peripheral sensor receptors

Question 1

role of somatosensory system

Answer 1

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

Question 2

basic sensory pathway

Answer 2

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

Question 3

basic anatomy of PNS

Answer 3

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

Question 4

Sensory receptor types (somatic afferents)

Answer 4

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

Question 5

General functions of sensory receptors

Answer 5

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

Question 6

Pacinian Corpuscle

Answer 6

Senses vibration:

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

Question 7

how is the intensity of the stimulus encoded

Answer 7

rate code: frequency of AP firing per neruon

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

Question 8

Conduction velocity

Answer 8

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

Question 9

Environment for receptor terminals

Answer 9

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

Question 10

Slow vs fast adapting response

Answer 10

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

Rapid: changing, impact, motion of object

Question 11

spatial resolution

Answer 11

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

Question 12

mechanoreceptors

Answer 12

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

Question 13

Merkel disks

Answer 13

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)

Question 14

Meisenners corpuscle

Answer 14

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

Question 15

Ruffini corpuscles

Answer 15

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

Question 16

Pacinian corpuscles

Answer 16

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

Question 17

Hair follicle receptors

Answer 17

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

Question 18

Thermo receptors and nociceptors

Answer 18

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

Question 19

Cooling receptors

Answer 19

increase firing rate when skin is cooled, Ad fibers

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

Question 20

Warming receptors

Answer 20

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

Question 21

Nociceptors

Answer 21

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