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Med Neuro Block 2 > Structure & Function of Peripheral Sensory Receptors > Flashcards

Structure & Function of Peripheral Sensory Receptors Flashcards

1
Q

What is the role of the somatosensory system?

A 
It allows us to sense:
Touch: pressure against skin
Temperature of skin
Proprioception: position of joints and muscles with respect to body
Pain: Tissue-damaging stimuli
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2
Q

How is the somatosensory system different from other sensory systems?

A

Somatosensory receptors are distributed throughout body.

Other sensory systems (vision, audition, olfaction, taste) are concentrated in small, specialized areas.

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3
Q

What is the basic pathway for all sensory stimuli to be perceived:

A

Stimulus ⇒ sensory receptors ⇒ spinal cord ⇒ medulla/brainstem ⇒ thalamus ⇒ cortex

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4
Q

Which direction do sensory pathways travel? Which direction do motor pathways travel?

A

Sensory pathways go up (periphery to cortex)

Motor pathways go down (cortex to muscles)

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5
Q

What is the DRG?

A

Cell bodies of sensory neurons innervating the neck on down

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6
Q

There is _______ DRG at each level of the spinal cord on each side.

A

1

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7
Q

DRG possesses __________ cell bodies with ____________ and _____________ process axons

A

pseudounipolar; peripheral; central

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8
Q

How are sensory receptors generally categorized?

A

Exteroreceptive
Proprioceptive
Interoceptive

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9
Q

Describe exteroreceptive receptors:

A

Code information from the external world, mainly via skin

a) Mechanoreceptors: touch
b) Thermoreceptors: warming and cooling
c) Nociceptors: sharp and burning pain

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10
Q

Describe proprioceptive receptors:

A

Code information about muscle length, muscle tension, joint angles

a) Muscle afferent receptors: Golgi Tendon Organs and Muscle Spindles
b) Joint and tendon afferents

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11
Q

Describe interoceptive receptors:

A

Code information about changes inside the body

a) Visceral afferent receptors: Localize sensation and pain very poorly

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12
Q

Functions of sensory neuron:

A

A. Encode stimulus quality, intensity, duration, location
B. Receptive field
C. Stimulus transduction
D. Intensity of the stimulus
E. Speed of action potential transmission

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13
Q

What is the receptive field?

A

The area in the periphery where application of an adequate stimulus causes response

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14
Q

Describe the example of stimulus transduction: Pacinian corpuscle

A

⇒ At peripheral terminal stimulus activates receptors and ion channels
⇒ Generates receptor potential
⇒ If receptor potential strong enough, generates action potentials
⇒ Signal (action potentials) are conveyed to spinal cord

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15
Q

Intensity of the stimulus is encoded by:

A

1) Each neuron: Frequency of action potential firing: rate code
2) Many neurons: Number of neurons firing: spatial summation code

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16
Q

Speed of action potential transmission (conduction velocity) depends on:

A

⇒ Axon diameter
⇒ Thickness of myelin
–Large myelinated Aα, Aβ fibers conduct APs very fast
–Thin myelinated Aδ fibers conduct APs moderately fast
–Unmyelinated C fibers conduct APs slowly

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17
Q

What is the use of the Compound Action Potential (whole peripheral nerve)?

A

To determine whether:
axons are missing, damaged or demyelinated

Used to diagnose peripheral neuropathies:
Diabetes
Herpes zoster infection (shingles)
Nerve entrapment
Multiple sclerosis
Complications from drug treatments
Nutritional deficiencies
18
Q

Environment for receptive terminals:

A

a) skin
b) muscle
c) joint

19
Q

Characteristics that set the sensitivity and function of different receptors:

A

a) Location: superficial vs. deep
b) Type of ending encapsulated or non-encapsulated
c) Slowly adapting vs. rapidly adapting response of the receptor
d) Spatial resolution for stimulus

20
Q

What is the significance of slowly adapting vs. rapidly adapting responses?

A

Determines sensitivity to constant vs. changing stimuli:
1) Slowly adapting— Respond best to a sustained, unchanging stimulus. Sense pressure and shape of objects

2) Rapidly adapting— Respond only when stimulus changes (i.e. on and offset). Sense impact and motion of objects on skin

21
Q

Spatial resolution for a stimulus depends on:

A

Receptive field size and innervation density

1) Superficial receptors: small receptive field size
Deep receptors: large receptive field size

2) Innervation density: Density is high in very sensitive areas; low in insensitive areas. 2-point discrimination best for fingers, mouth; worst for back, calves.

22
Q

Mechanoreceptors:

A

mediate tactile/touch sensation

a) Very sensitive to force (low threshold); don’t respond to noxious stimuli
b) Silent without stimulation
c) Have myelinated axons; fast conduction velocities; signal reaches spinal cord quickly

23
Q

Where would superficial mechanoreceptors be found? What are types of these receptors?

A

Superficial receptors: Found in border between epidermis and dermis

1) Merkel disks
2) Meissner’s corpuscles

24
Q

Characterstics of Merkel disks:

A
  • Fine touch, 2-point discrimination; Sharpest resolution of surface texture; bumpy vs. smooth
  • Receptive field: Multiple small spots. High density in finger tips, around mouth; Low density on back
  • Several Merkel disks innervated by single myelinated axon.
  • Slowly Adapting response, encodes amount of force
25
Q

Characterstics of Meissner’s corpuscles:

A
  • Fine touch, 2-point discrimination; Sense abrupt changes in edges, bumps, corners. Help adjust grip and release when lifting objects; Encode low-frequency vibration
  • Receptive field: Single spot.
  • Corpuscle encloses a stack of flattened epithelial cells; Sensory terminal entwined between layers; axon is myelinated
  • Rapidly Adapting response encodes on/offset of skin indentation
26
Q

Where would deep mechanoreceptors be found? What are types of these receptors?

A

Deep receptors: Found in dermis

1) Ruffini Endings
2) Pacinian Corpuscles

27
Q

Characteristics of Ruffini Endings:

A
  • Sense stretch of skin; Help determine shape of grasped objects
  • Receptive field: large and diffuse
  • Ruffini ending is encapsulated; myelinated axon surrounds collagen fibrils
  • Slowly Adapting response responds to stretching of skin
28
Q

Characteristics of Pacinian Corpuscles:

A
  • Respond to high frequency vibration; Most sensitive mechanoreceptor, even distribution throughout skin.
  • Receptive field: large and diffuse
  • Fluid filled capsule wrapped around bare nerve ending; filters out sustained stimuli; myelinated axon
  • Rapidly adapting response
29
Q

Hair Follicle receptors:

A
  • Respond to movement of hairs
  • Receptive field: around base of hair follicle
  • Bare axon wraps around base of hair follicle; axon is myelinated
  • Rapidly adapting response encodes velocity of hair movement
30
Q

Textures of objects are signaled by ___________

A

different receptors

31
Q

What is the spatial summation code?

A

Overall picture in brain is due to the sum of information provided by the different active and silent fibers

32
Q

Thermoreceptors:

A

a) Encode skin temperature (warming, cooling)

b) Discharge continuously (steady rate) at normal skin temperature (32 °C)

33
Q

What are the types of thermoreceptors?

A

1) Cooling receptors

2) Warming receptors

34
Q

Characteristics of Cooling receptors:

A
  • Increase firing rate when skin is cooled. Stop firing when skin is warmed.
  • Free nerve endings with myelinated axons
35
Q

Characteristics of Warming receptors:

A
  • Increase their firing rate when skin is warmed above 32 °C. Stop firing when skin is cooled. Range ≈ 29-43 °C.
  • Free nerve endings with unmyelinated axons (C fiber)
  • Very small receptive fields
36
Q

What do thermoreceptors respond best to?

A

changes in skin temperature

37
Q

Nociceptors (pain receptors):

A

Respond to stimuli that damage or threaten to damage tissue

38
Q

What makes up the majority of sensory neurons in the DRG?

A

Nociceptors

≈ 70% of all sensory neurons in the dorsal root ganglia

39
Q

Where is almost all of the innervation of nociceptors provided?

A

tooth pulp and cornea

40
Q

Two general types of nociceptors:

A

1) A-Mechanonociceptors

2) C Polymodal nociceptors

41
Q

A-Mechanonociceptors:

A

Axon is myelinated (A∂)
• Respond to intense mechanical force, sometimes intense heat (≥ 52 °C)
• Free nerve endings
• Small receptive fields
• Slowly adapting response
• Mediate fast, initial pain; sharp “pricking” quality; easy to localize

42
Q

C Polymodal nociceptors:

A

Axon is unmyelinated (C-fiber)
• Polymodal = many modes: Respond to intense mechanical force, high heat (≥ 45 °C), noxious chemicals (bradykinin, histamine, acid; capsaicin
• Free nerve endings; No sheath– respond to inflammatory chemicals
• Small receptive fields
• Slowly adapting response
• Mediate slow, aching, “burning” quality of pain; difficult to localize

Med Neuro Block 2 (13 decks)

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