Chapter 2: Heller and Schiff Flashcards
Touch
Defined as the variety of sensations evoked by stimulation of the skin by mechanical, thermal, chemical, or electrical events
Touch, for the most part, is a
Proximal sense (meaning we feel things that are close to us or actually contact us”
For a stimulus to be perceived it must actually come in contact with the _____
Skin
The skin itself is a multilayered sheet some ____ and __kg in weight
1.8m squared in area
4kg in weight (8.8lbs) on average adult
Skin is the bodies largest _____, protecting the rest of the body from _______ (due to its waterproofing), _______, and ________
Organ
Dehydration , physical injury, and ultraviolet radiation
The skin is also involved in the _______ mechanisms that regulate body temperature and blood pressure
homeostatic
Skin might be ____ or _____, ____ or ____, ____ or ____ (glabrous), ______ or ______
flat or furrowed
loose or tight
hairy or smooth (smooth = glabrous)
thick or thin
On the fingertips, ____ and ____ form intricate patterns of whorls and loops
Ridges and valley
these from in the 3rd or 4th month of fetal life
Outmost layer of the skin is called the:
Epidermis (which an be subdivided in several other layers)
The surface of the skin, the ______ is made up of dead or keratinized cell bodies from the deeper subdivisions of the epidermis that might have migrated outward as the skin renews itself from the inside out
corneum
Glabrous skin facts
- No hairs
- Overall density of end organs is greater
- Surface of glabrous skin is ridged as a result of dermal intrusions, called ‘plugs’ into the epidermis
Immediately below this protective layer of cellular ghosts is the _______, and below that is the _____
- epidermis proper,
- dermis
Dermis
A layer of nutritive and connective tissues (papalrri
Cutaneous end organs
Structures that are suspected of being responsible for transducing mechanical, thermal, chemical, or electrical energy into neural signals
-are found within the dermal layer or at the epidermal-dermal interface
Sweat glands (numbering over 2 million)
are found in the dermal layer or at the epidermal-dermal interface
In hairy skin
Hair follicles and the structures associated with them are embedded in the dermis (associated structures = fine muscle filaments(erector pilorus)
Fine muscle filaments(erector pilorus)
Reveal their presence in “hair-raising” experiences by the presence of goosebumps
Below the dermis
We find layers of connective tissue (superficial fascia) and subcutaneous fat that lie between the skin and the supportive formations of muscle and bones
A common experimental procedure involve:
Pushing on the skin - mechanically deforming it, either with infrequent pressure pulses or repetitive vibration
Viscoelastic
When the skin is touched, the energy the imposed on it at that point will be transmitted through the medium (it is “viscous”)
-Some (some is super important as it is not all) of the energy will be absorbed and stored, and is used to return the skin to its original state (skin is elastic)
As energy moves in a wave into the skin, it produces shearing forces that dissipate with distance from the source according to the ______
inverse square law
Mechanical vibration can also generate travelling _________ across the surface of the skin that may be transmitted over long distances
waves of energy
Surface waves may be reduced by placing a _______ around the moving contractor (as the waves will go very far with the vibrations)
static ring (surround)
^^^^
However, deeper waves may still tend to spread laterally
Thus the use of a surround may restrict the number of the most superficial receptors stimulated, but might not have an effect on the involvement of deeper ones
_________ will tend to spread laterally through whatever paths exist
Chemical or electrical
The electrical stimuli may find paths of least resistance through the _____ and ______ exudate in the pores of the sweat gland
Salty and electrically conductive
Any attempt to adjust the ______ above or below its normal level results in activation of local and central homeostatic mechanisms that strive to offset heat or cold
skins temperature
-therefore, changing the skin temp can influence blood pressure, peripheral nervous system
Cutaneous end organs suspected for transducing tactile stimuli in neural signals
Merkel’s disks (dermis), Ruffini cylinders, and Meissne’s Corpuscles
Merkel’s disks, Ruffini cylinders, and Meissne’s Corpuscles are found where?
Upper regions of the dermis
Pacinian corpuscles
Found in the subcutaneous connective and fatty tissues
-found primarily in glabrous skin, and do exist at much lower density in hairy skin
Single unit recording (best method available)
Used to determine which end organ produces a specific neural response to tactile stimulus
Method: A fine electrode is used to pick up the response of a single nerve fiber
Limitations: Only works to find out how a unit responds to tactile stimulation, not which end organ produces that response
A unit is classified as being ‘slowly adapting’ or having ‘a punctuate receptive field’ (small)
rather than being the response of a free nerve ending, or a ruffini cylinder
Microneurography
Relatively new method, provides the most direct measure possible through simultaneously recording a single-unit activity and human sensation
- conducted on awake humans through percutaneous (through the skin) microelectrodes instead of by dissection
- Found through this method they could electrically stimulate a single-unit nerve fiber and evoke tactile sensations that were localized to a particular region of skin
Cutaneous receptors are likely to be tightly packed in regions such as the _____,________,______
fingertips
lips
genitals
On the fingers, palms, and soles of the feet, the skin is smooth and is referred to as ________
The skin almost everywhere else on the body has hair andis simply and appropriately referred to as ____
glabrous
Hairy skin
Free nerve endings are found where?
Found throughout the body, even in body sites that devoid of any other type of colex cutaneous formation
The anatomy of the types of cutaneous end organs found in mammalian skin can be divided into two broad categories
1) Free (bare) nerve endings
2) Nerve endings either associated with or encapsulated within accessory structures
Free nerve endings
Fine sensory fibrils, which means the ends of neurons
Common encapsulated types incude:
Pacinain Merkel Meissner Ruffini Kruase and Basket endings (found around hair follicles)
The common encapsulated sensory endings range from
bare fibers, apposed to sensory cells (such as those found in merkel cell complex), to the intricately wrapped neruite found in the onion-like pacinian corpuscle
As of yet, physiological experiments _________ isolate single cutaneous end organs within the skin
Cannot !!
Defining the receptive field of “that unit”
The skin site, where , for example, mechanical stimulation evokes neural activity (opposed to say thermal stimulation) defines the field
The receptive field may be ______ ( perhaps a whole finger) or _______ (a mm or so)
Large
Punctate
The responses of the microneurography test are based on
1) Rate of adaptation
2) Size of receptive field
Units in glabrous skin sensitive to noninjurous mechanical stimuli have been classified into __ groups
Four (Large / small / fast/ slow)
The larger the fiber (A-fibers being the biggest, C-fibers being the smallest) that faster the rate of conduction
CRAZY
Two kinds of pain felt with injury
The sharp, fast component vs the dull, slow one
Homeostatis
Certain setpoints your body has (37 degrees celsius for instance for body temp)
Mechanical stimulation
Vibration and pressure (pressure pulses)
vibration vs pulse
Pulse = single pressure Vibration = has waves and a frequency
Inverse square law
Increase the distance by 2, reduce intensity by 4
Increase by 5, decrease by 25 (just square the number)
To get stimulus invariance you need
Variance
Subcutaneous =
below the skin
Classification by structure
What end organ produces a specific neural response
Due to more than one being present, for single-unit recording, they could not specifically identify
Merkel’s disks (dermis), Ruffini cylinders, and Meissne’s Corpuscles individual effects
The end organs, the presumed receptors, are scattered throughout the depth and breadth of skin, but
The density of innervation considers varies considerably, depending on the location of the body that is examined.
Cutaneous become more and more rare as we get to the _____,_______ and _________
upper arm, shoulder, and trunk
Sensitivity to tactile stimuli is related to
Density of innervation
Microneurography is typically not used in
Animals
Whether you use dissection procedure in animals or microneurography in humans,
the skin is stroked, prodded, heated, or cooled with stimuli that would normally evoke touch sensations
Body’s telephone line
The nervous system
A single neural unit does not have the exclusive rights to a given point on the skin
That particular piece of skin may be conducting units from parts of the body you are not recording
Noxious stimuli
Would it increase or decrease the firing rate?
There are as many as ___ different unit types found in the skin, including motor and sensory fibers
20
Pacinian Corpuscles
Sensitive to high frequency stimuli
Responds to vibratory stimuli
(when cooled it shows a reduction in overall sensitivity and frequency to which it is most sensitive)
Durative pressue
One that lasts a long time
Durative pressure stimulus produces two kinds of responses
1) Generator potentials
2) Propagated action potentials
Generator potentials
Below threshold for action potential (last duration of a stimulus)
The elementary response of the neural core is ______ but the layers filter the mechanical stimulus in a way to pass only the transient components
Slowly adapting
The size of the generator potential depends partly on the area of the _____ that is stimulated
dendrite
The location of a mechanical stimulus would presumably, be encoded by the location of the responding receptors
Receptors in your arm respond, you must have been touched in your arm
The intensity of the stimulus seems to be encoded in both the number of receptors responding, and in their rate of and duration of response
The greater number of receptors responding, the stimulus is more intense
If the receptors respond with a high rate and duration, then we know we have a more intense stimulus
Pacinian Corpuscles response to mechanical stimuli
Much more vigorous and predictable than its response to temperature changes, therefore it is an unlikely candidate for a thermal receptor
Physiological recordings indicate that there are thermoreceptors that respond specifically to cold or specifically to warmth
Many fewer warm spots than cold.
Virtually nothing is known about the warm and cold receptors
WOW
Cutaneous cold receptors produce their highest discharge rate at about ___, while warm receptors respond most vigorously to a ___ stimulus
28 degrees celsius
43 degrees celsius
Nociceptors
Respond specifically to to what would be classified as “painful” stimuli (Due to
No unique end organ seems to be implicated as the receptor for
Pain (Free nerve endings seem to be most likely candidate (see next slide for reasoning)
Why are pain free nerve endings the most likely candidate for pain?
Respond to almost all cutaneous stimuli, have extraordinarily high thresholds, have tiny receptive fields, have a persistent discharge when adequately stimulated, and seem to be served with the smallest of nerve endings
No specific structure has been tied to chemesthesis, which is _______
Chemical stimuli
All the information from the periphery (the skin) is carried to the ____ on individual nerve fibers (some longer than a meter)
Spinal cord
There are ___ vertebrae
33
As the nerve fibers approach the spine, nerve fibers join at each vertebral level to form a single nerve trunk before their enter the spinal cord
The cell bodies of these fibers clump together in the dorsal root ganglion of the spine
There are ____ sides to the spinal cord
2 (dorsal = sensory, ventral = motor)
Ganglia
Collection of cells
The ganglia from every level in the body form chains on either side of the spinal cord , one to each of the vertebrae
33 trunks on the left, 33 trunks on the right
Every spinal root is attached to a particular piece of skin
No connection
The interesting aspect of herpes, or shingles is that the area of skin affected by the infection will define the band of skin served by that spinal root
Implying the infection will hurt
Within the spinal cord, proximal ends of the first-order cutaneous sensory fibers divide into two major groups, based not only on body site, but rather upon function
1) Smaller fibers (spinothalamic system)
2) Larger fibers (Lemniscal system)
Smaller fibers
Apparently responsible for pain and temperature , form one bundle
Larger fibers
Carry mechanoreceptor information
Bundles of fibers divide into tracts and
send branches up and down the spinal cord
Afferent fibers
To the brain tracts (sensory)
Efferent
From the brain tracts (Motor), controlling muscles and glands
The spinal cord is the first place that connections can be made between and among nerves (Through synapses)
Here, the first-order sensory fibers make contact with one or more second-order neurons. They can interact with other neurons (including motor nerve fibers to either enhance or inhibit neural activity
Simple reflex arc, best known in the knee-jerk reflex, occurs completely in the spinal cord involving three neurons
1) Sensory neuron
2) Second-order interneuron
3) Motor fiber
Homunculus Figure 2.5
Picture of the body presented by the somatosensory cortex
Face and hands have a lot of ______ on the homunculus
Tissue
Saggital
If you were to cut the brain from front to back, to get a half cut perspective
What happened to the information that was encoded within the receptive field of a single unit? (unit being in the skin)
First, it had been combined with that from other first-order units (outside the spinal cord) and has been distributed among many other second-order units in the spinal cord
The two most important areas on the sensory cortex where tactile information is represented
Somatosensory I (SI) (thought to be primary) Somatosensory II (SII) (thought to be secondary)
______ helps with tuning the coordination of sensory motor abilities
Cerebellum
One way to get a homunculus
Map of the body can be charted by placing an electrode on different points on the surface of the cortex, than noting the sites where the stimulation of the skin evokes activity (when the points are connected , a systematic topographic projection is seen (figure 2.5)
Highly innervated areas of the body
Such as the lips, genitals, and fingertips
Cortical magnification
The relationship between the size of the cortical area and the area of the periphery so represented
The magnification factor has been found to vary from body site to body site, but is ____ for body sites such as the fingertips that are highly innervated
greatest
(i.e: in the monkey the glabrous skin of the hand occupies 100x more cortical tissue per unit body-surface area than the trunk or upper arm)
The receptive field in the cortex are ______ than those recorded peripherally, partly owing to the ______ of information on each of the cortical units
Larger
convergence
The size of the field is _______ to the sensitivity of the site
As a result, the number of cortical cells processing information from sites such as the fingertip is considerably greater than for sites such as the back
inversely proportional
Therefore, less spatial somatization in the back
Another way in which the information contained in cortical receptive fields differs from that represented in peripheral receptive fields is that
some cortical cells have fields that are sensitive to specific features of the stimulus
(i.e: a cell in the cortex might only be sensitive to stroking the surface of the forearm in a single direction or to stimuli of a certain frequency)
Feature detection
examples above in slide 110
Another organizing principle found to exist within the cortex is _________________
segregation based on receptor type (SA I, SA II)
The size of the cortical receptive fields and the number of cortical cells responding to stimuli of one type or another may not be fixed but appear to be ____
plastic
It is believed that the FA1 response is generated by
Meissner Corpuscles
It is believed that the FA2 response is generated by
Pacinian corpuscles
It is believed that the SA1 response is generated by
Merkel disks
It is believed that the SA2 response is generated by
Ruffini cylinders
Intensity or “loudness”
Perceived intensity
Absolute threshold
Minimal energy that can be felt
Decibels
Works on the log scale, too loud of a sound will cause injury to ears
A person can feel a vibratory stimulus that has an amplitude as low as ______
0.2 microns (250hz on the hand)
The threshold for a vibratory stimulus depends on its ______ and _______
frequency
temperature
If the stimulus is a train of pulses, other conditions being equal, threshold (and suprathreshold loudness) is much less dependent on the rate at which the pulses are presented
True
Within the same frequency channel, masking can occur ________, but changing the frequency will not work
across hands
Threshold varies by less than __dB per octave (doubling) the frequency, whereas the change in threshold can be as much as 12 dB for sinusoids
3
______ can also effect threshold by inhibiting or exciting individual receptors that are sensitive to both touch and thermal stimuli such as the pacinian
Temperature
Other factors that affect threshold include
The area of contactor, the duration of the stimulus, the static force of the stimulus, the presence of a surround, the age of observer, and hormone levels
loudness =
suprathreshold
Suprathreshold stimuli show a dependence on
Contractor area
The larger the stimulus
The greater the apparent intensity
The growth of loudness is unaffected by changes in other factors such as
(suprathreshold only)
Frequency
Temporal factors can have an effect on the perceived intensity of tactile stimuli, but in ___ different ways depending on the duration of the stimulus
2
Temporal summation is said to occur when either threshold decrease or loudness of the stimuli increase with duration
Can also be put as “Temporal summation is said to occur when either sensitivity increase or loudness of the stimuli increase with duration
Adaptation
The increase in threshold or the reduction in the apparent intensity of a stimulus with prolonged stimulation
There is a considerable reduction in loudness with stimuli that last _____________
hundreds of seconds
It has also been shown that adaption within one of these vibrotactile channels will not
necessarily raise the thresholds in another channel
At the physiological level, if the skin is driven with a step stimulus lasting a couple hundred milliseconds, some receptors may responds for hundreds of ms
Some receptor types will respond only to the onset then cease firing altogether (Fast adapting receptor types)
PG 48, last paragraph
Separating stimuli in both time and space will reduce the amount of ________
Masking (PG 50)
Tactile spatial information processing is typically evaluated with
Von Frey hairs, calipers, or similar devices
Two-point limen
Provides an indication of the spatial resolution of the skin
The ______ is both a test of spatial acuity and spatial memory
Error of Localization test
Practice has been shown to ______ the size of the two-point limen considerably
reduce
PG 52, PP 1
Temporal =
time
