2012 Group Project 4: Difference between revisions

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[http://brain.utah.edu/research/wachowiak/index.php Olfactory Systems Laboratory]
[http://brain.utah.edu/research/wachowiak/index.php Olfactory Systems Laboratory]
Revisiting human nose anatomy: phylogenic and ontogenic perspectives <ref name:"PMID22020897"><pubmed>22020897</pubmed></ref>
Dopamine systems in the forebrain<ref name:"PMID19731547"><pubmed>19731547</pubmed></ref>
Olfactory structures in staged human embryos<ref name:"PMID15604533"><pubmed>15604533</pubmed></ref>
Disorganized olfactory bulb lamination in mice deficient for transcription factor AP-2epsilon <ref name:"PMID19580868><pubmed>19580868</pubmed></ref>
The dual origin of the peripheral olfactory system: placode and neural crest<ref name:"PMID21943152"><pubmed>21943152</pubmed></ref>.


A paper published last year explored the individual neural crest and ectodermal contributions to the nasal placode through the use of genetic Cre-lox tracing in two mice species. One mouse species was Wnt1Cre, a neural-crest specific line. The other species was Crect, an ectodermal specific line.  The Cre-lox genetic tracing of the two species determined that olfactory ensheathing cells are neural crest in origin. Neural crest was also shown to contribute to cells of the olfactory epithelium and vomernasal organ along with GnRH-1 neurons. The findings of this paper allowed provided an understanding of the link relating neural crest defects to diseases such as [[#Glossary |'''anosmia''']]and Kallmann syndrome<ref name:”PMID21543621”><pubmed>21543621</pubmed></ref>.
A paper published last year explored the individual neural crest and ectodermal contributions to the nasal placode through the use of genetic Cre-lox tracing in two mice species. One mouse species was Wnt1Cre, a neural-crest specific line. The other species was Crect, an ectodermal specific line.  The Cre-lox genetic tracing of the two species determined that olfactory ensheathing cells are neural crest in origin. Neural crest was also shown to contribute to cells of the olfactory epithelium and vomernasal organ along with GnRH-1 neurons. The findings of this paper allowed provided an understanding of the link relating neural crest defects to diseases such as [[#Glossary |'''anosmia''']]and Kallmann syndrome<ref name:”PMID21543621”><pubmed>21543621</pubmed></ref>.

Revision as of 13:20, 10 September 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
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

Week 5

As the paired maxillary prominences enlarge and grow ventrally and medially, the ectodermal thickenings of the olfactory placode enlarge.

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

Image

Week 6

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. 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. The nasal pits differentiate to form the epithelium of the nasal passages.

Nasolacrimal groove:This groove forms 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 nasal bridge and nasal septum.

Olfactory bulb growth: 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 mitral cells 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.

Image

Week 7

Nasolacrimal duct and sac: The ectoderm at the floor of the nasal pit 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.

Intermaxillary process: The inferior tips of the medial nasal processes expand laterally and inferiorly and fuse.

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

Oronasal Membrane: 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 oronasal 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.


word linked to glossary

Image

Week 8

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 .

image




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

Olfactory Signal Transduction

When odorant molecules bind to receptors in olfactory epithelium, a G protein known as G(olf) is activated which then happen to activate adenylate cyclase, an enzyme which catalyses the formation of cyclic AMP. In most receptor cells, cAMP acts as a second messenger, however in the olfactory system cAMP bind to cation channels which permits sodium and calcium ions to travel through the membrane and enter the cell. The main effect of ion entry into the cell is depolarisation, and if the depolarization is great enough, an action potential is generated on the axon of the receptor cell. [5]


The Neurology of Smell

The Neurobiology of Olfaction

Olfactory System

Abnormalities

Kallmann's Syndrome

Introduction and Epidemiology

Kallmann's syndrome is a clinically and genetically heterogeneous disorder, described as a hypogonadotropic hypogonadism characterized by a diminished or absent sense of smell [6] [7]. The incidence of Kallmann's syndrome is uncertain but is estimated to occur in 1 in 10,000 to 1 in 50,000 people [8], affecting males to females in a 5:1 ratio [9]. Anosmia or hyposmia occurs as a results of impaired development of the olfactory bulbs and olfactory nerves [9]. Additionally, hypogonadism results due to the reduced production of Gonadotropin-releasing hormone (GnRH). Kallmann's syndrome can be inherited as an autosomal dominant,autosomal recessive trait, or an X-linked recessive trait [9].

Pathophysiology

Genetic Basis

Kallmann's syndrome can be X-linked , autosomal dominant or autosomal recessive[9]. To date, mutations in the following genes have been attributed to Kallmann's syndrome:

  • KAL1: Mutations in the KAL1 gene produce the X-linked form of Kallmann's syndrome. KAL1 gene encodes the glycoprotein anosmin 1 [10].
  • KAL2: Produces the autosomal-dominant form of Kallmann's syndrome. KAL2 encodes fibroblast growth factor receptor 1 (FGFR1)[11].


Pathological Mechanisms
Olfactory Neuronal Migration in Kallmann's Syndrome

Characteristic Features

Kallmann's Syndrome is a congenital hypogonadotropic hypogonadism (HH)[6]. 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 [12]. The following characteristics of Kallmann's syndrome may be present or not present in different cases, often varying according to genotype [6]:

Reproductive Features


Non-Reproductive Features

Diagnosis and Treatment

Congenital Anosmia

Genes involved

Current Research

Olfactory Systems Laboratory

A paper published last year explored the individual neural crest and ectodermal contributions to the nasal placode through the use of genetic Cre-lox tracing in two mice species. One mouse species was Wnt1Cre, a neural-crest specific line. The other species was Crect, an ectodermal specific line. The Cre-lox genetic tracing of the two species determined that olfactory ensheathing cells are neural crest in origin. Neural crest was also shown to contribute to cells of the olfactory epithelium and vomernasal organ along with GnRH-1 neurons. The findings of this paper allowed provided an understanding of the link relating neural crest defects to diseases such as anosmiaand Kallmann syndrome[19].

Glossary

Aplasia: Absent development of an organ or tissue.

Cerebellar ataxia: Reduced control over muscle coordination arising from defects or damage to the cerebellum.

Cryptorchidism: Failure of one or both testes to migrate into the scrotum during male foetus development.

Eunuchoidism: Male hypogonadism characterised by the failure of the testes to develop and an absence of secondary sexual characteristics.

Gynaecomastia: The development of abnormal mammary glands in males characterised by enlarged breasts.

Hypogonadism: A state which described reduced or absence of hormone secretion by the gonads (ovaries or testes).

Hypogonadotropism: Reduced or absent gonadotropin secretion, often characterised by FSH and LH deficiency leading to testicular or ovarian dysfunction.

Hypoplasia:Incomplete development of an organ or tissue.

Nystagmus: Refers to fast involuntary movements of the eyes that may impair vision. Can be described as a "rapid flicking side to side" movement.

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: Refers to the ability to conduct voluntary movements, however, with accompanied involuntary muscular movements.

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>21882432</pubmed>
  6. 6.0 6.1 6.2 <pubmed>22882983</pubmed>
  7. <pubmed>6932275</pubmed>
  8. <pubmed>16952059</pubmed>
  9. 9.0 9.1 9.2 9.3 <pubmed>21682876</pubmed>
  10. <pubmed>1913827</pubmed>
  11. <pubmed>12627230</pubmed>
  12. Smith, N. (2008). Characteristics of Kallmann’s syndrome and HH. Retrieved from http://kallmanns.org/node/96.
  13. 13.0 13.1 13.2 13.3 13.4 13.5 <pubmed>16932275</pubmed>
  14. Smith, N. (2008). Euchanoid Pattern [in Kallmann's Syndrome]. Retrieved from http://kallmanns.org/node/86.
  15. <pubmed>1080088</pubmed>
  16. <pubmed>6881209</pubmed>
  17. <pubmed>11531922</pubmed>
  18. <pubmed>11297579</pubmed>
  19. <pubmed>21543621</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