Somatosensory Systems

Abstract

Sensations of touch, temperature, pain and movement of joints may be perceived from all parts of the body. Specialized receptor cells convert the stimuli producing such sensations into electrical signals that are processed in the somatosensory pathways of the nervous system.

Keywords: mechanoreceptors; touch; pain; temperature sensation; body maps

Figure 1.

When the fingertip moves over a textured surface (in this case a grating of alternating grooves and ridges) with a velocity v, low‐threshold mechanoreceptors are excited. Vertical tick marks represent action potentials propagating along the axon. These occur cyclically, corresponding to the cyclic compression and relaxation of the skin, and provide information about the texture. The box shows a drawing of a Meissner corpuscle. a, myelinated axon; b, branching axon terminals within corpuscle; s, Schwann cells; c, collagen fibres attaching to epidermis (e). (Adapted from Andres KH and von During M (1973). In: Iggo A (ed.) Handbook of Sensory Physiology. Somatosensory System, pp. 3–28. Berlin: Copyright 1973, Springer‐Verlag GmbH & Co.)

Figure 2.

Structure of the spinal cord. (a) The dermatomes on the front of the body. C, cervical (red); T, thoracic (blue); L, lumbar (green); S, sacral (yellow). (b) A cross‐section of the spinal cord at the L4 level. The central core of grey matter is surrounded by white matter. Large myelinated ‘touch fibres’ proceed mainly up the dorsal column to the brainstem. Smaller ‘temperature and nociceptive fibres’ synapse on cells in the dorsal horn, which in turn cross the spinal cord and send axons up the anterolateral system to the brainstem. The dorsal horn can be divided into laminae (I to V shown). DRG, dorsal root ganglion cell; DC, dorsal column; ALS, anterolateral system.

Figure 3.

Central somatosensory pathways. (a) The dorsal column system conveying high‐resolution tactile information. (b) The spinothalamic tract is the major component of the anterolateral system which conveys pain and temperature information. Cross‐sections are shown at three levels of the central nervous system; the spinal cord, the medulla of the brainstem and a section through the cerebral hemispheres showing the cortex and the thalamus (sections are not to scale). DRG, dorsal root ganglion cell; DC, dorsal column; DCN, dorsal column nuclei; ML, medial lemniscus; ALS, anterolateral system; SST, spinothalamic tract.

Figure 4.

A cross‐section through the postcentral gyrus showing the topographic representation of the body surface (often called the homunculus). Regions with high acuity, such as the fingertips and the lips, have a disproportionately large representation. (Adapted from Penfield W and Rasmussen T (1950) The Cerebral Cortex of Man: a Clinical Study of Localization of Function. New York: Macmillan.)

Figure 5.

Whisker barrel fields in the cerebral cortex (upper figures) and the corresponding whiskerpads (lower figures) for three strains of mice. In the normal mouse (NOR) the barrel pattern matches the whiskerpad pattern. In the H/H and MAP strains, bred for additional whiskerpads (shown shaded), the barrel field has corresponding additional barrels (outlined in red). (Adapted from Welker, E and Van der Loos, H (1986) Quantitative correlation between barrel‐field size and the sensory innervation of the whiskerpad: a comparative study in six strains of mice bred for different patterns of mystacial vibrissae. Journal of Neuroscience6: 3355–3373. Copyright 1986, Society for Neuroscience.)

close

References

Davis KD, Kwan CL, Crawley AP and Mikulis DJ (1998) Functional MRI study of thalamic and cortical activations evoked by cutaneous heat, cold, and tactile stimuli. Journal of Neurophysiology 80: 1533–1546.

DiCarlo JJ, Johnson KO and Hsiao SS (1998) Structure of receptive fields in area 3b of primary somatosensory cortex in the alert monkey. Journal of Neuroscience 18: 2626–2645.

Edeline JM (1999) Learning‐induced physiological plasticity in the thalamo‐cortical sensory systems: a critical evaluation of receptive field plasticity, map changes and their potential mechanisms. Progress in Neurobiology 57: 165–224.

Goodwin AW and Wheat HE (1999) Effects of nonuniform fiber sensitivity, innervation geometry, and noise on information relayed by a population of slowly adapting type I primary afferents from the fingerpad. Journal of Neuroscience 19: 8057–8070.

Halata Z (1975) The mechanoreceptors of the mammalian skin. Ultrastructure and morphological classification. Advances in Anatomy, Embryology and Cell Biology 50: 1–77.

LaMotte RH, Friedman RM, Lu C, Khalsa PS and Srinivasan MA (1998) Raised object on a planar surface stroked across the fingerpad: responses of cutaneous mechanoreceptors to shape and orientation. Journal of Neurophysiology 80: 2446–2466.

Mima T, Nagamine T, Nakamura K and Shibasaki H (1998) Attention modulates both primary and second somatosensory cortical activities in humans: A magnetoencephalographic study. Journal of Neurophysiology 80: 2215–2221.

Olausson H, Lamarre Y; Backlund H et al. (2002) Unmyelinated tactile afferents signal touch and project to insular cortex. Nature Neuroscience 5: 900–904.

Patapoutian A, Peier AM, Story GM and Viswanath V (2003) ThermoTRP channels and beyond: mechanisms of temperature sensation. Nature Reviews Neuroscience 4: 529–539.

Rothwell JC, Traub MM; Day BL et al. (1982) Manual motor performance in a deafferented man. Brain 105: 515–542.

Tremblay F, Ageranioti‐Bélanger SA and Chapman CE (1996) Cortical mechanisms underlying tactile discrimination in the monkey 1. Role of primary somatosensory cortex in passive texture discrimination. Journal of Neurophysiology 76: 3382–3403.

Woolsey TA and Van der Loos H (1970) The structural organization of layer IV in the somatosensory region (SI) of mouse cerebral cortex. Brain Research 17: 205–242.

Further Reading

Buonomano DV and Merzenich MM (1998) Cortical plasticity: from synapses to maps. Annual Review of Neuroscience 21: 149–186.

Darian‐Smith I (1984) The sense of touch: performance and peripheral neural processes. In: Brookhart JM, Mountcastle VB, Darian‐Smith I and Geiger SR (eds) Handbook of Physiology – The Nervous System III, pp. 739–788. Bethesda, MA: American Physiological Society.

Gandevia SC, McCloskey DI and Burke D (1992) Kinaesthetic signals and muscle contraction. Trends in Neuroscience 15: 62–65.

Goodwin AW and Wheat HE (2004) Sensory signals in neural populations underlying tactile perception and manipulation. Annual Review of Neuroscience 27: 53–77.

Johansson RS, Westling G, Backstrom A and Flanagan JR (2001) Eye‐hand coordination in object manipulation. Journal of Neuroscience 21: 6917–6932.

Johnson KO, Hsiao SS and Twombly AI (1995) Neural mechanisms of tactile form recognition. Gazzaniga MS (ed.) The Cognitive Neurosciences, pp. 253–268. Cambridge, MA: MIT Press.

Jones EG and Diamond IT (1995) Cerebral Cortex, vol. 11: The Barrel Cortex of Rodents. New York: Plenum.

Romo R and Salinas E (2003) Flutter discrimination: neural codes, perception, memory and decision making. Nature Reviews Neuroscience 4: 203–218.

Scott SA (1992) Sensory Neurons. Diversity, Development and Plasticity. New York: Oxford University Press.

Usunoff KG, Marani E and Schoen JHR (1997) The trigeminal system in man. Advances in Anatomy, Embryology and Cell Biology 136: 1–126.

Vallbo ÅB (1995) Single‐afferent neurons and somatic sensation in humans. In: Gazzaniga MS (ed.) The Cognitive Neurosciences, pp. 237–252. Cambridge, MA: MIT Press.

Willis WD and Coggeshall RE (2004) Sensory Mechanisms of the Spinal Cord. New York: Plenum.

Willis WD and Westlund KN (1997) Neuroanatomy of the pain system and of the pathways that modulate pain. Journal of Clinical Neurophysiology 14: 2–31.

Contact Editor close
Submit a note to the editor about this article by filling in the form below.

* Required Field

How to Cite close
Goodwin, Antony W(Sep 2005) Somatosensory Systems. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0004082]