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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