somatosensation

touch receptors

touch receptors

vary based on type of stimulation it responds to, size of receptive field, and rate of adaption

mechanoreceptors

respond to mechanical stimulation of pressure

contain Messiner corpuscles, Merkel cell neurite complexes, Ruffini endings, Pacinian corpuscles

Include FA I & II, SA I & II,

FA I

mechanoreceptor that responds to edge contours and Braille at low-frequencies (3-40 Hz)

FA II

mechanoreceptor that responds to mechanical transients at high frequencies (50-700 Hz)

SA I

mechanoreceptor that responds to local spatial discontinuities, static texture, sustained pressure, and spatial deformations are frequencies <5 Hz

SA II

mechanoreceptor that responds to lateral stretch, hand shape, static force and has low sensitivity to vibrations

proprioceptive receptors

type of mechanoreceptor in muscles, joints and tendons that relays information about limb location, posture and the kinds of movements being made

spindles

convey rate muscle fibers are changing in length

in tendons provide information about tension in muscles

in joints react when at an extreme angle

thermoreceptors

signal information about skin temperature

warmth & cold fibers

nociceptors

transmit information about harmful stimulation that could cause damage

A-delta fibers and C fibers

signal to substantia gelatinosa

a delta fibers

nociceptors that respond to strong pressure and heat

myelinated & fast

C fibers

nociceptors that respond to pressure, heat, cold and chemicals

unmyelinated & slow

nerve trucks

axons from various tactile receptors combine

dorsal root ganglion

how tactile signals enter the spinal cord

2 major pathways: spinothalamic and dorsal column-medial lemniscal

spinothalamic

slow tactile pathway in spinal cord for nociception and thermal information

synapses multiple times

dorsal column medial lemniscal (DCML)

fast tactile pathway in spinal cord

medulla → ventral posterior nucleus of thalamus → somatosensory area 1 → somatosensory area2

cranial

pathway of tactile sensations in the face

uses trigeminal nerve V

somatotopical organization

adjacent areas on the skin are connected adjacently in the brain

somatosensory area 1

corresponds to BA3

BA3a = proprioception

BA3b = touch

substantia gelatinosa

where nociception arrives in the brain

moderate pain through cognition, emotion and social factors

analgesia

decreased pain sensation while being conscious

endogenous opiates

release to block transmission of pain

occurs in sport injuries

gate control theory

pain transmitting system is modulated by signals from the brain

feedback circuit is located in substantia gelatinosa

gate neurons

block pain transmission

light pain pathway

LGN → ventral lateral geniculate nucleus → PAG → locus coeruleus, rostral ventromedial medulla

anterior cingulate cortex

responds differently to hypnotic suggestions by increasing/decreasing activity

associated with perception not emotion of pain

prefrontal cortex

emotional response to pain, not perception of pain

Von Frey hair

19th century calibration of mechanical pressure on the human body using horse & human hair

two point threshold

minimum distance two simultaneous touches are just perceived as separate

distance corresponds to homunculus

funneling

separate close stimuli are perceived as a single more intense stimulus at the central location

tactile size constancy

distance on index finger feels bigger than the same distance on forearm BUT perceived distance is smaller that distance predicted by receptor density

haptic perception

knowledge derived from receptors on skin, muscle, tendons and joints

usually involves exploration

exploratory procedure

stereotypes hand movement pattern used to contact objects in order to perceive their properties

includes lateral motion, pressure, static contact, unsupported holding, enclosure, contour following

angular motion

spatial orientation sensed by rotating head side to side

linear motion

spatial orientation sensed by acceleration

tilt

spatial orientation sensed when leaning

roll

rotation around x axis (nose - back of head)

pitch

rotation around y axis (ear - ear)

yaw

rotation around z axis (head - toe)

pitch tilt

rotation of x & z axis

face plant / chin to chest

roll tilt

rotation of y & z axis

falling to the side / remove water from ears

vestibular system

contains 3 semicircular canals and 2 otolith organs

semicircular canal

3 quarter toroid shaped canals embedded in the bone filled with perilymph

inner smaller toroid is formed by a membrane and filled with endolymph

contains ampulla at cross sections

ampulla

cross section of semicircular canals

have crista with hair cells

hair cells

transduce mechanical movement in vestibular system into neural activity sent to the brain stem

high resting rate of action potentials

stereocilia

hair-like extension on tip of hair cell, deflections cause change in voltage and alters neurotransmitter release

push pull symmetry

hair cells in opposite ears respond complimentary to each other

one hyperpolarizes, the other depolarizes

angular velocity

changes in firing rate of hair cells in semicircular canal is proportional to _______ ________

otolith organs

sense acceleration and tilt

utricle & saccule in each ear

contains a macula

macula

specialized detector of linear acceleration and gravity

roughly planar and sensitive to shear forces

hair cells encased in gelatinous structure containing calcium carbonate crystals

otoconia

calcium carbonate crystals in gelatinous structure of macula on the otolith organs

vestibulo-ocular reflexes (VOR)

counter rotating the eyes to counteract head movement and maintain fixation on a target

thalamo-cortical

vestibular information reaches cortex through - pathways

visual input

vestibular cortical areas also respond to _______ _______

back projection

knowledge and expectations

info from lower level representations enhances features of higher level representations