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SF2- Exam 2 > Physiology of Somatosensation > Flashcards

Physiology of Somatosensation Flashcards

1
Q

What type of info does the somatosensory system give about the skin?

A

Pain

Temp

Pressure

Vibration

Texture

Shape

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2
Q

What type of info does the somatosensory system give about the muscles and joints?

A

Pain

Length

Degree of stretch

Tension

Contraction

Position

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3
Q

What are cell body locations for the primary afferent neurons involved in somatosensation? What is conveyed at each location?

A
  • Dorsal root ganglion- Information about the neck and below
  • Mesencephalic nucleus- Proprioceptive information about the face
  • Trigeminal ganglion- Everything else about the face
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4
Q

Which fiber types are myelinated?

A

žAα- I; Diameter: 13-20; Conduction Velocity: 75-120

Aβ - II; Diameter: 6-12; Conduction Velocity: 35-75

Aδ- III; Diameter: 1-5; Conduction Velocity: 5-35

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5
Q

List the fiber speeds from fastest to slowest

A

I> II>III>IV

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6
Q

Which fiber types respond to temperature?

A

Aδ and C fibers

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7
Q

Where are cold receptors located? What about heat receptors?

A

Cold receptors: Upper dermis

Heat receptors: Upper dermis and deeper dermis

NOTE: Thermoreceptors have a small receptive field

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8
Q

What is the transduction of thermoreceptors?

A
  • Conformation of non-selective cation channels are temperature- dependent
    • ​These cation channels change conformation based on temperature

Cold receptors (<30° C)

Heat receptors (>32° C)

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9
Q

What are two types of cold receptors and which fiber types can each be found on?

A
  • CMR1 (TRPM8)- On C fiber endings
  • TRPA1- On A delta fibers
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10
Q

What are two types of heat receptors and which fiber types can each be found on?

A
  • TRPV1- On C fiber endings
  • TRPV2- On A delta fiber endings
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11
Q

What is the adaptation for thermoreceptors?

A

Low and slow

*This makes sense because thermoreceptors allow us to survive

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12
Q

Thermoreceptors are considered polymodal. Why?

A

Because they respond to more than one thing, chemicals and temp.

NOTE: Nociceptors are naked nerve endings

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13
Q

Where in the body are nociceptors abundant?

A

In epithelia and connective tissue

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14
Q

Nociceptors respond to…

A
  • Chemicals from damaged tissue (chemosensitive)
  • Intense or deep touch (pinching, poking) (mechanosensitive)
  • Extreme temperature (thermosensitive)

NOTE: Nociceptors are polymodal and are naked nerve endings.

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15
Q

Which fibers types are nociceptors found on?

A
  • C fibers- Dull Pain (Difficult to distinguish where the pain is coming from)
    • Small diameter
    • Unmyelinated
  • A delta- Sudden sharp pain
    • Medium diameter
    • Lightly myelinated

NOTE: Nociceptors have large receptive fields

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16
Q

Types of skin mechanoreceptors

A
  • Hair follicle receptor
    • ​Light touch
    • Moving touch
  • Pacinian corpuscles
    • ​Deep pressure
    • Vibration
  • Meissner’s corpuscles
    • ​Fine touch
    • Close to the dermis
  • Merkel receptors
    • Pressure
    • Texture
  • Ruffini endings
    • ​Skin stretch
    • Deep pressure
    • Deep in skin
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17
Q

Do accessory organs around the receptor transform energy?

A

No.

Accessory organs direct, lessen, amplify the stimulus but they don’t transform energy

Ex: Hair

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18
Q

Hair follicle receptor are _______ (tonic/phasic) receptors.

A

Phasic

*They adapt quickly; frequency of APs slow down dramatically

19
Q

What fiber types are hair follicle receptors found on?

A

A beta

A delta

20
Q

What is the fiber for Pacinian Corpuscle?

A

A beta

21
Q

What allows the rapid adaptation seen in pacinian corpuscle?

A

Because of its fluid filled layers, the fluid disperses and evens itself out so that receptor in the middle is no longer being distorted. The receptor is no longer feeling pressure and channels close and action potentials are gone, even though the stimulus is still there.

22
Q

What is the transduction mechanism for Merkel’s cells?

A
  1. Neurotransmitter released by Merkel’s cell
  2. Neurotransmitter bind to ligand gated channels on primary afferent neuron
  3. AP propogated
23
Q

Which receptor is the only complex receptor in the somatosensory system?

A

Merkel’s cell

*Complex receptors separate the cell from the primary afferent neuron

24
Q

Muscle spindle

Acessory organ

Fiber type

Adaptation

A

Acessory organ: Intrafusal fibers

Fiber type: A alpha and A beta

Adaptation: low; slow

25
Q

Golgi Tendon

Fiber type

Adaptation

A

Fiber type: A alpha

Adaptation: very low

*Prevents too much contraction

26
Q

Where are the cell bodies of first order, second order, and third neurons located?

A

First order: Dorsal root ganglion, trigeminal ganglion, mesencephalic nucleus

Second order: Ipsilateral, dorsal horn of spinal cord, ipsilateral side of medulla, or ipsilateral pons

*Cross the midline to the contralateral side

Third order: In contralateral thalamic nuclei

  • Ventral posterior lateral nucleus
  • Ventral posterior medial nucleus

*Projects to primary somatosensory cortex

27
Q

What are the main sensory fiber types and what does each detect?

A

A alpha (I)- Proprioception

  • Large diameter, myelinated fibers

A beta (II)- Fine Touch

  • Large diameter, myelinated fibers

A delta (III)- Pain and temperature

  • Small diameter, lightly myelinated fibers

C (IV)- Pain and temperature

  • Small diameter, unmyelinated fibers
28
Q

What are the 3 main types of ascending sensory systems? What type of info does each type carry?

A
  • Dorsal Column- Medial Leminscus
    • Discriminative touch, vibration, proprioception
  • Spinthalamic/ Spinoreticular/ Spinomesencephalic
    • Crude touch, pain and temperature
  • Spinocerebellar
    • ​Proprioception

*Proprioception is somewhat conscious but some is also unconscious

29
Q

What are the three major divisions of the somatosensory cortex?

A
  • Primary somatosensory (SI)
    • ​In the postcentral gyrus
    • You are able to feel touch but won’t know the significance of touch
  • Seconday Somatosensory (SII)
    • ​Superior bank of the lateral fissure
    • ​Gives the significance of touch
  • Posterior Parietal Association
    • ​Broadmann’s area 5 and 7
30
Q

Explain the sensory homunculus theory.

A
  • Primary somatosensory cortex is “topographically” organized
  • The amount of cortex devoted to each body part is proportional to its level of sensory acuity
31
Q

What 5 components are necessary for conscious awareness?

A
  1. Stimulus has occurred
  2. Stimulus quality
  3. Stimulus location
  4. Stimulus intensity
  5. Stimulus duration
32
Q

What Brodmann’s area contributes to the primary somatosensory cortex (SI)?

A
  • Area 3a
    • Receives input from proprioceptors in muscles
  • Area 3b
    • Mostly receives cutaneous input from slowly and rapidly adapting receptors
  • Area 1
    • Receives input from rapidly adapting cutaneous mechano-receptors
  • Area 2
    • Mostly receives input from joints and deep tissues
33
Q

Brodmann’s area 3a receives input from_________

A

Proprioceptors in muscles

34
Q

Brodmann’s area 3b receives input from_________

A

Cutaneous input from slowly and rapidly adapting receptors

35
Q

Brodmann’s area 1 receives input from_________

A

Rapidly adapting cutaneous mechano-receptors (fine touch)

36
Q

Brodmann’s area 2 receives input from_________

A

Joints and deep tissues (plays a role in proprioception)

37
Q

Secondary somatosensory cortex (SII) is innervatd by _________.

A

Neurons from SI

38
Q

The seconday somatosensory cortex projects to ________

A

Insula cortex

39
Q

The secondary somatosensory cortex is believed to involved in…

A
  • Self-awareness
  • Emotion and psychopathology
  • Perception and Cognition
40
Q

The insula innervates regions of the ______ lobe believed to be important for tactile memory.

A

temporal

41
Q

Which division of the somatosensory cortex is critical for higher order processing?

A

Posterior Parietal Cortex

*Brodmann’s areas 5 and 7

42
Q

The circuitry necessary for discimative somesthesis must be sent to the _______________ for the meaning of the stimulus to be appreciated.

A

Posterior parietal association cortex

43
Q

Stereognosis

A

The ability to visualize and know what object is by tactile information only

*Requires an intact posterior parietal cortex

44
Q

Graphesthesia

A

Know what someone is drawing on skin without looking at it

*Requires an intact posterior parietal cortex

SF2- Exam 2 (16 decks)

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