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Sensation And Perception Of Cold Temperature Sample Assignment

Question: Construct a 2 page essay paper explaining how your peripheral nervous system senses one type of stimulus, then describe where and how it is perceived in your brain or central nervous system.

Ans: Perception is the process by which organisms interpret and organize sensation to produce a meaningful experience of the world. Sensation refers to the process of sensing our environment through touch, taste, sight, sound, and smell. This information is sent to our brains in raw form where perception comes into play. Here I will like to talk about “Cold Reception”. Sense of temperature is Epicritic Sensation. This occurs through the reception in the Peripheral Nervous System. The Somatosensory System is involved in reception of the stimuli involving temperature sense. The principle of activation is general which involves depolarization of the nerve ending and then initiation of the action potential. This occurs with the help of thermoreceptors which are the receptive portion of sensory neuron. The absolute and relative changes in temperature are recepted by them. Adequate stimulus for these receptors is cooling. For Cold Receptors firing rate increases during cooling and decreases. Let the stimuli be a touch of cold ice cube to a part of human body. The first thing thus involves the activation of activation of thermoreceptors.

Biochemistry of receptors:
TRPM8 channel mediates transduction of temperature in cold receptors. A mixed inward cationic current(mostly Ca2+ ions) is passed by this channel and the magnitude varies inversely with temperature. Sensitivity of this channel lies between 10-35°C. The channel can also be activated by binding it with an extracellular ligand (for example:- Menthol).We have got leak channels which pass an outward current(mostly K+   ions).Some leak channels derive from the family of two_pore domain(2P) domain potassium channels. Amongst the various members of these channels few close promptly at temperatures less than about  28°C (eg. TRAAK, TREK).
Another modulation by temperature is activity of the Na+/K+-ATPase. This enzyme is a P-type
pump which extrudes 3Na+ ions in exchange for 2K+ ions for each hydrolytic cleavage of ATP. This results in net movement of unit positive charge outwards from the cell, i.e. a hyperpolarizing current. The magnitude of this current is proportional to the pump activity which is favoured by lower temparatures and vice-versa. Cold reception is this constellation of various channels and pumps.

Central Nervous System pathway
The potential from these receptors runs through the spinal cord via Spinothalamic Pathway. The sensory information transmitted by are affective sensations which involves a retracting of organ from the point of stimulus like pulling back the part of body where cold receptors are activated. The cells of this pathway lie in the dorsal horn of spinal cord. Basically the pathways
of the temperature sensation runs together with the pain pathway which is the Lateral Spinothalamic  pathway . The endings of this pathway lie in the Brain Stem.

Processing:
The information from the brain stem is passed on to the  Somatosensory area in the human cortex.  It is located in the  postcentral gyrus of the parietal lobe. The processing of the temperature information takes place here which involves synapses in the deep regions of brain.
The processing like every other sensory information processing involves the homunuculus  and
in this case cortical homunculus.In the cortical homunculus a physical representation of the portion of the human body directly responsible for the movement and exchange of sense and motor information of the rest of the body occurs.The processing thus takes place makes the motor cortex to provide the muscle movement for the affected part to retract.

References

• Nervous System by Gregory A. Mihailoff, Charlie Briar
• Textbook of Clinical Neurology by Renato J. Verdugo

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Sensation And Perception Of Cold Temperature

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