S + P Chapter 13

Touch

• mechanical displacement of the skin

• determined by receptors in the skin and other internal tissues

• touch information travels through the spinal cord

Kinesthesia

perception of the position and movement of our limbs in space

Propriception

perception mediated by kinesthetic and internal receptors

Somatosensation

collectively, sensory signals from the skin, muscles, tendons, joints, and interval receptors

Nociception

pain perception

Interoception

perception of internal organs

A-beta fibers

wide-diameter, myelineated sensory nerve fibers that transmit signals from mechanical stimulation

A-delta fibers

intermediate-sized, myelinated sensory nerve fibers that transmit pain and temperature signals

C fibers

narrow-diameter, unmyelinated sensory nerve fibers that transmit pain and temperature signals

Layers of the Skin

Layers of the Skin

• epidermis

• dermis

  • subcutaneous tissue

Each receptor can be categorized by two criteria

• size of the receptive field

  • rate of adaptation

Touch receptors are called

mechanoreceptors, because they respond to mechanical stimulation (pressure, vibration, or movement)

A-beta fibers

• wide diameter, myelinated sensory nerve fibers that transmit signals from mechanical stimulation

How many types of mechanoreceptors are there?

• Meissner corpuscles

• Merkle Cell Neurite Complexes

• Pacinian corpuscles

• Ruffini Ends

Merkel (SA I)

• small receptive field

• slow adaptation rate

• sustained pressure, very low frequency (<~5 Hz)

• coarse texture and pattern

Meissner

• small receptive field

• fast adaptation rate

• temporal changes in skin deformation (~5 - 50 Hz); skin slip

• Low-frequency vibration; grasp stability

Ruffini

• large receptive field

• slow adaptation rate

• sustained downward pressure; lateral skin stretch (~ 5 - 50 Hz)

  • finger position

Pacinian

• large receptive field

• fast adaptation rate

• temporal changes in skin deformation ( ~50 - 700 Hz)

• high frequency vibration; fine texture

Diagram

Kinesthetic Receptors

• mechanoreceptors in muscles, tendons, and joints

  • play an important role in sense of where limbs are, what kinds of movements

Muscle Spindle

• sensory receptor located in a muscle that senses its tension

• receptors in tendons signal tension in muscles attached to tendons

  • receptors in joints react when joint bent to an extreme angle

Thermoreceptors

• signal information about changes in skin temp

• two distinct populations of thermoreceptors: warmth fibers, cold fibers

• C fibers (unmyelinated) and A-delta fibers (myelinated)

Response Rate of Thermoreceptors

Thermoreceptors (2 of 2)

• body is constantly regulating internal temperature

  • thermoreceptors respond when you make contact with an object warmer or colder than your skin

Nociception Pain

• determine perception of pain

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

A-delta fibers (nociceptors)

• intermediate-sized, myelinated sensory nerve fibers that transmit pain and temperature signals

C fibers (nociceptors)

• Narrow-diameter, unmyelinated sensory nerve fibers that transmit pain and temperature signals

Two stages of pain processing (receptor level)

• quick and sharp

• dull throbbing

  • difference in pain quality is due to

Labeled Lines

a theory of sensory coding in which each nerve fibers carries a particular stimulus quality

Dorsal Horn

• axons from tactile fibers enter the spinal cord in the dorsal horn

  • organized into multiple layers, or laminae

Somatopical Organization

• inputs to spinal cord organized somatotopically—adjacent areas of the skin project to adjacent areas in the spinal cord. (very important)

• complex calculations that enrich touch sensations occur in the dorsal horn

Two pathways to brain

• spinothalamic pathway

• dorsal column-medial lemniscal DCML

spinothalamic pathway

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

Dorsal column-medial lemniscal (DCML)

• carries tactile and kinesthetic information (Faster)

Primary Somatosensory Cortex

S1

Secondary Somatosensory

S2

Sensory Homunculus

• maplike representation the amount of somatosensory cortex devoted to each part of the body

Sensorimotor system

• motor and somatosensory cortex interact to produce movement

Phantom Limb Pain

• neural plasticity

• sudden loss of input to somatosensory cortex

• other areas will take over

• false stimulation = pain

• no response = pain

Treating phantom limb pain

• some have received transplants from donor cadaver

• when successful the somatosensory cortex will rewire to respond to the new hand

• other amputees have received prosthetic limbs with biomimetic feedback, which mimics biological signals

  • in some cases, users feel sensations emanating from the hand

Body image

• phantom limb pain represents a disruption in the body image

  • which is: the impression of our bodies in space

Gate Control Mechanisms

• pain information relayed from nociceptors to the substantia gelantinosa of the spinal cord

• excitation (nociceptors) and inhibition (neurons in substantia gelantinosa and a-beta fibers)

Analgesia

decreasing pain sensation during conscious experience

can occur thru

• stimulation of the gate-control mechanism

• release of endogenous opiates

• external substances like morphone, heroin, opium

Hyperalgesia

heightened response to normally painful stimulus

• nociceptors signal that damage is ongoing, cranking up the pain signal

Tactile Sensitivity

• sensitivity to mechanical pressure is known as mechanical touch

How would we measure tactile spatial acuity?

• two point threshold

Two pint threshold

• lab day

  • varies across the body, fingers/face/toes show the highest acuity

Haptic perception

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

• receptors in the skin help us maintain grasp

Exploratory procedures

• stereotypical hand movement pattern used to contact objects in order to perceive their properties; each exploratory procedure is best for determining one or more object properties

Haptic Search

• some material properties “popout” in haptic search tasks

  • rough among smooth, hard among soft, cool among war, edged surfaces among smooth

  • horizontal lines among vertical lines