GREAT-WRITERS ONLY
bobotheclown
perception_of_pleasure_and_pain_presentation.pptxPain and Pleasure
Pedro A. Colon, Brian Bocok, Kenya Gordon, sarah bourque, tabatha turnbo
Psychology 345
Jillian Watson-hulum
October 12, 2015
Somatosensory Cortex and Pleasure and Pain
Location
Function
Role
The Primary Somatosensory Cortex is located on the Postcentral Gyrus. It is the anterior part of the Parietal Love and lies behind the Primary Motor Cortex of the Frontal Lobe. The Somatosensory Cortex is the main sensory receptive area for the sense of touch. Processing primarily occurs in the primary somatosensory area in the parietal lobe of the cerebral cortex: information is sent from the receptors via sensory nerves, through tracts in the spinal cord and finally into the brain. The system works when activity in a sensory neuron is triggered by a specific stimulus such as pain, for instance. This signal then passes to the part of the brain attributed to that area on the body—this allows the stimulus to be felt at the correct location. The mapping of the body surfaces in the brain is called a homunculus and plays a fundamental role in the creation body image.
Picture Reference
https://classconnection.s3.amazonaws.com/360/flashcards/855360/png/untitled1327615025864.png
2
Somatosensory Cortex and Pleasure and Pain
Structure
General Somatosensory
Pathway
A somatosensory pathway will typically have three long neurons: primary, secondary and tertiary (or first, second, and third).
The first neuron always has its cell body in the dorsal root ganglion of the spinal nerve (if sensation is in parts of the head or neck not covered by the cervical nerves, it will be the trigeminal nerve ganglia or the ganglia of other sensory cranial nerves). The second neuron has its cell body either in the spinal cord or in the brainstem. This neuron's ascending axons will cross (decussate) to the opposite side either in the spinal cord or in the brainstem. The axons of many of these neurons terminate in the thalamus (for example the ventral posterior nucleus, VPN), others terminate in the reticular system or the cerebellum. In the case of touch and certain types of pain, the third neuron has its cell body in the VPN of the thalamus and ends in the postcentral gyrus of the parietal lobe.
3
Somatosensory Cortex and Pain and Pleasure
Pain detection
Specialized receptor cells
Mechonoreceptors
Thermoreceptors
Nociceptors (Pain receptors)
In the periphery, the somatosensory system detects various stimuli by sensory receptors, e.g. by mechanoreceptors for tactile sensation and nociceptors for pain sensation. The sensory information (touch, pain, temperature etc.,) is then conveyed to the central nervous system by afferent neurons. There are a number of different types of afferent neurons that vary in their size, structure and properties. Generally there is a correlation between the type of sensory modality detected and the type of afferent neuron involved. For example, slow, thin, unmyelinated neurons conduct pain whereas faster, thicker, myelinated neurons conduct casual touch.
Mechanoreceptors in the skin give us a sense of pressure and texture. Thermoreceptors detect changes in temperature through their free nerve endings. Nociceptors have free nerve endings that they use to detect pain. Functionally, nociceptors are specialized, high-threshold mechanoceptors or polymodal receptors. They respond not only to intense mechanical stimuli but also to heat and noxious chemicals—anything that may cause the body harm. Their response magnitude or the amount of pain you feel is directly related to the degree of tissue deformation inflicted. Pain signals can be separated into three types that correspond to the different types of nerve fibers used for transmitting these signals. The first type is a rapidly transmitted signal with a high spatial resolution called first pain or cutaneous pricking pain. This type of signal is easy to locate and generally easy to tolerate. The second type is much slower and highly affective called second pain or burning pain. This signal is more difficult to locate and not as easy to tolerate. The third type arises from viscera, musculature, and joints called deep pain. This type of signal is very difficult to locate and often intolerable and chronic.
References
"Sensory Receptors." ThinkQuest. Oracle Foundation, n.d. Web. (2012). http://library.thinkquest.org/05aug/00386/touch/sensoryreceptors.htm.
4
Somatosensory Cortex and Pain and Pleasure
Conscious touch
Regions of sensations
Cortical Homunculous
Motor
Sensory
Just as conscious vison and hearing depend on the primary visual and auditory cortex, the primary somatosensory cortex is essential for conscious touch experiences. When weak, brief stimuli are applied to the fingers, people are consciously aware of only those that produce a certain minimum level of arousal in the primary somatosensory cortex.
Researchers have identified the precise regions where sensations are interpreted and have come up with representative human figures that show proportionally how much of the brain is dedicated to sensation from various areas of the body. The technical term for such a figure is a homunculus, or “little man,” and people may refer to a “sensory homunculus” in particular to make it clear that they mean a visual representation of the somatosensory system. The head and hands of the figure are very large compared with other parts of the body, such as the limbs and the trunk. This is because so much of this region of the brain is dedicated to sensations from these parts of the body, which have many nerve endings, while the other parts have relatively few.
A cortical homunculus is a physical representation of the human body, located within the brain. A cortical homunculus is a neurological "map" of the anatomical divisions of the body. There are two types of cortical homunculus; sensory and motor. At the primary motor cortex, motor representation is arranged in an orderly manner, inverted. The toes are represented at the top of the cerebral hemisphere, while the mouth is represented at the bottom of the hemisphere, closer to the lateral sulcus. These representations lie along a fold in the cortex called the central sulcus. The homunculus is split in half, with motor representation for each side of the body represented on the the opposite side of the brain. Some body parts may be controlled by partially overlapping regions of cortex. The amount of cortex devoted to any given body region is proportional to how richly innervated that region is, not to the body region's physical size. Areas of the body with greater or more complex sensory or motor connections are represented as larger in the homunculus, those with fewer or less complex connections are represented as smaller. The resulting image is that of a distorted human body, with disproportionately huge hands, lips, and face.
References:
http://www.corpshumain.ca/en/images/HomunculusSensoriel_en.jpg
5
