Nociceptors have fibers in the ____ and ____ range.
The conduction velocity of an Aδ fiber is __-__m/s.
The conduction velocity of a C fiber is __-__m/s.
Aδ(type III) fibers are sensitive to ____________ and __________.
- Fast pain (Acute, sharp, or pricking pain)
C(type IV) fibers are sensitive to _____________ and __________.
- Slow pain (Chronic, burning, or aching pain)
________ is an unpleasant emotional response to either real or perceived tissue damage.
(Chronic/Acute) pain can be described as sharp, discrete, and short lasting. It is carried by Aδ fibers.
(Chronic/Acute) pain can be described as burning and difficult to localize. It is carried by C fibers.
_____________ are free nerve endings that are sensitive to mechanical, chemical, and thermal stimuli.
Most unmyelinated nociceptors respond to mechanical, thermal, and chemical stimuli. Since they respond to multiple stimuli, they are referred to as ___________ receptors.
___________ is the initial sharp pain, or "the twinge", that is carried by Aδ fibers.
___________ is the chronic pain occurring later, or "the throb", that is carried by C fibers.
What are the two types of congenital insensitivity to pain?
(Indifference/Insensitive) is a type of congenital insensitivity to pain in which the person can perceive the stimulus, but lacks the appropriate response (ex. Pulling away or withdrawal).
(Indifference/Insensitive) is a type of congenital insensitivity to pain in which the stimulus is not perceived and the patient is unable to describe the intensity of type of pain.
A skin injury is often followed by the triple response (pain triad) which entails:
- Local reddening
- Red flare
- Formation of a wheal on the skin
Following an injury, chemical substances are released at the site of a wound that sensitize nociceptive afferent endings to have a lower threshold for activation and an increased firing frequency. What chemicals could be released at the site of an injury?
- Proteolytic enzymes
The condition in which nociceptive fibers around a wound site are very sensitive, even to non-noxious stimuli, following a wound is referred to as ______________.
A phenomenon in which increased afferent input onto pain system neurons activates intracellular signaling pathways such that action potentials elicit larger synaptic potentials is known as ______________. For example, increased numbers of chemical receptors at synapses to make synaptic potentials larger and/or altered receptor dynamics such that their ion channels remain open longer.
Nociceptive activation that persists may result in reorganization of the spinal cord dorsal horn. This reorganization involves increasing or decreasing levels of neurotransmitter. As a result, receptors of non-noxious stimuli, such as mechanoreceptors, may become capable of activating neurons in the spinal cord that carry pain information. This is referred to as ______________.
Allodynia (pain caused by stimulus that is normally not painful)
The primary regulators of neurogenic inflammation following tissue injury are _____________ and ______________.
- Substance P
- Calcitonin-Gene Related Peptide (CGRP)
(Substance P/CGRP) acts on mast cells causing degranulation and release of histamine.
(Substance P/CGRP) produces vasodilation of peripheral blood vessels.
Calcitonin-Gene Related Peptide (CGRP)
Axons from the spinothalamic tract terminate in the (VPL/VPM) of the thalamus.
Axons from the trigeminothalamic tract terminate in the (VPL/VPM) of the thalamus.
(T/F) The periaqueductal tract is essential for pain modulation and control.
The periaqueductal gray tract originates in the ________ nucleus and descends in the spinal cord to terminate in the (ventral/dorsal) horn.
- Raphe nucleus
- Dorsal horn
Raphe nuclei neurons may be activated by ___________ and ___________.
- Endogenous opioids (beta-endorphin, enkephalin, dynorphin)
- Opiate drugs
What is gate control theory and how does it relate to pain modulation, such as shaking your hand after striking your thumb?
- Smaller diameter fibers (Aδ and C) are activated during pain transmission. These smaller diameter fibers inhibit interneurons that would otherwise inhibit pain transmission.
- Activation of larger diameter fibers, such as Aβ that conduct pressure and vibration, will excite the inhibitory interneurons. This causes a dulling of the pain sensation perceived. Hence, you shake your hand to activate Aβ fibers to relieve pain.
Inhibitory neurotransmitters released from the dorsal horn in the spinal cord include:
- Endogenous Opioids
Inhibitory neurotransmitters released by pathways descending from the brain include:
- Endogenous Opioids
(Substance P/CGRP/Histamine) produces plasma extravasation and edema (the wheal).