Flashcards in Somatosensory system Deck (79)
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1
What does the somatosensory system mediate?
Fine discriminatory touch (light touch, pressure, vibration, flutter)
Stretch (mechanosensation)
Proprioception
Thermosensation
Nociception (pain)
Pruriception
2
What are the 3 broad categories of the somatosensory system?
Exteroceptive division
Proprioceptive
Enteroceptive
3
What is the exteroceptive division?
Registers information from the surface of the body by numerous receptor types
4
What is the propceptive division?
Monitors posture and movement with sensors in the muscles, tendons and joints
5
What is the enteroceptive division?
Reports upon the internal state of the body and is closely related to autonomic function
6
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
7
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
8
What determines the amplitude of the receptor potential
Stimulus intensity
9
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
10
What is the sensory unit for touch, pressure and vibration modality?
Skin mechanoreceptors
11
What is the sensory unit for proprioception modality?
Joint and muscle mechanoreceptord
12
What is the sensory unit for temperature modality?
Cold and warm thermoreceptors
13
What is the sensory unit for pain modality?
Mechanical, thermal and polymodal nociceptors
14
What is the sensory unit for itch modality?
Itch receptors
15
What does threshold relate to?
The intensity of a stimulus required to excite a sensory unit
16
What is a low threshold unir?
Responds to low intensity (non-damaging) stimuli
17
What is a low threshold mechanoreceptor?
Mediates fine discriminatory touch
18
What is a low threshold thermoreceptor?
Mediates cold through to hot
19
What is an example of a high threshold unit?
Nociceptors; responds to high (noxious) but not low intensity stimuli
20
What is a high threshold mechanoreceptor?
Mechanical nociceptors that respond to high intensity mechanical stimuli
21
What is a thermal nociceptor?
Responds to extreme degrees of heat ; >45 or <10
22
What do chemical nociceptors respond to?
Substances in tissue;
Inflammation
Prostaglandins
Bradykinin
Serotonin
Histamine
K+
H+ ATP
23
What will polymodal nociceptors respond to?
At least 2 of:
High threshold mechanoreceptors
Thermal nociceptors
Chemical nocicpeotrs
24
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
25
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
26
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
27
What does a very fast adapting/ very dynamic response convey?
Responds only to very fast movement, such as rapid vibration
E.g. pacinian corpuscle
28
What differentiates the different types of primary sensory afferent fibres?
Axon diameter
Extent of myelination
Conduction velocity
Assoc sensory receptor
29
What are the different types of primary sensory afferent fibres?
Alpha - group 1
Beta - group 2
Delta - group 3
C - group 4
30
