Chapter 12 The Body Senses

Question 1

Tactile perception (touch）

Answer 1

perception that results from the mechanical deformation- indentation, vibration, or stretching- of the skin

• Two types of skin
• > Hairy skin: on head and forearms
• > Glabrous skin: skin without hairs; the lips and palms
• Two type of skin with two main layers:
• > Epidermis and dermis
• > With a variety of sensory receptors (mainly in the dermis)

Question 2

Mechanoreceptors

Answer 2

sensory receptors that transduce mechanical deformations of the skin into neural signals that are sent to the brain

Question 3

Two slow-adapting (SA) mechanoreceptors

Answer 3

SAI mechanoreceptors and SAII mechanoreceptor produce a burst of action potentials at the onset of skin deformation but then a lower and sustained response until the stimulus is removed from the skin.

Question 4

Two fast-adapting (FA) mechanoreceptors

Answer 4

FAI mechanoreceptors and FAII mechanoreceptors produce a burst of action potentials only at the onset and offset of skin deformation.

Question 5

Adapting

Answer 5

• fact that sensory fibers tend to reduce their firing rate during prolonged, unchanging stimulation from an initial high level to either a lower, sustained level (SA) or virtually to zero (FA)

Question 6

SAI mechanoreceptors: Perceiving Pattern, Texture, and Shape

Answer 6

slow-adapting mechanoreceptors with Merkel cell endings; they have relatively small receptive fields and are relatively densely arranged near the surface of the skin.

• Respond most strongly to identation of the skin
• Detailed perception of spatial patterns on surfaces
• Fine-grained patterns, surface curvatures, defines shape
• Spatial event plot showing how the pattern of action potentials produced by an individual SAI fiber matched up with the entire pattern of the stimulus.
• provide information about texture and shape, in addition to information about patterns like embossed letters and Braille dots.
• Reliable information about aspects of surface shape such as curvature.
• Information about orientation

Question 7

SAII mechanoreceptors: Perceiving Skin Stretch and Hand Conformation

Answer 7

slow-adapting mechanoreceptors; they have relatively large receptive fields and are relatively sparsely distributed relatively deeply in the skin.

• Unselective response to different Braille patterns
• Provide little information about patterns and textures
• Skin stretch
• Hand conformation
• The ability to perceive how the hand is configured is critical for maintaining precision grips and for recognizing object shape haptically.
• The perception of skin stretch also plays a role in the perception of movement across the skin.

Question 8

FAI mechanoreceptors: Perceiving Slip and Maintaining Grip Control

Answer 8

fast-adapting mechanoreceptors with Meissner corpuscle endings; they have relatively small receptive fields and are relatively densely arranged near the surface of the skin.

• Respond most strongly to low-frequency vibrations, conveying information about very small motions of the skin.
• Don’t respond to sustained stimulation but only to changes in stimulation
• Perceiving slip and maintaining control over the force of one’s grip on an object
• The FAI fibers are active at just two points in the process:
• > During the load phase: when the fingers touch the object and then grip it with enough force to lift it off the surface without having it slip through the fingers
• > During upload phase: when the fingers release the object after setting it back down

Question 9

FAII mechanoreceptors: Perceiving Fine Textures Through Transmitted Vibration

Answer 9

fast-adapting mechanoreceptors with Pacinian corpuscle endings; they have relatively large receptive fields and are relatively sparsely distributed relatively deeply in the skin.

• Pacinian corpuscles, the specialized endings of FAII mechanoreceptors, have an onion-like structure containing multiple layers of tissue separated by fluid- that is, many nested capsules surrounding a central capsule where the end of the FAII fiber resides.
• The layered tissue surrounding the end of the fiber is what gives the fiber a fast-adapting response profile
• FAII mechanoreceptors are exquisitely sensitive
• > Vibrations are transmitted across large distances within the dermis
• > Large receptive field
• Perceptions of objects and surfaces and roughness of fine textures based on vibrations

Question 10

The four types of mechanoreceptors also differ in the size of their receptive fields and their typical position (depth) within the layers of the skin.

Answer 10

• SAI and FAI: small receptive fields and are densely arranged near the surface of the skin; high spatial resolution
• SAII and FAII: larger receptive fields and are more sparsely distributed more deeply in the skin; lower spatial resolution

Question 11

Merkel cells

Answer 11

specialized endings of SAI mechanoreceptors, where transduction takes place

Question 12

Meissner corpuscles

Answer 12

endings of FAI mechanoreceptors

Question 13

Pacinian corpuscles

Answer 13

endings of FAII mechanoreceptors

Question 14

Two-point threshold

Answer 14

touching two nearby skin locations with a pair of pointed probes and asking the person to judge whether one or two locations were touched.
*The threshold is smallest on the fingertips and lips and is much larger (lower resolution) on the arms, legs, and torso.

Question 15

Confusion matrix

Answer 15

it shows how often people confused each stimulus letter with every other letter.

Question 16

C-tactile mechanoreceptors (CT mechanoreceptors)

Answer 16

provides information about skin stimulations experienced as pleasant, or pleasurable

• Unmyelinated mechanoreceptors
• Free nerve endings only present in hairy skin
• Carry signals relatively slow to the brain
• Respond to slow, gentle touch, sending signals to the insular cortex, an area of the brain that is also involved in perception of the pleasant-unpleasant dimension of taste and smell.

Question 17

Proprioception: Perceiving Position and Movement of the Limb

Answer 17

perception of the position and movement of body parts, based on the information in neural signals from specialized sensors within those body parts.
* Kinesthesis: specifically to the perception of movement of the limbs

Question 18

Muscle spindles

Answer 18

sensory organs that provide information about muscle length, as well as information about isometric forces on muscles, for proprioception.

• Produce signals in afferent nerve fibers in response to changes in muscle length
• Produce signals in response to isometric forces on a muscle, as when you simply hold a weight in your hand
• Provide most important information for proprioception

Question 19

Golgi tendon signals

Answer 19

sensory organs that provide information about muscle force for proprioception.

• Changes in length
• These signals convey information about joint angle
• When the angle of a joint changes, the muscles attached at the joint are stretched or contracted, which changes both muscle force and muscle length; thus, signals with information about muscle length also supply information about joint angle.

Question 20

Joint receptors

Answer 20

sensory organs that provide information about joint angle, probably to signal when a joint has reached the limit of its normal motion.

Question 21

Pain

Answer 21

unpleasant sensory and emotional experience caused by potential or actual tissue damage; pain can arise from a wide range of different causes and can evoke an equally wide range of perceptual experiences.

Question 22

Nociception

Answer 22

perception of pain; critical to survival

• Quick recognition of damage
• Extremely salient

Question 23

Nociceptive pain

Answer 23

pain that arises from tissue damage due to physical trauma

• Detected by specialized receptors
• Body’s early warning system
• Inflammatory pain
• Caused by damage to the peripheral or central nervous system

Question 24

Affective perceptions

Answer 24

unpleasant physical or emotional experiences- which motivate us to make the pain stop

Question 25

Discriminative perceptions

Answer 25

determine where the pain is coming from, what it feels like, and how intense it is.

Question 26

Nociceptors

Answer 26

transduce the physical stimuli associated with damaging mechanical, thermal, or chemical events

Question 27

Sensitization

Answer 27

mechanism that decreases the response threshold of nociceptors, so that even very low level stimulation of an injury site can cause pain

• Often associated with inflammation
• Lead an organism to favor a damaged part of the body
• Make healing occur more quickly and more completely

Question 28

Nociceptors transmite pain signals to the spinal cord via two different types of fibers (axons)

Answer 28

• A-delta fibers
• C fibers
• The two different types of fibers activate distinct types of cells in the spinal cord, maintaining the distinction between “first pain” and “second pain” signals.

Question 29

A-delta fibers

Answer 29

small myelinated; myelinated axons of nociceptors that transmit pain signals relatively rapidly, to produce a rapid response to potentially damaging mechanical stimuli and to excessive heat.

Question 30

C fibers

Answer 30

unmyelinated axons of nociceptors that transmit pain signals relatively slow

Question 31

Thermoreception

Answer 31

ability to sense the temperature of objects and surfaces in contact with the skin

• Perceiving their material properties
• Survival
• The external temperature affects the internal temperature of your body, which can function normally only if that internal temperature is maintained within a very narrow range.

Question 32

Thermoreceptors

Answer 32

Sensory receptors for the detection of temperatures within the range of about 17-43 degree C; included among the free nerve endings in the epidermis and dermis
* Temperatures below and above this range are often experienced as painful, in response to signals produced by A-delta fibers.

Question 33

Warm fibers

Answer 33

thermoreceptors that fire at an ongoing moderate rate in response to sustained skin temperatures in the range of 29-43 degree C.

Question 34

Cold fibers

Answer 34

thermoreceptors that fire at an ongoing moderate rate in response to sustained skin temperatures in the range of 17-40 degree C.
* Both types of fibers maintain their increased firing rate for several seconds but then adapt to the new temperature, and their firing rate falls back to the baseline level.

Question 35

Dorsal root

Answer 35

the bundled-together axons of dorsal root ganglion cells- enter the dorsal part of the spinal cord

Question 36

Ventral root

Answer 36

consists of the axons of motor neurons sending signals from the brain to the muscles.

Question 37

Dorsal column-medial lemniscal pathway (DSML pathway)

Answer 37

pathway for signals involved in tactile perception and proprioception; travels up the spinal cord on the ipsilateral side, crosses to the contralateral side in the medulla, and then goes through the ventral posterior nucleus of the thalamus and on to the somatosensory cortex; first synapse in the medulla

Question 38

Spinothalamic pathway

Answer 38

pathway for signals involved in nociception and thermoreception; crosses over to the contralateral side within the spinal cord and then goes through the ventral posterior nucleus of the thalamus and on to the cortex; first synapse in the spinal cord

Question 39

Ventral posterior nucleus (VP nucleus)

Answer 39

a nucleus of the thalamus; part of both the DCML pathway and the spinothalamic pathway.

Question 40

Somatosensory cortex

Answer 40

a region of the cerebral cortex in the anterior parietal lobe; receives signals carrying sensory information via the ventral posterior nucleus of the thalamus

• has a contralateral organization in the somatosensory cortex and vice versa.
• Somatosensory signals from the skin and muscles flow through a structure in the thalamus (VP nucleus) before traveling to the cortex.

Question 41

Primary somatosensory cortex (S1)

Answer 41

subregion of the somatosensory cortex; the first area to receive somatosensory signals from the ventral posterior nucleus of the thalamus; divided into four side-by-side strips known as areas 3a, 3b, 1, and 2.

• Many neurons in S1 respond selectively to specific orientations of tactile stimuli
• > Orientation tuning not unlike the orientation tuning of simple cells in area V1 of the visual system
• > Direction of motion of stimuli

Question 42

Secondary somatosensory cortex (S2)

Answer 42

subregion of the somatosensory cortex; receives signals from area S1
* Many of these S2 neurons do respond to stimulation of multiple fingers, suggesting that they integrate information from large regions of the fingers and hand.

Question 43

Somatotopic map

Answer 43

mapping of the body surface onto the somatosensory cortex, whereby adjacent locations on the cortex receive somatosensory signals from adjacent locations on the body.
* Somewhat disarranged and distorted
* Disarranged in that adjacent regions of the cortex don’t necessarily receive signals from adjacent parts of the body
* Distorted in that relatively more cortical space is devoted to receiving signals from body parts where sensory receptors are densely distributed and have small receptive fields, such as the fingertips and lips, while relatively less space is devoted to body parts with fewer receptors that have larger receptive fields, such as the torso, arms, and legs.
* Analogous to retinotopic mapping by the visual system and tonotopic mapping by the auditory system
o The disappropriate amount of cortical space devoted to certain body parts is analogous to cortical magnification in the visual system.

Question 44

Tactile information from mechanoreceptors

Answer 44

Area 3b and 1 -> proprioceptive signals to 3a and 2
* Nociceptive signals carrying discriminative information about the location and intensity of painful stimuli also flow to areas 3a and 3b and then to area S2, whereas signals carrying information about the unpleasantness of pain don’t flow to either S1 or S2 but to several other regions of the brain.

Question 45

From S1, tactile and proprioceptive signals travel along two pathways

Answer 45

• Dorsal pathway carries tactile information used to support touch-based action
• Ventral pathway carries both tactile and proprioceptive information used to support somatosensory object recognition and the formation of new somatosensory memories.

Question 46

Subareas of S1-3a, 3b, 1, and 2

Answer 46

• Each containing a full somatotopic map of the body
• All receive somatosensory signals directly from the VP nucleus of the thalamus.
• Each of these areas receives only certain types of signals, and each contains neurons that are specialized for representing the different types of information in those signals.

Question 47

Area 3a

Answer 47

respond to proprioceptive information carried by signals from muscle spindles and Golgi tendon organs located in tissues below the skin, but not to tactile stimulation of the skin

• 3a and 3b also receive some signals containing discriminative nociceptive information
• is specialized for processing proprioceptive and not tactile information

Question 48

Area 3b and 1

Answer 48

respond to tactile information carried by signals from mechanoreceptors in the skin. Area 1 neurons also receive somatosensory signals from are 3b.

Question 49

Area 2

Answer 49

respond to proprioceptive information carried by signals from muscle spindles and Golgi tendon organs and to tactile information carried by signals from mechanoreceptors in the skin; signals from areas 3a, 3b, and 1.

Question 50

Area 3b

Answer 50

some neurons showed sustained responses and produced very accurate spatial event plots.

Question 51

From area S1, signals travel along two pathways- Dorsal pathway

Answer 51

o Dorsal pathway carries information used to guide actions that require tactile and proprioceptive input

• Directly analogous to the dorsal “where”/”how” pathway of the visual system, which carries visual information needed to guide actions
• To the posterior parietal cortex- including specifically to the anterior and lateral intraparietal areas
• Perception for action- and from there into the premotor cortex

Question 52

From area S1, signals travel along two pathways- Ventral pathway

Answer 52

Ventral pathway carries tactile and proprioceptive information used in perceiving and remembering object shape and identity, and thus is analogous to the ventral “what” pathway of the visual system, which carries visual information about object shape and identity.

• Begins in S1 areas 3b and 1: 2-D tactile features
• Area 2 of S1: tactile information is combined with proprioceptive information
• This combined information then goes to area S2, where representations of 3-D shape are created.
• From S2-> prefrontal cortex

Question 53

Thermoreceptive signals carry information about temperature from skin to…

Answer 53

from the skin into the spinal cord and then along the spinothalamic pathway to the VP nucleus of the thalamus. From the thalamus, these signals travel to S1 and to other regions of the cortex.

Question 54

Contralateral insular cortex

Answer 54

nonpainful temperature sensations are represented in a somatotopic map and used for, maintaining homeostasis

Question 55

Ipsilateral insular cortex

Answer 55

relative intensities of temperature sensations are evaluated.

Question 56

Discriminative dimension of pain perception

Answer 56

perceptions that enable the person to locate the pain and to classify it in terms of its intensity and type

Question 57

Affective dimension of pain perception

Answer 57

unpleasant emotional responses to pain

Question 58

Pathways for discriminative dimension and affective dimensions

Answer 58

Both dimensions follow the spinothalamic pathway from the spinal cord to the VP nucleus of the thalamus

• Signals from thalamus related to the discriminative dimension flow to areas 3a and 3b within S1 and then to area S2
• Signals related to the affective dimension flow to the anterior cingulate cortex (ACC), to the amygdala and other emotion- mediating structures, and to the anterior insular cortex.
• Relate to feelings of empathy
• Discriminative dimension of pain perception
• > Runs through the somatosensory cortex and the posterior insular cortex
• Pathway for the affective dimension runs through the ACC and the anterior insular cortex
• > Unpleasantness and motivation to “make it stop”- is present whether the person is experiencing pain directly or empathically.

Question 59

Analgesia

Answer 59

top-down feedback in reducing sensitivity to pain by modulating the intensity of pain signals

Question 60

Endogenous opioids

Answer 60

compounds that belong to a class of substances called opiates; released by the body in response to painful or stressful experiences 
* Released by the pituitary gland, by the thalamus, and by descending nerve fibers within the spinal cord, in response to painful or stressful experiences.

Question 61

Endorphins

Answer 61

endogenous opioids that have an inhibitory effect on pain-related neural signals in many areas of the central nervous system, reducing the perceived intensity of pain

• Many regions of the CNS contain opiate receptors
• Endorphins are readily measurable in the circulating blood following strenuous exercise, which has led to the hypothesis that endorphins produce the sense of internal harmony and euphoria- the “runner’s high”- often associated with high-intensity exercise

Question 62

Stress-induced analgesia

Answer 62

being able to ignore pain and escape, but the pain should return once the stressful situation is resolved, so the animal will favor the injured body part to permit healing and prevent further injury

• Both humans and other animals
• Periaqueductal gray (PAG) region
• Tolerance
• Deployment of attention away from a painful stimulus reduces both the perceived intensity of pain and the level of activity in parts of the brain associated with the discriminative dimension of pain
• The placebo effect- based on the expectation that a treatment, even one with no objective therapeutic value, will be effective- can lessen both the experience of pain and the associated pain-related brain activity, whereas negative mood and anxiety can increase the intensity of perceived pain.

Question 63

Cortical plasticity

Answer 63

ability of the adult cortex to change the way it’s organized.

Question 64

Phantom limb

Answer 64

perception of a missing limb, as if it were still there, even though the part of the somatosensory cortex that previously received signals from the limb no longer does so.

• People who had an arm amputated sometimes report that stimulation of their face results in a feeling that both their face and a specific location on the phantom arm are being stimulated.
• > At the somatotopic map, the region of area S1 devoted to the face is very near the extensive region devoted to the arm.
• > Signals from the face activate not only the region of S1 devoted to the face but also the region formerly devoted to the now-missing arm.

Question 65

Haptic perception

Answer 65

actively using touch to perceive and identify objects by their 3-D shape and other material properties; involves the integration of information from tactile perception, proprioception, and thermoreception.

• depends on information about its weight and center of mass, along with simultaneous information about shape (both of which can be acquired most readily if the object can be picked up and enclosed in the hand) and probably on information about surface features such as texture and temperature.
• Depending on the size and shape of an object, its location, its movability, and other such factors, it may not be possible to touch its entire surface all at once.

Question 66

Exploratory procedures (EPs)

Answer 66

hand and finger movements typically used by people to identify objects haptically.

Question 67

People using different types of acquire different kinds of information about the object

Answer 67

• Lateral motion: texture; rubbing the skin along the object’s surface
• EP pressure: get information about hardness
• Contour following: running the fingers over an edge; for information about the exact shape of some part of the object
• Enclosure: grasping the whole object in the hand, for information about the shape of the object as a whole

Question 68

Tactile agnosia

Answer 68

an inability to recognize objects by touch, which can result from damage to the parietal cortex, specifically to area S2.

• S2 neurons respond to signals carrying both tactile and proprioceptive information
• > Local somatosensory information is integrated into an understanding of an object’s entire shape and material properties.

Question 69

Vestibular system

Answer 69

sense organs used to produce neural signals carrying information about balance and acceleration; includes the semicircular canals and the otolith organs.

Question 70

Semicircular canals

Answer 70

part of the vestibular system; three mutually perpendicular hollow curved tubes in the skull filled with endolymph; responsible for signaling head rotation.
* At the base of each canal is a small chamber called an ampulla, also filled with endolymph and containing a specialized structure called a crista, where the hair cells reside.

Question 71

Otolith organs

Answer 71

part of the vestibular system; consist of the utricle and the saccule; responsible for signaling when the head is undergoing linear acceleration or being held in a tilted position.

• Each of which contains a specialized structure with hair cells called a macula
• Within each macula, the hair cells are oriented in different directions and are embedded in a viscous fluid containing tiny crystals called otoconia.

Question 72

Perception of whole-body position, balance and movement

Answer 72

• Nerve fibers carrying neural signals from the hair cells in the semicircular canals and the otolith organs bundle together to form the vestibular nerve, which carries these signals to the vestibular complex in the brain stem.

• Contains multiple vestibular nuclei, which receive signals not only from the vestibular system, but also from the visual system, the system that controls eye movements, and the motor systems responsible for neck movements.
• Parietal insular vestibular cortex (PIVC), deep in the lateral sulcus, which also receives signals from virtually every other cortical region that receives signals from the vestibular nuclei.
• > Provide a representation of the position and orientation of the head, which can be used as a basis for maintaining balance during complex movements.
• > Produce a unified perception of whole-body position, balance, and movement.

Question 73

Vestibulo-ocular reflex

Answer 73

the hair cells in the semicircular canals produce signals in response to this head movement, which in turn cause signals to flow from the vestibular complex to the oculomotor system, which moves the eyes in a direction opposite to the direction of the head movement in order to keep the eyes pointed at the target while the head is moving

• Unconscious compensating movement of the eyes during head movements in order to maintain a stable gaze.
• Occur almost instantaneously

Question 74

Minimally invasive surgery (MIS)

Answer 74

laparoscopic surgery- in which a tiny incision is made in the skin, and small instruments mounted on long, thin shafts are inserted into the incision and guided to the appropriate location

Question 75

Arthroscopic surgery

Answer 75

repair problems in knee, shoulder, and other joints of injured athletes.

• The external incision is much smaller than in traditional surgery
• Less trauma to the patient
• More rapid recovery

Question 76

Robot-assisted minimally invasive surgery (RMIS)

Answer 76

remotely controlled sensors and manipulators are used to visualize and perform surgical procedures

• Improved dexterity
• The ability to reach areas inside the body that are inaccessible to traditional laparoscopic instruments, and reduction in hand tremor
• Complete absence of haptic feedback
• RMIS system are being developed that provide haptic feedback via specialized sensors mounted on the surgical instruments.