3 - Grover - Sensory Receptors Flashcards
Two Main Receptor Categories
Nonencapsulated
Encapsulated
Nonencapsulated Receptors
Bare terminals of myelinated and unmyelinated axons in contact with epithelial cells of skin
Ex:
Mechanical/thermal
Itch
Pain (nociceptors)
Merkel Endings
Disk-shaped terminal of myelinated axons
Contact merkel cells (vessicle holders), resembles synapse
Mechanoreceptors
Hair Follicle Receptors
Bending of hair distorys axon membrane opening stretch gated channels
Mechanoreceptors
Mechanoreceptors
Contain stretch gated cation channels
Pressure applied to skin is transmitted through capsule to the axon ending
Capsule alters transmission of pressure to sensory endings
Meissner Corpuscle
Stacked layers of Schwann cells
Located under epidermis of hairless (glabrous) skin
Mechanoreceptors
Light Pressure, Textures, Edges
Pacinian Corpuscle
Subcutaneous
Concentric layers of epithelial cells with fluid filled spaces
Single axon ending in center of corpuscle
mechanoreceptors
Ruffini Endings
Demis, subcutaneous, and connective tissue
Capsule contains collagen strands with intertwined axon endings
Stretching of skin applies tension to collagen–squeezing axon endings
Mechanoreceptors
What determines adaptation rate for encapsulated receptors?
Phsycial properties of capsule
How do Pacinian Corpuscles adapt?
Rapid Adaptation
Respond to sustained indentation with transient ctivity at onset and offset of stimulus–layers rearrange
Where will action potentials be generated?
(1, 2, 3, or 4)
2 and 4
None generated at 3
How do Pacinian Corpuscle’s best respond to changes?
Most sensitive to fast vibrations–fast change in pressure
“Event Detectors” - grasping an object in hand
Tuning Curve
Plots intensity vs frequency
Most sensitive at frequency where threshold intensity is lowest
Meissner Corpuscle Tuning?
Tuned to respond to lower frequencies of vibration than Pacinian Corpuscle
How do hair follicles adapt?
Rapid–stop firing when bent position is held
What are slowly adapting receptors?
Merkel Receptors (skin indentation)
Ruffini Receptor (stretching)
Free Nerve Endings (some can be rapid)
Low vs High Threshold Receptors
Free Nerve endings that function as mechanoreceptors are what type?
Examples?
Low = high sensitivity
High = low sensitivity
Free nerve endings that function as mechanoreceptors are high threshold
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Low Threshold = Meissner, Merkel, Ruffini, Pacinian, Hair Follicle
Where are Meissner’s corpuscles located?
Glabrous (hairless) skin
Hands, Feet (sensitive areas)
Receptive Field
What does a small receptive field size indicate?
Spatial location where a stimulus is effective for activating a single receptor cell
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Small receptive field = high spatial resolution
Where are receptive fields the smallest and largest?
What are the relative sizes for Meissner, Merkel, Ruffini, and Pacinian?
Smallest on digits of hands, largest on trunk and limbs
Large = Pacinian / Ruffini
Small = Meissner / Merkel
What type of receptors does Two-point Discrimination rely on?
Merkel/Meisner (small)
How do Merkel Cell receptors best function?
Signal weight, form, suface features
Best: Sustained response, steady pressure exerted by edges of objects held in hand
What is the most abundant receptor in the hand?
What are they best used for?
Meissner Corpuscle
Best used to detect tectures and edges as the hand is moved over surfaces
What does the combination of Merkel and Meissner receptors provide?
High spatial and high temporal resolution
