Sensory Receptor mechanisms and somatic sensations Flashcards
survival depends on what
sensation and perception
what is sensation
the ability to feel something physically, especially by touching
what is perception
Perception is the conscious interpretation of those stimuli. Awareness of the elements of environment through physical sensation
what is the modality of sensation
each of the principal types of sensation that we can experience (touch, pain, sight, sound, etc.)
what is the labeled line principle
nerve fibers transmit only impulses
how do different nerve fibers transmit different modalities of sensations
type of sensation felt when a nerve fiber is stimulated (e.g. pain, touch, sight, sound) is determined by the receptor activated and termination point in the cns i.e unique neurons in the CNS capable of decoding specific modalities
what is mechanoreceptive sensation stimulated by
by mechanical displacement
what are the types of mechanoreceptive sensations
-tactile sensation (skin)
-proprioceptive (position) sensation (m. and joints)
what are examples of tactile sensation (skin)
touch, pressure, vibration, tickle/itch
what are examples of proprioceptive (position) sensation (m. and joints)
-muscle stretch sense (e.g muscle is contracted or relaxed)
-joint position sense
what detects nociceptive sensation
detect pain (tissue damage)
what detects thermoreceptive sensation
detect heat and cold, change in temperature
somatosensory receptors are classified based on what
the type of sensation they detect
what do mechanoreceptors detect
tissue deformation
what are the 2 types of rmechanoreceptors
skin tactile receptors
muscle receptors
give examples of skin tactile receptors (4)
-free nerve endings
-expanded tip receptors (e.g. Merkel’s dics)
-encapsulated endings (e.g. Meissner’s corpuscle, Pacinian corpuscle, Krause’s corpuscle, Rufini’s end organ…)
-hair end-organ
give examples of muscle receptors
-muscle spindles
-golgi tendon receptors
give examples of thermoreceptors
specialized free nerve endings:
cold receptors and warm receptors
give examples of nociceptors
pain receptors; specialized free nerve endings
what is a receptor potential
when a stimulus excites a receptor, the change in the mem electrical pot of the receptor is called a receptor potential
the stimulation of the receptor causes what
opening of ion channels (Na+, K+) and the depolarization of the receptor mem
what are the mechanisms of stimulation of the receptor
-mechanical deformation which stretches the mem (e.g mechanoreceptors)
-application of chemicals (e.g. taste, smell)
-change in temperature (e.g thermoreceptors)
-tissue damage (e.g pain receptors)
increasing the intensity of the stimulus will lead to a greater ___ ____and eventually, to a greater AP ____
receptor potential
frequency
define the adaptation of receptors
when a continuous sensory stimulus is applied, the receptor responds at a high impulse rate at first then at a progressively slower rate until finally the rate of APs decreases to very few or to none at all
the speed of adaptation varies with what
the types of receptors
what are some rapidly adapting receptors
pacinian corpuscle
hair receptors
what are some slowly adapting receptors
muscle spindles
joint receptors
rapidly adapting receptors are best at detecting _____, while slowly adapting receptors are capable of detecting a ____
rapidly changing signals
long continuous signals
what is the receptive field of the neuron
is the area on a surface, like the skin that a stimulus must reach to activate that neuron
the area of each receptor field varies with what
varies inversely with the density of receptors in the region
give an example of low number of cutaneous receptors with receptive fields that are large in size
back and legs
give an example of large number of cutaneous receptors with receptive fields that are small in size
fingertips and ending of tongue
what is a method that is used to measure tactile acuity in rehab
two-point discrimination
what is two point discrimination
minimal distance at which 2 points of touch can be perceived as separate (measure of distance btw receptive fields)
what is indication of tactile acuity
if distance btw 2 points is less than minimum distance, only 1 point will be felt
describe the neuro mechanism when only one signal goes to the brain
when many primary sensory neurons converge onto a single secondary neuron= large receptive field and the 2 stimuli will be perceived as a single point
describe the neuro mechanism when two signal goes to the brain
when fewer neurons converge, secondary receptive fields are smaller. The 2 stimuli activate separate pathways and are perceived as distinct stimuli
what tactile receptors and sensations are deep
pacinian corspuscle
ruffini organ
what tactile receptors and sensations are superficial
merkel disks and free nerve endings
what are the six different types of tactile receptors
free nerve endings, meissner’s corpuscules, merkel’s discs, hair end-organ, ruffini’s end-organ, pacinian corspuscles
describe free nerve endings
-found everywhere in the skin (superficial layers) and in many other tissues
-detects crude touch and pressure sensations
-specialized free nerve endings (e.g thermoreceptors,pain)
-slow adapting fibers
describe Meissner’s corpuscles
-elongated encapsulated nerve endings of a large myelinated sensory nerve fiber
-located in the superficial layers of the skin (nonhair part)
-detect fine touch (discriminative, mvt of the objects on the surface of the skin) and low frequency vibration
-rapidly adapting receptors
describe Merkel’s discs
-located in the superficial layers of the skin (epidermis)
-detect touch and light pressure
-slowly adapting fibers
describe hair end-organ (free nerve ending of hair root)
-in contact with the root of the skin hair
-detects hair mvt
-rapidly adapting receptors
describe ruffini’s end-organ
-encapsulated endings located in the deeper layers of the skin
-detects heavy and prolongued touch and pressure signals
-slowly adapting fibers
describe pacinian corpuscles
-encapsulated endings located in the deeper layers of the skin
-detect tissue vibration or other rapid changes in the mechanical state of the tissues (deep pressure, stratch)
-rapidly adapting receptors
when do pain sensations occur and why is it considered a protective mechanism
occurs whenever tissue is being damaged
because it brings awareness of tissue damage + can prevent further damages to the body
what are the 2 types of pain and describe each
fast pain (prickling pain) ; felt within 0.1 sec of the stimulus and is sharp in character
slow pain(aching pain): begins after a second or more and is throbbing or aching in nature
what are pain receptors and where are they found widespread
specialized free nerve endings
widespread in many locations of the body:
-superficials layers of the skin
-internal tissues
-arterial walls
-bones, joints and m. surfaces
what can pain receptors be stimulated by
mechanical (stretch, tissue damage)
thermal (>± 45°C)
chemical (e.g lactic acid)
what type of adapting receptors are pain receptors
adapt slowly to the stimulus; catergory of very slow adapting receptors (i.e more stimulus, more response)
what are thermoreceptors
free nerve endings that code changes in temperature, primarily within the innocuous range
temperatures likely to damage an organism are sensed by ____ that may respond to ____ and ___
nociceptors
noxious cold and noxious heat
what is the sense of temperature
comparision of the signals from each of the 2 types of thermoreceptors
thermoreceptors respond to temperature changes with a ___ component ( ___ adapting) followed by a ____ component ( ___ adapting)
phasic rapidly
tonic slowly
what high discrimination receptors transmit signals thru type A-beta myelinated nerve fibers at 30-70 m/sec (e.g tactile sensations)
meissner’s corpuscles, merkel’s discs, hair receptors, Pacinian corpuscles, and ruffini’s end organs
what low discrimination receptors transmit signals thru type A-delta nerve fibers at 6-30 m/sec (fast pain, cold sensation) or thru type C unmyelinated fibers at 0.5-2 m/sec (slow pain, cold, warmth, crude touch & pressure sensations)
free nerve endings
sensory info enters the ___ thru the ____ of the ____
spinal cord
dorsal roots of the spinal nerves
what are the 2 pathways for sensory info
dorsal column-medial lemniscal system
antero-lateral system
sensory info in both pathways ____ (i.e cross the midline to the contralateral side)
decussate
where is sensory stimulation in one side of the body transmitted to
the brain hemisphere on the opposite side
_____ make the relay to transmit sensory stimulation from the receptor to the final point of the ____
3 order neurons
cerebral cortex
describe the dorsal column-medial lemniscal pathway (what sensations does it transmit, where does the signal originate form, what types of n. fibers, how does it transmit information)
-transmits tactile sensation (touch, vibration, fine pressure) and proprioceptive sensations (e.g limb position)
-signals originates from tactile receptors (e.g meissner’s, pacinian, ruffini’s, Merkel’s ) or proprioceptive receptors (eg muscle spindles)
-uses large myelinated nerve fibers for fast signal transmission
-transmits info w a high degree of spatial fidelity
what are the 3 order neurons in the dorsal column-medial lemniscal pathway
-1st order neuron synapse with 2nd order neurons at the dorsal column nucleus (medulla)
-2nd order neurons decussate at the level of the medulla (brainstem)
-2nd order neurons synapse with the 3rd order neurons in the thalamus
-3rd order neurons transmit indfo to the primary somatosensory cortex
describe the antero-lateral pathway (what sensations does it transmit, where does the signal originate form, what types of n. fibers, what degree of spatial orientation)
-transmits a broad spectrum of modalities (e.g. pain, thermal sensations, crude touch & pressure, tickle & itch, sexual sensations)
-signal originates from free nerve endings receptors (e.g. pain receptors, thermal receptors…)
-uses smaller myelinated (A-delta) and unmyelinated (C) fibers for slow transmission
-low degree of spatial orientation
what are the 3 order neurons for the antero-lateral pathways
-1st order neuron synapse with 2nd order neurons in the substantia gelatinosa (spinal cord)
-2nd order neurons decussate at the level of the spinal cord
-2nd order neurons synapse with the 3rd order neurons in the thalamus
-3rd order neurons transmit info to the primary somatosensory cortex
fast pain fibers are transmitted in the _____
slow pain fibers are transmitted in the _____
neospinothalamic tract (A delta fibers)
paleospinothalamic tract (C fibers)
describe the neospinothalamic tract
-fast pain fibers terminate at the somatosensory cortex
-fast-sharp pain can be highly localized if it is stimulataneously activated with tactile sensations (pain must stimulate other tactile receptors)
describe the paleospinothalamic tract
-slow pain fibers terminate at the thalamus level or below
-slow pain is poorly localized
describe the primary somatosensory cortex (located?, where does each side of the cortex recieve info, how is it organized)
-located in the post-central gyrus (in parietal lobe)
-highly organized with distinct spatial orientation (i.e. each area of the cortex is devoted to a given body region, map of the sensory representation)
-each side of the cortex receives info from the opposite side of the body
somatosensory area I is : “ so much more ___ and so much more ___ than ____ that in popular usage the tem somatosensory cortex almost always means ___”
extensive
important
area II
area I
describe Penfield’s Homunculus
unequal representation of the body:
-lips have a greater area of representation followed by the face, thumb, fingers, hand
-trunk and lower body have the least area
what is the name of the famous mtl neurosurgeon who did the mapping of the primary somatosensory cortex
Dr Wilder Penfield
the more a region of the body has receptors…
the better it’s area of representation in the somatosensory cortex
describe the cellular organization of the primary somatosensory cortex
-composed of 6 cellular layers
-within the layers the neurons are also arranged in vertical columns
-each column serves a specific sensory modality (ex: stretch, pressure, touch)
-different columns interact btw each other which allows the beginning of the analysis of the meaning of the sensory signals
t/f the degree to which we react to pain varies tremendously from person to person
true
how is the brain able to suppress inputs of pain signals
thru the analgesia system
describe the pain suppression (analgesia) system in the brain and spinal cord
1-pain source
2-pain messages move thru peripheral nerves and up the spinal cord
3-your brain interprets the messages as pain, including its location, intensity and nature (aching, burning, stinging)
4-your brain sends pain-suppressing chemicals to the pain source and triggers other responses
what is part of the analgesia sys
1- the periaqueductal gray of the mesencephalon and upper pons
2- the raphe magnus nucleus located in the lower pons
3- the pain inhibitory complex located in the dorsal horns of the spinal cord
what is the main NT involved in the analgesia sys
enkephalin (released at the 3 levels on figure)
why is pain in internal organs often sensed on the surface of the body
bc of reffered pain
describe the theory on reffered pain
nociceptors from several locations converge on a single ascending tract in the spinal cord. Pain signals from the skin are more common than pain from internal organs, and the brain associates activation of the pathway with pain on the skin
