Week 11: Touch

Tactile and haptic perception

perception achieved through contact with our skin

Kinesthesia/proprioception

our movement sense—our system for sensing the position and movement of individual body parts

Somatosensation

the sense of touch, which contains multiple modalities: pressure, vibration, pain, and temperature

Mechanoreceptors

respond to mechanical stimulation (pressure, vibration, movement)

Touch receptors

embedded in outer layer and underlying layer of skin

Kinesthetic receptors

located in muscles, tendons, and joints

Touch receptors

embedded in outer layer and underlying layer of skin

• size of the receptive field

• Rate of adaptation (fast vs slow)

• type of stimulation to which the receptor responds

3 criteria for categorizing touch receptors

Merkle cell neurite complexes

• small receptive fields

• slow adaptation rate

• detect sustained pressure

• spatial deformation

• function: texture perception and pattern/form perception

Ruffini endings

• large receptive field

• slow adaptation rate

• detect sustained downward pressure and lateral skin strech

• function: finger position

Meissner corpuscles

• small receptive field

• fast adaptation rate

• detect temporal changes in skin deformation

• skin slip

• function: low frequency vibration detection and stable grasp

Pacinian corpuscles

• large receptive field

• fast adaptation rate

• detect temporal changes in skin deformation

• function: high frequency vibration detection and fine texture perception

Kinesthetic receptors

mechanoreceptors in muscles, tendons, and joints; play a role in sense of where limbs are and what kind of movements are made

Muscle spindle

a sensory receptor located in a muscle that senses tension

Thermoreceptors

sensory receptors that signal information about changes in skin temperature; warmth and cool fibers

Nociceptors

sensory receptors that transmit information about noxious stimulation that causes damage or potential damage to skin

• a-alpha

• a-beta

• a-delta fibers

• c fibers

4 grou[s of somatosensory nerve fibers

A-alpha

widest diameter, greatest myelination nerve fibers coming form proprioceptors

A-beta

wide diameter fibers coming form mechanoreceptors in the skin

A-delta fibers

intermediate sized, myelinated sensory nerve fibers that transmit pain and temperature signals; quick sharp pain

C fibers

Narrow diameter, unmyelinated sensory nerve fibers that transmit pain and temperature signals; throbbing sensation

Labeled lines

each fiber type from the skin codes a particular touch sensation

Dorsal horn

a region of the spinal cord where axons from touch, pain, and temperature fibers enter; organized into multiple layers or laminae

Somatotypically

inputs to spinal cord are organized this way; adjacent areas of the skin project to adjacent areas in the spinal cord

Spinothalamic pathway

carries most of the information about skin temperature and pain (slower)

Dorsal column-medial lemniscal (DCML) pathway

carries signals from skin, muscles, tendons, and joints

Primary somatosensory cortex

S1

Secondary somatosensory cortex

S2

somatotypically

Touch sensations are represented . . . in the brain

brain

Adjacent areas on skin connect to adjacent areas in . . .

Homunculus

maplike representation of regions of the body in the brain

Body image

the impression of our bodies in space; systematically distorted towards top-heaviness

Phantom limb

sensation perceived from a physically amputated limb of the body

Neural plasticity

the ability of neural circuits to undergo changes in function or organization as a result of previous activity

Pain

• triggered by nociceptors

• responses to noxious stimuli can be moderated by anticipation, religious belief, prior experience, watching others respond, attention, and excitement

Anterior cinculate

a region of the brain associated with the perceived unpleasantness of pain sensations

Prefrontal cortex

a region of the brain concerned with cognition and executive control

Gate control theory

a description of the system that transmits pain that incorporates modulating signals from the brain and benign touch receptors

Analgesia

decreasing pain sensation during conscious experience; endogenous opiates --> placebo effects

Pain sensitization

nociceptors provide signal where there is impending or ongoing damage to body's tissue; "nociceptive" pain

Hyperalgesia

once damage has occurred, site can become more sensitive

Allodynia

sensory fibers that normally do not produce pain, become pain inducers

Neuropathic

pain as a result of damage to or dysfunction of nervous system

Haptic perception

knowledge of the world that is derived from sensory receptors in skin, muscles, tendons, and joints, usually involving active exploration

• lateral motion: texture

• pressure: hardness

• Static contact: temperature

• unsupported weight: weight

• enclosure: global shape, volume

• contour following: global shape, exact shape

Exploratory procedures

Mechanoreceptors that have a slow adaptation rate and small receptive field size are called

Merkel cell neurite complexes

_____ responds best to sustained downward pressure and particularly to lateral skin stretch. They are important for finger position

Ruffini Endings

Which of the following is NOT a type of mechanoreceptor?

Thermoreceptors

Which of the following terms described the perception of the position and movement of out limbs in space?

Kinesthesis

The A-delta and C fibers transmit information from ______

thermoreceptors and nociceptors

The ____ horm is the region at the rear of the spinal cord that recieves input from receptors in the skin?

Dorsal

The ____ pathway is the route from the spinal cord to the brain that carries signals from skin, muscles, tendons, and joints?

Dorsal column-medical lemniscal

Which of the following parts of the bady has the largest representation in the somatosensory map?

Hands