Ch. 13 Flashcards
pain as a function
serves as a warning system that tells us when something might be internally wrong or when an external stimulus might be dangerous, enabling us to defend our bodies as quickly as possible
temperature sensations as a function
enable us to seek or create a thermally safe environment
mechanical sensations as a function
guide action, furthering perception, and play an important role in our intimate sexual and reproductive activities
social touch as a function
a powerful means of communicating our thoughts and emotions nonverbally and is a calming influence in the face of stress
touch
the sensations caused by stimulation of the skin, muscles, tendons, and joints;
Sensations caused by mechanical displacements of the skin
- includes the perception of temperature changes (thermal sensation), the sensation of pain, itchiness, pleasant effects of stroking, and the internal sensations of kinesthesia
tactile
referring to the result of mechanical interactions with the skin
kinesthesia
perception of the position and movement of our limbs in space
proprioception
perception mediated by kinesthetic and internal receptors
somatosensation
collectively, sensory signals from the skin, muscles, tendons, joints, and internal receptors
glabrous
in reference to skin, lacking hair
- touch receptors embedded all over the body, in both glabrous and hairy skin
touch receptors and neural fibers
A touch receptor is connected to a “nerve fiber” composed of its axon and myelin sheath, if present
four types of nerve fibers carry information about somatosensation
A-alpha fiber, A-beta fiber, A-delta fiber, C fiber
A-alpha fiber
a wide-diameter, myelinated sensory nerve fiber that transmits signals from proprioceptive receptors in muscles and tendons; carry information from proprioceptive receptors in muscles and tendons
A-beta fiber
a wide-diameter, myelinated sensory nerve fiber that transmits signals from mechanical stimulation; connected to receptors that respond to pressure and vibration
A-delta fiber
an intermediate-sized, myelinated sensory nerve fiber that transmits pain and temperature signals; carry information about temperature, pain, and itch
C fiber
a narrow-diameter, unmyelinated sensory nerve fiber that transmits pain and temperature signals; carry information about temperature, pain, and itch
mechanoreceptor
a sensory receptor that responds to mechanical stimulation (pressure, vibration, or movement)
- A-beta fibers
epidermis
the outer of two major layers of skin
dermis
the inner of two major layers of skin, consisting of nutritive and connective tissues, within which lie the mechanoreceptors
Meissner corpuscle
a specialized nerve ending associated with fast-adapting (FA I) fibers that have small receptive fields
- small receptive field
- fast adaptation rate
- Maximum feature sensitivity of temporal changes in skin deformation (~5-50 Hz); skin slip
- Primary perceptual function of low-frequency vibration and grasp stability
Merkel disc
a specialized nerve ending associated with slowly adapting (SA I) fibers that have small receptive fields
- Small receptive field
- Slow adaptation rate
- Maximum feature sensitivity of sustained pressure, very low frequency (< ~5 Hz)
- Primary perceptual functions of coarse texture and pattern
Pacinian corpuscle
a specialized nerve ending associated with fast-adapting (FA II) fibers that have large receptive fields
- Large receptive field
- Fast adaptation rate
- Maximum feature sensitivity of temporal changes in skin deformation (~50-700 Hz)
- Primary perceptual functions of high-frequency vibration and fine texture
Ruffini ending
a specialized nerve ending associated with slowly adapting (SA II) fibers that have large receptive fields
- Large receptive field
- Slow adaptation rate
- Maximum feature sensitivity of sustained downward pressure and lateral skin stretch (~5-50 Hz)
- Primary perceptual function of finger position
four types of mechanoreceptors can be independently classified according to two attributes describing how they function
- size of the receptive field
- rate of adaptation (fast versus slow)
tactile receptive field of mechanoreceptors
patch of the body where a stimulus will produce a response
- fields are generally classified as small (around 10-20 square millimeters) or large (from 60 square millimeters to the size of an entire finger)
rate of adaptation of mechanoreceptors
- A fast-adapting (FA) receptor responds with bursts of action potentials, first when its preferred stimulus is applied and then again when the stimulus is removed
- A slowly adapting (SA) receptor remains active throughout the period during which the stimulus is in contact with its receptive field
other labels for neural fibers
slowly adapting type I (SA I) fibers, slowly adapting type II (SA II) fibers, fast-adapting type I (FA I) fibers, fast-adapting type II (FA II) fibers
slowly adapting type I (SA I) fibers
- Respond best to steady downward pressure
- Fine spatial details
- Very-low-frequency vibrations
- Especially important for texture and pattern perception
- When a single S I fiber is stimulated, people report feeling “pressure”
- Assumed that these fibers terminate in Merkel discs
slowly adapting type II (SA II) fibers
- Respond to sustained downward pressure and particularly to lateral skin stretch (Lateral skin stretch occurs when we grasp an object)
- When a single SA II fiber is stimulated, people experience no tactile sensation at all
- For stimulation to be detectable, more than one SA II fiber must be stimulated
- Assumed to terminate in Ruffini endings, but recent research has questioned whether these expanded terminals are as numerous as traditionally believed
fast-adapting type I (FA I) fibers
- Respond best to low-frequency vibrations
- Helps you correct your grip
- When a single FA I fiber is stimulated, people report a very localized sensation that they describe as “wobble” or “flutter”
- These fibers are assumed to terminate in Meissner corpuscles
fast-adapting type II (FA II) fibers
- Respond best to high-frequency vibrations
- Such vibrations occur whenever an object first makes contact with skin, as, for example, when a mosquito lands on your arm
- Such vibrations are also generated when an object that you’re holding contacts another object, so they help you determine how hard you’re tapping your pencil on your desk for example
- When a single FA II fiber is stimulated, people report a more diffuse sensation in the skin that corresponds to a “buzz”
- These fibers have been shown to terminate in Pacinian corpuscles
kinesthetic
referring to perception involving sensory mechanoreceptors in muscles, tendons, and joints
muscle spindles
muscle receptors that convey the rate at which the muscle fibers are changing in length
- perceive the angle formed by a limb at a joint
Golgi tendon organs
receptors in the tendons that provide signals about the tension in the muscles attached to the tendons
thermoreceptor
a sensory receptor that signals information about changes in skin temperature
two distinct populations of thermoreceptors
warmth fiber and cold fiber
warmth fiber
a sensory nerve fiber that fires when skin temperature increases
cold fiber
a sensory nerve fiber that fires when skin temperature decreases
- outnumber warmth fibers by a ratio of about 30:1
neural fibers that serve kinesthetic receptors
A-alpha and A-beta fibers
neural fibers that serve cold and warmth fibers
C fibers and A-delta fibers
- both have free nerve endings
free nerve ending
the terminus of a neural fiber without a specialized ending
- nerve endings are bare
thermoTRP channel
thermally sensitive transient receptor potential ion channel found in sensory neurons
body is constantly working to regulate internal temperature so the skin is kept between 30°C and 36°C
- Neither cold nor warmth fibers respond much while skin temperature remains within this range
- If skin temperature rises above 36°C, warmth fibers will begin to fire
- If skin temperature falls below 30 °C, cold fibers will begin to fire
- Thermoreceptors also kick into gear when we make contact with an object that is warmer or colder than our skin
nociceptor
a sensory receptor that responds to painful input, such as extreme heat or pressure
- have bare nerve endings
neural fibers that serve nociceptors
- A-delta fibers respond primarily to strong pressure or heat
- C fibers respond to intense stimulation of various sorts: pressure, heat or cold, or noxious chemicals
many painful events seem to occur in two stages, which may reflect the onset of neural fiber signals
1) a quick, sharp burst of pain –> A-delta fibers
2) followed by a throbbing sensation –> C fibers
thermoTRP channels in enabling nociceptors
these channels allow nociceptive neurons to detect thermal and chemical stimulation that produces pain
C tactile (CT) afferent
a narrow-diameter, unmyelinated sensory nerve fiber that transmits signals from pleasant touch
- Preferably responds to mechanical stimulation in the form of slow moving, lightly applied forces (like petting)
- Located only in hairy skin
labeled lines
a theory of sensory coding in which each nerve fiber carries a particular stimulus quality
dorsal horn
a region at the rear of the spinal cord that receives inputs from receptors in the skin
- Where axons enter the spinal cord
- organized into multiple layers (laminae)
from skin to brain
- the axons of various tactile receptors are combined into single nerve trunks
- information must move up through the spinal cord
- inputs of the cord are organized in a somatotopic manner
- once in the spinal cord, touch information proceeds upward toward the brain via two major pathways: spinothalamic pathway, dorsal column-medial lemniscal (DCML) pathway
- from the thalamus, much of the touch information is carried up to the cortex into somatosensory area 1
- neurons in S1 communicate with somatosensory area 2 and other cortical areas
laminae of the dorsal horn
- Pain and pleasant touch fibers enter the uppermost laminae
- A-beta fibers from mechanoreceptors enter in a deeper layer of the laminae
somatotopic
referring to normal somatosensation; referring to spatial mapping in the somatosensory cortex in correspondence to spatial events on the skin
Once in the spinal cord, touch information proceeds upward toward the brain via two major pathways
- spinothalamic pathway
- dorsal column-medial lemniscal (DCML) pathway
spinothalamic pathway
the route from the spinal cord to the brain that carries most of the information about skin temperature and pain
- Slower of the two pathways
- Carries most of the information from thermoreceptors and nociceptors
dorsal column-medial lemniscal (DCML) pathway
the route from the spinal cord to the brain that carries signals from skin, muscles, tendons, and joints
- Includes wider-diameter axons and fewer synapses
- Conveys information more quickly to the brain
- Tactile and kinesthetic information carried along this pathway is used for planning and executing rapid movements
- Neurons in this pathway first synapse in the cuneate and gracile nuclei, near the base of the brain
- Activity is then passed on to neurons that synapse in the ventral posterior nucleus of the thalamus
somatosensory area 1 (S1)
the primary receiving area for touch in the cortex
- Located in the parietal lobe just behind the postcentral gyrus
somatosensory area 2 (S2)
the secondary receiving area for touch in the cortex
- Lies in the upper bank of the lateral sulcus
homunculus
a maplike representation of regions of the body in the brain
- Twin homunculus because there are corresponding spatial maps in the left and right hemispheres
body image
the mental representation of how our bodies appear in space
- People’s body image proves to be systematically distorted toward top-heaviness, with expanded shoulders and upper arms but with lower arms and legs reduced in size
- The body representation can be changed by experience as well as direct transformation to the body itself
anterior cingulate cortex (ACC)
a region of the brain associated with the perceived unpleasantness of a pain sensation
substantia gelatinosa
a region of interconnecting neurons in the dorsal horn of the spinal cord; where neurons carrying nociceptive signals arrive at the dorsal horn
gate control theory
a description of the pain-transmitting system that incorporates modulating signals from the brain
- According to this theory, the bottom-up pain signals from the nociceptors can be blocked via a circuit located in the spinal cord
neurons in the dorsal horn actively inhibit pain transmission…
what is transmitted to somatosensory areas in the brain is the combined output of pain excitation from the nociceptors and this inhibition
inhibitory neurons in the dorsal horn receive input signals from two different sources
- A-beta fibers coming from the skin, which respond to benign touch rather than pain
- The top-down pathways from the brain
areas of the brain that correspond to the emotional aspects of painful experiences
Thalamus, insula, anterior cingulate cortex (ACC)
analgesia
decreasing pain sensation during conscious experience; damping of pain sensations
responses to noxious stimulation can be affected by…
analgesic drugs, effects of anticipation, religious belief, prior experience, or excitement
endogenous opiate
a chemical released by the body that blocks the release or uptake of neurotransmitters necessary to transmit pain sensations to the brain
placebo effect
decreasing pain sensation when people think they’re taking an analgesic drug but actually are not
- Placebos actually inhibit nociceptive processing as early as the dorsal horn
- Placebos can enhance positive effects as well as reduce negative ones
hyperalgesia
an increased or heightened response to a normally painful stimulus
- when pain surpasses normal expectations
inflammatory
an increased or heightened pain response to a normally painful stimulus
nocebo effect
increasing pain sensation when people expect pain
neuropathic pain
Pain that arises in the absence of immediate trauma because of damage to or dysfunction of the nervous system
neural plasticity
the ability of neural circuits to undergo changes in function or organization as a result of previous activity
phantom limb
sensation perceived from a physically amputated limb of the body
biomimetic feedback
a system that attempts to closely mimic biological signals
- found in bionic limbs
- Stimulates residual nerves so that the user can experience sensations like in tactile events
tactile sensitivity across the body
- Your skin is sensitive to mechanical pressure all over, but not uniformly so
- Thresholds vary across different sites of the body
- In general, tactile pressure sensitivity is highest on the face, followed by the trunk and upper extremities (arms and fingers), and then the lower extremities (thigh, calf, foot)
- Sensitivity to temperature changes and pain varies as a function of body site
two-point touch threshold
the minimum distance at which two stimuli (e.g., two simultaneous touches) are just perceptible as separate
(spatial acuity)
- varies across the body
- mediated by the SA I (and possible FA I) tactile receptors
common method requires participants to decide whether two tactile pulses delivered to the skin appear to be either simultaneous or successive in time
Participants can resolve a temporal difference of only 5 milliseconds
people may differ in tactile sensitivity
- Tactile sensitivity declines with age
- Studies of blind people who read Braille are an exception to this trend
- Genes affect tactile sensitivity
haptic perception
knowledge of the world that is derived from sensory receptors in skin, muscles, tendons, and joints, usually involving active exploration
exploratory procedures
a stereotyped hand movement pattern used to touch objects in order to perceive their properties; each procedure is best for determining one (or more) object properties
- Each exploratory procedure is optimal for obtaining precise details about one or two specific properties
types of exploratory procedures
- lateral motion –> texture
- pressure –> hardness
- static contact –> temperature
- unsupported holding –> weight
- enclosure –> global shape, volume
- contour following –> global shape, exact shape
tactile agnosia
the inability to identify objects by touch; caused by lesions of the parietal lobe
frame of reference
the coordinate system used to define locations in space
egocenter
the center of a reference frame used to represent locations relative to the body
endogenous
in reference to spatial attention, a form of top-down (knowledge-driven) control in which attention is voluntarily directed toward the site where the observer anticipates a stimulus will occur
exogenous
in reference to spatial attention, a form of bottom-up (stimulus-driven) attention reflexively (involuntarily) directed toward the site at which a stimulus has abruptly appeared
