Somatosensory Flashcards
(101 cards)
1
Q
What does sensation entail?
A
- ability to transduce, encode and perceive info generated by external and internal stimuli
2
Q
What do specialized neurons (receptors) do?
A
- convert energy into neural signals or afferent sensory signals
3
Q
Afferent sensory signals activate central neurons capable of representing what aspects of the stimulus?
A
- qualitative (what it is) and quantitative (how strong it is) aspects
- sometimes location of stimulus in space
4
Q
What is an adequate stimulus?
A
- preferred or most sensitive stimulus modality (somatic, visual, auditory, electrosensory)
5
Q
What are polymodal receptors?
A
- naturally sensitive to more than one stimulus modality
6
Q
What are nociceptors?
A
- sensitive to extremely strong stimuli of various kinds (temp, pressure, chemicals)
- many are polymodal
7
Q
How do sensory neurons code stimulus intensity?
A
- through changes in AP frequency or graded membrane potential changes
- strong stimuli = high frequency or strong depolarization = lots NT release
8
Q
What is the dynamic range?
A
- range of intensities for which receptors can encode stimuli
9
Q
What is threshold detection?
A
- weakest stimulus that produces a response in a receptor 50% of the time
10
Q
What is saturation?
A
- top of the dynamic range; all available sensory transducing proteins have been stimulated or neuron can’t fire any faster
11
Q
What is the graphical relationship between stimulus intensity and AP frequency?
A
- relationship is linear and can be across a large range of intensities or small range of intensities
12
Q
How does a large change in stimulus effect AP frequency for a large range of intensities and how does this affect perception?
A
- large change in stimulus causes a small change in AP frequency
- results in large dynamic range but poor sensory discrimination
13
Q
How does a small change in stimulus affect AP frequency for a small range of intensities and how does this affect perception?
A
- small change in stimulus causes a large change in AP frequency
- small dynamic range and high sensory discrimination
14
Q
What is range fractionation?
A
- groups of receptors can work together to increase dynamic range without decreasing sensory discrimination
15
Q
What are the three broad classes of receptors that encode stimulus duration and how do they do it?
A
- Phasic
- Tonic non-adapting
- Tonic slow adapting
- encode stimulus duration in AP firing rates
16
Q
How do phasic receptors record stimulus duration?
A
- produce APs only at the beginning or end of the stimulus
- encode changes in stimulus
17
Q
How do tonic non-adapting receptors record stimulus duration?
A
- produce APs as long as the stimulus continues
18
Q
How do tonic slowly adapting receptors record stimulus duration?
A
- AP frequency decreases if stimulus intensity is maintained at the same level
19
Q
All sensory receptors have ______. Only receptors that generate APs have _______.
A
- receptor potential
- generator potential
20
Q
Somatosensory afferents convey information from the ____ to ____.
A
- skin surface to central circuits
21
Q
How does the ascending path start for “touch”?
A
- receptor endings
- mechanosensory afferent fiber
- dorsal root ganglion cells
- ipsilateral at start of ascending path
22
Q
How does the ascending path start for pain/temperature?
A
- receptor endings
- pain and temperature afferent fiber
- dorsal root ganglion cells
- contralateral projecting neuron carries info to contralateral spinal cord then ascends
23
Q
How does transduction in a mechanosensory afferent (Pacinian corpuscle) occur?
A
- deformation of the capsule leads to a stretching of the membrane afferent fiber, increasing the probability of opening mechanotransduction channels in the membrane
- opening these channels leads to depolarization which if sufficient generates an action potential
24
Q
For receptors that fire spikes what is detected for weak stimulus?
A
- nothing is “detected” if stimulus too weak to generate a spike
25
What is the receptive field?
- area of skin surface over which stimulation results in a significant change in AP rate
26
What is the two point discrimination threshold?
- a distance of separation of two stimuli where they can be identified as discrete
- dependent on the size of receptive fields
27
What are dermatomes?
- body surface mapped to segments of spinal cord
| - Cervical, thoracic, lumbar, sacral
28
What is adaptation?
- a property that derives from either the ion channel properties or the physical properties of the sensory "organ" in which the receptor is found
- slowly or rapidly adapting
29
Which somatosensory afferents are slowly adapting?
- merkel
| - ruffini
30
Which somatosensory afferents are rapidly adapting?
- pacinian corpuscle
| - meissner cell
31
Which somatosensory afferents have small receptor fields?
- merkel
| - meissner
32
Which somatosensory afferents have large receptor fields?
- pacinian
| - ruffini
33
What is the sensory function of merkels?
- form and texture perception
34
What is the sensory function of meissners?
- motion detection
| - grip control
35
What is the sensory function of pacinians?
- perception of distant events through transmitted vibrations
- tool use
36
What is the sensory function of ruffinis?
- tengential force
- hand shape
- motion direction
37
What are the receptive field areas of the somatosensory afferents?
- merkel: 9 mm2
- meissner: 22 mm2
- ruffini: 60 mm2
- pacinian: entire finger or hand
38
What is spatial acuity?
- distance needed to discriminate two points
39
What is the spatial acuity of the somatosensory afferents?
- merkel: 0.5 mm
- meissner: 3 mm
- ruffini: 7+ mm
- pacinian: 10+ mm
40
What is the peak sensitivity of the somatosensory afferents?
- ruffini: 0.5 Hz
- merkel: 5 Hz
- meissner: 50 Hz
- pacinian: 200 Hz
41
Based on the properties of each somatosensory afferent, which would be used to read Braille?
- merkel's disc
- small receptive field
- small spatial acuity
42
What do proprioceptors provide information about?
- the position of body parts
43
What are the two types of proprioceptors and what specific information do they provide?
- muscle spindle: length info
| - golgi tendon organ: tension info
44
What is the proprioceptive pathway from muscle spindles (lower body) to the brain?
1. muscle spindle afferents
2. ipsilateral sacral spinal cord
3. clark's nucleus (in lumbar spinal cord)
4. dorsal spinocerebellar tract to cerebellum and dorsal column nuclei
45
What is the proprioceptive pathway from muscle spindles (upper body) to the brain?
1. muscle spindle afferents
| 2. ipsilateral in cervical spinal cord to external cuneate nucleus
46
What is the mechanosensory pathway of face touch?
1. mechanosensory receptors on face
2. trigeminal ganglion*
2. principle nucleus of trigeminal complex
3. crosses to contralateral
4. travels up trogeminal lemniscus to ventral posterior medial nucleus of thalamus
5. primary somatic sensory cortex
47
What is a key feature of somatotopic organization?
- 4 parallel streams of processing
| - 3a, 3b, 1, 2
48
Parallel streams for different sub-modalities is a common theme and can be seen in which systems?
- somatotopic organization
| - same principle operates in higher order visual and auditory system
49
What are the lateral connections in the somatosensory cortex good for?
- make it easier to process in time
50
Where does somatosensory information from the ventral posterior complex (thalamus) travel to?
- to all areas of the primary somatosensory cortex but primarily to area 3b
51
Where does information from 3a go?
- to area 2
| - to secondary somatosensory cortex
52
Where does information from 3b go?
- to area 1
- to area 2
- to secondary somatosensory cortex
53
Where does information from area 1 go?
- to secondary somatosensory cortex
54
Where does information from area 2 go?
- to parietal areas 5, 7
| - to secondary somatosensory cortex
55
Where does information from the secondary somatosensory cortex go and what is it's purpose?
- to amygdala and hippocampus
| - possibly for learning
56
Where des information from the parietal areas 5, 7 go?
- to motor and premotor cortical areas
57
What is the primary function of area 3a?
- to process proprioceptors
58
What is the primary function of area 3b?
- to process low threshold cutaneous receptors
| - tactile sense
59
What is the primary function of area 1?
- to process low threshold cutaneous receptors
| - texture
60
What is the primary function of area 2?
- to process tactile and proprioceptors
| - size and shape
61
Different properties of touch sensation overlap in the ____ but are segregated ____.
- periphery
| - centrally
62
These columns of neurons are clustered and specialized for specific aspects of sensory modality from the ____ to ____.
- pia
| - ventricles
63
What reveals inherent property of cortical "plasticity"?
- denervation (damage to afferents)
- differential stimulation (dominant use of specific afferents)
- result: cortex has capacity to rewire
64
Experimentally, how can you record nociception?
- apply a heat stimulus to the hand and record from the afferent neuron further up
65
When applying an increasing heat stimulus, what response do you see in nociceptors and non-nociceptive thermoreceptors?
- nociceptor: no response at low temps, rapid increase in response/firing after 45 degrees
- non-nociceptive thermoreceptor: increase in response/firing until 45 degrees (still fires but no increase)
66
What is one way that the dynamic range can be reset?
adaptation
67
What kind of afferent axon do muscle spindles have?
- Ia, II
- thick and myelinated
- fast
68
What kind of afferent axon do touch (merkel, meissner, pacinian, and ruffini cells) have?
- A-beta
- thick and myelinated
- fairly fast
69
What type of afferent axons do nociception/temp have?
- A-delta
- thin, myelinated
- fairly slow
70
What type of afferent axons do nociceptive/temp/itch have?
- C
- thin, no myelination
- slow
71
What two sensations can pain be separated into and which types of axons is this due to?
- first sharp pain (A-delta fiber)
| - second duller, diffused pain (C fiber - unmyelinated)
72
What receptor is activated by capsaicin? What else is this receptor activated by?
- VR-1 receptor (TRPV-1)
| - also activated by heat greater than 43 degrees
73
What kind of receptor is VR-1?
- a vanilloid receptor
| - polymodal nociceptor
74
What are endo vanilloids?
- natural ligands that are produced by peripheral tissues in response to injury
75
Why are some other types of receptors not sensitive to capsaicin?
- they have even higher threshold to heat >45 degrees
| - for example VRL-1
76
Where do primary afferents in the dorsal root ganglia send their axons?
- send axons via dorsal roots to terminate in the dorsal horn of the spinal cord
77
Where do second-order neurons in the dorsal horn send their axons?
- send axons across midline to ascend to higher levels in the anterolateral column of the spinal cord
78
Where do C fiber afferents terminate?
- Rexed's laminae I and II of dorsal horn
79
Where do A-delta afferents terminate?
- laminae I and V
80
The second order neurons in which laminae cross the midline and ascend?
I and V
81
If there was a lesion of the dorsal column and anterolateral column in the left side, what effects on sensation would be experienced?
- from the left lower body: lesioned mechanoreceptive afferents resulting in reduced sensation of two-point discrimination, vibration, and proprioception
- from the right lower body: lesioned nociceptive afferents resulting in reduced sensation of temperature and pain
82
What is the pathway from the anterolateral system to determine where a touch is coming from (sensory discriminative)?
1. Anterolateral system
2 ventral posterior nucleus
3. somatosensory cortex (S1 S2)
83
Were does the anterolateral system project to determine if a stimulus is unpleasant/painful?
- amygdala
- hypothalamus
- periaquiductal grey
- superior colliculus
- reticular formation
84
Where does the anterolateral system project for affective-motivational processing?
1. midline thalamic nuclei
| 2. anterior cingulate cortex and insular cortex
85
What is visceral pain information relayed by?
- interneurons that are also used to relay surface pain information
86
What is the principle path for visceral pain?
1. somatosensory afferent
2. dorsal root ganglion cells
3. spinal cord (midline)
4. dorsal column nuclei in medulla (contralateral)
5. Ventral posterior nuclear complex of thalamus
6. insular cortex
87
What is hyperalgesia?
- peripheral sensitization of pain responses
| - ex. increased sensitivity to pain after sunburn
88
What is allodynia?
- pain induced by normally innocuous stimulus
89
Which substances augment receptor function or reduce threshold for firing?
- H+, 5-HT, Bradykinin, ATP, Prostaglandin, histamine
90
How does aspirin and ibuprofin cause pain relief?
- they reduce prostaglandin synthesis by inhibiting COX
91
What do nociceptors do to contribute to swelling?
- release peptides
92
What is neuropathic pain and why does it occur?
- sometimes spontaneous
- occurs when the afferent fibres or central patways for pain are damaged
- AIDs, diabetes, shingles, MS, and stroke or amputation
93
Why is neuropathic pain hard to treat?
- it is unresponsive to conventional analgesics
| - since analgesics target initial peripheral or spinal points of pain generation/reception
94
Why is neuropathic pain a result of amputation?
- the pain/itching/tingling is generated centrally due to rewiring of circuits in the absense of sensory input from the amputated limb
95
What are some mutations that cause pain insensitivity?
- PRDM12
- NTKR1
- both affect development of nociceptive neurons
96
What is a mutation that causes pain sensitivity?
- SCN9A - Nav1.7
- "hell gene"
- neuropathic pain/burning brought on by mild heat or exercise
97
What is the gate theory of pain?
- the stimulation of mechanoreceptors stimulate an interneuron which inhibits the dorsal horn projection neuron that nociceptors stimulate
98
Where does descending modulation of ascending pain pathways come from?
- raphe nuclei: stimulate interneuron that inhibits nociceptor axon terminal
- locus coeruleus: inhibits nociceptor axon terminal and inhibits dorsal projection neuron
99
What is PAG stimulations affect on pain?
- PAG stimulation is analgesic through actions on a number of brainstem nuclei
100
How can PAG be stimulated?
- opiate receptors are present on PAG
| - electrical stimulation
101
What can block the analgesic effect of PAG?
CB1 blockers
