PHYL2002 Study Guide - Final Guide: Collagen, Noxious Stimulus, Golgi Tendon Organ
Sensory Processing and Somatosensation
• Stimulus features encoded by sensory systems
o Modality → light, sound, touch, pain, heat, cold, smell, taste
o Spatial information → body location and location in external space
o Intensity → threshold and perceived strength above threshold
o Quality → colour, sharpness of pain, pitch of sound
• Modality
o 4 modalities
▪ Touch
▪ Proprioception
▪ Temperature
▪ Nociception
o Each sensory system selectively transduces or converts a
particular form of stimulus energy into electrical charges
o Made possible by specialized membrane proteins and ion channels
• Accessory structures
o Do not transduce stimulus energy
o Are not neurons or receptor cells
o Can be cellular or non-cellular
o Play an important role in determining how stimulus energy gets to
the transducing cells
• Types of potentials
o Receptor potential → proportional to stimulus
o Integrative action → transforms receptor potential to action
potential
o Action potential → all or none response
o Output signal → transmitter release from synaptic terminal
• Proprioceptive receptors
o Provide information about mechanical forces arising in body
o Give continuous information about position of limbs and other
body parts
o Muscle spindles
▪ Found in most skeletal muscle
▪ Respond to changes in length
▪ 4-8 specialized intrafusal muscle fibers → distributed
among extrafusal fibers → force-producing fibers
▪ Sensory afferents coupled around central part of intrafusal
muscle fibers
▪ Tension on intrafusal fibers activates mechanically gated
ion channels in nerve endings
▪ Innervation arises from
• Primary endings → group Ia afferents → rapidly
adapting responses to changes in muscle length
• Secondary endings → group II afferents → produce
sustained responses to constant muscle length
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