2012 Group Project 2

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Somatosensory Development

--Mark Hill 12:23, 15 August 2012 (EST) This is a better project title.

- Touch, Pain, Hot/Cold, Pressure Reception


Introduction

History of Discoveries

Central Somatosensory Differentiation

This is just preliminary work and will be edited later:


Making Connections between Afferent Sensory Fibres and the Central Nervous System (CNS)

Stage 23;

  • Axons of primary afferent neurons extend to the spinal cord. When these afferent neurons reach the CNS, axons of these afferent neurons bifurcate and begin to extend into the Primordium of the dorsal funiculus


Stage 24:

  • the afferent axons have extended 1 segment rostrally and 1 segment caudally relative to the axons' point of entry
  • the afferents start to grow within the white matter (periphery of Spinal Cord)

Stage 28 –

  • unbranched afferent axonal fibres invade gray matter at the border of Dorsal horn
  • axonal fibres extend rostrally and caudally and start sending fine collateral fibres into the gray matter of spinal cord (the cellular, central region of spinal cord)

Stage 29:

  • afferent fibres have extended 100-200μm into gray matter of the Dorsal Horn

Reference: <pubmed>2918087</pubmed>


Adult Central Somatosensory Pathway

Touch

The sense of touch allows individuals to perform a myriad of functions through the receptors deep within dermal and epidermal layers of the skin. This sensory modality, though it’s development is not greatly understood among the five acknowledged sense subsets, it is essential for survival and development throughout life. Receptors that are established throughout embryonic development linked to touch are mechanoreceptors/transducers such as Pacinian Corpuscle, Meissner’s Corpuscle, Meker-cell-neurite complexes and Ruffini endings. Function and development of these receptors will be discussed in this section.

Touch Receptors

Pacinian Corpuscle These receptors and nerve endings are found in the subcutaneous tissue of the skin and are also referred to as lamellar corpuscles. When stimulated these nerve endings result in action potentials which respond to the detection of changes in pressure against the skin in relation to vibrations sensations. This can allow for the ability of individuals to establish distinctions between rough and smooth surfaces.

Link to Pacinian Corpuscle image 1. http://thediagram.com/3_1/pacinian.html 2. http://www.biologymad.com/nervoussystem/nerveimpulses.htm

Meissner’s Corpuscle

Meker-cell-neurite complexes

Ruffini Endings

Embryonic Development

Neural Components

References

1. [1] 2. [2] 3. [3] 4. [4]

Pain

Hot/Cold

Thermoreceptors(1)

- Convey information regarding the temperature of the nerve ending in the tissue

o Free nerve endings

o Ion channels responsible for action potentials are called Transient Receptor Potential channels. Their activity is modulated by temperature

- Two type, warm and cold

- Warm- 30-45

- Cold – 20 – 30

- Frequency of action potentials codes for the relevant temperature

o As temperature increases, the frequency of warm thermoreceptors increases

o As temperature decreases, the frequency of cold thermoreceptors increases.

- Receptors

o Warm – TYPV1 to V4

o Cold – TRPM8 and TRPA1

Some current research (2)

From:

1. Stanfield, C. L., and W. J. Germann. 2011. Principles of human physiology. Pearson/Benjamin Cummings, San Francisco, CA.

2. Hjerling-Leffler, J., F. Marmigere, M. Heglind, A. Cederberg, M. Koltzenburg, S. Enerback, and P. Ernfors. 2005. The boundary cap: a source of neural crest stem cells that generate multiple sensory neuron subtypes. Development 132:2623-2632.


- The thermosensitive neurons travel in the dorsal root ganglion, as with other sensory neurons such as proprioceptive, mechanosensitive and nociceptive neurons.

- DRG neurons pseudounipolar

o One process detects the stimuli in the tissues

o The other relays it into the dorsal horn

- Mixture of small-diameter, slow, unmyelinated C fibers and larger, faster Aδ fibers

- This article is great for understanding how temperature sensation works, but not to great on the embryology behind it(1)

- Another good article for a more molecular understanding(2)

- Understanding – more recent(3)


1. Patapoutian A, Peier AM, Story GM, Viswanath V. ThermoTRP channels and beyond: mechanisms of temperature sensation. Nature reviews Neuroscience. [Review]. 2003 Jul;4(7):529-39.

2. Bandell M, Macpherson LJ, Patapoutian A. From chills to chilis: mechanisms for thermosensation and chemesthesis via thermoTRPs. Current opinion in neurobiology. [Research Support, N.I.H., Extramural Research Support, Non-U.S. Gov't Review]. 2007 Aug;17(4):490-7.

3. Schepers RJ, Ringkamp M. Thermoreceptors and thermosensitive afferents. Neuroscience and biobehavioral reviews. [Review]. 2010 Feb;34(2):177-84.

Pressure

Current Research

Glossary

References


External Links

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