peripheral sensor receptors Flashcards
role of somatosensory system
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
basic sensory pathway
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
basic anatomy of PNS
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
Sensory receptor types (somatic afferents)
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
General functions of sensory receptors
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
Pacinian Corpuscle
Senses vibration:
Vibration impinges on PC, activates ion channels in neuron membrane, generator potentials, APs, AP propagate to sp cd
how is the intensity of the stimulus encoded
rate code: frequency of AP firing per neruon
Spatial summation code: number of neurons firing-> information to sp cd is summated together
Conduction velocity
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
Environment for receptor terminals
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
Slow vs fast adapting response
Slow: Sustained, unchanged stimulus, pressure, shape of object
Rapid: changing, impact, motion of object
spatial resolution
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
mechanoreceptors
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
Merkel disks
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)
Meisenners corpuscle
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
Ruffini corpuscles
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