chapter 15 part 2 Flashcards
why do pacinian corpuscle fibers respond well to rapid vibration?
the corpuscle wraps around a nerve fiber and is made up of a series of layers with fluid between each layer - the fluid transmits rapidly repeated pressure like vibration to the nerve fiber, but not continuous pressure
what mechanism is responsible for sensing vibration of the skin
pacinian corpuscle (PC)
-nerve fibres associated with PCs respond best to high rates of vibration
- fibers without the pC only respond to continuous pressure
according to Katz, what two cues does perception of texture depend on?
spatial cues:
- determined by the size, shape, and distribution of surface elements (bumps and grooves)
temporal cues: determined by the rate of vibration as skin is moved across finely textured surfaces - fine textures that can only be perceived as fingers move across the surface
duplex theory of texture perception
two receptors may be responsible for the process of texture perception
do we use spatial or temporal cues to detect texture?
recent research by hollins and reisner suggests that we use temporal cues
- in order to detect differences between fine textures, ps needed to move their fingers across the surface
cortical responses to surface texture (lieber and sliman bensmaia)
cortical neurons that fired best to coarse textures received input from SA1 neurons in the skin (merkel)
and…
neurons that fired best to fine textures received input from PC receptors (pacinian corpuscles)
three types of object perception
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 determine the two point threshold
haptic perception: perception in which three dimensional objects are explored with the fingers and hand
which systems interact with each other in haptic perception?
the sensory system- involved in detected cutaneous sensations such as touch, temperature, and texture and the movements and positions of your fingers and hands
the motor system - involved in moving fingers and hands
the cognitive system - involved in thinking about the information provided by the sensory and motor systems
exploratory procedures
distinctive movements that people use to identify objects
- different types are EPs are used for different object qualities
research has shown that people can accurately identify most common objects within one or two seconds using active touch
how are cortical neurons specialized for tactile object perception
neurons in the ventral posterior nucleus, which is the tactile area of the thalamus, have centre surround receptive fields that are similar to the centre surround receptive fields in the lateral geniculate nucleus, which is the visual area of the thalamus
cortical physiology of tactile object perception
in the cortex we find some neurons with centre surround receptive fields and others that respond to more specialized stimulation of the skin
monkeys have neurons in the somatosensory cortex that respond when the monkey grasps a specific object
how is cortical responding affected by attention?
steven hsiao and coworkers
- found that cortical responding in monkeys increases when they focus on what is being presented to their fingers (vs focusing on an unrelated visual stimuli)
pain
multimodal phenomenon containing a sensory component and an affective or emotional component
three types of pain
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 - examples include carpal tunnel syndrome (caused by repetitive tasks such as typing), spinal cord injury, brain damage due to stroke
nociceptive pain
-caused by activation of receptors in the skin called nociceptors, which are specialized to respond to tissue damage or potential damage
direct pathway model of pain
pain occurs when nociceptor receptors in the skin are stimulated and send their signals directly from the skin to the brain
gaps in the direct pathway model of pain
situations in which pain is affected by factors in addition to stimulation of the skin
soldiers denying pain from serious wounds because of the fact that wounds have a positive aspect: help them escape from the battlefield to the safety of a behind the lines hospital
phantom limb - people who have had a limb amputated continue to experience the limb
- signals are send from the part of the limb that remain - brain - cutting nerves doesn’t eliminate the limb or the pain - pain must originate in the brain, not the nociceptors
gate control model of pain
idea that that pain signals enter the spinal cord from the body and are transmitted from the spinal cord to the brain
however, there are additional pathways that influence the signals sent from the spinal cord to the brain
signals from these additional pathways can act to open or close a gate, located in the spinal cord, which determines the strength of the signal leaving the spinal cord
think about how rubbing an area makes it hurt less
how does input to the gate control system occur along three pathways?
nociceptors:
fibers activate a circuit containing only excitatory synapses, and therefore send excitatory signals to the transmission cells
mechanoreceptors:
fibers from mechanoreceptors carry information about nonpainful tactile stimulation - ex rubbing skin sends inhibitory signals to the transmission cells, telling them to close the gate
central control:
fibers contain information related to cognitive functions such as expectation, attention, and distraction and carry signals down from the cortex - activity coming down from the brain can also close the gate and decrease transmission cell activity, decreasing pain overall
interpersonal touching or social touch
one person touching another
CT afferents
unmyelinated nerve fibres contained in hairy skin and are involved in social touch
speacialized for slow stroking
social touch hypothesis
CT afferents and their central projections are responsible for social touch
compared to other systems, which sense the discriminative functions of touch, like sensing details, texture, vibration, and object, the CT system is the basis of the affective function of touch (pleasure, positive emotions)
insula
main area of the brain that receives signals from CT afferents - involved in positive emotions
slow stroking creates connections between the back of the insula, which receives sensory information, and the front of the insula, which is connected to emotional areas of the brain
placebo effect
a relief from symptoms resulting from a substance that has no pharmacological effect - the belief that the placebo is an effective therapy leads to a reduction in pain
pain and attention
sometimes pain occurs not when we are injured, but when we realize we are injured
distracting from pain can sometimes decrease pain
emotions and pain
ps looking at positive pictures compared to negative pictures, or no pictures, were able to withstand pain for long (hand in cold water)
however, all of the groups had the same ratings of intensity for pain, suggesting that the content of the pictures influenced the amount of time it took for the groups to reach the same level of pain
multimodal nature of pain
experience of pain has both sensory and emotional components
brain areas and pain
perception of pain is accompanied by widespread brain acitivity in areas like the subcortical structures such as the hypothalamus, the amygdala, the thamalamus and areas of the cortex including the somtatosensory cortex, the anterior cingulate cortex, the prefrontal cortex, and the insula
opioids and pain perception
opiate drugs tend to reduce pain and induce feelings of euphoria
- act of receptors in teh brain that respond to stimulation by molecules with specific structures
why does naloxone work on heroin overdoses
its structure is similar to heroin’s and attaches to the same receptor sites, preventing it from binding
endorphins
chemical that is naturally produced in the brain and that causes analgesia (reduces pain)
social touch and pain
social touch reduces pain
- couples holding hands while feeling moderately painful stimuli - also synchronizes brain waves
empathy
ability to share and vicariously experience someone else’s feeling
- ex. mirror neurons
seeing someone else in pain can trigger pain mechanisms in our brain
physical-social pain overlap hypothesis
pain resulting from negative social experiences in processed by some of the same neural circuitry that processes physical pain
