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Neuroscience > Exam 2: Somatosensory (17 and 18) > Flashcards

Exam 2: Somatosensory (17 and 18) Flashcards

1
Q

what are the 3 sensory systems?

A
  1. somatosensory
  2. visceral sensory
  3. special sensations
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2
Q

somatosensory sensations

A

touch, nociception (pain/tissue damage), vibration, proprioception (muscle load, movement, and joint angles), pruriception (itch), and thermoception

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3
Q

visceral sensations

A

distention (gassiness), hypoxia (lack of oxygen)

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4
Q

special sensations

A

Vision
Auditory
Vestibular
Gustatory (taste)
Olfactory (smell)

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5
Q

primary afferent neurons

A

neurons that are doing the sensing in the PNS
- cell body is in the DRG and central terminal is in the dorsal horn
- The peripheral end of its axon generates an action potential in response to the stimulus its tuned to

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6
Q

what is the main somatosensory nerve for the head?

A

trigeminal nerve (CN 5)

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7
Q

where are the somata of the primary afferent neurons?

A
  1. in the dorsal root ganglia where their cell body is and axon is in the peripheral area for sensing
  2. in the cranial nerve sensory ganglia
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8
Q

peripheral processes

A

include primary afferent neurons which remain outside the CNS
- processes of dorsal root ganglion neurons are distributed to the body via spinal nerves

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9
Q

central processes

A

enter the CNS as dorsal roots which contain only sensory axons

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10
Q

what 2 things the spinal nerves contain?

A

sensory and motor axons which make them “mixed”

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11
Q

dermatome

A

innervation of specific parts of the body from the spinal nerves
- each nerve innervates its own dermatome

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12
Q

what makes a primary afferent neuron specific?

A

depends on the sensory receptors at the end of the nerve fiber and their sensitivity

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13
Q

what 5 groups of sense do primary afferent neurons respond to?

A

touch, thermoception, puriception (itch), proprioception, and nociception

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14
Q

touch (5)

A

Fine touch
Pressure
Vibration
Movement against the skin
Hair movement

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15
Q

proprioception (4)

A

Limb and trunk position
Muscle length
Movement
Muscle load

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16
Q

nociception (4)

A

–> pain and tissue damage
Heat
Cold
Chemical pain
Mechanical pain

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17
Q

mechanoreception

A

sensing mechanical force ⇒ texture, pressure, vibration, movement, stretch
- Receptors are broadly distributed through the body ⇒ many are in the skin

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18
Q

filterning (touch receptors)

A

the type of encapsulation, depth in the skin, and the sensory receptor proteins expressed by the neuron determine the stimulus
- there are many different touch receptors

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19
Q

density (touch receptors)

A

Determines how well we sense different kinds of touch

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20
Q

resolution

A

(two point discrimination) measures the distance in our sense of touch

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21
Q

proprioception definition

A

the sense of the position, movement, and load on the limbs and trunk
- mechanoreceptors but are specialized to sense muscle length, load

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22
Q

muscle spindles

A
  • organs that sense muscle length
  • Nerve endings are wrapped around a special intrafusal muscle fiber embedded
  • Fire when a muscle is stretched ⇒ provide information required to adjust muscle contraction in response to external forces
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23
Q

Golgi tendon organs

A
  • sense muscle load
  • Embedded in collagen fibers of tendons
  • Compressed by tension
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24
Q

what do Golgi tendon organs prevent?

A

Help prevent muscles from exerting more force than they can safely bear
- Sensitive to the force exerted by tendon

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25
Q

Piezo2 and how it works

A

receptor protein expressed in mechanoreceptor neurons
- form a trimer as a mechanically gated Na+ channel which depolarizes the nerve ending and causes the afferent nerve to fire an action potential
- the tiny hole in the middle acts as the sodium channel but only if the arms are distorted a little bit
- Sodium comes in and triggers an action potential

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26
Q

how does a muscle cell sense the amount of load?

A

the longer the depolarization and channels opened, the cell communicates that there is more load to the CNS
- The frequency of action potentials encodes the strength and duration of the stimulus

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27
Q

Local (spinal) reflexes

A

input to the brain from proprioceptors or cutaneous receptors causing reflexive response
- Direct pathway to cerebellum
and somatosensory cortex via thalamus

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28
Q

what do reflexes require and where does this happen?

A

few (1-2) synapses ⇒ all synapses occur in spinal cord

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29
Q

which pathway to the brain is ipsilateral?

A

Spinocerebellar tract
- can also be contralateral if it crosses over and then crosses again later

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30
Q

which pathway to the brain is contralateral?

A

Dorsal column pathway and spinothalamic tract

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31
Q

spinocerebellar tract

A

carrying proprioception in the lateral funiculus of the spinal cord ⇒ cerebellum gets input from cerebral cortex

32
Q

dorsal column track

A

carrying touch, vibration (does not synapse before going up to the spinal cord)
- goes to the cerebral cortex

33
Q

Somatotopically organized

A

the receptive fields of the axons in the dorsal columns form a map of the body

34
Q

Fasciculus cuneatus

A

carries axons from the upper body

35
Q

Fasciculus gracilis

A

carries axons from the lower body

36
Q

medial lemniscus

A

output axons from FG and FC nuclei ascend here and cross the midline at the sensory decussation and ascend to the thalamus
- synapse in the ventral posterior lateral nucleus of the thalamus

37
Q

spinothalamic trac (STT)

A
  • carrying temperature, pain, itch, some touch
  • ventral lateral funiculi of the contralateral spinal cord
  • projects from the ventral posterolateral nucleus (VPL) of the thalamus to the primary somatosensory cortex (S1)
  • Pain information also projects to limbic cortex ⇒ motivation to the avoid
38
Q

what happens if spinothalamic axons get cut as they cross the midline or as they ascend to the thalamus?

A

you cannot detect pain that bothers you

39
Q

where does the primary somatosensory cortex receive somatosensory information from? (2)

A
  1. The periphery ⇒ the most direct route for information
  2. Densely of all cortical regions
40
Q

where do the dorsal column and spinothalamic tract both project?

A

primary somatosensory cortex S1

41
Q

where does Somatosensory information from the trigeminal nerve go?

A

to the ventral posteromedial nucleus (VPM) of the thalamus to primary somatosensory cortex

42
Q

homunculus

A

the motor or sensory distribution along the cerebral cortex
- lower leg and foot at the top, knee, trunk, hand, face, mouth

43
Q

Stroke on the right somatosensory cortex does what?

A

affects sensations on the left side of the body
- Contralateral to cerebral cortex

44
Q

Stroke in the right side of the cerebellum does what?

A

affects motor control of the right side of the body
- Ipsilateral to cerebellum ⇒ not aware of these

45
Q

what are the similarities between the dorsal column pathway and spinothalamic tract pathway

A

the relay neurons synapse at the ventral posterolateral nucleus of the thalamus and the thalamocortical neurons synapse on S1 post central gyrus

46
Q

differences between the dorsal column and spinal thalamic tract pathways?

A
  • dorsal senses touch, vibration, and proprioception while STT is pain, temperature, and itch
  • dorsal relays across the midline at the medulla sensory decussation and STT crosses at the spinal cord (anterior commissure)
  • dorsal tract axons ascend at the medial meniscus and STT ascends on the STT tract
47
Q

where does the trigeminothalamic tract synapse?

A

at the ventral posterior medial nucleus of thalamus to S1 cortex

48
Q

where is the primary somatosensory cortex for the body and the trigeminal system?

A

in the S1 primary somatosensory cortex

49
Q

where does pain information go aside from S1?

A

it also goes to the limbic cortex as motivation to avoid pain for good/bad feelings

50
Q

pain

A

an unpleasant sensory and emotional experience associated with actual or potential tissue damage

51
Q

what is different about pain neurons compared to touch neurons?

A

Carried into CNS by thin primary afferent axons with slow conduction velocities
- often unmyelinated (2m/s) or with small diameter myelinated axons (10m/s)
- carried via the STT neurons

52
Q

nociceptors

A

signal tissue damage or threat of tissue damage with free nerve endings ⇒ no encapsulsation
- Mechanical injury ⇒ cutting/scraping
- Heat injury ⇒ burning
- Cold ⇒ frost bite
- gut distention ⇒ gas pain
- Chemical injury ⇒ acid

53
Q

mechanical nociceptors

A

high threshold, increased force and increased firing, small point like receptive fields

54
Q

heat nociceptors

A

respond to heat and capsaicin (form red peppers)
Thermal thresholds 45 degree celsius (~115 F)

55
Q

TPV1 receptor (David Julius)

A

transmembrane receptor for painful heat and capsaicin (protein)

56
Q

cold nociceptors

A

threshold is 0 degrees celsius ⇒ freezing
- Their thresholds don’t overlap much with those of cooling receptors ⇒ cooling receptors are different (25 deg C)

57
Q

polymodal receptors

A

respond to many things ⇒ mechanical, heat, and chemical stimuli
- Thermal thresholds 43-45 degrees C
- High mechanical thresholds
- Respond to chemical agents

58
Q

where do nociceptor nerve endings go?

A

in the superficial skin as well as epidermis and dermis and axons extending into deeper layers
- terminals have transduction proteins sensitive to heat, cod, pressure, acid

59
Q

acute pain

A

normal pain in response to injury or threat of injury and lasts as long as the stimulus

60
Q

persistent pain

A

outlasts the injury or threat of injury and related to healing
- Protective during healing process

61
Q

chronic pain

A

outlasts duration of healing and the injury itself

62
Q

inflammatory pain and its paradox

A

most common type of persistent pain
- inflammation promotes healing
- Inflammation causes more pain
- Inflammation reduces likelihood of further injury

63
Q

non steroidal anti-inflammatory drugs

A

(NSAIDS: aspirin, ibuprofen) block production of prostaglandins ⇒ reduce inflammatory pain and effect on healing is uncertain

64
Q

sensitization of nociceptors occurs during what kind of pain?

A

persistent pain
- causes decreased threshold and larger response
- Contributes to increased pain after injury

65
Q

prostaglandins

A

inflammatory agents

66
Q

what % of people have chronic pain? how long is the threshold?

A

50% and >3 months
- 600 billion annually

67
Q

neuropathic pain

A

chronic pain caused by nerve injury ⇒ nerve compression, amputation, chemotherapy, diabetes, etc.

68
Q

what 2 things does neuropathic pain lead to?

A
  1. Loss of innervation ⇒ anethesia in affected area
  2. Loss of growth factors released by cut nerves ⇒ adjacent nerves behave abnormally and respond to their usual stimuli but encode pain
69
Q

what does stimulation of the region around the cerebral aqueduct (central/periaqueductal gray) produce in rats?

A

analgesia aka it kills pain

70
Q

stimulation of parts of the rostral portion of the ventromedial medulla can facilitate what?

A

enhanced pain

71
Q

neurons release what for the analgesic effects of pain morph like stuff in inhibitory circuits?

A

release endorphins

72
Q

what types of stimulation can be activated to treat pain? (3)

A
  • Spinal cord stimulation
  • Transcutaneous electrical stimulation
  • Placebo analgesia
73
Q

anesthesia

A

loss of all sensation

74
Q

general anesthesia

A
  • causes loss of consciousness with no reaction to pain
  • Used mainly for major surgery
  • Isofluorane, propofol
75
Q

local anesthesia

A

used for minor and sometimes major surgeries
- Injectable ⇒ novacaaine
- Blocks action potential generation/propagation by blocking voltage gated sodium channels

76
Q

analgesia

A

specific loss of pain sensation
- Non steroidal anti inflammatory drugs (NSAIDS) ⇒ ibuprofen or aspirin
- Opiods: drugs derived from or related to opium

77
Q
A

Neuroscience (18 decks)

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