Over time, and through repeated stimulation of the reflexive response, neural pathways are set up that extend into higher and higher levels of the CNS.•Gradually movement patterns of the reflexes comes under voluntary control.


• For feeding behavior, movement patterns mature as motor activity is directed by higher centers such as the thalamus and cerebral cortex. • This process is termed encephalization of feeding.• Indeed, after a reflex appears and dominates movement, it is gradually modified or broken up to form components that then can be recombined with other components to create new movements.• In children, as distinct from adults, the progression of feeding skills and acceptance of the feeding process is clearly intertwined with developmental phases (both physical and cognitive) and existent reflex patterns available from which to progress.


•The repertoire of oral-motor behaviors, including oral reflexes, oral-postural control, control of oral secretions, various categories of eating behaviors, vocal behaviors, and voluntary, nonverbal performance, emerge in a developmental and functional hierarchy. •They are performed by a common set of neuromotor systems—labial, lingual, velar, pharyngeal, mandibular, laryngeal, respiratory, and body postural control—using a common set of movements.


•Reflexes are the earliest developed, sensory-guided, oral movements. •During the first three months, the infant is provided with a pool of unconditioned reflexes that subserve survival. • These include the rooting reaction, the suckle-swallow reflex, bite-release reflex, gag reflex, startle reflex, and reflexive closure of the vocal folds.

Rooting Reflex

•The rooting reflex is a stereotypic response to stroking around the mouth that results in movement of the head toward the source of stimulus allowing the infant to latch onto the nipple.•Once the infant is in a feeding ready state (i.e., arousal state), touch stimulation in the perioral area elicits the reflex.

Rooting Reflex

The infant opens her mouth with the tongue slightly extended, and turns her head toward the source of stimulation.

Rooting movements gradually become weaker and start to fade by the 3rd month of life, but may normally persist until 5 months.

If rooting movements continue beyond the 7th month, it may indicate some level of defective functioning in the cortical area, or damage to the CNS.

If the rooting reaction is absent in early infancy, it could indicate some level of damage to the brainstem.

Suckle-Swallow Reflex

The infantile swallow is part of the highly complicated suckling (suck-swallow) reflex.

Suckle feeding entails reflex feeding activity which is organized at the subcortical level, either at the pons or medulla.

It is important to recognize that even though the normal neonate is well prepared to suck and swallow at birth, the physical and motor maturation during the first year alter both the form of the oral structures and the methods by which the infant extracts milk from a nipple.

Each of these changes influences the infant's eating skills.


We have discussed that at birth, the tongue is disproportionately large in comparison with the lower jaw.

Also, the upper jaw protrudes over the lower jaw by approximately 2 mm.

So, when the mouth is closed, the jaws do not rest on top of each other and the tip of the tongue lies between the upper and lower jaws.

There is a "fat pad" in each of the cheeks.

It is thought that these pads serve as a prop for the muscles in the cheek, maintaining rigidity of the cheeks during suckling.


In the normal infant, the oral phase of swallowing is characterized by suckle feeding.

Suckling is a rhythmic movement which involves good lip seal and compression of a nipple.

The lower jaw and tongue compress against the upper jaw and palate to create negative intra-oral pressure.

The tongue moves in an extension-retraction pattern with loose approximation of the lips in what is sometimes referred to as “lip-suck.”

The rhythmical backward and forward pattern of the tongue combines with opening and closing of the jaw to draw (express) liquid into the mouth.


The posterior portion of the oropharynx is closed off by apposition of the tongue and soft palate, allowing the region of the posterior oral cavity to act as a reservoir.

During suckling, the soft palate may move towards the tongue, a motion that does not normally occur in the adult swallow.

While suckling, infants continue to breathe, as the nasal passageways remain open.

As the tongue moves back, it comes in contact with the tensed soft palate.

This causes liquid to squirt into the valleculae.


•Once the valleculae are filled, the swallow response is initiated.•The larynx elevates, but to a lesser extent than in the adult because of its high positioning in the neck.•The epiglottis often contacts the base of the tongue and soft palate.•As the tongue continues to move the liquid back into the pharynx, the epiglottis folds somewhat laterally around the laryngeal vestibule directing the stream of liquid to pass to the sides of the larynx instead of over it.


A prominent pharyngeal wave is seen during this phase, a finding not generally noted in the adult swallow.

While engaging in nutritive suckle feeding, maintenance of an adequate level of ventilation is important.

Two distinct patterns of feeding, namely continuous and intermittent, have been identified in the newborn infant and are thought to be important in the regulation of ventilation (Mathew, 1991).

The continuous phase occurs at the start of a feed when the infant sucks non-stop for at least 30 seconds, usually longer.


• Prolonged bursts of sucking (10-30) may occur at a rate of 2 sucks per second.•During this time, airflow is constantly interrupted by the need for regular swallowing.•During each burst, 1-4 swallows may occur. •After this stage, the infant sucks more intermittently, with short suckling bursts followed by pauses.• Infants use different breathing tactics depending on whether they were sucking or pausing (Craig, Lee, Freer, & Laing, 1999).

Breathing Characteristics

•During the pause period, the breathing pattern of term infants appears more orderly and consistent than during the sucking periods.•Also, breathing duration is significantly more regular in pause periods than in sucking periods. • Indeed, continuous swallowing in the sucking period prevents a regular temporal breathing pattern from being established. •Moreover, it appears that sucking is the dominant component of feeding and that breathing as well as swallowing adapt to meet the demands of sucking.

Breathing Characteristics

Since sucking pressure and frequency determine the volume of milk in the infant’s mouth, swallowing versus breathing frequency will be affected by the amount of milk in the mouth.

Given that the duration of a suck is considerably shorter than the duration of a breath, it appears that the infant ventilatory system is suitably flexible to modulate breathing to meet the changing demands of feeding.

Nutritive Sucking Rates

•Various studies have examined nutritive sucking rate in full-term infants.• Factors which have been found to influence nutritive sucking rates include nipple size (Christensen, Dubignon, & Campbell, 1976), maternal sedation (Casaer, Daniels, Devlieger, DeCock & Eggermont, 1982), length of feeding session (Crump, Gore, & Horton, 1958), and taste of the fluid (Maller & Turner, 1973).

Sucking

•By 3-4 months, suckle phases out to be replaced by sucking.• In the mature or “true” suck, the tongue, lips, mandible, and hyoid bone move together in alternating directions (up-down jaw movements; forward backward tongue movements).• The lips approximate more firmly and the total effect is increased negative pressure and a greater pull of liquid (and soft food) into the mouth. • The infant uses a combination of suck and suckle until approximately 6 months of age when the more efficient suck pattern begins to predominate.

Suck

Sucking, unlike suckling, is not a continuous process.

Upon accumulation of sufficient fluid in the mouth, a swallowing response interrupts sucking and nasal breathing.

Specifically, the closure of the nasopharyngeal and laryngeal sphincters in response to the presence of food in the pharynx is responsible for the interruption of the nasal breathing.

Bite Reflex

The automatic phasic bite-release pattern is a response to tactile input on the biting surfaces of the gums or teeth.

It is characterized by a stereotyped rhythmic vertical bite and release pattern.

This reflex pattern of vertical bite to pressure stimulus persists until approximately 6 months of age.

It is then integrated into the mature pattern of rotary chewing.

A prolonged or persistent biting reflex—the “tonic bite”—is pathologic.

It may be seen in children with cerebral palsy and its presence may inhibit food acceptance or progression to higher textures.

Gag Reflex

• The gag reflex, an oral protective reflex, is evident, not only at birth, but throughout adulthood. • It is an automatic response to tactile input to the posterior section of the tongue, soft palate, or pharyngeal area that reduces somewhat in strength by 7 months of age.•A highly sensitive or hyperactive gag reflex can make transitioning to and swallowing of solid foods very difficult and sometimes impossible.•A hypoactive or absent gag reflex can present a life-threatening situation if the individual is unaware that foods are pressed in the back of the throat.

Other Protective Reflexes

•Other oral protective reflexes include glottic closing-opening, and sneeze-cough.•Reflexive head and neck extension and glottic opening are protective against interference with breathing and are also active during the inspiratory phase of crying.•Reflexive head and neck flexion and glottic closing are protective against the inspiration of liquids and noxious inhalants.•Reflexive sneezing serves to clear the nasopharyngeal area of foreign matter, whereas reflexive coughing serves to clear the laryngeal and oropharyngeal areas.

The Startle Reflex

Finally, the startle or Moro reflex, is a characteristic reaction of infants to any loud noise, sudden movement, or rapid change in position.

The reaction consists of a sudden extension and abduction of the arms, hands, and fingers from their usual flexed posture to adduction and flexion on the chest.

It is strongest during the first 3 months of life and gradually becomes weaker and less apparent, although it never completely disappears.

Development of Oral Motor Control SystemsThe developmental sequence for eating and early sound production is part of a larger schema for the acquisition of movement.

The development of the underlying features of rhythmicity, stability-mobility, separation of movement, and reversion to earlier movement patterns is seen in all motor control systems.

Between the ages of 4-12 months, cortical control is added to the reflexive movement sequences and the early movement patterns become less automatic.

Separation of tongue and lip movement from the jaw begins.

Development of Oral Motor Control Systems

• The infant transitions from bottle/breast nursing, to spoon feeding, to cup drinking.•Oral-motor movements during this period consist of sucking, munching, tongue thrusting, tongue lateralization, and tongue elevation. •Active oral movements that compose suckling continue to predominate in bottle drinking and breastfeeding.• For semisolids presented by spoon, the infant will use suckling, sucking, or small vertical movements of the jaw with occasional up-down movements of the tongue in a munching pattern.


•Munching is the earliest pattern of chewing and is composed of the rhythmical flattening and spreading of the tongue combined with some up-down movement of the jaw. • It begins about 5 months of age with the introduction of solids and develops as a combination of two primitive patterns—bite-release and suckle.•Simple tongue protrusion, or tongue thrust, is also emerging at this time when the direction of tongue movement shifts from the backward-forward orientation of suckling to the up-down orientation of sucking.


The tongue is carried upward with the jaw in the suck phase and protrudes slightly between the gum pads or lips at the point of swallow.

Spoon feeding may be temporarily difficult because of this tongue position, requiring food to be placed on the back of the tongue.

Gagging may also occur regularly as the young infant learns to eat foods having a greater variety of textures, as when moving from liquids to purees, to semisolids, to solids, and finally to mixed textures.

An immature form of tongue lateralization response predominates at 6-7 months.

Development of Oral Motor Control SystemsFood placed at the side of the tongue causes the tongue’s middle section to elevate and rock toward the stimulus.

This rolling movement of the tongue toward the side of the mouth projects food toward (future) molar surfaces.

By 8 months, as more controlled lateral tongue movements and use of the tongue to transfer food from the center to the side of the mouth begins, vertical and lateral-diagonal-circular movements of the jaw become evident.

Around 9 months of age, a second tongue pattern, elevation, emerges and alternates with the simple protrusion during swallow.


As the tongue moves up-down while drawing food and liquid into the mouth, the swallow may be triggered as the jaw and tongue tip are in an elevated position.

As the elevated pattern occurs with greater frequency, the jaw begins to separate from the tongue as it returns to the lowered position.

The tongue remains briefly elevated to the alveolar ridge, lagging briefly behind the lower jaw as it descends.

For the first time, the tongue descends independently from the jaw.


• The young infant now has the ability to start taking sips from a glass with some assistance at approximately 12-14 months of age. • Feeding development from 12-24 months involves increased variability in the combination of lip, tongue, and jaw movements.• Increased postural stability and independence of oral structure movement permits manipulation of different food types and different eating behaviors.


• When the child reaches 18 months of age, the child can drink from a glass without too much spillage or assistance.

• By 18-24 months, a normal child should have mastered chewing, cup drinking, and straw drinking.

Developmental Sequence Summary

Age Reflexes Oral, Fine, Gross Motor Development

1-3 Months •Rooting and suck-swallow reflexes are present at birth•Tonic neck reflex present

•Head control is poor •Secures milk with suckling pattern, the tongue projecting during a swallow•By the end of the third month, head control is developed

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4-6 months •Rooting reflex fades •Bite reflex fades•Tonic neck reflex fades by 16 weeks

•Changes from a suckling pattern to a mature suck with liquids•Sucking strength increases•Munching pattern begins•Grasps with a palmer grasp•Grasps, brings objects to mouth and bites them

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7-9 months •Gag reflex is less strong as chewing of solids begins and normal gag is developing

•Munching movements begin when solid foods are eaten•Rotary chewing begins•Sits alone•Has power of voluntary release and resecural•Holds bottle alone•Develops an inferior pincer grasp


Age Oral, Fine, Gross Motor Development

10-12 months •Bites nipples, spoons, and crunchy foods •Grasps bottle and foods and brings them to the mouth•Can drink from a cup that is held•Tongue is used to lick food morsels off the lower lip•Finger feeds with a refined pincer grasp

Gastroenterology

•The physiological development of the gastrointestinal (GI) tract is influenced by several factors. •In utero, the fetal GI tract is exposed to amniotic fluid that contains physiologically active factors such a growth factors, hormones, enzymes, and immnoglobulins.•Introduction of human milk in breastfeeding provides growth factors and hormones as well as digestive enzymes to enhance the newborn’s ability to digest and absorb feedings.•These play a role in mucosal differentiation and GI development as well as the development of swallowing and intestinal motility.

Gastroenterology

•Digestion and absorption in the newborn requires:• Coordinated sucking and swallowing; • Gastric emptying;• Intestinal motility; • Salivary, gastric, pancreatic, and

hepatobiliary secretions; • Intestinal cell function to synthesize

enzymes, absorb nutrients, and offer mucosal protection; and

• Expulsion of undigested waste products. •The full-term newborn is prepared to digest and absorb an adequate supply of nutrients for normal growth and development from breast milk or formula.

Gastroenterology

• The digestive capacity of the infant matures and increases during the first year of life. • Feeding stimulates release of several

hormones that are related to GI motility, intestinal development, and pancreatic cell function. • The developing stomach and intestine

provide an increasing ability to handle various nutrients and textures provided by food. • However, esophageal motility is decreased in

the newborn compared to older infants and children.

Gastroenterology

•In addition the lower esophageal sphincter (LES) is primarily above the diaphragm and LES pressure is less for the first months of life. •Gastric emptying may be delayed in early infancy and intestinal motility is more disorganized. •Due to these physiological realities, infants commonly experience regurgitation or "spitting up." •Stomach capacity at birth is 10 to 12 ml, as compared to 200 ml at 1 year, so newborns require small frequent feeds.

Gastroenterology

•Transit time through the small intestine is slower for infants than for adults. •This may help to insure adequate digestion and absorption of nutrients. •However, passage through the large intestine is more rapid. •Infants are at increased risk for dehydration if water and electrolyte reabsorption in the large intestine are further compromised.

Nutrition and Hydration

•The newborn has an immature kidney, and can maintain water and electrolyte balance only within a fairly narrow range of intakes and losses. •In addition, the pituitary gland produces only limited quantities of the antidiuretic hormone (ADH) vasopressin, which normally inhibits diuresis. •These factors limit the newborn's ability to concentrate urine and to cope with fluid and electrolyte stress, i.e., electrolyte-dense formula, limited fluid intake, and diarrhea.

DEVELOPMENTAL INFLUENCES ACROSS THE LIFESPAN Part 2.

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