Topic 11: The Cutaneous Senses Flashcards
Why are conditions that result in losing the ability to feel things dangerous?
Absence of the warning signals provided by touch and pain.
What makes it difficult to interact with the environment with the loss of an ability to feel things?
Loss of feedback
Sense of our body’s position and the movement of our
limbs
Proprioception
Describe the case of Ian Waterman
Suffered complications from a viral infection that damaged sensory neurons from his neck down
As a result, he was completely unable to sense the position of his limbs and also lost the sense of touch
Couldn’t feel his body; used inappropriate amounts of force
Ability to perceive sensations based on the stimulation of receptors in the skin
Cutaneous senses
Enables us to perceive the properties of surfaces including details, texture, and shape
Sense of touch
Heaviest organ in humans, and one of the largest by
total surface area
Skin
Describe the role of skin in maintaining regular bodily functions
Gives us information about the external environment, prevents body fluids from escaping, and protects us by keeping bacteria, chemical agents, and dirt from getting inside
What are the two different kinds of human skin?
Hairy skin: Hair follicles
Glabrous skin: No hair follicles
Where is glabrous skin found?
Areas most sensitive to touch and the parts we use to explore our environment (Palms, feet, lips, tongue)
Outer layer of dead skin cells
Epidermis
Receptors that respond to mechanical stimulation of the skin
Mechanoreceptors
Where are the mechanoreceptors located?
In the epidermis and dermis
Which two mechanoreceptors are located close to the surface of the skin?
Merkel receptors
Meissner corpuscles
Merkel receptors and Meissner corpuscles have — receptive fields
Small
Describe the firing and adaptation of Merkel receptors
Fires continuously, as long as the stimulus remains present
It adapts slowly to stimulation, so it is a slowly-adapting fiber (SA1)
Merkel rceptors are associated with the perception of…
Fine details, texture, and shape
Describe the firing and adaptation of Meissner corpuscles
Fires only when the stimulus is first applied, and again when it is removed
Adapts rapidly to stimulation, so it is a rapidly-adapting fiber (RA1)
Meissner corpuscles are associated with…
Perceiving motion across the skin
What are the two mechanoreceptors located deeper in the skin?
Ruffini cylinders
Pacinian corpuscles
Ruffini cylinders and Pacinian corpuscles have — receptive fields then mechanoreceptors located closer to the surface of the skin
Larger
Describe the firing and adaptation of Ruffini cylinders
Fire continuously, as long as the stimulus remains present
Adapts slowly to stimulation, so it is also a slowly-adapting fiber (SA2)
Ruffini cylinders are associated with…
The perception of skin stretching
Describe the firing and adaptation of Pacinian corpuscles
Fire only when the stimulus is first applied, and again when
it is removed
Adapts rapidly to stimulation, so it is also a rapidly-adapting fiber (RA2)
Pacinian corpuscles are associated with…
Perceiving vibrations and fine texture
Why is the somatosensory system unique compared to the other sensory systems?
Sensory receptors are distributed throughout the body
Signals need to travel long distances to reach the brain
Brings signals from all over the body from the skin to the brain
Spinal cord
How many segments does the spinal cord have?
31
Bundle of fibers through which the segments of the spinal cord receive signals
Dorsal roots
What are the two major pathways through which signals are sent to the brain after they enter the spinal cord?
The medial lemniscal pathway
The spinothalamic pathway
Carries signals for
proprioception, pressure
and fine touch
Medial lemniscal
Carries signals about pain,
irritation, itchiness, and
temperature
Spinothalamic
Describe the pathway of signals from the mechanoreceptors to the brain
Signals travel through one of the two spinal cord pathways
Signals pass through the thalamus
End at the contralateral primary somatosensory cortex (S1)
How is S1 organized?
A map that corresponds to to the different locations of the body (homunculus)
Which portion of S1 is associated with sensations on the lips and face?
Lower portion
Which portion of S1 is associated with sensations on the hands and feet?
Higher portion
Which areas of the body correspond to disproportionately large sections in S1?
Areas that we typically use to explore the environment (hands, tongue, feet, etc.)
How can perceiving details be studied?
Tactile acuity
The smallest amount of detail that can be detected on the skin
Tactile acuity
Tactile acuity differs based on…
Location and type of skin
Describe the typical results of a two-point threshold (sensitivity) test
Glabrous skin = detect 2 points until about 3mm apart
Hairy skin = only detect 2 points until about 2-5cm
apart
Test of tactile acuity in which the narrowest spacing possible to detect is identified
Grating acuity
Test of tactile acuity involving identifying shapes and
patterns in the absence of
visual cues
Shape perception
What are three tests of tactile acuity?
Two-point threshold (sensitivity) test
Grating acuity
Shape perception
How do mechanoreceptors relate to perceiving detail?
Firing pattern closely correlates to the details on the surface
Which mechanoreceptor is associated with the perception of fine details?
Merkel receptors
Parts of the body sensitive to detail are likely to have more —
Merkel receptors
Describe the relationship between the brain and the size of the receptive
fields on the skin
The smaller the receptive field, the better the detail acuity
Explain how smaller receptive fields lead to the perception of more details
When two points are hit in an area with small receptive fields, the two points would hit different fields whereas when this happens in an area with large receptive fields, two points would only hit the same field (overlapping point in the brain)
Which mechanoreceptors respond best to vibrations?
Pacinian corpuscles
Explain how Pacinian corpuscles respond to vibrations
The corpuscles contain many layers with fluid in between
Constant pressure moves the fluid only once and therefore the neuron only fires once, but vibrations cause the fluid to constantly move causing the neuron to keep firing
The physical, tactile surface of an object created by its peaks and valleys
Surface texture
Theory describing that our perception of a texture depends on spatial and temporal cues
Duplex theory of texture perception
Provided by large surface elements, like bumps and grooves, that can be felt when the skin is resting on a surface
Spatial cues
Provide information through vibrations and only occur when one moves across a surface
Temporal cues
Spatial = perception of —
textures, temporal = perception of — textures
Course, fine
How do different textures get represented differently in our brains?
Each texture seemingly causes a unique pattern of neurons to fire
Touch in which a person is actively exploring an object, typically by using the fingers
and hands for humans
Active touch
Occurs when touch stimuli are applied to the skin,
and the person simply “receives” it
Passive touch
Perceptual process in which three-dimensional objects are explored
Haptic perception
List the systems involved in haptic perception and their roles
Somatosensory system – detecting touch, temperature, texture, etc.
Motor system – moving your hands and fingers
Visual system – perceiving the visual details of the object
Cognition – thinking about the meaning of all this information
How long does it take people to accurately identify most common objects?
1-2 seconds
How do people accomplish object identification?
Through the use of exploratory procedures that differ depending on the quality they are trying to judge
Give six examples of exploratory procedures
Lateral motion
Pressure
Enclosure
Contour following
Static contact
Unsupported holding
Deficits in tactile perception and detail perception by touch resulting from damage to S1
Weakened stereognosis
The complete inability to recognize objects by touch alone resulting from damage to S1
Astereognosis
