touch Flashcards
where are touch receptors?
embedded in outer layer (epidermis) and underlying later (dermis) of skin
what are the three criteria of touch receptors?
- type of stimulation to which they respond
- size of receptive field
- rate of adaption
what do tactile receptors respond to?
mechanical stimulation: pressure, vibration or movement
what are meissner corpuscles?
fast adaption with small receptive field
what are merkel cell neurite complexes?
slow adaption, small receptive field
what are pacinian corpuscles?
fast adaption, large receptive field
what are ruffini endings?
slow adaption, large receptive feild
what does the slow - adapting type 1 (SAI) mechanoreceptor do?
perceives pattern, texture and shape and responds to onset of stimulus and continues to respond at a lower level for the duration of stimulus
what do slow adapting types respond best to?
skin indention and allows identification of texture
what do merkel cells provide info on?
weight, form and surface features
what do fast adapting type 1 (FAI) mechanoreceptors perceive?
slip and maintaining grip control
what are meissner corpuscles responsible for?
detecting textures and edges as hand moves over surfaces - able to signal speed and direction and light touch
what do slow adapting type 2 (SAII) mechanoreceptors percieve?
skin stretch and hand conformation
what do SAII respond to?
for the duration of the stimulus and to the stretching of skin to help give information about movement and posture
what do fast adapting type 2 (FAII) mechanoreceptors percieve?
fine textures through transmitted vibration
what do the pacinian corpuscles do?
very sensitive to vibrations transmitted through an object and are the largest of the mechanoreceptors located deep in the dermis
how finely can we resolve temporal details?
two tactile pulses can be delivered over time, in a manner analogous to spatially separated two point threshold stimuli
what is the time sensitivity difference of touch?
5 ms
what is the time sensitivity difference of vision?
25 ms
what is the time sensitivity difference of audition?
0.01 ms
what is the two point threshold?
threshold smaller on fingertips and lips and larger on arms, legs and torso
is there a brain pathway for tactile information?
there is inconclusive evidence that the mechanism by which
mechanoreceptors transduce mechanical force is analogous to
the mechanism by which hair cells in the cochlea transduce
movement of their stereocilia into neural signals sent through
auditory nerve fibers
what is proprioception?
the unconscious perception of movement and spatial orientation
what are kinesthetic receptors?
mechanoreceptors in muscles, tendons and joints
what do kinesthetic receptors do?
sense of where limbs are, what kinds of
movements are made
what is muscle spindle?
a sensory receptor located in a muscle that
senses its tension
what do the receptors in tendons do?
signal tension in muscles attached to tendons
what do receptors in joints do?
react when joint is bent to an extreme angle
what happened to ian waterman?
cutaneous nerves connecting Waterman’s kinesthetic mechanoreceptors to brain destroyed by viral infection
so lacks kinesthetic senses, dependent on vision to tell
limb positions
what is nociception?
introduced by sherrington with the intent of distinguishing between detection of a noxious or
potentially harmful event and our responses to it
what are nociceptors?
sensory receptors that transduce the physical stimuli associated with damaging mechanical, thermal, or chemical events;
are included among the free nerve endings in the epidermis and dermis
what is sensitization?
mechanism that decreases the response threshold
of nociceptors, so that even very low level stimulation of an injury site can cause pain
what are a-delta fibers?
myelinated axons of nociceptors that transmit pain signals relatively rapidly, to produce a rapid response to potentially damaging mechanical stimuli and to excessive heat
what are c fibers?
unmyelinated axons of nociceptors that transmit pain
signals relatively slowly
what do nociceptors transmit?
pain signals to the spinal cord via two
different types of fibers
what are the two fibers that nociceptors transmit via?
a delta fibers and c fibers
how fast do a delta fibers transmit action potentials?
relatively rapidly (about 2–4 m/sec), produce a rapid response to potentially damaging mechanical stimuli and to excessive heat
how fast do c fibers transmit action potentials?
relatively slowly (about 1 m/sec), produce a slower response to a wide range of pain stimuli
what do heat receptors detect?
temperatures over 25°,
but they do not continue to
detect heat when it gets too hot (e.g., extremely hot and harmful temperature of 45°C or hotter)
what do cold fibers respond to?
cool temperatures between 10°C and 20°C, but they
do not respond to very cold
temperatures, below 10°C
how numerous are cold and hot receptors in comparison?
cold are about 30 times more
do we notice thermal sensation when temp is maintained?
no
what happens if skin is abruptly warmed?
the firing rate of warm fibers increases
what happens if skin is abruptly cooled?
the firing rate of cold fibers increases
what is the dorsal column–medial lemniscal
pathway (DCML pathway)?
pathway for signals involved in tactile perception and
proprioception; travels up the spinal cord on the ipsilateral
side, crosses to the contralateral side in the
medulla, and then goes
through the ventral posterior
nucleus of the thalamus and
on to the somatosensory
cortex
what is the spinothalamic pathway?
pathway for signals involved in nociception and
thermoreception; crosses over to the contralateral side within the spinal cord and then goes through the ventral posterior nucleus of the thalamus and
on to the cortex
how is touch sensations represented in the brain?
somatotopically
what is S1 and S2?
primary somatosensory cortex called S1; secondary
somatosensory cortex called S2
what are the two divisions of the vestibular system?
semicircular canals for rotary motion/balance and otolith organs (utricle and saccule) for linear acceleration/head tilt
what is movement of hair cells responsible for?
sending signals in each of the systems
