PSYC2274 Chapter Notes - Chapter 13: Prefrontal Cortex, Hyperalgesia, Receptive Field
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- Touch is used to refer to the sensations caused by mechanical displacements of the skin.
- Occur any time you make contact with an object.
- Tactile (adjective of touch) refers to these mechanical interactions.
- Touch includes perception of temperature changes, sensation of pain, itchiness, and
internal sensations arising from muscles, tendons, and joints that inform us of the
positions and movements of our limbs in space (kinesthesia).
- Proprioception incorporates sensory input from locations internal to the body.
- Perception mediated by kinesthetic and internal receptors.
- Somatosensation further encompasses the input from touch receptors in the skin as well
as the proprioceptive system.
- Collectively, sensory signals from the skin, muscles, tendons, joints, and internal
receptors.
- Pain serves as a warning system.
- Temperature sensations enable us to seek or create a thermally safe environment.
- Mechanical sensations play an important role in our intimate sexual and reproductive
activities.
- Provide powerful means of communicating our thoughts and emotions
nonverbally.
- Touch is important because we can use it to identify and manipulate objects that can’t be
seen or heard.
TOUCH PHYSIOLOGY
Touch Receptors in the Skin
- Touch receptors are embedded all over the body, in both hairless and hairy skin.
- Also found within our mouths and our muscles, tendons, and joints.
- Tactile receptors are embedded in both the outer layer (epidermis) and underlying layer
(dermis).
- Skin has multiple types of tactile receptors.
- Each type of receptor can be characterized by three attributes:
- 1. Type of stimulation to which receptor responds.
- Respond to different stimuli (pressure, vibration, temp. Change, etc.)
- 2. Size of the receptive field.
- Receptors are activated when stimulation is applied to a particular area
of the body → the receptive field.
- Size of receptive field is the extent of the body area that elicits a receptor
response.
- 3. Rate of adaptation (fast vs. slow).
- Fast-adapting (FA) receptor responds with bursts of action potentials.
- Slow-adapting (SA) receptor remains active throughout the period during
which the stimulus is in contact with its receptive field.
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2
TACTILE RECEPTORS
- These are called mechanoreceptors because they respond to mechanical stimulation or
pressure.
- A sensory receptor that responds to mechanical stimulation (pressure, vibration,
or movement).
- Consists of a “nerve fiber” and an associated expanded ending.
- Nerve fiber is composed of its axon and myelin sheath.
- All fall into a myelinated class called A-beta fibers → have relatively wide
diameters that permit very fast neural conduction.
- Transmits signals from mechanical stimulation.
- The 4 populations of tactile receptors are found in the hairless skin (glabrous).
- Nerve fibers of tactile receptors are assumed to terminate in different expanded endings.
- Expanded endings are:
- Meissner corpuscles → specialized nerve ending associated with FA I fibers
that have small RFs.
- Merkel cell neurite complexes → specialized nerve ending associated with SA
I fibers that have small RFs.
- Pacinian corpuscles → specialized nerve ending associated with FA I fibers
that have large RFs.
- Ruffini endings → specialized nerve ending associated with SA II fibers that
have large RFs.
- Endings of Meissner and Merkel = located at the junction of the epidermis and dermis.
- Pacinian and Ruffini receptors are embedded more deeply in the dermis and underlying
subcutaneous tissue.
- The 4 types of mechanoreceptors can be independently classified according to their
adaptation rates and the sizes of heir receptive fields.
- These 2 dimensions lead to a second set of labels for the mechanoreceptor types.
- SA I, SA II, FA I, FA II.
- SA I fibers respond best to steady downward pressure, fine spatial details, and very low
frequency vibrations of less than about 5 Hz.
- Important for texture and pattern perception.
- When a single SA I fiber is stimulated, people report feeling “pressure.”
- SA II fibers respond to sustained downward pressure, and particularly to lateral skin
stretch (such as when we grasp an object).
- For stimulation to be detected, more than one SA II fiber must be stimulated.
- FA I fibers respond best to low-frequency vibrations from about 5-50 Hz.
- Will help you correct your grip if your coffee cup starts slipping out of your hand.
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- When a single fiber is stimulated, people report a very localized sensation that
they describe as “wobble” or “flutter.”
- FA II fibers respond best to high-frequency vibrations from about 50-700 Hz.
- Occur whenever an object first makes contact with the skin or with another object.
- When 1 single fiber is stimulated, people report a more diffuse sensation in the
skin like a “buzz.”
- The 4 types are always working together.
- SA I and FA I fibers → one affords acuity and the other sensitivity to low-
intensity stimulation.
- Mechanoreceptors in hair skin → additional receptors are found near hair follicles.
- Hairy skin appears to play a unique role in pleasant touch.
THERMORECEPTORS
- Located in both epidermal and dermal layers of the skin.
- Inform us about changes in skin temperature.
- 2 distinct populations:
- Warmth fibers → fires when skin temp increases
- Cold fibers → fires when skin temp decreases
- Outnumber warmth ones by about 30:1.
- Neural fibers that mediate cold and warmth include unmyelinated C-fibers and faster-
conducting myelinated A-delta fibers.
- Normal skin conditions = 30 degrees C - 36 degrees C (86-96 degrees F).
- Neither cold/warmth fibers respond much while skin temp remains within this
range.
NOCICEPTORS
- This is where pain signals begin from.
- A sensory receptor that responds to painful input.
- Have bare nerve endings.
- Respond to various forms of tissue damage or to stimuli that have the potential to damage
tissue.
- Lack specialized endings and can be divided into two types by their nerve fibers.
- Myelinated A-delta fibers respond primarily to strong pressure or hear.
- Unmyelinated C-fibers respond to intense stimulation of various sorts: pressure,
heat or cold, or noxious chemicals.
PLEASANT TOUCH RECEPTORS
- Emotional properties of nonpainful bodily touch are mediated by a class of unmyelinated
peripheral C fibers known as C tactile afferents (CT afferents) that are not related to
either pain or itch.
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Document Summary
Touch is used to refer to the sensations caused by mechanical displacements of the skin. Occur any time you make contact with an object. Tactile (adjective of touch) refers to these mechanical interactions. Touch includes perception of temperature changes, sensation of pain, itchiness, and internal sensations arising from muscles, tendons, and joints that inform us of the positions and movements of our limbs in space (kinesthesia). Proprioception incorporates sensory input from locations internal to the body. Perception mediated by kinesthetic and internal receptors. Somatosensation further encompasses the input from touch receptors in the skin as well as the proprioceptive system. Collectively, sensory signals from the skin, muscles, tendons, joints, and internal receptors. Temperature sensations enable us to seek or create a thermally safe environment. Mechanical sensations play an important role in our intimate sexual and reproductive activities. Provide powerful means of communicating our thoughts and emotions nonverbally.
