Somatosensory System Flashcards
what are the 4 main somatosensory receptors in the skin
pacinian corpuscles
meissner’s corpuscles
Merkel’s disks
Ruffini’s endings
what are somatosensory receptors called
mechanoreceptors
what are 2 types of skin
hairy skin and glabrous skin (smooth)
what are the 2 layers of skin
epidermis and dermis (thicker layer underneath)
which mechanoreceptors are near the top of the dermis
merkels disk and meissner’s corpuscle
which mechanoreceptors are deep in the dermis
Pacinian corpuscle and Ruffini’s ending
sensory axons
unmyelinated axon branches inside of mechanoreceptors that contain ion channels sensitive to mechanical force
how do different mechanoreceptors differ to detect a large rage of stimuli
- different size receptive fields
-different response to pressure (adaptation) - preferred stimulus frequencies
3 different types of mechanosenstve ion channels
- membrane stretch -> ap
- force applied to extracellular protein -> ap
-force applied to intracellular protein -> ap
Meissner’s corpuscle: adaptation, receptive field size, frequency detection
rapid adaptation, small receptive field, detects low frequencies (ex. hand over rough surface)
Pacinian corpuscle: adaptation, receptive field size, frequency detection
rapid adaptation, large receptive field, detects high frequency (ex. vibrations hand on speaker)
Merkel’s disk: adaptation, receptive field size, frequency detection
slow adaptation, small receptive field, detects very low frequencies (ex. hand over a smooth surface).
Ruffini’s ending: adaptation, receptive field size, frequency detection
slow adaptation, large receptive field, detects very low frequencies (ex. hand over a smooth surface).
mechanoreceptor adaptation
reduced response to physical stimuli over time
mechanoreceptor capsule
20-70 layers filled with fluid surrounding sensory axon
mechanoreceptor adaptation mechanism
probe presses on site, indentation of sensory axon, generate action potential -> adaptation (capsule layers move so no more indentation to sensory axon, back to resting membrane potential
mechanoreceptor adaptation: what happens when stimuli/ pressure removed from mechanoreceptor
receptor action potential due to disruption to the sensory neuron.
2 point discrimination
minimum distance necessary to differentiate between 2 simultaneous stimuli; point where you can no longer differentiation between 2 separate stimulus points
what is sensitivity of an area determined by
density of mechanoreceptors and size of receptive fields
qualities of more sensitive areas of the body
more mechanoreceptors (higher density) and smaller RF
how does a sensory receptor send signals to spinal cord
through doral root
dorsal root ganglion
collection of cell bodies in dorsal root
4 main afferent axons
A alpha, A beta, A delta, C
axons with largest diameter and most meylin ranked from most -> least
A alpha, A beta, A delta, C
A alpha axon sensory receptors
proprioceptors (skeletal muscles)
A beta axon sensory receptors
mechanoreceptors (skin)
A delta axon sensory receptors
pain and temp
C axon sensory receptors
temp, pain, itch
how many segments are in the spinal cord
30
what are the 4 groups of the spinal cord
cervical, thoracic, lumbar, sacral
A beta axon pathway through spinal cord
dorsal root -> branches off into gray matter (spinal reflexes) and white matter pathway to brain
dorsal column-medial lemniscal pathway
sensory neuron -> A beta axon -> doral root of spinal cord -> dorsal column nuclei (medulla) -> VP nucleus (thalamus) -> primary somatosensory cortex (S1)
medial lemniscus pathway
pathway of sensory info from dorsal column in the medulla to the VP nucleus in the thalamus
where does sensory info cross midline and processing goes from ipsilateral to contralateral: dorsal column-medial lemniscal pathway
medial lemniscus pathway (medulla)
where does sensory info cross midline and processing goes from ipsilateral to contralateral: trigeminal touch pathway
pons
trigeminal touch pathway
tactial/ sensory information from above the neck/ face to S1
trigeminal touch pathway mechanism
trigeminal nerve -> principal sensory trigeminal nucleus in the pons -> contralateral shift in the VP nucleus (thalamus) -> S1
what area of the somatosensory cortex receives input
Area 3b (from thalmus)
proprioception
sense of limb position in space
where does area 3b send info
area 1, area 2 and areas 5 and 7
what info does area 1 recive
texture infow
what info does area 2 recive
shape and size information
what info does area 3a recive
input from muscle spindles from proprioception (limb position in space)
what area if the primary somatosensory cortex (S1)
area 3b
S1 orginization
cortical columns and digit representation
S1 digit representation
the little finger (D5) represented most medially and the thumb (D1) most laterally; each digt contains slow and fast adapting neurons
somatotopic map
a spatial arrangement of neurons that corresponds to body parts (larger body part, more neurons dedicating to information processing)
where does vestibular information cross the midline -> contralateral:
medial lemniscus (medulla)
main vestibular pathway
vestibular nerve, medial vestibular nucleus, VP nucleus (thalamus), vestibular cortex
