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38 Cards in this Set
- Front
- Back
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Two main somatosensory pathways and course
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Dorsal Columns - travel to medulla ipsilaterally, synapse (at nucleus gracilis or cuneatus), decussate on way to thalamus, synapse and travel to primary somatosensory cortex
Spinothalamic Tract - synapses in outer layers of dorsal horn, crosses over anterior white commissure, ascends in STT (anterolateral system) then medial lemniscus to thalamus, synapses then goes to cortex |
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4 Somatosensory Perceptal modalities and which tract use
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Tactile - cutaneous, fine or discrimitive touch; for size, shape, texture of objects and movement across skin (DORSAL COLUMNS)
Proprioception - for sense of static position and movement (kinesthesia) of body; for manipulating and identifying objects; "deep" (DORSAL COLUMNS) Thermal - temperature (warm and cool) - (SPINOTHALAMIC) Pain - noxious damaging stimuli (SPINOTHALAMIC) |
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Free nerve endings are for
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Pain
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Two types of superficial nerve endings and two types of deep nerve endings and roles
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Superficial
Meissner's Corpuscle - encapsulated, layered - touch Merkel's Disc - unencapsulated - touch Deep Pacinian Corpuscles (encapsulated, layered) - vibration Ruffini's Endings (encapsulated, thin layer) - pressure |
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Key points of tactile or cutaneous receptors
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Meissner's and Merkel disc
Mechanoreceptors, complexes produce depolarizing receptor potentials to send APs (ion channels are NOT voltage or ligand gated but stretch gated) |
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Adaption role, slow vs rapid
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How long sensation is perceived
We want sensation of touch to come on and off (i.e. need to be desensitized, ex don't feel shirt after wearing) We need some to NOT adapt (i.e. holding something in hand) |
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2 Slowly adapting cutaneous receptors and role
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Encode stimulus form, pressure, shape and texture
Superficial Merkel ending/epithelial cell complex - small receptor fields for touch, static edges, shape, rough texture Deeper Ruffini ending - bigger receptor fields, for shape of GRASPED object, pressure, stretch of skin |
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2 Rapidly adapting cutaneous receptors
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Respond to onset, usually offset of stimulus
Superficial Meissner corpuscle - smaller receptor field for touch, edges, FLUTTER, TEXTURE as objects moved across skin, adjust grip Deeper Pacinian corpuscle - bigger receptor field, for vibration, movement of fine textured objects across skin |
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Which receptor for shape of grasped object? Adjustment of grip
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Shape - Deep Ruffini (slow adapt)
Adjust grip - superficial meissner (fast adapt) |
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Receptor field size receptor vs receptor, location on body
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Small RF - superficial Merkel (slow adapt) and superficial meissner (rapid adapt)
Big RF - deep ruffini (slow adapt) and deep pacinian (fast adapt) On fingers and face receptor fields are even smaller and with higher density to allow more discrimination and more cortical representation |
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2 pt discrimination
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Minimum distance needed for two separate touches to be applied AND sensed as two individual touches
Thumb, index finger and lip have VERY short distance whereas back, forearm and calf have very long distances |
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Dermatomes
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Skin layers formed by orderly arrangements of receptor fields to specific spinal nerves. Horizontal in trunk and vertical in limbs.
Maps have different magnifications of body parts |
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Proprioception and Receptors
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Detects stationary body position and movement (kinesthesia)
Receptors: encapsulated muscle spindles (muscle stretch response, in parallel, 1a afferent) and Golgi tendon organs (tension, in series, extrafusal, 1b afferent) Both carry information back to dorsal horn spinal cord |
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Classification of nerve fiber types
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Classified by size/AP speed
Fastest to slowest: A to C or I to IV I and II/alpha and beta - fastest - myelinated, large, proprioception and cutaneous information. Some preganglionic ANS III - small myelinated TEMP and some nocioceptors, D fibers IV - unmyelinated (C FIBERS) - SLOWEST - PAIN C is slower than D |
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Two main cortical entrant pathways for somatosensory
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Dorsal column/medial lemniscus - fine touch and proprioception
Anterolateral/spinothalamic tract - pain and temperature (also have many diffuse synapses in thalamus) |
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1st degree afferents
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involved in reflex. 1a from muscle stretch fibers
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Monosynaptic pathways
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Flexion/withdrawal when step on glass
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Spinocerebellar path
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Carries unconscious proprioception (eyes closed) to cerebellum
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Where do all somatosensory pathways have the primary neuron cell body
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Dorsal root ganglion
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Dermatomes Cervical, Thoracic, Lumbar and Sacral
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Cervical - Head behind ear up to scalp and down to upper pectoral. Down most of arm (except medial arm and forearm) and hand
Thoracic - Mid and lower chest, back, abdomen, stops around inguinal canal Lumber - All below inguinal canal area (except posterior leg and foreleg, lateral foreleg and lateral dorsum of foot) Sacral - genitals, posterior leg and foreleg, lateral foreleg and lateral dorsum of foot) |
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Dorsal Column/Medial Lemniscus Role, Path, neurons
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Role: Proprioception (conscious), vibration, fine touch
Path: Primary afferents enter dorsal horn, ascend ipsilaterally in fasiculus gracilis (legs) or fasciculus cuneatus (arms) to corresponding nuclei in rostral medulla. Synapses there. Second order neuron decussates there (legs ventral to arms) and ascends to VPL in thalamus. Synapses. (TTT sends head info to VPM near here). Both ascend via 3rd order to somatosensory cortex (in parietal) |
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Sensory information to the head path
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Touch receptors travel via trigeminal ganglion to main sensory nucleus of V (all but pain and temp which is spinal nucleus of V). Then cross over into medial lemniscus to put head on homonculus to VPM in thalamus
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Spinothalamic Tract Role, Path, neurons
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Role: Pain and temp
Path: 1st order neurons enter at dorsal root to synapse in superficial most layer of dorsal horn (marginal layer and substantia gelatinosa). decussate at anterior/ventral white commissure then ascend contralaterally to medulla (most lateral parts), synapse at VPL, 3rd order neurons leave to somatosensory cortex, thalamus, anterior cingulate and insular cortex Spinal nucleus of V provides info for face and is located just dorsal to STT in medulla |
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Locations 3rd order STT neurons project
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thalamus, parietal (somatosensory cortex), anterior cingulate, insular cortex
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Hemi-cord damage produces what sensation loss (touch vs pain/temp paths)
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IPSILATERAL touch loss about at the level of the damage (i.e. T7 damage loss at T7 dermatome)
CONTRALATERAL pain/temp loss about two levels down (b/c synapses immediately and decussates for a few levels) |
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Damage to rostral medulla produces what sensation loss (touch vs pain/temp paths)
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Deficits in touch and pain BOTH contralaterally (if after touch decussation/synapses)
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Somatosensory Thalamus nuclei and locations
Parallel processing |
Intralaminal nuclei - connections for pain and temp (dots along top of thalamus)
VPL (Lateral posterioventral are) - legs and trunk somatotropic. Medial lemniscus and STT VPM - face information - little more medial posterioventral area). TTT Parallel processing: VPL and VPM get mostly cutaneous input from medial lemniscus; but some from STT (pain) VPS gets proprioceptive VPI gets pain VPS (superior ventroposterior complex) - proprioceptive input VPI (inferior) - pain input along with intralaminar nuclei |
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Mammunculus of thalamus
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Head takes up most of VPM, body takes up of VPL to correllate to receptor field density (more sensation on face vs other areas)
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Somatosensory Cortex Brodmann's areas
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Primary cortex has Brodmann's areas 1, 2, 3a and 3b (maps within each of these areas too)
Cutaneous/superficial/fine touch information to Brodmann's area 1 and 3b - easiest to map b/c many small RFs, no temperature but good for discriminative touch Deeper proprioceptive information to Brodmann's areas 3a and 2 - get information from 1 and 3b too to start integrating and processing Goes brodmann's 4 (precentral gyrus [MOTOR] that becomes 3a, 3b, 1, 2 in post central gyrus then 5, 7 in posterior parietal complex |
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Homonculus on somatosensory cortex
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At top inside goes genitals, toes to trunk, then neck, and head (non trigeminal parts), down to shoulder to fingers, then face moving down to lower lip, then teeth, gums, jaw, then tongue and mastication muscles
SI revision puts genitals between feet and hands not most medial |
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Damage to areas 3b and 1 vs areas 2 and 3a
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3b and 1 - deficits in size, shape, texture discrimination
2 and 3a - proprioceptive loss |
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Secondary somatosensory cortex input, role, loss effect
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Input - 3b (cutaneous) and VPI (pain), and areas 5 and 7 (complex fxn, ex. BIL coordination of hands, reaching, grasping, integration)
Role: assimilation, cordination, and integration Loss: deficits in tactile learning, intermanual transfer |
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Columns of cortical areas
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Very distinct same RF location, submodality and selectivity areas that are functionally organized into 500 micrometer layers that are produced by intracortical synaptic connectivity
Thalamic fibers in and deep cortical and subcortical nuclei output goes I to VI from top to deep |
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Human Brain Plasticity after limb amputation
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For arm ex.
Face homonculus parts expand into unused arm area, this can lead to phantom limb Also for people using hands a lot, the area can expand pushing others out of way anyway without any loss Can occur in cortex OR both cortex and thalamus. Unknown mech, hippocampus mediated |
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Receptor Type, Layer, Encapsulation, Function, RF, and adaptation for
a) Meissner Corpuscle |
Superficial
Encapsulated Touch Small RF Rapid adapt |
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Receptor Type, Layer, Encapsulation, Function, RF, and adaptation for
b) Merkel Ending |
Superficial
Nonencapsulated Touch Small RF Slow adapting |
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Receptor Type, Layer, Encapsulation, Function, RF, and adaptation for
c) Ruffini Ending |
Deep
Encapsulated Pressure Big RF Slow adapting |
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Receptor Type, Layer, Encapsulation, Function, RF, and adaptation for
d) Pacinian Corpuscle |
Deep
Encapsulated Vibration Big RF Rapid adapt |
