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What does the map of the sensory cortex reveal about the density of touch receptors? Explain.

Cutaneous sensation ultimately projects to the postcentral gyrus of the brain's sensory cortex. The map of this region shows that a larger area of the cortex is devoted to analysis of cutaneous sensations arising from the hands (particularly fingertips) and the tongue and lips than from most other areas of the body.

Describe the importance of referred pain in the diagnosis of deep visceral pain and give examples.

Deep visceral pain is poorly localized, but damage to visceral organs may cause pain in characteristic somatic locations. Examples: 1. Pain in the left pectoral region, arm, and shoulder areas = myocardial ischemia (heart problems). 2. Pain between the scapulae of the back = stomach ulcers.

Define sensory adaption

Receptors stop responding to maintained stimuli.

Which parts of your body have the highest density of touch receptors? What benefits may be derived from that fact?

The face, particularly the lips and fingertips have the highest density of touch receptors. Benefits = Identify objects, temperatures, textures, and other sensory info of importance.

"Our perception of the external world are created by our brains." Discuss this concept, using the phantom limb phenomenon to support your argument.

The sensory receptors transduce different forms of energy into nerve impulses that are transmitted to our brains for interpretation. The brain interprets impulses arriving along different neural pathways as a compliation of unique sensations from particular receptors or regions in the body. Our perceptions, therefore, are the result of this blend of sensory input applied to a background of continuous and dynamic consciousnerve activity. The role of the brain in sensory perception is shown by the phantom limb phenomenon, in which the brain is "tricked" by the arrival of impulses along nerves that had originally served the missing limb, and as a result of the amputation, the brain mistakenly refers the pain to the missing limb.

How did your right and left hands feel when placed in the same lukewarm water bath? Explain how this occurred.

The hand that was previously in warm water felt colder, while the hand that was previously in cold water felt warmer. This is because the perceived temperature of the lukewarm water is produced by the combined effects of the water temperature on separate receptors for cold and heat. The cold receptors adapted somewhat in the hand that was previously in cold water, so that the perceived temperature was warmer than it would otherwise have been. Similarly, the heat receptors were partially adapted in the hand that was previously in the hot water, so it felt cooler when placed in the lukewarm water.

Describe the map of the motor cortex. How does it compare with the map of the sensory cortex? What does the map of the motor cortex reveal about motor control?

The motor cortex is located on the postcentralgyrus. Those areas of the body that have the greatest representation are those that have the greatest number of muscle groups and exhibit the finest muscle activity (such as the face and fingers). Interestingly, those areas of the body that have the largest density of touch receptors also receive the greatest motor innervation and have correspondingly larger representation on both the sensory and motor regions of the cortex, respectively. The motor cortex map reveals that large areas are devoted to the motor activity of the face (particularly the tongue and lips) and hangs, whereas relatively small areas are devoted to the trunk, hips, and legs.