2012 Group Project 4

From Embryology

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
Week 4

All five facial swellings form initially surrounding the stomodeum.

The frontonasal prominence is the facial swelling which gives rise to olfactory placodes. It overlies the forebrain and arises from neural crest cells derived from midbrain and forebrain. [3]

Like the majority of placodes, some mesenchymal cells migrate away from the placodal epithelium and differentiate as either secretory cells or glial cells.[4]

Some specialised areas in the rostrolateral regions of the head of the olfactory placode contain cells of cranial non-neural ectoderm. These cells differentiate to form the primary neurosensory cells of the future olfactory epithelium. This differentiation is a cuboidal-to-columnar transformation and so are distinguishable from the surrounding cuboidal epithelium.

image

'Stage 13 This will explain the telencephelon development [5]
Stage 14 explanation [6]
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


Week5:

A:As the paired maxillary prominences enlarge and grow ventrally and medially, a pair of ectodermal thickenings form on the frontonasal prominence and begin to enlarge-Nasal placodes.

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. The subsequent ossification of the ethmoid bone around these axons creates the perforated cribriform plate.

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.

Nasolacrimal groove- The groove between the lateral nasal process and the adjacent maxillary prominence.

The medial nasal processes migrate toward each other and fuse to form the primordium of the bridge and septum of the nose. 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 .

N: Olfactory bulb growth:forms as the nasal pits differentiate to form the epithelium of the nasal passages. An outgrowth is formed where the axons of the primary neurosensory cells synapse,this is seen at the floor at each cerebral hemisphere. The synpasing cells differentiate to become the secondary sensory neurons (mitral cells) of the olfactory pathways.

Olfactory nerve formation: formed due to the lengthening of the axons of the secondary olfactory neurons as the proportions of the face and brain lenghthens. As a result, the CNS olfactory tracts look stalk-like. Olfactory nerve: the olfactory tract and bulb together. Week 7:

A: Nasolacrimal duct and sac: The ectoderm at the floor of the nasal pit(see description of week 6) invaginates into the underlying mesenchyme. The duct becomes lined by bone during the ossfication 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.

Separation fo nasal and oral cavity: the floor and posterior wall of the nasal sac proliferate to form thickened ectoderm-Nasal fin.

the sac enlarges as vacuoles develop within the nasal fin which fuse with the nasal sac. As a result of this, the nasal fin thins and is labelled as the oronalsal membrane

Primitive choana: formed as the oronasal membrane ruptures.

The floor of the nasal cavity at this stage is formed by a posterior extension of the intermaxillary process called the primary palate. Palatal sheleves will later form to separate the two cavities.

Week 8:

A: Nasal septum and philtrum:ectoderm and mesoderm of the frontonasal prominence and the medial nasal processes proliferate and grows down from the roof of the nasal cavity to fuse with the upper surface of the primary and secondary palates along the midline .


SINUSES: A:

EFFECT OF AMNIOTIC FLUID ON THE DEVELOPMENT OF OLFACTION IN THE FETUS (current research in the field):


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

Congenital Anosmia

Genetic and Molecular Basis

Characteristic Features

Treatment

Kallmann's 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 [7] [8]. The incidence of Kallmann's syndrome is uncertain but is estimated to occur in 1 in 10,000 to 1 in 50,000 people [9], affecting males to females in a 5:1 ratio [10]. Anosmia or hyposmia occurs as a results of impaired development of the olfactory bulbs and olfactory nerves [10]. Additionally, hypogonadism results due to the reduced production of Gonadotropin-releasing hormone (GnRH). Kallmann syndrome can be inherited as an autosomal dominant or autosomal recessive trait, a digenic trait or an X-linked recessive trait [10].

Pathophysiology

Olfactory Neuronal Migration in Kallmann's Syndrome

Characteristic Features

Kallmann's Syndrome is a congenital hypogonadotropic hypogonadism (HH)[7]. 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 [7]:

Reproductive Features

  • Hypogonadotropism leading to failed or arrested puberty [12]
  • Hypogonadism
  • Cryptorchidism (males)
  • Gynaecomastia (males)

Non-Reproductive Features

  • Affected sense of smell: decreased (hyponosmia) or absent (anosmia) sense of smell [12]. Anatomically, the olfactory bulbs and olfactory tracts demonstrate aplasia or hypoplasia [12].
  • Eunuchoidism bone structure, defined by long limbs as a result of inadequate calcification[13]
  • Unilateral renal aplasia [14]
  • Cleft palate[12]
  • Pes cavus [12]
  • Neurological symptoms
    • Synkinesia
    • Abnormalities in eye movement
    • Cerebellar ataxia
    • Evoked horizontal nystagmus
    • Sensorineural deafness
    • Spatial attentional abnormalities
    • Spastic paraplegia
    • Mental retardation [12][15] [16] [17]

Diagnosis and Treatment

Genes involved

Current Research

Olfactory Systems Laboratory

Glossary and Abbreviation

Aplasia: Absent development of an organ or tissue.

Cerebellar ataxia:

Cryptorchidism:

Eunuchoidism:

Gynaecomastia:

Hypogonadism:

Hypogonadotropism:

Hypoplasia:Incomplete development of an organ or tissue.

Non-Reproductive Features:

Nystagmus:

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.

Pes cavus: A deformity of the foot characterised by an overexaggerated arch and hyperextension of the toes. Also referred to as clawfoot.

Spastic paraplegia: A hereditary paraplegia characterised by stiffness and contraction in the lower limbs as a result of neuronal dysfunction.

Synkinesia:

References

  1. <pubmed>3548583</pubmed>
  2. http://www.nobelprize.org/nobel_prizes/medicine/laureates/2004/press.html
  3. <pubmed>21882426</pubmed>
  4. <pubmed>16677629</pubmed>
  5. <pubmed>putpmidhere</pubmed>
  6. Cite error: Invalid <ref> tag; no text was provided for refs named PMIDreference
  7. 7.0 7.1 7.2 <pubmed>22882983</pubmed>
  8. <pubmed>6932275</pubmed>
  9. <pubmed>16952059</pubmed>
  10. 10.0 10.1 10.2 <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 12.2 12.3 12.4 12.5 <pubmed>16932275</pubmed>
  13. Smith, N. (2008). Euchanoid Pattern [in Kallmann's Syndrome]. Retrieved from http://kallmanns.org/node/86.
  14. <pubmed>1080088</pubmed>
  15. <pubmed>6881209</pubmed>
  16. <pubmed>11531922</pubmed>
  17. <pubmed>11297579</pubmed>

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