The basic anatomy of the peripheral nervous system

Question 1

Which argument argued that there was no need for nociceptors?

Answer 1

Intensity Theory

Question 2

Specificity Theory

Answer 2

Stated that nociceptors were required.

Question 3

Depending on the nature of the stimuli, it may contact the receptive field of many type of neurons? T/F

Answer 3

True

Question 4

Example of hot plate contacting the skin.

Answer 4

1. Hot plate contacts the skin
2. This will activate Merkel cells and other type of touch receptors.
3. As well as the free nerve endings that signal pain and temp.
4. Afferents of signals are than sent to appropriate sites in the CNS.

Question 5

Nociceptors are used to…?

Answer 5

Teach us to avoid things that can cause us harm. Also used as a healing mechanism by protecting ourselves.

Question 6

Congenital Insensitivity to pain is caused by three known mutation, what are they?

Answer 6

1. Mutation in nerve growth factors (critical for nociceptor development)
2. Mutation in trkA ( Receptor for never growth.
3. Mutations in voltage gated sodium channels called Nav1.7 (loss of nociceptor function)

Question 7

SCN9A channelopathy causes what?

Answer 7

Causes congenital inability to experience pain

Question 8

Mutation that increases the activity of Nav1.7 leads to?

Answer 8

Erythromelalgia or Paroxysmal extreme pain disorder.

Question 9

Mutation that render Nav1.7 channels nonfunctional leads to?

Answer 9

Insensitivity to pain.

**This highlights the importance of sodium channels in pain.

Question 10

Erythromelalgia (PE) is a rare autosomal-dominant painful condition with spontaneous burning pain of the feet and hands and also increase skin temperature. what is this due to?

Answer 10

Mutations in SCN9A, encoding a sodium channel alpha subunit.

Question 11

Afferent fibers synapse in the Dorsal Horn and project up separate pathways to the brain. what two pathways?

Answer 11

1. One pathway is for sensory discrimination aspect of pain
2. The second is for emotional aspects of pain. (Limbic system)

Question 12

Anatomy of peripheral nerve fibers are?

Answer 12

• Large Myelinated “Aβ” fiber
• Small Myelinated “Aδ” fibers
• Unmyelinated “C’” fiber

Question 13

Aβ-fibers characteristics are?

Answer 13

• Myelinated
• Non-nociceptive
• Very fast conduction
• Convey light touch, vibration
• May become nociceptive after nerve injury

Question 14

Aδ-fibers characteristics are?

Answer 14

• Myelinated nociceptors (30%)
• Fast conduction
• Convey fast “Pricking” pain, punctate stimuli, cold, and thermal

Question 15

Nociceptive C-fibers?

Answer 15

• Unmyelinated nociceptors
• Slow conduction
• Convey slow “burning” “aching” Pain;
• Polymodal (high-threshold mechanical thermal, cold)

Question 16

Types and Characteristics of Sensory Fibers

Answer 16

1. Muscle spindle (Ia) and Golgi tendon (Lb) (Low motor neurons alpha)
2. Meissner, merkel, pacinian corpuscles (“Aβ”)
3. Sharp pain, cold, and some touch (δ) (Pre-ganglion)
4. Slow pain, heat, itch, some touch (C-fiber) (Post-ganglion)

Question 17

Sensory neurons are referred to as?

Answer 17

Pseudounipolar

• They have single axon that bifurcates.
• One branch innervates peripheral target and the other Spinal cord.

Question 18

Sensory NEURONS have no Dendrites. T/F

Answer 18

TRUE

• the cell body is in either dorsal root (DRG) , trigeminal ganglion (TG)
• DRG below the neck source of sensory
• TG above the neck (sensory)

Question 19

Trigeminal (TG)

Answer 19

• 3 branches (v1,v2,and v3)
• 2 TG total
• Touch projects to main TG sesnory nucleus
• Pain projects to spinal TG nucleus.
• Proprioception projects to Mesencephalic TG nucleus

Question 20

Large diameter thats heavily myelinated neurons innervate?

Answer 20

Touch or Movement of hair

Question 21

Small diameters that are unmyelinated neurons terminate where?

Answer 21

FREE NERVE ENDINGS

- sense painful stimuli

Question 22

First and second pain are mediated by what two fibers?

Answer 22

• FIRST PAIN A-delta

- SECOND PAIN C-fibers

Question 23

Acute pain has two phases, what are they?

Answer 23

• SHARP PAIN (fast) (A-delta fibers do this )

- BURNING PAIN (slow and delayed) (c-fibers do this)

Question 24

Fast Pain (stinging)

Answer 24

-Is well defined with regards to location and so is its strength

Question 25

Slow Pain (aching and burning)

Answer 25

• Diffused, poor localization

- Difficult to estimate its strength

Question 26

Phsiologically-defined nociceptor classes in mouse skin..

Answer 26

The majority of C-FIBERS are Polymodal

-mechanical

Question 27

Nociceptors respond to______ and do not respond to______.

Answer 27

1. Noxius pinprick or pinch

2. Non-noxius mechanical force

Question 28

A-fibers evoke pricking pain, what are the types

Answer 28

• Type one: heat mechanical and chemical stimuli (velocity 25 m/sec)
• Type two: A-delta fibers (Velocity is 15 m/s)

Question 29

Low threshold c-fibers mechano-receptors

Answer 29

• Respond to innocuous stimulation (Pleasant touch)

- No somatosensory cortical representation to insular cortex.

Question 30

C-fibers are functionally diverse

Answer 30

• The respond to different stimuli

- They have diff phenotype and use peptide or non-peptide neurotransmitters

Question 31

Small, medium, and large diameter refers to what fibers?

Answer 31

• small: c-nociceptors
• Medium: A-delta fibers
• Large: A-beta and proprioceptors

Question 32

Allodynia ( >45 degree C)

Answer 32

Is the experience of pain from a non-painful stimulation of the skin, such as light touch.

Question 33

Hyperalgesia (

Answer 33

Abnormally heightened sensitivity to pain.

- eg. when getting pinched hurts but hyperalgesia makes it feel 10x worse.