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What is the somatosensory system?

Allows us to sense: touch, temperature, propioception, pain


What are teh exteroreceptive sense?

mechanoreceptor: touch
thermoreceptors: warming and cooling
nociceptors: sharp and burning pain


Receptive field?

area in the periphery where application of an adequate stimulus causes response


Stumulus transduction?

At peripheral terminal stimulus activates receptors and ion channels; generates receptor potential; receptor potential strong enough generates action potentials


Intensity of stimulus is encoded by what?

Each neuron through frate code of frequency
in many neurons through number of neurons firing the spatial summation code


what are the different types of nerve fibers?

Aalpha, Abeta (both are large and mylenaited)
Adelta (thin and myelinated)
C fibers (unmyelinated)


Glaborous skin specializes in what?

Has severl different types of specilalized sensor receptor


Spatial resolution depends on what?

receptive field size and innervation density


What are mechanoreceptors?

mediate tactile/touch sensation, very sensitive to force(low threshold),have myelinated axons, superficial receptors in border between epidermis and dermis


What are merkel disks?

type of mechanoreceptorss: Responsible for fine touch, 2point discrimination, receptive field, multiple small spots, several disks for one axon, slowly adapting response encodes amount of force


What are Meissner's corpuscles?

[mechanoreceptors] Fine touch, 2-point discrimination. Sense abrupt changes in edges. Help adjust grip. Receptive field: single spot. Corpuscle encloses a stack of flattened epithelial cells. Rapidly adapting responses encodes offset of skin indentation.


What are Ruffini Endings?

Sense stretch of skin, help determined shape of grasp objects. Receptive field: large and diffuse. Ruffini ending is encapsulated. Slowl adapting resposne sto stretching skin


What are pacinian corpsucles?

[mechanoreceptors] Respond to high frequency vibration; MOst sensitve mechanoreceptor even distribution throughout skin.
Receptive field: large and diffuse
Fluid filled capsule wrapped around bare nerve endings filters out sustained stimuli
Rapidly adapting response


What are hair follicle receptors?

[mechanoreceptors], respond tot movement of hairs, receptive field is around base of hair. Bare axon wraps around base of hair follicle; rapidly adapting response encodes velocity of hair


Spatial summation code is what?

OVerall picture in brain is due to sum of information provided by different active and silent fibers


Thermoreceptors are what?

Encode skin temp (warming, cooling). Discharge continuously (steady rate) @ normal skin temp


What are cooling receptors?

[thermoreceptor] increase firing when skin is cooled. Free nerve endings with myelinated axons. Small receptive fields; infrequent distribution


What are warming receptors?

increase firing rate when skin is warmed aboved 32 C. Stop firing when skin is cooled. Free nerve endings with unmyelinated axons


What are nociceptors?

Respond to stimuli that damage or threaten to damage tissue; 70% of DRG are nociceptors and provide almost all innervation to tooth pulp and cornea


What is Mechanonociceptors?

[nociceptor] Adelta axon
Respond to intense mechanical force, sometimes intense heat
free nerve ending
small receptive fields
slowly adapting response
mediate fast initial pain, sharp pricking, easy to localize


What are polymodal nociceptors?

Respond to intesne mechancial force, high heat, noxious chemicals
free nerve endings,
small receptive fields
slowly adapting response
mediate slow aching, "burning" pain


What does the DC/ML transmit sensations of?

light touch


What are teh components of the DC/ML system?

3 neurons
1st in sensory ganglion
2nd in spinal cord and/or braiinstem
3rd in thalamus


In the DC/ML system waht is the 1st neurons responsibility?

Peripheral process transmits info from mechanoreceptor
cell body i DRG
Central process transmits info via dorsal root and ascends within ipsilateral dorsal colum
terminates in dorsal column nuclei


What is the role of the 2nd Nueron in the DC/ML system?

Cell body in ucleus gracillis or nucleus cuneatus
terminates in ventral posterior lateral nucleus of thalamus
axon decussates to contralat side and ascends in medial lemniscus


What is the role of the 3rd neuron in the DC/ML system?

Cell body in VPL of thalamus
Axons pass through posterior limb of termial capsule
Terminates in SI cortex (postcentral gyrus, primary somatosensory cortex)


What does the faciculus gracilis contain?

Located medially, contains axons from below T7


What does the faciculus cuneatus contain?

Axons from about T7 in DC/ML system and it's located laterally


What is the role of Somatotopy in the 1st neuron of the DC/ML system?

Sacral dermatomes located medially, and each level on the way up located progressively laterally helps perserve info about location and nature of stim


What occurs in a unilateral spinal cord leasion in relation to DC/ML system?

Loss of light touch, pressure, vibration and propioception on ipsilateral side below lesion