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Summary Somatic sensation
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Lecture 8 : Somatic sensation. Pain. Autonomic nervous systemSomatic sensory receptors:
Mechanoreceptors Thermoreceptors Chemoreceptors
- Transduce pressure/ stretch/ vibration/ tissue - measure T° - sense a variety of substance/ chemical
damage changes
- one or more unmyelinated axon brch ● = naked n endings supplied by
● skin ○ thin myelinated fb ● Chemical that excite :
- epidermis/ dermis/ subcutaneous tissue ■ cold receptors ○ bradykinin
■ peak at about ○ serotonin
○ hairy 30° ○ histamine
- hair-follicle receptors ○ unmyelinated fb
- Ruffini endings ■ warmth recpt ● stimulates ONLY slow pain,
- Merkel disks ■ peak at about after injury ⇒ inflammation
- Pacinian corpuscles 43° ○ axon reflex
- non-myelinated n ending - comfort zone = 30-36°
- at skin T° <17°, cold PAIN
○ hairless/ glabrous - at skin T° >45°, paradoxical cold
- Merkel disks
- Meissner corpuscles - Body T° = balance btw
- Pacinian corpuscles thermogenesis/ thermolysis
● Transduction
- nerve ending stimulation → deflection →
mechanical sensitive (stretch) cation channels →
AP triggered if threshold is attained → nerve
fibers of first order neuron → second order
neuron → third order neuron → Thalamus
- Somatic sensation = combination of at least 4 sensory modalities : touch/ T°/ body position
(proprioception)/ pain (nociception)
- Sensory unit = a single afferent neurons w all its receptor endings distributed in a receptive field
- high receptor density → small receptive field → greater acuity/ discriminative ability of the input
(fingertips)
- overlapping receptive fields → interactions btw sensory inputs and improves sensory
discrimination (arms& legs)
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