Chapter 15 Flashcards
cutaneous
anything related to skin
involved in somatosensory system
3 parts of somatosensory system
cutaneous (perception of touch and pain)
proprioception (sense position of body and limbs)
kinesthesis (sense movement of body and limbs)
skin (+ functions)
heaviest and largest organ
functions:
warns us of danger
protects us from bacteria or chemical agents
helps keep our organs and fluids inside body
epidermis
outer layer of skin (visible to us)
made up of dead skin cells
dermis
below the epidermis
contains mechanoreceptors
mechanoreceptors
sensory receptors that respond to pressure, stretching, and vibration
two ways neurons fire in the skin
slowly adapting receptors (SA - continuous firing from pressure)
rapidly adapting receptors (RA - firing only occurs at the beginning and end of a pressure, none in the middle)
mechanoreceptors near the epidermis
merkel receptors (SA1, specific details of touch)
meissner corpuscles (RA1, handgrip control)
both contain small cutaneous receptive fields
(M&Ms are small)
cutaneous receptive fields
area of skin that influences neural firing
mechanoreceptors deeper in the dermis
ruffini cylinders (SA2, stretching of skin, like pinching)
pacinian corpuscles (RA2, vibration and fine texture through movement)
both contain large cutaneous receptive fields (can’t sense details)
(Power Rangers are large)
corpuscles
onion-like structure
transmit electrical signals (neural firing) to nerve fibers (axons) when rapidly applied pressure (vibration) occurs but NOT when there is continuous pressure
neural pathway from skin to brain
nerve fibers fire from peripheral nervous system (skin areas) to central nervous system (brain and spinal cord)
2 major pathways into spinal cord
medial lemniscal pathway (large fibers, proprioceptive/position and touch info)
spinothalamic pathway (small fibers, temperature and pain info)
where do neurons fire after going from the two major pathways into the spinal cord?
both pathways go from spinal cord to ventrolateral nucleus of thalamus
from thalamus to somatosensory cortices (both located in parietal lobe)
somatosensory cortices
contains organized map of various parts of our body
somatosensory receiving area (S1)
secondary somatosensory cortex (S2)
both located in parietal lobe
homunculus
latin for “little man”
another name to refer to body map
disproportionately represents body parts; magnification shows more use of body parts equating to perceiving more details in that body part
experience dependent plasticity
our brains can change and adapt to experience and training for touch and other senses (ex. learning to play chords on guitar or read braille)
cortical representation of particular function becomes larger if that function is used often
representations of our brain areas are not totally fixed
tactile acuity
our ability to detect details on the skin
high density or crowdedness of merkel receptors
high tactile acuity = larger areas in somatosensory cortex have smaller cutaneous receptive fields in the skin
two different ways of perceiving tactile acuity
two point threshold (minimum separation needed between two points to perceive them as two points)
grating acuity (placing grooved stimulus on the skin and asking people to indicate the orientation/direction of the grating)
surface texture
being able to sense our touch based on bumps and grooves of surface
duplex theory of texture perception
we can perceive textures based on 2 cues:
spatial cues (detect texture based on size, shape, and distribution of surface element)
temporal cues (detect detailed texture based on the rate of vibration as skin is moved across the surface)
active touch
person explores object by touching them
humans rely on this to interact with environment
passive touch
object is applied to the skin (person is not doing the touching)
haptic perception
our ability to perceive 3D objects by actively exploring the object with our hands and fingers
psychophysical research - we can identify objects accurately in 1-2 seconds
three systems in haptic perception
sensory system (cutaneous sensations like touch, temperature, texture)
social touch
interpersonal touch
focuses on effect of a person touching another person
CT afferents
in the hairy part of skin, contain unmyelinated nerve fibers
can detect touch through slowly stroking the hair but causes the neurons to fire slowly
social touch hypothesis
touch may be involved based on two functions:
discriminative function of touch (sensing details, texture, vibration, and objects from the skin/mechanoreceptors; activated in somatosensory cortex)
affective function of touch (sensing pleasure and positive emotions (CT afferents); associated with social touch; activated in insula based on slow stroking)
pain
unpleasant sensory and emotional experience associated with actual or potential tissue damage
functions to warn us about dangerous situations (e.g., burning yourself)
three types of pain
inflammatory (damage to tissues and joints or by tumor cells; ex. sunburn)
neuropathic (damage to central nervous system; ex. multiple sclerosis - body pain or weakness, dizziness, loss of vision)
nociceptive (caused by nociceptors signaling impending damage to the skin)
nociceptors
specialized skin receptors that cause nociceptive pain
types of nociceptors respond to heat, chemicals, severe pressure, and cold
direct pathway model of pain
early model in 1950s and 1960s suggesting that pain is caused when nociceptors are activated and sent to the brain
problems:
pain can be affected by mental state
pain can occur without stimulation of skin (phantom limb)
pain can be affected by attention
three pathways for activating gate control system
nociceptors (neurons fire to open gate and transmission cells - pain increases)
mechanoreceptors (neurons from skin inhibits firing by closing gate and transmission cells - pain is inhibited)
central control (cognitive functions like attention, expectation, and distractions send neurons to fire from cortex to the gate control system to open or close gate)
multimodal nature of pain
people describe pain based on two components/modes:
sensory (describing pain based on what they physically feel)
affective (describing pain based on emotional association)
gate control model
there are different pathways by which pain is signaled to the spinal cord via a gate control system or circuit, which is sent to the brain
gates located in dorsal horn of spinal cord in which neurons fire and cause the gates to open or close (closed = less pain, open = more pain)
when gates open or close, the neural info is sent to transmission cells (neurons that send pain info to brain, like messengers)
opiods
drugs used to reduce pain and increase euphoria
four cognitive ways of influencing pain
expectation (surgical patients request less medication when they know what to expect; placebos can be effective)
shifting attention (virtual reality technology has been used to keep patients’ attention on other stimuli)
content of emotional distraction (participants could keep their hands in cold water longer when shown positive pictures)
hypnotic suggestion (fMRI study showed that hypnosis can produce pain and activate brain areas related to pain)
how do brain chemicals affect pain perception
brain contains opiate receptors to process chemicals involved in pain
naloxone can be used to revive someone who overdoses (drug that blocks heroin from getting into opiate receptor sites in the brain; but can increase pain because it prevents release of endorphins)
why do we have opiate receptors
our body produces natural painkillers (endorphins)
endorphins
endogenous morphine
naturally occurring painkiller
empathy
ability to share and vicariously experience someone else’s feeling
anterior cingulate cortex and anterior insula associated with empathy
