The basic anatomy of the peripheral nervous system Flashcards
Which argument argued that there was no need for nociceptors?
Intensity Theory
Specificity Theory
Stated that nociceptors were required.
Depending on the nature of the stimuli, it may contact the receptive field of many type of neurons? T/F
True
Example of hot plate contacting the skin.
- Hot plate contacts the skin
- This will activate Merkel cells and other type of touch receptors.
- As well as the free nerve endings that signal pain and temp.
- Afferents of signals are than sent to appropriate sites in the CNS.
Nociceptors are used to…?
Teach us to avoid things that can cause us harm. Also used as a healing mechanism by protecting ourselves.
Congenital Insensitivity to pain is caused by three known mutation, what are they?
- Mutation in nerve growth factors (critical for nociceptor development)
- Mutation in trkA ( Receptor for never growth.
- Mutations in voltage gated sodium channels called Nav1.7 (loss of nociceptor function)
SCN9A channelopathy causes what?
Causes congenital inability to experience pain
Mutation that increases the activity of Nav1.7 leads to?
Erythromelalgia or Paroxysmal extreme pain disorder.
Mutation that render Nav1.7 channels nonfunctional leads to?
Insensitivity to pain.
**This highlights the importance of sodium channels in pain.
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?
Mutations in SCN9A, encoding a sodium channel alpha subunit.
Afferent fibers synapse in the Dorsal Horn and project up separate pathways to the brain. what two pathways?
- One pathway is for sensory discrimination aspect of pain
- The second is for emotional aspects of pain. (Limbic system)
Anatomy of peripheral nerve fibers are?
- Large Myelinated “Aβ” fiber
- Small Myelinated “Aδ” fibers
- Unmyelinated “C’” fiber
Aβ-fibers characteristics are?
- Myelinated
- Non-nociceptive
- Very fast conduction
- Convey light touch, vibration
- May become nociceptive after nerve injury
Aδ-fibers characteristics are?
- Myelinated nociceptors (30%)
- Fast conduction
- Convey fast “Pricking” pain, punctate stimuli, cold, and thermal
Nociceptive C-fibers?
- Unmyelinated nociceptors
- Slow conduction
- Convey slow “burning” “aching” Pain;
- Polymodal (high-threshold mechanical thermal, cold)
Types and Characteristics of Sensory Fibers
- Muscle spindle (Ia) and Golgi tendon (Lb) (Low motor neurons alpha)
- Meissner, merkel, pacinian corpuscles (“Aβ”)
- Sharp pain, cold, and some touch (δ) (Pre-ganglion)
- Slow pain, heat, itch, some touch (C-fiber) (Post-ganglion)
Sensory neurons are referred to as?
Pseudounipolar
- They have single axon that bifurcates.
- One branch innervates peripheral target and the other Spinal cord.
Sensory NEURONS have no Dendrites. T/F
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)
Trigeminal (TG)
- 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
Large diameter thats heavily myelinated neurons innervate?
Touch or Movement of hair
Small diameters that are unmyelinated neurons terminate where?
FREE NERVE ENDINGS
- sense painful stimuli
First and second pain are mediated by what two fibers?
- FIRST PAIN A-delta
- SECOND PAIN C-fibers
Acute pain has two phases, what are they?
- SHARP PAIN (fast) (A-delta fibers do this )
- BURNING PAIN (slow and delayed) (c-fibers do this)
Fast Pain (stinging)
-Is well defined with regards to location and so is its strength
Slow Pain (aching and burning)
- Diffused, poor localization
- Difficult to estimate its strength
Phsiologically-defined nociceptor classes in mouse skin..
The majority of C-FIBERS are Polymodal
-mechanical
Nociceptors respond to______ and do not respond to______.
- Noxius pinprick or pinch
2. Non-noxius mechanical force
A-fibers evoke pricking pain, what are the types
- Type one: heat mechanical and chemical stimuli (velocity 25 m/sec)
- Type two: A-delta fibers (Velocity is 15 m/s)
Low threshold c-fibers mechano-receptors
- Respond to innocuous stimulation (Pleasant touch)
- No somatosensory cortical representation to insular cortex.
C-fibers are functionally diverse
- The respond to different stimuli
- They have diff phenotype and use peptide or non-peptide neurotransmitters
Small, medium, and large diameter refers to what fibers?
- small: c-nociceptors
- Medium: A-delta fibers
- Large: A-beta and proprioceptors
Allodynia ( >45 degree C)
Is the experience of pain from a non-painful stimulation of the skin, such as light touch.
Hyperalgesia (
Abnormally heightened sensitivity to pain.
- eg. when getting pinched hurts but hyperalgesia makes it feel 10x worse.
