Abstract
This paper is going to look at the somatosensory system. This system is a sensory system made up of receptors that generate sensory variables such as pain and touch. The paper will start with a short introduction before looking at the anatomy and the physiology of the system. The paper will then look at the system and its relation to the brain and the spinal cord before concluding.
Introduction
The somatosensory system is a very wide system that has a web of receptors and centers of production that generate sensory variables such as temperature, body positioning, pain, and touch. These sensory receptors cover the skin, bones, joints external organs, and many other body parts and one of the main sensory modalities that are very crucial is touch. Touch is also called tactician or tactile somatosensory and is one of the five conventional senses since its impression comes from a mixture of sensory receptors. The somatosensory system is referred to as somatic senses in the medical realm to reflect all the processes involved in the whole system. This system reacts to diverse stimuli using a wide variety of receptors that transmit information through the tracts in the spinal cord to the central nervous system. Various reflectors are involved in the transmission process and they include thermal receptors, nociceptors, mechanical receptors, and chemical receptors.
Processing of transmitted information takes place in the prime somatosensory part of the parietal lobe in the cerebral cortex. This system starts its work when the sensory neuron is activated by some special stimuli which include heat and this signal is relayed to a part of the central nervous system that responds to a specific part of the body. This works through point-to-point mapping of the body surfaces in the central nervous system to create what is scientifically known as the body image through a process called Homunculus (Hayward, 2004). This brain surface which is called a cortical map is not mutable and there are marked shifts that can occur in response to serious injuries or stroke. This system is spread all over the vital parts of the body of all mammals and vertebrates and the most important parts of the system are sensory receptors and afferent neurons that are found in the peripheral parts such as the human skin and deeper parts such as neurons in the brain.
Structure of the somatosensory pathway
A somatosensory pathway has three very long neurons and the first neuron has a cell body found in the dorsal root ganglion of the spinal nerve while the second one has its cell body located either in the spinal cord or the brainstem. The second neuron also has ascending axons which keep on crossing to either side of the spinal cord or the brainstem and these axons terminate the thalamus, the reticular system, or the cerebrum (Nolet, 2002). The third neuron addresses various types of pains and its neuron starts in the thalamus and ends at the postcentral part of the parietal lobe. In the periphery, the somatosensory system detects different types of stimuli. In the periphery, the somatosensory system detects a wide range of stimuli relayed by the sensory receptors such as the mechanical receptors and the nociceptors, and this sensory information is relayed to the central nervous system the various types of afferent neurons (Saladin, 2004). These afferent neurons vary in size, structure, and features and there is always a link between the sense variable detected and the type of the specific neuron used to notice that sensory variable.
For example, the neurons that have not been myelinated relay pain faster because they are thin while myelinated neurons are used to relay casual touch. In the spinal cord, the somatic sensory system has a wide network of pathways that extend from the rest of the body to the brain. Their main area of focus in the brain is the postcentral part of the cerebral cortex and the neurons that work in this part include the dorsal column medial pathway and the VSP pathway. It is worth noting that most pathways that go up to include synapses that start at the thalamus and they have a reticular structure that extends to the cortical area. Other ascending pathways including the pathways that control posture are usually projected to the cerebellum and they include the ventral and the spinal tracts which also target the neurons involved in the local segmental reflexes. In the central nervous system, the main somatosensory area is found in the postcentral area of the parietal lobe and this is the basic sensory receptive area for the tactile sense where there is a map called the homunculus (Robles, 2001). Areas of this part of the central nervous system relate to specific areas of the body and they depend on the level of the somatosensory variables from the specific part of the brain where the somatic senses responsible for various sensory variables are determined. For example, there is a big part of the cortex whose primary work is to detect sensations in the hands while the back has a smaller area that determines the posture of a mammal because the somatosensory information involved with posture targets the cerebral part of the brain of a mammal.
Physiology of the somatosensory system
The initial sensation made by the somatic senses starts with the activation of the physical receptor and these somatosensory receptors are found in the skin, muscles, or organs. The somatosensory receptors resemble each other in structure and they all have a free nerve ending located in a specific capsule the mechanical receptors are usually activated by pressure while the chemical receptors are activated by chemicals (Hayward, 2004). Vibrations also act as activators especially when fingers are scanned across a surface and this means that mammals can sense fine textures where the spatial scale does not go beyond 200 Hz which is the normal frequency sensitivity. The general principle applied is the same for all the different types of receptors because in each case, the stimuli depolarize the nerve ending which in turn activates the action potential, which later travels internally to the spinal cord
Summary
To summarise, it is important to note that the somatosensory system detects experiences such as touch, pressure, temperature, and all the variables that belong to proprioception or the sensations of muscle movement and joint position. These include posture, movement, internal senses, and facial expressions and it is also important to note that internal senses involve sensory information found inside the body such as all forms of internal aches. Touch may be one of the five human senses but it is imperative to bear in mind that when someone touches something, diverse feelings, perceptions, and vibrations are elicited. This means that touch refers to more than one sense which are medically lumped together to form the somatic senses.
Conclusion
The somatosensory system is a key element of the peripheral and central nervous system because it contains subservient modalities like touch, pressure, temperature, and pain. The paper has also found out that specific sensory variables are associated with special peripheral receptors and axons that have specific dimensions and projection pathways and their features render the central and peripheral regions susceptible to a wide range of toxic substances. The analysis of these features is very important in the study of the three most significant types of toxic neuropathy. The somatosensory system therefore informs people and all the mammals about their external conditions through contact, posture and movement and it also monitors the temperature and also generates responses to painful or hurting stimuli (Flanagan, 2000). As seen in the literature review earlier in the paper, the sensory information that is processed by the somatosensory senses travels along diverse anatomical pathways and these pathways are determined by the nature of information carried by each sensory neurone. It is worth noting that most pathways that go up include the synapses that are start in the thalamus and they take a reticular formation as they join get the cortex to link up with other pathways that include the pathways that determine the posture of a mammal.. These are usually projected to the cerebellum and they include the ventral and the spinal tracts which also target the neurones involved the local segmental reflexes.
References
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Robles, G.(2001). Force Can Overcome Object Geometry in the perception of Shape through Active Touch. Nature 412 (6845):445-8.
Saladin, K. (2004). Anatomy and Physiology. NY: McGraw-Hill.