2012 Group Project 4: Difference between revisions

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== History of Discovery ==
== History of Discovery ==
Julius Kollmann was revolutionary and prominent German scientist from the late 1800s, early 1900s. He was involved in a wide variety of fields ranging from anatomy, to anthropology<ref name:"PMID3548583"><pubmed>3548583</pubmed></ref>. He published a textbook called the Atlas of the Development of Man 2 in 1907. Included in this textbook were a great number of diagrams depicting olfactory development. For example a diagram of the riechpiakode which is the olfaction placode. Kollmann explains that the placode is formed from multiple layers of ectoderm.      
Julius Kollmann was revolutionary and prominent German scientist from the late 1800s, early 1900s. He was involved in a wide variety of fields ranging from anatomy, to anthropology<ref name:"PMID3548583"><pubmed>3548583</pubmed></ref>. He published a textbook called the Atlas of the Development of Man 2 in 1907. Included in this textbook were a great number of diagrams depicting olfactory development. For example a diagram of the riechpiakode which is the olfaction placode. Kollmann explains that the placode is formed from multiple layers of ectoderm       


The 2004 Nobel Prize in Physiology or Medicine was won by Linda B. Buck and Richard Axel for their work on the olfactory system<ref>http://www.nobelprize.org/nobel_prizes/medicine/laureates/2004/press.html</ref>
The 2004 Nobel Prize in Physiology or Medicine was won by Linda B. Buck and Richard Axel for their work on the olfactory system<ref>http://www.nobelprize.org/nobel_prizes/medicine/laureates/2004/press.html</ref>

Revision as of 11:53, 29 August 2012

Olfaction Development

Introduction

The sense of smell, or otherwise known as Olfaction is the sense mediated by sensory cells located in the nasal cavity. Chemo receptors within the naval cavity are activated by chemicals in the air which are known as odorants. Odorants produce olfactory sensation at very low concentration, and through the reaction with chemoreceptors enables the sense of smell in humans. The olfactory system are often divide into a peripheral mechanism, activated by an external stimulus and transforming it into an electric signal in neurons, and a central mechanism where all signals formed by olfactory are integrated in the central nervous system and processed to recognise odor. Over 1000 genes which make up three percent of the total human genome which encode for olfactory receptor types which can each detect a small number of related molecules and respond with different level of intensity. It has been discovered that olfactory receptor cells are highly specialized to particular odors.

History of Discovery

Julius Kollmann was revolutionary and prominent German scientist from the late 1800s, early 1900s. He was involved in a wide variety of fields ranging from anatomy, to anthropology[1]. He published a textbook called the Atlas of the Development of Man 2 in 1907. Included in this textbook were a great number of diagrams depicting olfactory development. For example a diagram of the riechpiakode which is the olfaction placode. Kollmann explains that the placode is formed from multiple layers of ectoderm

The 2004 Nobel Prize in Physiology or Medicine was won by Linda B. Buck and Richard Axel for their work on the olfactory system[2]

Timeline of developmental process

Week/Stage Description Image
'Stage 12. By stage 12, most embryos have well defined nasal placodes which lie on either side of rostral neuropore. [3].
'Stage 13 This will explain the telencephelon development [3]
Stage 14 explanation [4]
Stage 15 word linked to glossary explanation
Stage 16 info image


    • This is an organisation of relevant materials taken out of the textbook, still to be revised and translated into carnegie stages.

A: anatomy description

N: neuronal description

Week 4:

A:All five facial swellings form by the end of the 4th week. These initially surround the primitive oral cavity, the stomodeum, which is separated from the gastrointestinal tract by the oropharyngeal (buccopharyngeal or oral) membrane (see Fig. 16-15C). The important facial swelling is the frontonasal prominence which gives rise to the nasal placode. the frontonasal prominence overlying the forebrain, arises from neural crest cells derived from the midbrain and forebrain, whereas the maxillary and mandibular prominences receive neural crest cell contributions from both the midbrain and hindbrain (see Fig. 16-12).

N: Very early, some cells in the nasal placode differentiate to form the primary neurosensory cells of the future olfactory epithelium.

Week5:

A:the paired maxillary prominences enlarge and grow ventrally and medially. Simultaneously, a pair of ectodermal thickenings, called the nasal or olfactory placodes (also called nasal discs or nasal plates) form on the frontonasal prominence and begin to enlarge (see Fig. 16-15C).

N:At the end of the 5th week, the primary neurosensory cells cells sprout axons that cross the short distance to penetrate the most cranial end of the telencephalon (Fig. 9-25A). The subsequent ossification of the ethmoid bone around these axons creates the perforated cribriform plates.

Week 6:

A: the ectoderm at the center of each nasal placode invaginates to form an oval nasal pit, dividing the frontonasal prominence into the lateral and medial nasal processes (Fig. 16-16A, B). The groove between the lateral nasal process and the adjacent maxillary prominence is called the nasolacrimal groove (naso-optic furrow) the medial nasal processes migrate toward each other and fuse to form the primordium of the bridge and septum of the nose (see Fig. 16-16A, B). At the end of the 6th week, as the medial nasal processes start to merge, the dorsal region of the deepening nasal pits fuse to form a single, enlarged ectodermal nasal sac lying super posterior to the intermaxillary process (see Fig. 16-19A, B).

N:as the nasal pits differentiate to form the epithelium of the nasal passages, the area at the tip of each cerebral hemisphere (where the axons of the primary neurosensory cells synapse) begins to form an outgrowth called the olfactory bulb (Fig. 9-25B-D). The cells in the olfactory bulb that synapse with the axons of the primary sensory neurons differentiate to become the secondary sensory neurons (mitral cells) of the olfactory pathways. The axons of these cells synapse in the olfactory centers of the cerebral hemispheres. As the changing proportions of the face and brain lengthen the distance between the olfactory bulbs and their point of origin on the hemispheres, the axons of the secondary olfactory neurons lengthen to form stalk-like CNS olfactory tracts. Traditionally, the olfactory tract and bulb together are referred to as the olfactory nerve.

Week 7:

A: The groove between the lateral nasal process and the adjacent maxillary prominence is called the nasolacrimal groove (naso-optic furrow) (Fig. 16-16C). During the 7th week, the ectoderm at the floor of this groove invaginates into the underlying mesenchyme to form a tube called the nasolacrimal duct and lacrimal sac. This duct is invested by bone during the ossification of the maxilla. After birth, it functions to drain excess tears from the conjunctiva of the eye into the nasal cavity. By the end of the 7th week, the inferior tips of the medial nasal processes expand laterally and inferiorly and fuse to form the intermaxillary process (Fig. 16-16C, D) From the end of the 6th week to the beginning of the 7th week, the floor and posterior wall of the nasal sac proliferate to form a thickened, platelike fin, or keel, of ectoderm separating the nasal sac from the oral cavity. This structure is called the nasal fin (see Fig. 16-19B). Vacuoles develop in the nasal fin and fuse with the nasal sac, thus enlarging the sac and thinning the fin to a thin membrane called the oronasal membrane, which separates the sac from the oral cavity (see Fig. 16-19C). This membrane ruptures during the 7th week to form an opening called the primitive choana (see Fig. 16-19D, E). The floor of the nasal cavity at this stage is formed by a posterior extension of the intermaxillary process called the primary palate (see Fig. 16-19E). At this point the nasal and oral cavity are continuous but these will be separated by the formation of the palatal shelves.

Week 8:

A: While the secondary palate is forming, ectoderm and mesoderm of the frontonasal prominence and the medial nasal processes proliferate to form a midline nasal septum that grows down from the roof of the nasal cavity to fuse with the upper surface of the primary and secondary palates along the midline (see Fig. 16-20). The nasal cavity is now divided into two nasal passages that open into the pharynx behind the secondary palate through an opening called the definitive choana (see Fig. 16-20D).

SINUSES: A: Sinuses develop from invaginations of the nasal cavity that extend into the bones. Two of the sinuses appear during fetal life (maxillary and ethmoid) and the other two (sphenoid and frontal) appear after birth. Specifically, the maxillary sinuses form during the 3rd fetal month as invaginations of the nasal sac that slowly expand within the maxillary bones. The resulting cavities are small at birth but expand throughout childhood. The ethmoid sinuses form during the 5th fetal month as invaginations of the middle meatus of the nasal passages (the space underlying the middle nasal concha) and grow into the ethmoid bone. These sinuses do not complete their growth until puberty. The sphenoid sinuses actually represent extensions of the ethmoid sinuses. These extensions enlarge within the sphenoid bones throughout infancy and childhood.

The frontal sinuses do not form until the 5th or 6th postnatal year and expand throughout adolescence. Each frontal sinus actually consists of two independent spaces that develop from different sources. One forms by the expansion of the ethmoid sinus into the frontal bone, and the other develops from an independent invagination of the middle meatus of the nasal passage. Because these cavities never coalesce, they drain independently.

Schoenwolf, G.C., Bleyl, S.B., Brauer, P.R. and Francis-West, P.H. (2009). Larsen’s Human Embryology (4th ed.). New York; Edinburgh: Churchill Livingstone.

Structure

During different stages of embryonic development

Normal Function

The Neurology of Smell

The Neurobiology of Olfaction

Olfactory System

Abnormalities

Kallman Syndrome

Introduction and Epidemiology

Kallmann syndrome is a clinically and genetically heterogeneous disorder, described as a hypogonadotropic hypogonadism characterized by a diminished or absent sense of smell [5]. The incidence of this disease is between 1 in 10,000 and 1 in 60,000 people, affecting males to females in a 5:1 ratio[6]. Anosmia or hyposmia occurs as a results of impaired development of the olfactory bulbs and olfactory nerves [7]. Additionally, hypogonadism results due to the reduced production of Gonadotropin-releasing hormone (GnRH) [8]. Kallmann syndrome can be inherited as an autosomal dominant or autosomal recessive trait, a digenic trait or an X-linked recessive trait [9][10].

Genetic and Molecular Basis

Characteristic Features

Kallmann's Syndrome is a congenital hypogonadotropic hypogonadism (HH). Kallmann's Syndrome has the classical HH absence of puberty but is distinguished from other HH syndromes by an affected sense of smell. There exists additional characteristics that are not specific to Kallmann's syndrome but may aid in correct diagnosis of this particular HH [11]. The following characteristics of Kallmann's syndrome may be present or not present in different cases, often varying according to genotype:

Reproductive Features

  • hypogonadotropic [12]
  • hypogonadism:

Non-Reproductive Features

  • Affected sense of smell: decreased (hyponosmia) or absent (anosmia) sense of smell [12]
  • Eunuchoidism [13].

Diagnosis and Treatment

Congenital Anosmia

Genetic and Molecular Basis

Characteristic Features

Treatment

Genes involved

Current Research

Olfactory Systems Laboratory

Glossary and Abbreviation

Olfactory bulb: The primary part of brain which processes olfactory information.

Olfactory epithelium: mucous membrane superior to the nasal cavity which contain olfactory nerve cells.

Olfactory nerve cell: Cells in the olfactory epithelium which detect various odors and signal the information to the CNS.

Pheromone: Any molecules (scent) released by animals and affect the behavior of organisms of the same species via the olfactory system.

References

  1. <pubmed>3548583</pubmed>
  2. http://www.nobelprize.org/nobel_prizes/medicine/laureates/2004/press.html
  3. 3.0 3.1 <pubmed>putpmidhere</pubmed>
  4. Cite error: Invalid <ref> tag; no text was provided for refs named PMIDreference
  5. Schoenwolf, G. C. & Larsen, W. J. (2013). Human Embryology (4th ed.). Philadelphia, PA: Elsevier Inc.
  6. Schoenwolf, G. C. & Larsen, W. J. (2013). Human Embryology (4th ed.). Philadelphia, PA: Elsevier Inc.
  7. Schoenwolf, G. C. & Larsen, W. J. (2013). Human Embryology (4th ed.). Philadelphia, PA: Elsevier Inc.
  8. Schoenwolf, G. C. & Larsen, W. J. (2013). Human Embryology (4th ed.). Philadelphia, PA: Elsevier Inc.
  9. Schoenwolf, G. C. & Larsen, W. J. (2013). Human Embryology (4th ed.). Philadelphia, PA: Elsevier Inc.
  10. <pubmed>21682876</pubmed>
  11. Smith, N. (2008). Characteristics of Kallmann’s syndrome and HH. Retrieved from http://kallmanns.org/node/96.
  12. 12.0 12.1 <pubmed>16932275</pubmed>
  13. Smith, N. (2008). Characteristics of Kallmann’s syndrome and HH. Retrieved from http://kallmanns.org/node/86.


External Links

The Neural Basis of Olfaction

Development of the Olfactory System

The Development of the Olfactory System 2

General Physiology of Olfaction

Neural Development


External Links Notice - The dynamic nature of the internet may mean that some of these listed links may no longer function. If the link no longer works search the web with the link text or name. Links to any external commercial sites are provided for information purposes only and should never be considered an endorsement. UNSW Embryology is provided as an educational resource with no clinical information or commercial affiliation.

--Mark Hill 12:22, 15 August 2012 (EST) Please leave the content listed below the line at the bottom of your project page.


2012 Projects: Vision | Somatosensory | Taste | Olfaction | Abnormal Vision | Hearing