Week 8 Flashcards

(68 cards)

1
Q

Somatosensory system unique in 2 ways

A
  1. receptor organ is the skin-largest sensory organ in body

2. sensations produced are quite varied

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2
Q

4 distinct somatic sensations

A
  1. fine touch
  2. proprioception sensations
  3. pain
  4. temperature
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3
Q

pain receptor sub-types (nociceptors)

A
  1. mechanical
  2. thermal
  3. polymodal (combo of mechanical and thermal)
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4
Q

Important shared nociceptor quality of neurons

A

all have bare nerve endings

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5
Q

Receptor types are different in:

A
  1. morphology of peripheral ending
  2. sensitivity to stimulus energy
  3. diameter of axon
  4. whether axon has myelin or not
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6
Q

sensitivities of morphology of peripheral ending

A

the closer to the surface the more sensitive to fine touch

the deeper, the more sensitive to pressure

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7
Q

nerve endings types that fire only at beginning of stimulus

A

meissner corpuscle
&
pacinian corpuscle

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8
Q

nerve endings types that fire during entire stimulus

A

merkel cells
&
ruffini endings

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9
Q

order of cell types from fine touch to pressure

A
  1. meissner corpuscle (closest to surface)
  2. Merkel cells
  3. pacinian corpuscle
  4. ruffini endings (deepest)
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10
Q

Diameter of axon significance (generally)

A

larger the axon, the faster the signal travels

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11
Q

C-fibers

A

smallest diameter of axon

*for slow burning pain

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12
Q

A-delta fibers

A

medium seized diameter

*for sharp pain

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13
Q

A-Beta fibers

A

largest diameter

*for subcutaneous mechanoreceptors

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14
Q

TRPA1 channels

A

sensitive to chemical and mechanical stimuli

-mediate painful sensations

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15
Q

3 somatosensory CNS pathways

A
  1. anterolateral system (pain)
  2. Dorsal Column Medial Lemniscal system (touch)
  3. Spino-Cerebellar Tract
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16
Q

Cross sites of dorsal column path vs anterolateral

A
  1. Dorsal colum medial lemniscal pathway crosses at medulla (important for touch)
  2. anterolateral crosses immediately at the spinal cord (important for pain)
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17
Q

Spinal cord Graymatter areas of dorsal column medial lemniscal system (horns and layers)

A
  1. dorsal horn (layers I-V) *sensory
  2. Intermediate horn (layers VI & VII)
  3. Ventral horn *motor (layers VIII & IX)
    - layer X around central canal
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18
Q

6 notable nuclei of spinal cord gray matter & corresponding layers

A
  1. posterior marginal (layer 1)
  2. substantia gelatinosa (layer 2, some 3)
  3. Nucleus proprius (layers 3, 4, 5, 6)
  4. Clarke’s nucleus (layer 8)
  5. interomediolateral nuclei (layer 7)
  6. motor nuclei (layer 9)
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19
Q

spinal cord white matter divisions

A
  1. dorsal columns
  2. lateral columns
  3. ventral columns
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20
Q

Dorsal root

A

swelling, collection of cell bodies of sensory neurons (dorsal root ganglion)

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21
Q

ventral root

A

axons from motor neurons from gray matter

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22
Q

Dorsal Colum Medial Lemniscal system pathway (summary)

A
  1. pseudo-unipolar neurons synapse at dorsal horn
  2. dorsal horn synapses at dorsal column nuclei
  3. dorsal column nuclei cross via medial lemniscus
    - ->synapses at VPL & P of thalamus
  4. Thalamus synapses at Primary somatosensory (SI)
  5. SI synapses at SII and Parietal cortex
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23
Q

1st order neurons of Dorsal column system

A

receptor cells with somas in dorsal root ganglia

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24
Q

1st order neuron 3 possible courses

A
  1. enter dorsal column and ascend to more rostral CNS areas
  2. synapse in dorsal horn
  3. synapse in ventral horn (for reflexes)
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25
fibers in dorsal column topographical manner
fibers from caudal areas occupy most medial portions of dorsal column
26
fasciculus gracilis
medial bumps of upper cord -conveys somatosensory info from lower limbs & lower trunk
27
fasciculus cuneatus
lateral bumps of upper cord -conveys somatosensory info from upper limbs, upper trunk, and neck
28
fasciculus gracilis & cuneatus synapse location
synapse in medulla to dorsal column nuclei 1. nuclei gracilis 2. nuclei cuneatus
29
2nd order neurons of dorsal column system
neurons in dorsal column nuclei (medulla) cross at INTERNAL ACRURATE FIBERS then proced as the MEDIAL LAMNISCUS and synapse at VPL and P (thalamus)
30
3rd order neurons
neurons from VPL & P of thalamus that synapse at SI or Parietal cortex
31
Primary somatosensory cortex (SI) and Primary motor cortex important similarity
They have the same homunculus - sensory & motor areas adjacent to each other - distorted body map shows higher density of receptors on hands and face
32
Cerebral corex layers I-VI distinctions
- layers II, III, V, VI have neurons that project OUT of the cortex - layer IV is the INPUT layer of the cortex
33
3 general types of cerebral cortical projections
1. associational 2. collosal 3. projectional
34
Associational projections
cortex will project to the neighboring cortical areas next to a given area
35
Callosal projections
cortical areas will project to mirror areas in other hemisphere
36
projectional projections
project outside cortex to sub-cortical areas (specified targets)
37
SI cortical layers II and III projections
project to associational motor connections & associational cortices
38
SI cortical layer V projections
projects to - dorsal column nuclei - dorsal horn of spinal cord - striatum & brain stem
39
SI cortical layer VI projections
projects to VPL & P of thalamus
40
secondary somatosensory cortex importance (2)
first processing where both sides of body are represented, and most effected by ATTENTIONAL STATE Relays somatosensory info to limbic system (amygdala & hippocampus)
41
Nociception
reception of signals in CNS by activation of receptors specialized for tissue damage information
42
Pain
PERCEPTION of an aversive sensation
43
Nociceptor chemical sensitivity
decrease threshold or directly activate chemicals include: histamine, ATP, 5HT, prostaglandin, E2, substance P, bradykinin
44
Origin of pain
- injury of peripheral nerves, or loss of them (phantom limb) - CNS damage in ventrobasal thalamus (thalamic syndrome)
45
1st order neurons of anterolateral system
``` the nociceptor (A-delta & C fibers) ``` -->both release glutamate, and substance P (excitatory)
46
Lissauer's Tract
where A-delta and C fibers split entering the cord going up and down a few segments -->Gray matter (posterior marginal and nucleus proprius)
47
2nd order neurons (2 classes)
in dorsal horn 1. neurons in posterior marginal 2. neurons in nucleus proprius
48
Referred Pain
perception of pain from viscera felt as cutaneous pain -may be due to divergence of cutaneous/visceral input on nucleus proprius on the cord
49
2nd order neuron locations
fibers immediately cross travel in ventral portion of white matter (called antero-lateral section)
50
7 general targets of 2nd order neurons (aka 3rd order neurons or sub-systems) and gray matter area they originate at
1. spino-thalamic (posterior marginal and proprius) 2. spino-reticular tract (proprius) 3. spino-mesencephalic (posterior marginal & proprius) 4. spino-cervical 5. dorsal column nuclei 6. spino-hypothalamic tract 7. spino-ponto-amygdalo tract
51
importance of spino-reticular tract
reticular formation is part of the arousal system
52
importance of spino-ponto-amygdalo tract
experiencing pain can lead to aggression
53
2 principle thalamic targets (and gray matter origin)
1. medial group: intralamina nuclei and central nucleus (from proprius) 2. lateral group: VPL & P (from post. marginal & proprius)
54
medial group cortical targets
projects diffusely to ipsilateral cortex (associational)
55
lateral group cortical targets
SI, SII, cingulate gyrus, PFC
56
Antero-lateral system summary
1. pseudo unipolar cells project to the dorsal horn gray matter (proprius & post. marginal) 2. crosses immediately at the cord and continues ventrally in white matter 3. projects to thalamus (intralaminar, VPL, P) 4. projects to Associational cortex, SI, SII, PFC
57
2 other cerebral cortical areas involved in pain processing
insula & cingulate cortex
58
insula
involved in integrating sensory, emotional, and cognitive aspects of pain
59
Gate Theory of Pain
firing of neurons in the cord that cause pain is a balance b/w nociceptive input and activity of non-pain input to cord A-beta cutaneous mechanoreceptors stimulation blcoks pain from C-fibers by integrating the interneuron and the proprius -->weaker activation of proprius
60
Central Gray Analgesia
when central gray nucleus is stimulated-->no perception of pain
61
Lesions of dorsolateral funiculus
suppresses stimulus induced analgesia
62
Descending control of pain system
1. PFC-->central gray 2. central gray -->raphe MAGNUS & nucleus reticularis (medulla) 3. medulla nuclei inhibit the dorsal horn of the spinal cord
63
DBS treatment of pain
DBS of area 25, cingulate cortex, and PFC all project to nucleus accumbens -->may be responsible for placebo/expectation effect
64
Acupuncture mechanism for pain relief
ublock chi lines defies neuro-anatomy *results in activation of hypothalamus & nucleus accumbens, deactivates cingulate cortex, amygdala, hippocampus *activates descending pathway deactivates limbic areas of pain association
65
applying 5HT or NE directly to the cord
produces analgesia | *medullary nuclei use 5HT as a transmitter, and others use NE
66
mechanism of 5HT/NE on cord
1. NE/5HT activates inhibitory interneuron | 2. NE/5HT directly inhibit nucleus proprius
67
Morphine mechanism
activates descending systems by suppressing activity of GABA (inhibitory) interneurons -these normally inhibit the descending systems
68
morphine mu receptors
Pre-synaptically: morphine inhibits release of neurotransmitter (by Decreasing Ca++ influx post-synaptically: morphine hyperpolarizes surface