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8/14/2019 OVCMT, NA- lec. 4
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Hierarchy of Response to SensationHierarchy of Response to Sensation
spinal cord- reflex
brainstem- complex motor
response (unconscious)
thalamus- crude
localisation of sensation,
typically pain
higher brain- preciselocalisation and
interpretation of sensation
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Classification of Sensory NeuronsClassification of Sensory Neurons
1 neuron- sensory receptorcord
2 neuron- cord thalamus
3 neuron- thalamus1
somatosensory cortex
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Classification of Sensory ReceptorsClassification of Sensory Receptors
free nerve endings- pain,
thermal
encapsulatednerve
endings- vibration,
pressure
separate cells- taste,
vision, hearing
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Classification by LocationClassification by Location
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Classification by StimulusClassification by Stimulus
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Graded Membrane PotentialsGraded Membrane Potentials
graded potentials are deviations from
the resting membrane potential
may be hyperpolarising(inhibitory) or
depolarising(excitatory)
both have variable amplitudes
dissipate over a short distance (1-2mm)
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Generator PotentialsGenerator Potentials
receptor is essentially the dendrite of the 1 sensory neuron stimulus is always excitatory stimuli- touch, proprioception, smell
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Receptor PotentialsReceptor Potentials
uses a synapse between receptor and 1 sensory neuron
stimulus may be excitatory or inhibitory
stimuli- taste, hearing, equilibrium, vision
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AdaptationAdaptation
refers to a decrease in the rate
of response to a stimulus over time
receptors may be rapidly adapting
or slowly adapting
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Somatic SensationsSomatic Sensations
1 neuron- sensory receptorcord
2 neuron- cord thalamus
3 neuron- thalamus1
somatosensory cortex
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Tactile SensationsTactile Sensations
corpuscle of touch-
discrim. touch, pressure,vibration
type 1 mechanorec-
discrim. touch, pressure
type 2 mechanorec-
crude touch hair root plexus- crude
touch
lamellated corpuscle-
pressure, vibration
free nerve ending-
nociception, itch, tickle
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Proprioception- Muscle Spindles & GTOsProprioception- Muscle Spindles & GTOs
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Embryological Basis of Deep Somatic PainEmbryological Basis of Deep Somatic Pain
31 somites correspond to
each spinal nerve
dermatome, myotome andsclerotome of a particularsomite are all innervated by
the same spinal nerve
this has implication for painlocalisation
pain from one structure
may register as comingfrom another that isinnervated by the samenerve
more common withdeeper structures
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Spinothalamic TractSpinothalamic Tract
1 somatic neuronscarrying pain signals enter
the cord and may travel
up or down several
segments
synapse with 2 sensory
neurons occurs in the
cord
2 neuron sendscollaterals to various sites
involved in reflex activity
and perception of pain
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Pain TransmissionPain Transmission
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Referred PainReferred Pain
proposed mechanism ofviscerosomatic / somatovisceral
reflex
irritation of one structure
facilitates its spinal nerve
innocuous sensory information
from other structures innervated
by the same spinal nerve may
then be perceived as painful
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Common Visceral Referral PatternsCommon Visceral Referral Patterns
irritation of surrounding peritoneum can involve additional spinal
nerves and therefore, change the original referral pattern
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Effects of PainEffects of Pain