peripheral sensor receptors Flashcards

1
Q

role of somatosensory system

A

allows our body to sense our environment:
Touch- pressure against skin
Temperature
Proprioception: position of joints, muscles
Pain: tissue-damaging stimuli

Somatosensory (S1) system is unique: distributed throughout body skin, muscles, joints, bone

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2
Q

basic sensory pathway

A

stimulus-> sensory receptors -> spinal cord -> medulla/brainstem -> thalamus –> cortex

Sensory neurons are part of the PNS, with cell bodies in the DRG neurons innervate neck and below

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3
Q

basic anatomy of PNS

A

1 DRG at each spinal level, each at spinal cord
1 DRG has 10-20 k cell bodies
Length of axons can be up to 1 meter in leg

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4
Q

Sensory receptor types (somatic afferents)

A

Exteroreceptive: external word, skin (Mechanoreceptors non painful touch and vibration), (Thermoreceptors- warming and cooling), (Nociceptors- pain, themal)

Proprioceptive: muscle length tension, joint angle (muscle afferents- muscle spindles, golgi tendon organs, joint and tendon organs)

Interoceptive: internal organs, viceral afferents- localize sensation and pain poorly, baroreceptors, blood pressure, and pH

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5
Q

General functions of sensory receptors

A

Encode the stimulus: quality (what is it pain touch temo), intensity (light stroke, intense pressure), duration, and location

REceptive field: area in periphery where an adequate stimulus causes response in a neuron

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6
Q

Pacinian Corpuscle

A

Senses vibration:

Vibration impinges on PC, activates ion channels in neuron membrane, generator potentials, APs, AP propagate to sp cd

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7
Q

how is the intensity of the stimulus encoded

A

rate code: frequency of AP firing per neruon

Spatial summation code: number of neurons firing-> information to sp cd is summated together

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8
Q

Conduction velocity

A

AP speed

Axon diameter (larger diameter, faster)
More myelination= faster

Large myelination: Aa (muscle spindles and Golgi tendon organ), Ab (light touch, vibration, pressure)

Thin myelin: Ad (nociceptors- fast pain), cooling receptors

Unmeyleinated: C fibers (nociceptors- slow pain), warm receptors

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9
Q

Environment for receptor terminals

A

Skin: specialized endings-> tune sensory neuron to respond to specific physical stimuli

Charachteristics that determine sensitivity and function: location (superficial vs deep), and ending (Encapsulated vs non encapsulated

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10
Q

Slow vs fast adapting response

A

Slow: Sustained, unchanged stimulus, pressure, shape of object

Rapid: changing, impact, motion of object

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11
Q

spatial resolution

A

2 point discrimination threshold

Depends on: Receptive field size of each neuron and innervation density
Sensitive areas, high density of receptors, small size receptive fields

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12
Q

mechanoreceptors

A

touch pressure vibration
very sensitive to force (low threshold), dont respond to painful stimuli, silent without stimulation, myelinated axons fast conduction velocity
5 types: Merkel disks, meissners, ruffini, pacinian, hair follicle receptors

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13
Q

Merkel disks

A

superficial in epidermis, fine touch 2 pt discrimination, sense sustained pressure, Rec. field is several small touch domes, high density in finger pads, lips and mouth

Several disks are innervated by a single axon (myelinated), slow adapting

# of APs= indentation force 
this is the sharpest resolution of texture, surface of objects (braille)
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14
Q

Meisenners corpuscle

A

superficial in epidermis, fine 2 pt discrimination, sense abrupt changes in edges, bumps, corners of object

glabrous skin only
Receptive field: single spot, high density in finger tips, lips, mouth

Corpuscle encloses stack of schwann cells, axon is myelinated (Ab), rapidly adapting response on and off switch

of APs fired=# times skin is indented

Tells you to adjust grip and release when lifting objects

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15
Q

Ruffini corpuscles

A

deep in dermis, stretch of skin, sense gravity force against skin, receptive field: large and diffuse

Axon surrounds collagen fibrils, axon is myelinated, slowly adapting response to skin stretch skin

Determine shape of grasped objects, skin stretch around objects

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16
Q

Pacinian corpuscles

A

deep, detect tiny, high-frequency vibrations tuning fork, violin strings

Extremely sensitive, receptive field: very large diffuse, detect high frequency vibration

Large fluid filled capsule wrapped around bare nerve ending, capsule filters out sustained stimulus

Axon is myelinated, rapidly adapting response

17
Q

Hair follicle receptors

A

Movement of hairs, receptive field axon wraps around base of follicle. axon is myelinated, rapidly adapting

18
Q

Thermo receptors and nociceptors

A

have free nerve endings, thermoreceptors (slowest at 32C)- respond best to changes in skin temperature

19
Q

Cooling receptors

A

increase firing rate when skin is cooled, Ad fibers

Stop firing when skin is warmed very small nerve rec field, infrequent distribution

20
Q

Warming receptors

A

C fibers, increase firing when warm, stop when cold, small RF

21
Q

Nociceptors

A

pain receptors, that damage/threaten to damage tissue (almost all innervation is in tooth pulp+ cornea)

A-mechanonociceptors: Respond to intense force, sometimes intense heat, free nerve ending Ad, small RF, slow adapting- immediate pain

C polymodal nociceptors: many modes, intense force or high heat, chemicals C fiber, free nerve ending is accessible to inflammatory chemicals, slow adapting- slow pain burning, dull pain