PSL300H1 Study Guide - Midterm Guide: Stimulus Modality, Nociception, Somatosensory System
ProfessorDoug Mac Kay
SPECIAL AND SOMATIC SENSES
5 special senses: vision, hearing, equilibrium, taste and smell
4 somatic sense: touch, temperature, proprioception and nocioception
unconscious to visceral data: blood pressure, blood-glucose concentration, internal
Receptors and Neurons
every sensory system begins w/ receptors: cells, not necessarily neurons, convert
stimulus energy into electrical signals. → transduction
receptor convert stimulus E. if receptor = neuron, then fires AP. if not neuron = can
release NT to excite neuron.
***each receptor → adequate stimulus: form of E to which it's most responsive. but
can also respond to other sensory modalities.***
receptors classed according to adequate stimuli:
chemoreceptors chemical ligands. monitor lvls of O, pH and organic molecules
mechanoreceptors mechanical E: pressure, vibration, gravity, acceleration, sound
simple receptors: neurons w/ free nerve endings. sense temp. + noxiouos stimuli.
myelinated or unmyelinated axons.
complex neural receptors: neurons w/ endings in many layer connective tissue
envelope. when pressure applied → capsule compressed → inside of capsule
most special sense receptors = cells that release NT onto sensory neurons.
stimulus → specialized cell (ex. hair cell) → synapses on nerve → responds and
transduction involves ion channels on receptor's membrane:
stim opens/closes ion channels directly/via second messenger. usually channel
opened→ Na+ or other cation enters into cell → depolarization. some cases → K+
leaves cell → hyperpolarization. in vision → light closes cation channels =
threshold → for every receptor. minimal stimulus that activates it → producing AP.
some photoreceptors activated by a single photon. chemoreceptors activated by
single odurant. perceptual threshold: minimal stimulus that will make you aware of a
sensation. depends on attention.
sensory systems involve series of neurons: first neuron = primary (first order)
sensory neuron → synapse onto secondary sensory neurons → tertiary sensory
at each stage → presynaptic neurons = input to one or few postsynaptic neurons →
convergence, allowing secondary, tertiary and higher neurons to combine info from
stimulus modality: sensory systems indicate modality by labeled lines (ex. activity on
neurons in visual pathway in interpreted by CNS to mean light)
complex neural receptors
primary sensory neuron
secondary sensory neuron
tertiary sensory neuron
INTRO TO SENSES