Chapter 14 Erica Ocker
Overview of the Cutaneous System: Skin Comel (1953) called the skin the monumental disguise of the human body The skin serves as a warning function and a way to prevent body fluids from being released Layer of dead skin cells Epidermis Mechanoreceptors “Comel (1953) called the skin the monumental disguise of the human body for a good reason. It is the heaviest organ in the human body. The skin acts as a warning function and a way to prevent body fluids from being released. It also keeps bacteria, chemical agents, and dirt from entering our bodies and causing us infections. Skin is the visible surface and it is made of dead skin cells. The outermost layer is the epidermis and below the epidermis is the mechanoreceptors. The mechanoreceptors are responsible for sensing pressure, stretching, and vibrations. “ (Goldstein, 2010)
Mechanoreceptors Many of the perceptions that we feel from stimulation of the skin are due to the four types of mechanoreceptors within our skin The two mechanoreceptors are the Merkel receptor and the Meissner corpuscle Near the epidermis The other two mechanoreceptors are the Ruffini cylinder and the Pacinian corpuscle. Located deeper in the skin. -”Many of the strategic perceptions that we feel from stimulation of the skin are due to the four types of mechanoreceptors that are located in the epidermis and the dermis. -We can tell the receptors apart by their different structures and how fibers associated with the receptors respond to stimulation -The two mechanoreceptors are the Merkel receptor and the Meissner corpuscle. They are located near the surface of the skin, near the epidermis. -The Merkel receptor fires nonstop when it is being stimulated and the Meissner corpuscle fires only when the stimulus is first applied and when it is removed. The Merkel receptor senses fine details and the Meissner corpuscle controls handgrips. “ “-The other two mechanoreceptors are the Ruffini cylinder and the Pacinian corpuscle. These two are located deeper in the skin. The Ruffini responds constantly and the Pacinian corpuscle responds when the stimulus is applied and removed. The Ruffini is responsible for responding to the skin stretching and the Pacinian is responsible for responding to vibrations and fine texture. “ (Goldstein, 2010)
(Goldstein, 2010)
Pathways from Skin to Cortex Peripheral nerves enter the spinal cord via the dorsal root Two major pathways Medial Lemniscal Large fibers Spinothalamic Smaller fibers Fibers synapse in the ventrolateral nucleus “-Nerve fibers from receptors in the skin travel in packages called peripheral nerves that enter the spinal cord through the dorsal root. -The nerve fibers go up the spinal cord and to two major pathways: the Medial lemniscal pathway and the spinothalamic pathway -The lemniscal pathway has large fibers that are responsible for perceiving touch. The spinothalamic pathway has smaller fibers that transfer signals related to temperature and pain. -Fibers from both pathways cross over to the other side of the body when they are heading to the thalamus. Most of these fibers synapse in the ventrolateral nucleus in the thalamus. “ (Goldstein, 2010) -
(Goldstein, 2010)
Maps of the Body on the Cortex Signals go from the thalamus to the somatosensory receiving area The somatosensory cortex is organized into a map that matches certain locations on the body Homunculus Fingers are represented by large portions of the brain on the map “Signals travel from the thalamus to the somatosensory receiving area in the parietal lobe of the cortex and to the secondary somatosensory cortex. -The somatosensory cortex is organized into maps that match different locations on the body -The homunculus is Latin for “little man”. This the body map. Some areas of the skin are represented by large portions of the brain -For example, fingers, which are responsible for detecting details through touch are represented by very large portions of the brain on the map.” (Goldstein, 2010)
(Goldstein, 2010)
(Goldstein, 2010)
The Plasticity of Cortical Body Maps Cortical representation of certain areas on the body can become much bigger William Jenkins and Michael Merzenich (1987) Monkey’s cortical area expanded after the fingertip was used much more often than normal “The cortical representation of a certain function can become much bigger if that function is used a lot. -Experience-dependent plasticity -William Jenkins and Michael Merzenich (1987) showed that increasing stimulation of a specific area of the skin causes the cortical area receiving area to become much larger. --Measured the cortical areas matching each monkey’s finger. They trained monkeys to complete a task that involved the excessive use of a certain fingertip and then measured the cortical map again. The area of the excessively used finger tip on the cortical map was much larger after that finger tip had been used much more often.” (Goldstein, 2010)
(Goldstein, 2010)
Perceiving Details Braille Allows blind people to read through raised dots Dots are arranged to represent letters, punctuation and other common words Braille readers read 100 words per minute compared to visual reader’s 250 to 300 word ability Tactile Detail Perception “Perceiving details with the skin is greatly shown by the use of Braille. This system allows blind people to read through a series of raised dots Each character is made up of a cell that is made up of one-six dots The dots are arranged differently to represent certain letters, punctuation and other speech sounds/words 100 words per minute which is slower than someone who can see at 250 to 300 words The ability of Braille readers to identify patters of small dots based on the sense of touch depends on tactile detail perception.” (Goldstein, 2010)
Textbook Citation Goldstein, B. E. (2010). Sensation and Perception. Belmont: Wadsworth. (Goldstein, 2010)