Chapter 13: The Body Senses Flashcards
Extend the traditional five senses by other senses
Skin deformation (tactile perception)
Muscle stretch and joint angle (proprioception)
Pain (nociception)
Temperature (thermoreception)
Object shape (haptics)
Balance and body acceleration (vestibular senses)
Tactile Perception
Perception that results from mechanical deformation- indentation, vibration, or stretching- of skin
Sense of Touch
Is difficult to define because it give information about so many different aspects of tactile stimuli
Skin
Protects tissues against issues against injuries and helps regulation of body temperature
2 main types of skin
Hairy skin and glabrous (hairless)
2 main layers of skin
Epidermis and the dermis
Mechanoreceptor
Sensory receptors that transducer mechanical deformations of the skin into neural signals that are sent to the brain
Specialized endings of main mechanoreceptor types of mechanoreceptor
- Merkel cells (SAI) and Meissner corpuscles (FAI)
- Endings of SAII mechanoreceptors (Ruffini) and the FAII endings (Pacinian corpuscles)
- Hairy skin mechanoreceptors
4 main types of mechanoreceptors
Slow-adapting type I (SAI)
Fast-adapting type I (FAI)
Slow-adapting type II (SAII)
Fast-adapting type II (FAII)
Slow Adapting SAI: Specialized ending
Merkel cell
Slow Adapting SAI: Position in skin layers
Upper dermis
Slow Adapting SAI: density of distribution
Relatively dense, especially in fingertips
*small receptive fields
Slow Adapting SAI: spatial resolution
High
Slow Adapting SAI: Sensitivity to temporal variation
Low
Slow Adapting SAI: Skin deformation that elicits strongest response
Indentation by edges, curves, and textured
Slow Adapting SAI: Functions supported
Perceiving pattern, texture, and shape
Slow Adapting SAI: Timing of response
Line graph shows one long response over time
Slow Adapting SAII: Specialized ending
Unknown
Slow Adapting SAII: Positions in skin layers
Dermis
Slow Adapting SAII: Density of distribution
Relatively sparse
* relatively large receptive field
Slow Adapting SAII: Spatial resolution
Low
Slow Adapting SAII: sensitivity to temporal variation
Low
Slow Adapting SAII: skin deformation that elicits strongest response
Stretch
Slow Adapting SAII: Functions supported
Perceiving skin stretch and hand conformation
Slow Adapting SAII: Timing of response
Line graph shows one long response over time
Fast Adapting FAI: Specialized ending
Meissner corpuscle
Fast Adapting FAI: Position in skin layers
Upper dermis
Fast Adapting FAI: Density distribution
Relatively dense, especially in fingertips
*small receptive field
Fast Adapting FAI: Spatial resolution
High
Fast Adapting FAI: Sensitivity to temporal variation
Medium
Fast Adapting FAI: Skin deformation that elicits the strongest response
Motion and low-frequency vibration
Fast Adapting FAI: Functions supported
Perceiving slip
Maintaining group control
Fast Adapting FAI: Timing of response
Line graph shows two short spikes at beginning and end of stimulus
Fast Adapting FAII: Specialized ending
Pacinian corpuscle
Fast Adapting FAII: Position in skin layers
Lower dermis
Fast Adapting FAII: Density of distribution
Relatively sparse
*large receptive field
Fast Adapting FAII: Spatial resolution
Low
Fast Adapting FAII: Sensitivity to temporal variation
High
Fast Adapting FAII: Skin deformation that elicits strongest response
High- frequency vibration
Fast Adapting FAII: Functions supported
Perceiving fine textures through transmitted vibration
Fast Adapting FAII: Timing of response
Fast acting line graph shows two short responses at beginning and end stimulus
Two- Point Threshold
Minimum distance at which person’s judgements are 75% correct when touched with 2 probes
Confusion Matrix
Shows how often people confused each stimulus letter with every other letter
FAI Fibers and Grip Control
Only respond to changes in stimulation
*FAII mechanoreceptors respond to tiny vibrations in the tool and send signals that you use to perceive maintain the stability of grasp
Perceiving pleasant touch
New research suggests that there are specific receptors for pleasant touch
- C-tactile mechanoreceptors (CT mechanoreceptors) are a type of free nerve endings only present in hairy skin
- the respond to slow, gentle touch, sending signals to the insular cortex, and area of the brain involved in pleasure perception
These receptors initially may have developed to support grooming behavior
* Unmyelinated (carry signals relatively slowly to brain)
What makes pleasant touch pleasant?
Neutral temperatures and intermediate speeds
Brain pathway for tactile information
There is inconclusive evidence that the mechanism by which mechanoreceptors transducer mechanical force is analogous to the mechanism by which hair cells in the cochlea transducer movement of their stereocilia into neural signals sent through auditory nerve fibers
Proprioception
Perception of position and movement of body parts, based on info in neural signals from specialized sensors within those body parts
Three sensory organs provide information related to how the body and its parts are positioned
Proprioception information
- Muscle spindles
- Golgi tendon organs
- Joint receptors
Muscle spindles
Sensory organs that provide info about muscle length, as well as info about isometric forces on muscles, for proprioception
*provide most info for proprioception
Golgi tendon organs
Sensory organs that provide info about muscle, for proprioception
*signals in response to changes in muscle force (length and joint angle change)
Joint receptors
Sensory organs that provide info about joint angle, probably to signal when and joint has reached the limit of its normal motion
Signals from Muscle Spindles and Golgi Tendon Organs
Produce signals in response to changes in muscle length and force
Nociception vs Pain
Nociception- perception of nociceptive pain
Pain- unpleasant sensory and emotional experience cause by potential or actual tissue damage
- can arise from wide range of different causes and can evoke an equally wide range of perceptual experiences
Three general categories of pain
Nociceptive
Inflammatory
Neuropathic
Nociceptive Pain
Pain that arises from potential or actual tissue damage due to physical trauma
Inflammatory Pain
Pain that arises after tissue damage has occurred, when chemical substances released by damage tissue either activate pain receptors or reduce their threshold
Neuropathic Pain
Pain caused by damage to PNS and CNS
Two dimensions of pain
Affective: anterior cingulate cortex, the amygdala, and anterior insular cortex
Discriminative: S2 and the posterior insular cortex
Nociceptors
Sensory receptors that transducer the physical stimuli and transmit neural signals associated with nociceptive and inflammatory pain
- included among free nerve endings in epidermis and dermis
Nociceptors transmit pain signals to the spinal cord via two difference types of fibers
A- delta fibers
C fibers
A-delta fibers
Myelinated axons of nociceptors that transmit pain signals relatively rapidly, to produce rapid response to potentially damaging mechanical stimuli and to excessive heat
- immediate, sharp pain
C fibers
Unmyelinated axons of nociceptors that transmit pain signals relatively slowly
- prolonged, dull, throbbing pain
Sensitization
Mechanism that decreases response threshold of nociceptors so that even very low-level stimulation of an injury site can cause pain
Thermoreceptors
Sensory receptors for the detection of temperatures in range of 17-43 degrees Celsius
- included among free nerve endings in epidermis and dermis
Warm fibers:
- 29-43 - Heat receptors tend to detect temperatures over 25C (77F)
Cold fibers:
- 17-40
- they respond to cool temperatures between 10C (50F) and 20C (68F)
Thermoreception
The ability to sense the temperature of objects and surfaces in contact with the skin
Between Body and Brain
- Part of spinal nerve where nerve fibers for body senses enter
- Axons of mechanoreceptors and other types of sensory receptors within a small area of the skin converge into a peripheral nerve bundle
- Axons of sensory neurons involved in proprioception within a muscle or joint converge into a nerve bundle
- Then all the nerve bundles from each region of skin and each region of muscle tissue enter the spinal cord via one of the spinal nerves
- Cell bodies of all these bipolar neurons are clustered together into a single dorsal root ganglion
Dorsal Root Ganglions
- Each is adjacent to single vertebra
- Each vertebra has one ganglion on left and one on right side
- Dorsal root enters the dorsal part of the spinal cord
Within the spinal cord and then from the spinal cord into the brain, sensory signals follow two different pathways:
Dorsal column- medial lemniscal pathway
Spinothalamic pathway
Dorsal column-medial lemniscal pathway
Pathway for signals involved in tactile perception and proprioception
- travels up spinal cord on the ipsilateral side, crosses to contralateral side in the medulla, and then goes through ventral posterior nucleus of thalamus and on somatosensory cortex
Spinothalamic pathway
Pathway for signals involved in nociception and thermoreception
- crosses over the contralateral side within spinal cord and then goes through ventral posterior nucleus of thalamus and on to the cortex
Ventral posterior nucleus
Nucleus of thalamus
- part of both DCML pathway and spinothalamic pathway
Somatosensory Cortex
Region of cerebral cortex in anterior parietal lobe
- receives signals carrying sensory info via ventral posterior nucleus of thalamus
Primary Somatosensory Cortex (S1)
- first area to receive somatosensory signals from ventral posterior nucleus of thalamus
- divided into areas 3a, 3b, 1, and 2
*responds selectively to specific orientations of tactile stimuli
Secondary Somatosensory Cortex (S2)
Receives signals from area S1
Somatotopic Map
Mapping of body surface onto somatosensory cortex, whereby adjacent locations on the cortex receive somatosensory signals from adjacent locations on the body
The ventral pathway
A “what” pathway, carrying information used in perceiving object shape and identity
- S1: 3b and 1+ 3a+ 2 —> S2 —> prefrontal cortex and hippocampus
The dorsal pathway
A “where/how” pathway, carrying information used in planning action
S1—> posterior parietal cortex (anterior and lateral intraparietal areas)
Cortical Representation of Temperature
- Thermoreceptive signals carry information about the temperature 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
- Contralateral insular cortex is a site where non painful temperature sensations are represeanted in a somatotopic map and used for maintains constant body temperature
- Ipsilateral insular cortex is a site where the relative intensities of temperature sensations are evaluated
Affective dimensions of Pain Perception
Actually experiencing pain, as opposed to viewing someone else experiencing pain, results in the activation of different brain areas
How top-down processes change pain perception
Recent investigations of the cognitive and emotional dimensions of the pain experience reveal a number of top-down factors that affect the intensity and duration of pain
Endogenous Opioids
Compounds that belong to class of substances called opiates
- released by body in response to painful/ stressful stimuli
Endorphins
Endogenous opioids that have an inhibitory effect on pain-related neural signals in many areas of CNS, reducing perceived intensity of pain
Placebo Effect
Pain reduction due to fake treatment, with no actual therapeutic value
- occurs because a person believe treatment is real and expects to benefit from it
Cortical Plasticity
- If brain ceases to get input, the area that is not being used can be taken over by an adjacent area
- Research finding suggest that parts of the brain that are involved in making fine perceptual discriminations rewire themselves as needed
Phantom Limb
Perception of missing limb, as if it were still there, even though parts of somatosensory cortex that previously received signals from the limb no longer does so
Learning affects cortical organization
Cortical space devoted to certain learning gets larger
Haptic Perception
Actively using touch to perceive and identify objects by their 3D shape and other material properties
- involved integration of info from tactile perception, proprioception, and thermoreception
Haptic Procedures
Involves active manual exploration of objects in the world
- Information about motion
- Information about shape
- Tactile agnosia
Haptic Procedures: information about motion
Involves rubbing the skin along the object’s surface
- the exploratory procedure (EP) pressure is used to get information about hardness
Haptic Procedures: Information about shape
Is typically obtained via two different EPS, running the fingers over an edge and grasping the whole object in the hand
Haptic Procedures: Tactile agnosia
Is inability to recognize objects by touch, which can result from damage to the parietal cortex, specifically to area S2
Exploratory Procedures
- depending on the size and shape of an object, its location, it’s no ability, and other such factors, it may not be possible to touch its entire surface all at once
- in these cases and in cases in which objects are entirely touchable, people typically move their hands and fingers over the object
*hand and finger movement typically used by people to identify objects haptically
Rubber Hand Illusion
Phenomenon in which people perceive stimulation if own hand as originating from a fake hand and even perceive the fake hand as their own
The Vestibular System
Sense organs used to produce neural signal carrying info about balance and acceleration
- includes semicircular canals and otoliths organs
The vestibular system has two main divisions
Semicircular canals
Otoliths organs
Semicircular canals
- part of vestibular system
- three mutually perpendicular hollow
- responsible for signaling head rotation
Otoliths organs
Responsible for signaling when head is undergoing linear acceleration or being held in tilted positions
- utricle- horizontal movement
- saccule- vertical movements
Vestibule-ocular reflex
An unconscious compensating movement of the eyes during head movements in order to maintain a stable gaze
Vertigo
A false sensation in which an individual or the individual’s surroundings seem to move or spin
- most commonly cause by loose otoconia in a semicircular canal
Haptic feedback is critical for surgical procedures where the surgeon must apply precisely calibrated forces
- in traditional surgery, the surgeon manipulates the surgical instruments directly, and naturally receives haptic feedback from the instruments
- in robot- assisted minimally invasive (RMIS), the surgeon never touches the surgical instruments, so there is a complete absence of haptic feedback
RMIS systems are being developed that provide haptic feedback via specialized sensors mounted on surgical instruments
Haptic feedback is critical for surgical procedure where the surgeon must apply precisely calibrated forces
