Medulla oblongata at its lower end (at the plane of motor decussation)

Medulla oblongata at its lower end (at the plane of motor decussation)

Structural characteristics

  1. At this level structure of medulla oblongata is almost similar to the structure of spinal cord, with centrally positioned gray matter and peripheral white matter.
  2. Ventral horn of gray matter gets separated from main mass due to decussation of pyramidal tract fibers which pass backwards and laterally to approach lateral white column before passing downwards to the spinal cord.

Structural detail
Gray matter:

  1. Central gray matter is traversed by more dorsally pushed central canal lined by ependyma.
  2. Apex of posterior horn of spinal cord is represented at this level by nucleus of spinal tract of trigeminal nerve. On either side it is directed backwards and laterally with further abduction.
  3. Medial to nucleus of spinal tract of trigeminal nerve, gray matter shows, on either side, two small bulge of gray matter, nucleus gracilis (medial) and nucleus cuneatus (lateral) which receive the fibers of fasciculus gracilis and fasciculus cuneatus respectively, which are the ascending tracts in posterior column of white matter.
  4. Anterior gray horn becomes detached from main mass of gray matter by decussating fibers of corticospinal (pyramidal) tract.

Topographically, cells of anterior horn is a part of gray matter of medulla oblongata. But functionally, these are upwards continuation of cells of anterior horn of upper cervical segments of spinal cord. These cells form following two nuclei.

  1. Supraspinal nucleus of first cervical nerve: It is the upward continuation of anterior horn cells of first cervical segments of spinal cord. Axons of these neurons pass downward and are distributed along the ventral root of first cervical nerve.
  2. Ascending nucleus: It is the upward continuation of spinal nucleus of accessory nerve which is continuous below up to fifth cervical segment of spinal cord. Above it is continuous with nucleus ambiguous.

Medulla oblongata at its lower end (at the plane of motor decussation)

White matter: Pattern of three white columns (funiculi) of spinal cord, namely anterior, lateral and posterior, is grossly maintained.

  1. Anterior column: On either side of ventral median fissure, area of anterior white column mainly presents the bundle of pyramidal tract fibers which shows decussation of fibers at this level. Through anterior column, also traverse tectospinal tract, vestibulospinal tract, anterior spinothalamic tract.
  2. Lateral Column:
    1. Peripherally: Dorsal and ventral spinocerebellar tracts.
    2. Centrally:
    1. Lateral corticospinal tract which is formed at this level after decussation of fibers of pyramid.
    2. At the center of lateral white column, a scattered group of nerve cells intermingled with nerve fibers form brainstem reticular formation.
    3. Lateral spinothalamic tract.
  3. Posterior column: It present upward continuation of fasciculus gracilis and fasciculus cuneatus of posterior white column of spinal cord. As already mentioned earlier, these two tracts will relay in next order of neurons in nucleus gracilis and nucleus cuneatus which are seen to appear at this level of medulla oblongata, ventral to the corresponding tracts.

Source: Easy and Interesting Approach to Human Neuroanatomy (Clinically Oriented) (2014)


Medulla oblongata at its middle

Medulla oblongata at its middle

Structural characteristics

  1. There is no more existance of gray matter area which is homologous to anterior horn.
  2. Gray matter of posterior horn presenting nucleus gracilis, nucleus cuneatus and spinal nucleus of trigmenial nerve gets detached from central gray matter. This detachment is because of the arched fibers arising from nucleus gracilis and nucleus cuneatus which decussate ventrally to form ascending fiber tract which is called medial lemniscus.
  3. Central canal surrounded by central gray matter is pushed more dorsally. Central gray matter presents appearance of cranial nerve nuclei.
  4. It is the plane of medulla oblongata from where upward typical relationship of central gray matter and peripheral white matter of spinal cord is lost. It results intermingling of gray and white matters.

Structural details

  1. On either side of ventral median fissure bulge of pyramid presents sections through descending (efferent) fibers of pyramidal (corticospinal) tract.
  2. Lateral to fibers of pyramid, inferior olivary nucleus starts appearing. It looks like a small irregularwalled sac whose cavity opens backwards and medially. Inferior olivary nucleus is the most prominent part of olivary nuclear complex of human brain. Rudimentary components are dorsal and medial olivary nuclei which together are known as accessory olivary nuclei.
  3. Ascending (afferent) tracts, e.g. dorsal and ventral spinocerebellar tracts, lateral and anterior spinothalamic tracts are found to be in corresponding positions as noticed in previous section of medulla oblongata.
  4. Nucleus gracilis and nucleus cuneatus are seen to be more prominent in this section. These nuclei receive fibers from fasciculus gracilis and fasciculus cuneatus which carry conscious proprioceptive sensation and sense of tactile discrimination from lower and upper halves of body respectively.
  5. Dorsolateral to nucleus cuneatus, a smaller accessory cuneate nucleus is seen. It receives fibers of fasciculus cuneatus which carry same sensations from uppermost part (head-end) of body. Cuneocerebellar tract from this nucleus end in cerebellum as spinocerebellar pathway above T1 spinal cord segment.
  6. Central core of the section presents scattered nerve cells and reticulum (network) of fibers to form brainstem reticular formation.
  7. Posterior gray horn separated from central gray matter is represented by spinal nucleus of trigeminal nerve which is capped on the surface by fibers of sensory root of trigeminal nerve carrying pain and temperature sensation, called spinal tract of trigeminal nerve.

Nucleus gracilis and nucleus cuneatus are the medial and lateral mass of gray matter on either side of posterior median septum. These are also the components of posterior gray horn which are detached from central gray matter.
Reason for separation of spinal nucleus of trigeminal nerve, nucleus gracilis and nucleus cuneatus from central gray matter is due to followingcharacteristic of structure of medulla oblongata at this level.

Medulla oblongata at its middle

Fasciculus gracilis and fasciculus cuneatus are the two ascending tracts of posterior column of spinal cord which carry sense of conscious proprioception and tactile discrimination from lower and upper halves of body respectively. Reaching the medulla oblongata upto this level, fibers of these two tracts relay in corresponding nuclei lying ventrally. Processes of next order of neurons in nucleus gracilis and nucleus cuneatus, before ascending further upwards to relay in thalamus, decussate to cross the midline. During decussation, these fibers presents following three characteristics.

  1. Fibers of both nucleus gracilis and nucleus cuneatus pass forwards arching along the lateral aspect of central gray matter horizontally in a curved fashion that is why they are called internal arcuate fibers.
  2. After decussation, the fibers form a compact bundle just behind the bulge of pyramid, before this compact bundle of fibers ascend upwards to reach thalamus. This bundle is known as medial lemniscus (Plural – Lemnisci).
  3. During formation of medial lemnisci, fibers from nucleus gracilis (carrying sensations from lower half of body) are positioned anterior to the fibers from nucleus cuneatus (carrying sensation from upper half of body).
    Behind medial lemniscus, pass tectospinal tract medial longitudinal fasciculus.

Central gray matter: It encircles the central canal of medulla oblongata which is pushed more posteriorly. It presents following cranial nerve nuclei which are interrelated ventrolaterally.

  1. Hypoglossal nerve nucleus (XII): It is the nucleus of somatic efferent column, lying ventral to central canal of medulla oblongata.
  2. Nucleus ambiguous (IX, X, XI): It

Source: Easy and Interesting Approach to Human Neuroanatomy (Clinically Oriented)


Medulla oblongata at the level of olive

Medulla oblongata at the level of olive

he medulla oblongata (medulla) is one of the three regions that make up the brainstem. It is the most inferior of the three and is continuous above with the pons and below with the spinal cord. The medulla houses essential ascending and descending nerve tracts as well as brainstem nuclei.

In this article, we shall look at the anatomy of the medulla – its external features, internal anatomy, and blood supply.

External Anatomy of the Medulla

The medulla is conical in shape, decreasing in width as it extends inferiorly. It is approximately 3cm long and 2cm wide at its largest point.

The superior margin of the medulla is located at the junction between the medulla and pons, while the inferior margin is marked by the origin of the first pair of cervical spinal nerves. This occurs just as the medulla exits the skull through the foramen magnum.

Anterior Surface

There are several structures visible on the anterior surface of the medulla – namely the three fissures/sulci, the pyramids, the olives, and five cranial nerves.

In the midline of the medulla is the anterior median fissure, which is continuous along the length of the spinal cord. However, it is interrupted temporarily by the decussation of the pyramids (see below). As we move away from the midline, two sulci are visible – the ventrolateral sulcus and the posterolateral sulcus.

The pyramids are paired swellings found between the anterior median fissure and the ventrolateral sulcus. Information on the pyramids can be found here. The olives are another pair of swellings located laterally to the pyramids – between the ventrolateral and posterolateral sulci.

Arising from the junction between the pons and medulla is the abducens nerve (CN VI). Extending out of the ventrolateral sulcus is the hypoglossal nerve (CN XII). In the posteriolateral sulcus, three more cranial nerves join the medulla (CN IX, CN X, and CN XI).

Posterior Surface

Unlike the anterior surface of the medulla, the posterior surface is largely obstructed from view and is relatively devoid of features. In order to appreciate the posterior surface, the cerebellum must be removed.

Similar to the anterior surface, the posterior surface has a midline structure – the posterior median sulcus – which is continuous below as the posterior median sulcus of the spinal cord. Above, the sulcus ends at the point in which the fourth ventricle develops.

As we move lateral from the midline, the fasciculus gracilis and fasciculus cuneatus are seen, separated by the posterior intermediate sulcus.

Medulla oblongata at the level of olive

Internal Anatomy of the Medulla

The internal structures of the medulla must be viewed in cross section to understand the layout. Three levels of the medulla are typically discussed (inferior – superior):

  • Level of decussation of the pyramids
  • Level of decussation of the medial lemnisci
  • Level of the olives

The medulla itself is typically divided into two regions: the open and the closed medulla. This distinction is made based on whether the CSF-containing cavities are surrounded by the medulla (closed medulla) or not (open medulla). The medulla becomes open when the central canal opens into the fourth ventricle (see Fig. 3).

Some features are seen in all three cross sections. Anteriorly we can see the paired lumps representing the pyramids which are separated by the anterior median fissure. Centrally, the central canal can be seen as it rises to form the fourth ventricle in the final cross section.

Level of the Decussation of the Pyramids

This is the major decussation point of the descending motor fibres. Roughly 75% of motor fibres housed within the pyramids cross diagonally and posteriorly, and continue down the spinal column as the lateral corticospinal tracts.

At this level, the central portion of the medulla contains gray matter, while the outer portions consist of white matter. The posterior white matter contains the fasiculus gracilis and the more lateral fasiculus cuneatus. Corresponding portions of gray matter extend to these regions and are the nucleus gracilis and nucleus cuneatus respectively.

Unchanged from the spinal cord, the spinocerebellar tracts (posterior and anterior) are located laterally, with the lateral spinothalamic tract situated between them. The large trigeminal nucleus and tracts can be found posterior to these tracts. This is a continuation of the substantia gelatinosa of the spinal cord.

Level of Decussation of the Medial Lemniscus

This level marks the sensory decussation occurs of the medial lemniscus. (Fig. 5). Purple lines have been used to represent the internal arcuate fibres as they run from the nucleus gracilis and nucleus cuneatus around and anterior to the central gray matter to form the medial lemniscus.

Lateral to the medial lemniscus, the trigeminal nucleus and spinal tract can once again be seen, as can the spinocerebellar tracts and the lateral spinothalamic tract. Similarly, the posterior structures are much the same at this level.

Centrally, the hypoglossal nucleus and medial longitudinal fasciculus are seen. Moving laterally, the nucleus ambiguous can be seen. Between this structure and the pyramids is the inferior olivary nucleus.

Medulla oblongata at the level of olive

Level of the Olives

This level shows significant change in structure both externally and internally when compared with previous levels. The central canal has now expanded into the fourth ventricle and as such makes this region the open medulla.

The large inferior olivary nucleus is responsible for the external expansion of the olives. The related medial and dorsal accessory olivary nuclei can be seen medial and posterior to this structure respectively.

The large inferior cerebellar peduncles come into view and are surrounded by multiple nuclei. The two vestibular nuclei (medial and inferior) are both found towards the midline while the two cochlear nuclei are found somewhat above and below the peduncles. Now a much smaller structure, the trigeminal tract and nucleus is seen adjacent to the peduncle.

The nucleus ambiguous remains as it was previously, while the hypoglossal nucleus has migrated with the central canal posteriorly, joined by the medial longitudinal fasciulus. An additional cranial nucleus comes into view lateral to the hypoglossal – the dorsal vagal nucleus. Moving further lateral, the nucleus of tractus solitarius comes into view.

Centrally, the medial lemniscus hugs the midline posterior to the pyramids, as does the tectospinal tract.

Between the peduncle and the olivary nuclei resides the lateral spinothalamic tract and the more lateral anterior spinocerebellar tract.

Vasculature

The vasculature of the medulla is complex and is dependent on the level being viewed (Fig. 7). The following attempts to simplify this complexity. Despite this it may suffice the reader to know that the vessels that supply the medulla include: the anterior spinal, the posterior spinal, the posterior inferior cerebellar, the anterior inferior cerebellar, and vertebral arteries.

Throughout the medulla, the anterior spinal artery supplies a region beginning at the central canal (or anterior border of the fourth ventricle), and fans out to encompass the pyramids.

Below the level of the olives the posterior half of the medulla is supplied by the posterior spinal artery. No other regions are supplied by this vessel. The remaining portions are supplied by the posterior inferior cerebellar and vertebral arteries.

In cross section through the olives both the posterior inferior cerebellar and vertebral arteries take on greater territories posterolaterally and anterolaterally respectively. They continue to do so as the medulla ascends.

At the highest point in the medulla, the anterior inferior cerebellar artery supplies the outermost portions of the posterior region.


Tegmental part at lower half of pons

Tegmental-part-at-lower-half-of-pons

Gray matter: Some cranial nerve nuclei and nuclei of pontine part reticular formation. l Abducent nerve nucleus: It is the nucleus of somatic efferent group. Fibers of abducent (VIth cranial) nerve arising from this nucleus supply lateral rectus muscle of eyeball which is developed from preoccipital myotome of paraaxial mesoderm. This nucleus is situated deep to a paramedian bulge adjacent to posterior median sulcus. The bulge is called facial colliculus because the surface of abducent nucleus is winded by fibers of facial nerve.

  • Motor nucleus of facial nerve: This is the nucleus of special visceral efferent column which supplies muscles developed from mesoderm of second branchial arch.efferent nucleus of facial nerve, situated lateral to motor nucleus of facial nerve. It has a component called lacrimatory nucleus. Parasympathetic secretomotor fibers from these nuclei are directed to supply to submandibular and sublingual salivary glands, and lacrimal gland.
  • Spinal nucleus of trigeminal nerve: This is exteroceptive variety of general somatic afferent nucleus of trigeminal nerve, which receives pain and temperature sensation from skin of face. Though called spinal nucleus, main part of this nucleus extends throughout whole length of medulla oblongata. Its lower end extends upto 2nd cervical segments of spinal cord and upper end extends to the lower half of pons. This nucleus is situated in the lateral part of tegmentum of lower end of pons. It receives sensory fibers of trigeminal nerve which caps dorsal aspect of the nucleus to form spinal tract of the nerve.
  • Vestibular nucleus of vestibulocochlear nerve:
    This is proprioceptive type of special somatic afferent nucleus of vestibulocochlear nerve. It is composed of superior, lateral, medial and inferior parts. Vestibular nucleus is situated partly in lower part of pons and upper part of medulla. It is placed in superficial plane at the lateral angle of pontomedullary junction. This nucleus receives afferent fibers which are nothing but vestibular fibers of VIIIth cranial nerve carrying sense of equilibrium or balance.

Tegmental-part-at-lower-half-of-pons
Efferent fibers are:

    1. Vestibulocerebellar fibers
    2. Vestibulospinal fibers
    3. Medial longitudinal bundle: Which connect vestibular nucleus with nuclei of IIIrd, IVth, VIth and XIth cranial nerves and anterior horn cells of upper cervical segments of spinal cord. It causes reflex movement of eyeball and head and neck in response to change of position body.
    4. Cochlear nucleus of vestibulocochlear nerve: It is exteroceptive type of special somatic afferent nucleus of cochlear component of vestibulocochlear nerve. It is made up of dorsal and ventral components lying dorsal and ventral to inferior cerebellar peduncle fibers at the level of pontomedullary junction.

    1. Connections of cochlear nuclei:
  • Afferent: Fibers of cochlear component of vestibulocochlear nerve carrying sense of hearing from receptors (organ of Corti) at internal ear relay in dorsal and ventral cochlear nuclei.
  • Efferent: Axons of cochlear nuclei will have to reach upto corresponding thalamic nuclei to carry impulse to sensory area of cerebral cortex. While ascending through central core of brainstem to reach the thalamus, at the level of lower end of pons, relayin a nucleus, called nucleus of trapezoid body. Before the relay, axons of both dorsal and ventral cochlear nuclei partly remain in the same side, partly cross the midline to relay in nucleus of trapezoid body of opposite side. In horizontal section, the fibers show a trapezoid shape, for which the decussating and nondecussating fibers are called trapezoid body, so the nucleus is also accordingly named.

Problems with the learning process

Problems with the learning

In some infants, perceptual processing that depends upon innate recognition may be damaged and perceptual attributes that lead to salience may not be perceived. Perception that depends upon temporal processing may be slowed and crossmodality may be impaired. Meaning may be more easily accessed visually (i.e. what is seen may make more sense than what is heard). Infants learn from the repeated familiar and respond to difference – a learning style used in the ‘habituation to repeat stimulus’ in developmental experiment.

Learning from the familiar needs repeated stimulus and is enhanced if as many features as possible are fixed and what is remembered depends upon the match between context and item. This is a stage of normal development referred to as ‘context bound’ learning, when children recognize their own cups or shoes, for example, but not ‘cupness’ or a sentence said by one person in one place but not another. Some children get stuck in this stage and require a sustained high degree of contextual or environmental sameness to show a skill. This is particularly shown in autism.

Children learn from ‘contingency’ – the event that follows within 3–5 seconds of their action. This may be disrupted by a number of mechanisms, such as:
1. failure of the adult to make the response (depressed/mentally ill caregiver);
2. the child not giving a clear enough signal (as for those who are blind or who have cerebral palsy).

Aspects of maternal or caregiver behavior that promote learning need to be sensitively adjusted to developmental level. Thus at 2 years of age, language input needs to be explicitly directive and adult actions tied to the focus of child interests. By 3 years less parental direction is needed because the child has more language and is learning to manage her own goal-setting and problem-solving skills.

Play complexity is enhanced by caregiver behaviors that maintain a child’s focus of attention rather than redirect it. Children also learn more through the process of learning itself. For example, learning particular names of shapes accelerates shape learning generally, as though attention to the ‘shape concept’ allows noticing of ‘shapeness’. The child’s ability to inhibit and select responses and to try alternatives is crucial to all cognitive learning. This is seen in the progression from the ‘trial and error’ approach, where repeatedly forcing the square into the round hole is a less useful strategy than trying alternative placements with inset puzzles, which shows more flexibility of mental skills.

The progress from sensorimotor play, from mouthing to manipulation at 6–10 months, then to imitation and ‘definition by use’ play by 12 months is followed by increasing creativity in play. Make-believe play with dolls, in which the child is reconstructing events observed, is an important element of this period. It indicates early symbolic representation and concept formation. The child begins to use language to direct or describe the action of his play, and as command of language improves the need to act out the events decreases. Lack of ideas, failure of pretence and inability to play constructively are indications of a developmental problem. The cognitive stage of mental symbolic development allows more complex thinking, including reflection and planning. Symbols (word ) facilitate thinking about, and reference to, situations that are not in the ‘here and now’. Answering simple questions dealing with nonpresent situations presents difficulty before 3 years and even primary and junior school children still tend to be concrete in their way of thinking (i.e. real objects, here and now). Early in school life, judgments are made intuitively on superficial appearances. With increasing experience and language at their disposal, children can imagine complex situations, think out the most appropriate solution and anticipate the outcome.

This requires the ability to think abstractly and imaginatively. Thus, children develop logical thinking from assimilating experience into schemes or general laws that they can apply to a range of situations. The use of symbols also helps to inhibit prepotent responses of behaviors and allows increasing distancing from the ‘here and now’ (rather like the red card in football games). Children are developing skills of representation and object substitution in the second year, but the skill of mentally comparing reality with representation (dual reality) is not clearly seen in research studies until aged 3 years. For example, children shown where an object is hidden in a scale model of a room can find it in the real room at 3 years, but not at 30 months. At 3–6 years, children get increasingly skilled at knowing that others can hold particular views, even false views, and thus have what has been called a ‘theory of mind’. In the classic Wimmer and Perner task, roughly half the 4- to 5-year-old children could correctly show ‘knowing’, whereas over 90% of 6- to 9


Cognitive and Learning Development

Learning Development

Children learn about their world by listening, observing, copying and experimenting. The world of infants is very small and their repertoire of skills limited. They learn about their world through observation, by reaching and grasping objects and by copying sounds and actions. By contrast, toddlers are mobile and their worlds are large. Their motor skills are greater and they begin to attempt constructional tasks, thereby learning about aspects such as size, shape, the properties of objects and space.
The child is an active participant in the learning process. Progress depends upon not only the learning opportunities, but also the child’s learning strategies and processes. Information processing in infants is related to later cognitive abilities in memory and speed of processing, thus in visual recognition tasks, habituation, learning, object permanence and attention, including crossmodality.

In older children, the features of new problem solving that are linked to learning are variability, ability to shift focus, frequency of self-correction and diversity of strategies.


B Cells

B Cells

B-Cell Development

B cells constitute approximately 10% of peripheral blood leukocytes. They develop in the bone marrow from hematopoietic stem cells but achieve maturity in peripheral lymphoid organs. Early progenitors committed to the B-cell lineage (pro–B cells) begin recombination at the immunoglobulin heavy-chain loci. Successful recombination leads to expression of μ–heavy chain, distinguishing them from pre–B cells. With the surrogate light chain and the Ig-α/β signaling machinery, an immunoglobulin-like heterodimer is expressed on the surface (pre–B-cell receptor). The pre–B-cell receptor signals a halt to μ–heavy-chain recombination, and Igκ or Igλ light-chain recombination begins. The surrogate light chain is replaced by a successfully formed κ or λ light chain, and the B-cell receptor is expressed as surface IgM, which distinguishes the immature B cell.

B Cells

B-Cell Responses

B cells provide humoral immunity against extracellular pathogens through the production of antibodies that neutralize pathogens and toxins, facilitate opsonization, and activate complement. Primary infection or vaccination results in prolonged production of high-affinity specific antibodies, the basis of adaptive humoral immunity. On the other hand, IgM antibodies are produced in the absence of infection, are of lower affinity, play a role in first-line defense against bacterial infection, and assist in clearance of endogenous cellular debris. Naïve follicular B cells reside in the follicles of secondary lymphoid tissues. Antigen arrives in these lymphoid organs through circulation of soluble molecules or immune complexes or via transportation by dendritic cells. The B cells, via the B-cell receptors, process the antigens in the context of MHC class II and then migrate to the T cell–B cell interface, the border between the T-cell zone and B-cell follicle, where they encounter primed TH cells of cognate specificity. This generates signals from T-cell–derived cytokines and triggers binding between CD40 ligand (CD40L, on T cells) and CD40 (on B cells) that sustains B-cell activation and promotes immunoglobulin class switching. Signaling through CD40 and its interaction with CD40 ligand on T cells is essential for the induction of isotype switching.

The effector T-cell cytokines have various functions: IL-1 and IL-2 promote B-cell activation and growth, IL-10 causes switching to IgG1 and IgG3, IL-4 and IL-13 cause switching to IgE, and TGF-β causes switching to IgA. IFN-γ, or some other undefined product of TH1 cells, appears to induce switching to IgG2. Activated B cells either migrate into the follicle and, with continued T-cell help, initiate the germinal center reaction or migrate to the marginal zone and differentiate into short-lived plasma cells. These latter cells secrete antibody for 2 to 3 weeks, which provides a rapid but transient source of effector molecules.

The B cells in the germinal center undergo specificity diversification through somatic hypermutation, and high-affinity variants are selected by survival advantage, a process termed affinity maturation. Thus within the germinal centers, sequential cycles of proliferation, B-cell receptor diversification, and selection amplify high-affinity variants of the original activated B cell. The cells that then exit the germinal center reaction give rise to the memory compartment, which consists of affinity-matured memory B cells and long-lived plasma cells. When memory cells reencounter antigen, they divide rapidly and expand their numbers or differentiate into antibody-secreting plasma cells. These long-lived plasma cells are terminally differentiated B cells incapable of further division that home to the bone marrow and secrete high-affinity class-switched antibody. These B cell responses are orchestrated with the help of T cells and their cytokines and are termed T-cell–dependent B-cell responses.


Sound Perception

Sound Perception

The ear is fully developed at birth and sound perception is possible in utero. Speech perception and recognition of voices of different speakers are present shortly after birth. The capacity for smell and touch as well as the other senses are similarly developed at birth and play an important part in the perceptual learning about the environment.


Atopic Dermatitis

Atopic dermatitis

Although atopic (infantile or flexural) dermatitis may begin at any age, it usually commences from about the sixth week onwards. It is characterized by a chronic, relapsing course. In the infantile phase lesions are present mainly on the head, face, neck, napkin area, and extensor aspects of the limbs. As the patient grows older and enters childhood, the eruption shifts to the flexural aspects of the limbs. Chronic atopic cheilitis may also be evident. Pruritus is intense and constant scratching and rubbing leads to lichenification and frequent bouts of secondary bacterial infection. Atopic eczema is commonly associated with dry skin (xerosis). Vesiculation is uncommon. there is an increased risk of dermatophyte and viral infections. The disease improves during childhood and, in over 50% of cases, clears completely by the early teens. approximately 75% of patients with atopic dermatitis have a family history of atopy and up to 50% have associated asthma or hay fever. The condition typically worsens in the winter months.

Atopic dermatitis

It is associated with an increased incidence of contact dermatitis, particularly affecting the hand. Other features that may be seen include ichthyosis (50%), nipple eczema, conjunctivitis, keratoconus, bilateral anterior cataracts, sweat-associated itching, wool intolerance, perifollicular accentuation, food intolerance and white dermatographism. 5 Infraorbital folds (DennieMorgan folds) are said to be characteristic of atopic dermatitis, particularly when double.


Psoriasis

Psoriasis

Psoriasis is a chronic relapsing and remitting disease of the skin that may affect any site. It is one of the commonest of all skin diseases, with a reported incidence of 1–2% in Caucasians. It is rare among blacks, Japanese, and native North and South american populations. Males and females are affected equally. Although psoriasis may occur at any age, it most frequently presents in the teens and in early adult life (type I psoriasis). A second peak in which the disease is often milder appears around the sixth decade (type II psoriasis).

Psoriasis

The classic cutaneous lesion of psoriasis vulgaris (plaque psoriasis), developing in about 85–90% of patients with psoriasis, is raised, sharply demarcated, with a silvery scaly surface. The underlying skin has a glossy, erythematous appearance. If the parakeratotic scales are removed with the fingernail, small droplets of blood may appear on the surface (auspitz’s sign); this is diagnostic. plaques, when multiple, are often symmetrical and annular lesions due to central clearing are a common finding. the scalp, the extensor surfaces (mainly the knees and elbows), the lower back, and around the umbilicus are particularly affected. the clinical features, however, show regional variation: scalp involvement often shows very marked plaque formation, whereas on the penis scaling is commonly minimal and the features may be mistaken for Bowen’s disease. Linear lesions (linear psoriasis) follow previous trauma (koebnerization).

Source: P. McKee, J. Calonje – McKee’s Pathology of the Skin (Elsevier)