Peripheral Somatosensory System Flashcards
What are the 4 main classes of somatosensory receptors?
- Tactile (innocuous) sensations
- Proprioception
- Thermal sensations
- Nociceptive (painful) sensations
What are tactile (innocuous) sensations mediated by?
Mediated by low threshold mechanoreceptors, Merkel, Ruffini, Meissner & Pacinian types
What receptors is proprioception mediated by?
Mediated by muscle (spindle) & joint (Golgi tendon) receptors, some inputs from cutaneous mechanoreceptors
What receptors are thermal sensations mediated by?
Mediated by thermoreceptors localised to discrete zones that exhibit hot & cold sensitivity
What receptors are nociceptive (painful) sensations mediated by?
Mediated by mechanical, thermal & polymodal nociceptors
What are the 5 cutaneous skin receptors?
- Meissner corpuscles
- Merkel’s
- Pacinian corpuscles
- Ruffini endings
- Nociceptors (free nerve endings)
Describe the morphology of ;
a) Meissner Corpuscles
b) Merkel’s
c) Pacinian Corpuscles
d) Ruffini endings
e) Nociceptors (free nerve endings)
a) looping axonal terminals that inter-twine supporting cells
b) dome structure atop axon terminals
c) sensory axon surrounded by fluid filled capsule, onion-shaped appearance
d) nerve terminals intertwined with collagen fibrils
e) free nerve endings that penetrate epithelial cells, no morphological specialisation
Receptive field of sensory receptors in skin;
What is a receptive field?
A region of space in which the presence of a stimulus will alter the firing of that neuron. In the somatosensory system, cutaneous receptive fields are regions of the skin or of internal organs. Some types of mechanoreceptors have large receptive fields, while others have smaller ones.
How can the receptive fields of cutaneous sensory receptors be tested?
Testing the receptive field of sensory receptors using a stimulus probe on the hand, and recording action potentials from a single median nerve axon.
Receptive fields for main types of cutaneous sensory receptors:
What is 2 point discrimination?
Two point discrimination is the ability to discern that two nearby objects touching the skin are truly two distinct points, not one. Two point discrimination thresholds vary across body surface
What is two point discrimination sensitivity correlated with?
Density of sensory innervation;
- Areas of high sensitivity – fingertips , face
- Areas of low sensitivity – torso, limbs
Summary of mechanoreceptor afferents
What do muscle spindle receptors respond to?
Muscle spindles provide sensory feedback from muscle fibres on body position and movement.
What do Golgi tendon organ receptors respond to?
Golgi tendon organs regulate muscle tension or force of contraction, and prevent muscle overloading.
