somatosensory system
1. cutaneous sense: responsable for perceptions such as touch and pain that are usually caused by stimulation of the skin (also help protect ourselves from injury and motivate sexual activity)
2. proprioception: the ability to sense the position of the bo
the skin
-largest, most heavy organ
-protects our bodies from the outside and provides us with information about various stimuli that contact it (heat, pain, pressure, etc)
epidermis
outer layer of the skin, including a tough layer of dead skin cells
dermis
below epidermis
mechanoreceptors
receptors within the skin that respond to mechanical stimulation, such as pressure, stretching, and vibration
slowly adapting (SA) receptors- respond with prolonged firing to continued pressure
rapidly adapting (RA) receptors- respond with bursts of firin
pathways from skin to cortex
-cutaneous receptors are distributed over the whole body
-signals must reach the brain before stimulation of the skin can be perceived (long journey must be traveled)
-signals are first conducted from the skin to the spinal cord, which consists of 31 segm
medial lemniscal pathway
has large fibers that carry signals related to sensing the positions of the limbs (proprioception) and perceiving touch
-transmit signals at high speed, which is important for controlling movement and reacting to touch
spinothalamic pathway
consists of smaller fibers that transmit signals related to temperature and pain
ventrolateral nucleus
most fibers synapse in here in the thalamus, but some synapse in other thalamic nuclei
-because the spinal cord crosses, the signals originating front the left side of the body reach the thalamus in the right hemisphere and vice versa
somatosensory cortex
from the thalamus, signals travel tot he somatosensory receiving area (S1) in the parietal lobe of the cortex and possibly also to the secondary somatosensory cortex (S2)
-signals can travel between S1 and S2 to additional somatosensory areas
-the cortex
homunculus
-body map on the somatosensory cortex
-adjacent areas of the skin project to adjacent areas in the brain, and that some areas on the skin are represented by a disproportionately large area of the brain (ex: area devoted to the thumb is are large as area d
plasticity of cortical body maps
-experience-dependent plasticity- cortical representation of a particular function can become larger if that function is used often (ex: kittens raised in a vertical environment, greebles)
-this means that while we can specify the general area of the cort
perceiving details
-the ability of Braille readers to identify patterns of small raised dots based on the sense of touch depends on tactile detail perception
-tactile acuity- the ability to detect details on the skin. the classic way to measure this is using the two-point t
receptor mechanisms for tactile acuity
-high density of Merkel receptors in the fingertips, because the fingertips are the parts of the body that are most sensitive to details
-a comparison of grating acuity on different parts of the hand shows that better acuity is associated with less spacin
cortical mechanisms for tactile acuity
-there is a parallel between tactile acuity and the representation of the body in the brain
-regions of high acuity, like the fingers and lips, are represented by larger areas on the cortex, which provides extra neural processing to accurately sense fine
perceiving vibration
-Pacinian corpuscle is primarily responsible for sensing vibration
-the presence of the corpuscle surrounding the nerve fiber determines which pressure stimuli actually reach the fiber. the corpuscle consists of a series of layers with fluid in between ea
perceiving texture
-surface texture- the physical texture of a surface created by peaks and valleys. touch, which involves direct contact with the surface, provides a more accurate assessment of surface texture than vision.
-spatial cues- provided by relatively large surfac
duplex theory of texture perception
-our perception of texture depends on both spatial and temporal cues
-movement, which generates vibration as the skin scans a surface, makes it possible to sense the roughness of fine surfaces
-in an experiment, adapting the Pacinian corpuscle receptor (w
perceiving objects
-active touch- touch in which a person actively explores an object, usually with fingers and hands
-passive touch- occurs when touch stimuli are applied to the skin, as when two points are pushed onto the skin to detainee the two-point threshold
-haptic p
identifying objects by haptic exploration
-haptic perception is a good example of situation in which a number of different systems are interacting with each other
1. sensory system- involved in detecting cutaneous sensations, such as touch, temperature, and texture and the movements and positions
exploratory procedures (EPs)
-distinctive movements made to identify objects. types of Eps depend on the object qualities that participants are asked to judge.
-people can accurately identify most common objects within 1 or 2 seconds
-lateral motion and contour following to judge tex
physiology of tactile object perception
-in order for the brain to control everyday tasks, such as screwing a lid on a bottle, it needs to have access to information about the size and contour of the lid, and the amount of force needed to grasp the lid. this information is provided by receptors
inflammatory pain
caused by damage to tissue or inflammation of joints or by tumor cells
neuropathic pain
caused by lesions or other damage to the nervous system
nociceptive pain
caused by activation in the skin called nociceptors, which are specialized to respond to tissue damage or potential damage
-a number of different kinds of nociceptors response to different stimuli- heat, chemical, pressure, cold
questioning the direct pathway model of pain
-according to this model, pain occurs when nociceptor receptors in the skin are stimulated and send their signals directly from the skin to the brain
-however, there are situations in which pain is affected by factors in addition to stimulation of the ski
gate control model
-begins with the idea that pain signals enter the spinal cord front he body and are then transmitted from the spinal cord to the brain. there are also additional pathways that influence the signals sent from the spinal cord to the brain.
-the central idea
input to the gate control system occurs along 3 pathways
-nociceptors- fibers from nociceptors activate a circuit consisting entirely of excitatory synapses, and therefore send excitatory signals to the transmission cells. excitatory signals from the + neurons in the dorsal horn "open the gate" and increase the
cognition and pain
-expectation- in a hospital study in which surgical patents were told what to expect and were instructed to relax to alleviate their pain, patients requested fewer painkillers following surgery and were sent home 2.7 days earlier than patients who were no
the brain and pain
-pain matrix- all of the brain regions that are involved in pain perception, which are widely distributed throughout the brain.
multimodal nature of pain
-sensory component and affective component
-experiment in which participants were asked to rate both components of pain, and were hypnotically influenced.
-presenting images to decrease or increase the unpleasantness (affective component) of the pain did
chemicals in the brain
-opiate drugs act on receptors in the brain that respond to stimulation by molecules with specific structures
-naloxone can save someone from a heroine overdose, attaches itself to opiate site instead
-occupy same receptors site for endorphins, endogenous
the effect of observing touch and pain in others
-activates areas in S1 in the observer that would also be activated in the S1 of the person actually experiencing it
-reflects empathy?
synesthesia
a condition in which stimulation of one modality, like vision, results in an experience in another modality, like touch. when this person observes another person being touches, he or she experiences touch on the same part of his or her own body.