Chapter 15: The Cutaneous Senses Flashcards
functions of touch
- Signals pain, reducing the chance of injury
- Makes it easier to interact with the environment (less force is needed)
- Motivating sexual activity
- Social function
somatosensory system
the system that includes the cutaneous senses, proprioception, and kinesthesis
cutaneous senses
responsible for perception such as touch and pain
proprioception
the ability to sense the position of the body and limbs
Kinesthesis
the ability to sense the movement of the body and limbs
Comel, 1953 on the skin
the skin is the monumental facade of the human body
epidermis
the outer layers of the skin, including a layer of dead skin cells
dermis
the layer of skin below the epidermis
mechanoreceptors
Receptors that respond to mechanical stimulation such as pressure, stretching, and vibration
4 types of mechanoreceptors
- merkel receptors
- meissner corpuscles
- rufficini cylinders
- pacinian corpuscles
merkel receptor
a disk-shaped receptor in the skin associated with slowly adapting fibres and the perception of fine details
location of the merkel receptor
Located near the epidermis
receptive fields of merkel receptors
small receptive field
alternative name for merkel receptors
Also called a slowly adapting (SA1) fibre because it fires continuously as long as the stimulus is on
meissner corpuscles
a receptor in the skin, associated with RA1 mechanoreceptors. It has been proposed that the Meissner corpuscle is important for perceiving tactile slip and for controlling the force needed to grip object
location of meissner corpuscles
Located near the epidermis
receptive field size of Meissner corpuscles
small receptive field
alternative name for meissner corpuscles
Also called a rapidly adapting fibre (RA1) because it fires when the stimulus is first applied and when it is removed
cutaneous receptive field
the area of skin which, when stimulated influences the firing rate of the neuron
ruffini cylinder
associated with perceiving stretching of the skin
location of ruffini cylinders
Located deep in the skin
size of receptive field of ruffini cylinders
Has a large receptive field
alternative name of ruffini cylinders
Also called a slowly adapting (SA2) fibre because it fires continuously as long as the stimulus is on
pacinian corpuscle
associated with sensing rapid vibrations and fine texture
where are pacinian corpuscles located?
deep in the skin
size of receptive field of pacinian corpuscles?
Has a large receptive field
alternative name of pacinian corpuscles
Also called a rapidly adapting fibre (RA2 or PC) because it fires when the stimulus is first applied and when it is removed
where are cutaneous receptors located
Cutaneous receptors are distributed all over the body
dorsal root
a bundle of fibres
how many segments does the spinal cord have?
31
where does the spinal cord receive signals from?
the dorsal root
2 major cutaneous pathways
- medial lemniscal pathway
- spinothalamic pathways
The medial lemniscal pathway
consists of large fibres that carry signals related to proprioception and perceiving touch
speed of signals in the medial lemniscal pathways
Transmits signals at a high speed
the spinothalamic pathway
consists of smaller fibres that transmit signals related to temperature and pain
where do cutaneous fibres cross over & synapse?
Fibres from both pathways cross over to the other side of the body and synapse in the ventrolateral nucleus of the thalamus
what brain areas are associated with cutaneous functions?
Many brain areas are associated with cutaneous functions
Primary somatosensory cortex (S1)
the area of the cortex in the parietal lobe that receives signals that originate from the body and stimulation of the skin
Secondary somatosensory cortex (S2)
the area in the parietal lobe next to S1 that processes neural signals related to touch, temperature, and pain
insula
important for sensing light touch
Anterior cingulate cortex (ACC)
involved in pain
The Jacksonian march
Jackson, 1870 noticed that seizures in epilepsy patients progressed around the body in an orderly way
stimulating S1
stimulating the ventral part of S1 (lower on the parietal lobe) caused sensations on the lips and face, stimulating higher on S1 caused sensations in the hands and fingers, and stimulating the dorsal S1 caused sensations in the legs and feet
Homunculus
a body map that shows that adjacent areas of the skin project to adjacent areas in the brain. Areas with more tactile receptors are disproportionately larger.
what does recent research show about the homunculus?
Recent research shows that S1 is divided into four interconnected areas, each with its body map
braille
the system of raised dots that enables blind people to read with their fingertips
speed of braille reading
Experienced Braille readers can read at a rate of about 100 words/ minute, slower than the average visual reader who averages 250-300 words/ minute
tactile acuity
the capacity to detect details of stimuli presented to the skin
two-point threshold
the minimum separation between two points on the skin that when stimulated is perceived as two points
how is two-point threshold measured?
Measured by gently touching the skin with two points and having the person indicate whether they feel one or two points
grating acuity
the narrowest spacing of a grooved surface on the skin for which the orientation can be accurately judged
how is grading acuity measured?
Measured by pressing a grooved stimulus onto the skin and asking the person to indicate the orientation of the grating
acuity (cutaneous)
the narrowest spacing for which orientation can be accurately judged
Merkel receptors vs. Pacinian corpuscles in the firing of a grooved stimulus
- Merkel receptors’ firing reflects the pattern of the grooved stimulus
- Pacinian corpuscles’ firing doesn’t match the pattern of the grooved stimulus
areas with more -> less Merkel receptors
- fingers
- upper lip
- big toe
- back
- thigh
- upper arm
what body parts have smaller receptive fields?
Cortical neurons that receive signals from body parts with better acuity
what mechanoreceptor is associated with vibration perception and why?
Pacinian corpuscles are associated with vibration perception because the fibres associated with the corpuscle respond poorly to slow rates of vibration but well to high rates of vibration
Lowenstein, 1960 Pacinian corpuscle experiment
when pressure is applied to the corpuscle, the fibre responds when the pressure was first applied and when it was removed, but not to continuous pressure. When pressure is applied to the fibre, it fired to continuous pressure.
surface texture
The physical texture of a surface created by peaks and valleys
duplex theory of texture perception
states that our perception of texture depends on both spatial and temporal cues
who proposed the duplex theory of texture perception?
David Katz, 1925
spatial cues
provided by relatively large surface elements that can be felt both when the skin moves across the surface elements and when it is pressed onto the elements
temporal cues
occur when the skin moves across a textured surface. Provides information in the form of vibrations that occur as a result of the movement over the surface
Hollins & Risner, 2000 magnetic estimation experiment
showed that when participants touched surfaces without moving their fingers and judged roughness using magnetic estimation, they sensed little difference between two fine textures. However, when they were allowed to move their fingers across the surface, they could detect the differences between the fine textures
what theory does Hollins & Risner’s 2000 magnetic estimation experiment support?
the Duplex theory of texture perception
what determines the ability to detect differences in texture by running a tool over a surface?
vibrations transmitted through the tool to the skin
Lieber & Bensmaia, 2019 textures in monkeys experiment
Studied how textures are represented in the brain by training monkeys to place their fingers on a rotating drum. Found that 1) different textures caused different firing patterns in an individual neuron and 2) different neurons responded differently to the same texture
neurons that fire best to coarse textures receive input from ___
merkel receptors
neurons that fire best to fine textures receive input from ___
pacinian corpuscles
active touch
touch in which a person actively explores an object, usually with fingers and hands
passive touch
occurs when touch stimuli are applied to the skin as when two points are pushed onto the skin to determine the two-point threshold
haptic perception
perception in which 3D objects are explored with the fingers and hand
3 systems involved in haptic exploration
the sensory, motor, and cognitive systems
sensory system
is involved in detecting cutaneous sensations such as touch, temperature and texture
motor system
is involved in moving the fingers and hands
cognitive system
is involved in thinking about the information provided by the sensory and motor systems
how long does it take people to identify common objects
1-2 seconds of active touch
Exploratory procedures (EPs)
the distinctive movements that people make as they try to identify objects
how is the type of EPs determined?
depends on the object qualities the participants are asked to judge
what cortical neurons are more specialized?
Cortical neurons become more specialized as they move toward the brain
centre- surround receptive fields in the cutaneous system
Neurons in the ventral posterior nucleus (tactile area of the thalamus) have centre-surround receptive fields
attention & cortical neuron response
Cortical neurons’ response is affected by whether the perceiver is paying attention
Hsiao et al’s., 1993 attention and cortical response study
recorded the response of monkeys’ S1 & S2 neurons to raised letters. In the tactile-attention condition, monkeys had to perform a task that required focusing attention on the letters being presented to their fingers. In the visual attention condition, monkeys had to focus their attention on an unrelated visual stimulus. Found that the response was larger for the tactile-attention condition
pain
an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage
3 types of pain
inflammatory, neuropathic, and nociceptive
inflammatory pain
caused by damage to tissue or inflammation of joints or by tumour cells
neuropathic pain
caused by lesions or other damage to the nervous system
nociceptive pain
caused by the activation of nociceptors
nociceptors
specialized to respond to tissue damage or potential damage
direct pathway model of pain
States that pain occurs when nociceptive receptors in the skin are stimulated and send their signals directly from the skin to the brain
criticisms of the direct pathway model of pain
- most American soldiers wounded at Anzio beachhead in WWll denied pain or had very little pain
- phantom limbs
phantom limbs
when people who have a limb amputated continue to experience the limb
gate control model of pain
the idea that perception of pain is controlled by a neural circuit that takes into account the relative amount of activity in nociceptors, mechanoreceptors, and central signals. This model has been used to explain how pain can be influenced by factors other than the stimulation of receptors in the skin
who proposed the gate control model of pain?
Ronald Melzak and Patrick Wall, 1965
nociceptors in the gate control model of pain
activate a circuit consisting of excitatory synapses and send excitatory signals to transmission cells. Excitatory signals from the + neurons in the dorsal horn open the gate. Increased activity in transmission cells = more pain
mechanoreceptors in the gate control model of pain
carry information about non-painful tactile stimulation. When activity reaches the - neurons, inhibitory signals are sent to transmission cells to close the gate and decrease the firing rate of transmission cells and pain.
central control in the gate control model of pain
fibres that contain information related to cognitive functions. Activity coming down from the brain also closes the gate, decreasing the firing rate of transmission cells and pain.
placebo
a pill that patients believe contains a drug, but contains no active ingredients
placebo effect
the decrease in pain from a substance that has no pharmacological effect
Bingel et al., 2011 placebo effect study
participants rated pain in 4 different conditions: baseline, no expectation, positive expectation, and negative expectation. The pain was reduced slightly in the no expectation condition, dropped significantly in the positive expectation condition and increased significantly in the negative expectation condition
nocebo effect
an increase in pain from a substance that one believes will have a negative effect
what brain activity is associated with the placebo effect?
increases in networks associated with pain perception
what brain activity is associated with the nocebo effect
increases in hippocampal activity
effect of attention on pain
Distracting patients from their pain can help reduce it
effect of emotions on pain
Positive emotions are associated with decreased pain
pain perception and type of images
had patients look at positive, neutral, or negative images while their hand was immersed in cold water and told them to remove their hand when it began to hurt. Found that participants removed their hands more quickly when viewing the negative, followed by the neutral pictures.
pain perception and type of music
found that participants reported lower levels of main when listening to pleasant music
Ian Waterman
- Gradually lost control of his limbs following a common cold
- His muscles still worked and his brain was receiving signals from his body conveying sensations such as pain and differences in temperature. However, the brain seemed to have lost the notion of where the different parts that it was supposed to move were located
2 types of nerve fibres
sensory and motor fibres
motor fibres
signal to our muscle fibres telling them to contract
sensory fibres
start either in the skin or in the muscles and come in different sizes
large sensory fibres
convey information concerning touch, muscle sensitivity, and sense of movement
small sensory fibres
convey information concerning muscle fatigue, temperature and certain forms of pain
what is the heaviest organ in the body?
the skin
what’s the function of the skin?
Protects the organism from keeping damage agents from penetrating the body
two types of mechanoreceptors located close to the surface of the skin
Merkel receptors and Meissner corpuscles
two types of mechanoreceptors located deeper in the skin
Ruffini cylinders and pacinian corpuscles
how do nerve fibres travel to the spinal cord?
in bundles (peripheral nerves)
what happens when there is plasticity in neural functioning?
leads to multiple homunculi and changes in how cortical cells are allocated to body parts
raised pattern identification
using such patterns to determine the smallest size that can be identified
what area has the highest density of Merkel receptors?
the fingertips
what body areas have larger areas of cortical tissue devoted to them?
body areas with high acuity
examples of spatial cues
bumps and grooves
example of a temporal cue
fine texture
support for spatial vs. temporal cues
- Past research showed support for the role of spatial cues
- Recent research by Hollins and Reisner shows support for the role of temporal cues
how do participants detect fine textures?
by moving their fingers across the surface
how are touch neurons organized in the cortex?
some neurons have center-surround receptive fields and others respond to more specialized stimulation of the skin
changes in cortical maps
Cortical maps can change based on how much a body part is used and in response to injury
example of plasticity in monkeys
found that the cortical map of a monkey’s fingertip greatly expanded after training
example of plasticity in humans
musicians who use their left hands to play string instruments have greater than normal cortical representations for the fingers on their left hand
Hand dystonia
a condition which causes the fingers to curl into one’s palm
cortical maps in patients with hand dystonia
The map of fingers in area S1 is abnormally organized in some patients with dystonia
