Flashcards in Somatosensory system Deck (79)
What does the somatosensory system mediate?
Fine discriminatory touch (light touch, pressure, vibration, flutter)
What are the 3 broad categories of the somatosensory system?
What is the exteroceptive division?
Registers information from the surface of the body by numerous receptor types
What is the propceptive division?
Monitors posture and movement with sensors in the muscles, tendons and joints
What is the enteroceptive division?
Reports upon the internal state of the body and is closely related to autonomic function
What are the neurones involved in the somatosensory pathway?
1st order (PNS): cell body location in the dorsal root ganglion or cranial ganglion
2nd order (CNS): cell body location in dorsal horn of spinal cord or brainstem nuclei
3rd order (CNS): cell body in thalamic nuclei
What will stimulus (mechanical, thermal or chemical) do to ion channels?
Opens cation selective ion channels in the peripheral terminal of primary sensory afferents eliciting a depolarizing receptor potential
What determines the amplitude of the receptor potential
What are important properties of sensory units?
Modality - what type of stimulus excites the sensory receptor
Threshold - what intensity of the stimulus is required for excitation of the sensory receptor
Adaptation rate - does the sensory unit discharge action potentials continuously during the stimulus or does it respond preferentially to a changing stimulus
Conduction velocity - how rapidly does the sensory unit conduct action potentials along its axon
Site and extent of peripheral termination
What is the sensory unit for touch, pressure and vibration modality?
What is the sensory unit for proprioception modality?
Joint and muscle mechanoreceptord
What is the sensory unit for temperature modality?
Cold and warm thermoreceptors
What is the sensory unit for pain modality?
Mechanical, thermal and polymodal nociceptors
What is the sensory unit for itch modality?
What does threshold relate to?
The intensity of a stimulus required to excite a sensory unit
What is a low threshold unir?
Responds to low intensity (non-damaging) stimuli
What is a low threshold mechanoreceptor?
Mediates fine discriminatory touch
What is a low threshold thermoreceptor?
Mediates cold through to hot
What is an example of a high threshold unit?
Nociceptors; responds to high (noxious) but not low intensity stimuli
What is a high threshold mechanoreceptor?
Mechanical nociceptors that respond to high intensity mechanical stimuli
What is a thermal nociceptor?
Responds to extreme degrees of heat ; >45 or <10
What do chemical nociceptors respond to?
Substances in tissue;
What will polymodal nociceptors respond to?
At least 2 of:
High threshold mechanoreceptors
What is adaptation in the somatosensory context?
Feature of sensory units that determines whether they change their firing rate only in response to a stimulus of changing intensity, or fire continuously throughout a constant stimulus
What does a slowly adapting/ tonic response convey?
Continuous information to CNS while terminal deformed
Provides information about position, degree of stretch or force e.g. stretch receptors
What does a fast adapting/ dynamic response convey?
Detects changes in stimulus strength (rate of movement)
Number of impulses is proportional to the rate change of stimulus
Includes muscle spindles, hair follicle afferents
What does a very fast adapting/ very dynamic response convey?
Responds only to very fast movement, such as rapid vibration
E.g. pacinian corpuscle
What differentiates the different types of primary sensory afferent fibres?
Extent of myelination
Assoc sensory receptor
What are the different types of primary sensory afferent fibres?
Alpha - group 1
Beta - group 2
Delta - group 3
C - group 4