chapter 15 - touch

kinesthesia

ability to sense movement of body and limbs

proprioceptions

ability ti sense position of the body and limbs

somatosensation

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

cutaneous

sensations based on stimulation of skin receptors

layers of the skin

epidermis, dermis, subcutaneous tissue

messier corpuscles

• fast adaptation, small receptive field (FA I)

• heavy pressure - close to surface of skin

• fire only when stimulus is first applied and when it is removed

• controls hand grip

Merkel cell neurite complexes

• slow adaption, small receptive field (SA I)

• light touch - close to surface of skin

• fire continuously whole time stimulus is present

• detects fine details

pacinian corpuscles

• fast adaptation, large receptive field (FA II)

• vibration and fine texture

• fires only when stimulus is first applied and when it is removed

ruffini endings

• slow adaptation, large receptive field (SA II)

• skin stretch

• fires continuously to stimulation

• typing or playing instrument

two point threshold

minimum distance at which two stimuli are just perceptible as separate

tactile sensitivity

• touch - sensitive to time differences of 5 ms

• vision - sensitive to time differences of 25 ms

• audition - sensitive to time differences of 0.01 ms

thermoreceptors

• changes in skin temp, respond when touching object warmer or cooler than skin

• warmth fibers, cold fibers

nociceptors

• sensory receptors that transmit information about noxious stimulation that could damage skin

• a-delta fibers and C fibers

a-delta fibers

• intermediate sized, myelinated sensory nerve fibers

• transmit pain and temperature signals

c-fibers

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

categories of discriminative touch

tactile, thermal, pain, itch, pleasant touch

kinesthetic receptors

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

• joint receptors react when joint is bent to extreme angle

• tendon receptors provide signals about tension in muscles

muscle spindles

convey the rate at which the muscle fibers are changing in length

where do skin mechanoreceptor project?

dorsal horn

dorsal column medial lemniscal pathway

• consists of large fibers that carry proprioceptive and touch information - faster

• crosses over and synapses in thalamus

spinothalamic pathway

• consists of smaller fibers that carry temperature and pain information - slower

• crosses over and synapse in thalamus

homunculus

maplike representation of regions of the body in the brain

body image

impression of our bodies in space

phantom limb

sensation perceived from a physically amputated limb of the body

purpose for pain

• emotional, cultural, and experiential components

• relays info about tissue injury

receptors for pain

• nociceptors

• mechanical injury, extreme temperature, chemicals

analgesia

• decreasing pain sensation during conscious experience

• endogenous opiates

endogenous opiates

chemicals released in body to block release or uptake of neurotransmitters transmitting pain sensation tp brain

gate control theory

• system that transmits pain that incorporates modulating signals from brain

• located in dorsal horn of spinal cord

• block pain transmission can be activated by extreme pressure, cold, or other noxious stimulation applied to another site distant from source of pain

areas s1 and s2

sensory aspects of pain

anterior cingulate

region of brain associated with the perceived unpleasantness of pain sensations

prefrontal cortex

• region of brain concerned with cognition and executive control

• may contribute to pain sensitization

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

tactile agnosia

• inability to identify objects by touch

• caused by lesions to the parietal lobe

the where system of touch

knowing where objects are in the environment using only touch perception

egocenter

the center of a reference frame used to represent locations relative to the body