Lecture 12: Pain and Vestibular Control Flashcards
Describe pain from stimulus to perception
- Transduction
- Transmission
- Modulation
- Perception
What is involved in transduction of pain
Translation of noxious stimulus into neural activity
What is involved in modulation of pain stimulus
Facilitation of inhibition of neurons and interneurons in spinal cord
What is involved pain perception
Result of the integration of projection pathways with modulation, to produce final conscious subjective and emotional response
What is mechanical deformation in pain perception
Stretches or damages the receptor membranes and opens ion channels
What is the result of application of chemicals in pain perception
Opens ion channels in chemoreceptors
What is the result of the change in temperature in pain perception
Alters permeability of the membrane of thermoreceptors
Pain is detected through ___
Free nerve endings
___fibers detect immediate, sharp pain
A-delta fibers
__fibers detect dull, burning pain
C- fibers
Are free nerve endings myelinated or non-myelinated
Non-myelinated
Where are pain free nerve endings located
Skin, joints, internal organs, and bones
T or F: pain occurs in brain
False, no pain free nerve endings in brain
What do transient receptor potential channels detect
Detect temperature
__ receptors increase AP frequency with an increase in temperature or certain chemicals
Warm receptors
Where are warm receptors located
C- nerve fibers
___ receptors increase AP frequency with decrease in temperature
Cold receptors
Where are cold receptors located
Alpha-delta nerve fibers with non-myelenated endings
What is the resting skin temperature
30 degrees Celsius
At what temperature are heat nociceptors activated at
> 45 degrees Celsius
Which fibers have mechanical nociceptors and noxious thermal nociceptors
Alpha-delta fibers
Which receptors respond to mechanical damage- cutting, crushing, pinching
Mechanical nociceptors
What receptors respond to extreme heat and cold
Noxious thermal nociceptors
What fibers contain thermal nociceptors and polymodal nociceptors
C-fibers
What do receptors respond to thermal gradients
Thermal nociceptors
What receptors respond to various noxious, damaging stimuli- thermal, mechanical and chemical
Polymodal nociceptors
How many pathways are required to transmit pain to the brain and what are they
3
1. First order sensory neuron
2. Second order sensory neuron
3. Third order sensory neuron
What is the first order sensory neuron
Afferent neuron in the periphery that first detects pain signal
Where is the cell body for first order sensory neuron located
DRG
Where is the cell body of second order sensory neuron located
Soma in spinal cord or brain stem
Where is the third order sensory neuron located
Located in thalamus, synapses in cortex (layers 2-6)
What pathway does pain travel on
Spinothalamic, specifically lateral spinothalamic
Where does the 2nd order synapse occur
Thalamus
What does the 2nd order synapse relay
Perception of pain
Where does the 3rd order synapse occur
Somatosensory cortex
What does the 3rd order synapse relay
Location of pain
Are nociceptors adaptive or non-adaptive
Non-adaptive- nociceptors are activated as long as lesion is present
Tissue damage causes hyperalgesia which is
Increased sensitivity to pain
What fibers are activated on initial/acute pain stimulation
Alpha-delta fibers
Which fibers are activated over time, dull pain sensation that increases in intensity
C fibers
Inflammatory response to pain over time releases…
Bradykinins, prostaglandins, substance P, K+, and H+
___ in the ECF stimulate polymodal nociceptors and contribute to tissue inflammation
Bradykinins
____stimulates mast cells to release histamine
Substance P
___enhances pain sensitivity beyond the somatosensory circuit
Substance P
Describe the pathway/mechanism of action of substance P
- Substance P binds a neurokinin 1 receptors in neurons and numerous other non-neuron cell types
- Initiates vasodilation and inflammation
- Sensitizes afferent pain fibers to increase pain perception
Repeated stimulation of ___ fibers enhances pain
C fibers
Repeated stimulation of dorsal horn neurons causes ____
Central sensitization
Central sensitization results in the recruitment of additional ___ receptors that make C fibers more sensitive
Glutamate receptors
Central sensitization, recruitment of glutamate receptors to make C fibers more sensitive results in ____ of C-fiber nociceptors
Memory
Where is pain modulated
CNS
What is the endogenous opioid mechanism
Pain relieving pathway, activate opiate receptors that block release of substance P in the spinal cord and periaqueductal gray matter of the mid brain
The pain afferent neuron releases ___ as NT. Another neuron releases ___ at presynaptic synapses to inhibit release of ___ and alleviate pain
Pain neuron: substance P
Another neuron: enkephalin
Inhibit release of: substance P
What NT is released to counteract the pain initiated by substance P
Enkephalin
What are the endogenous opioid substances
Endorphins, enkephalins (met-Enk and Leu-EnK) and dynorphins
What are endogenous opioids synthesized by
Nerve cells
What drugs mimic actions of endorphins at synapses in pain modulating networks
Morphine, Demerol and perocdan
What drug blocks the pain modulating/relieving action
Naloxone- mu-Opiod receptor competitive antagonist
Where are mu-receptors concentrated
Dorsal horns in spinal cord
What is the preferred receptor for B-endorphin
Mu/delta
What is the preferred receptor for endomorphin-1 and 2
Mu
What is the preferred receptor for met-enk and leu-enk
Delta
What is the preferred receptor for dynorphin A and B
Kappa
Describe the descending pathway of pain regulation
- Noxious stimulus on nociceptor
- Travel on afferent pain fiber
- Release substance P
- Signal periaqueductal gray matter
4a. Periaqueductal gray matter acts on medulla and reticular formation to activate inhibitory inter neuron in DH
4b. Periaqueductal signals to active enkephalin releasing neurons - Enkephalin releasing neurons act on raphe nucleus in brain stem
- Raphe nucleus release serotonin on inhibitory neuron
- Inhibitory neuron releases endogenous opiate to counteract substance P
How does an epidural nerve block work with opioids and other drugs
Epidural blocks somatic and visceral pain by blocking transmission of pain without interfering with sensory and motor function or depressing SNS.
Opioids bind opioid receptors
How do serotonin and NE modulate pain
Act by stimulating enkephalin releasing interneurons or pain modulating nuclei in brainstem
How do NSAIDS affect pain control
Block COX2, critical enzyme to synthesize prostaglandins, this decreases sensitization to pain
How do endocannabinoids modulate pain
Modulate pain following sustained physical activity
How do exogenous opioids modulate pain
Agonize endogenous opioid receptors
The ___ system measures orientation, position and movement of head
Vestibular
What does the vestibular system measure
Static tilt of head, linear acceleration, and rotary acceleration
What movements are facilitated by vestibular system
Correction of posture and balance, maintain focus of the eyes and head moves
__bone houses the vestibular system and cochlea
Temporal bone
The vestibular system is composed of 3 ___ and 2 ___
3 semicircular canals and 2 ampullae
Which structure contains ridge of hair cells
Ampulla, Crista ampullaris
2 ampulla are connected to a ___ and ___
Utricle and saccule
What fluid are the utricle and saccule coated in
Endolymph
Hair cells synapse with a ___ at the base
Sensory neuron
sensory neuron in a hair cell leads into the ___nerve
CN VIII
Bending towards the large cilia causes ___ channels to open
K+
Membrane depolarization of the hair cells causes __channels to open
Ca2+
Opening of Ca2+ channels within the hair cells causes exocytosis of ___ and __
Glutamate and aspartate
Bending the hair cells in the opposite direction of large cilia results in ___
Hyperpolarization
___detect rotational acceleration and deceleration
Semicircular canals
___ causes a bend in the cupola in the opposite direction
Deceleration
Canals on opposite side of the head provide ___information
Directional
Ex: if you rotate head clockwise the direction of flow would be ___ in each canal, providing information on direction
Opposite
___ and ___ detect linear acceleration and deceleration
Utricle and saccule
__ detects horizontally oriented macula
Utricle
___ detects vertically oriented macula
Saccule
___ and ___ detect head tilt
Utricle and saccule
When the head tilts the ___ pull down causing the firing rate to change
Otoliths
___ and ___ cause cilia to bend in opposite direction than the movement of the head
Otoliths and endolymph
Utricle and saccule otolith organs project to the ____ to facilitate alpha-gamma co-activation
Vestibulospinal tracts
Crista ampulla of the semicircular canals feed the ____ to provide compensatory eye movements in response to rotation
Medial longitudinal fasciculus
___ receives and returns input to fine tune coordination of postural and oculomotor reflexes
Flocculonodular node of the cerebellum
What are the 3 targets of CN VIII via the vestibular nuclei
- Vestibulospinal tracts
- Medial longitudinal fasciculus
- Flocculonodular node of the cerebellum
What is the vestibuloocular reflex
Eyes rotate to head movement to allow unchanged visual perception of a target
What is the goal of the vestibuloocular relfex
Move extraoccular eye muscles to maintain visual contact with the target
When the head is rotated what structures are activated
Canals and otoliths
What nerve and nucleus are activated with head rotation
Vestibular nerve and nuclei
What tracts are activated when you rotate the head
Lateral and medial vestibulospinal tracts
What side are extensors and flexors activated on when the head is rotated
Extensors are induced on the side to which the head is rotated and the flexors are induced on opposite side
During VSR the vestibular sensory nerves synapse on the nerves in ___ nuclei
Vestibular
During VSR the neurons in the vestibular nuceli act on ___ muscles via the ___ tract, facilitating several vestibular reflexes
Axial muscles, vestibulospinal tracts
What does the extrapyramidal tract do during VSR
Control the eye and head position to maintain eyes on target while head or body is in motion
What is the vestibulo-colic reflex
Head and neck muscles adjust to maintain head position
What is peripheral vestibular syndrome
Labyrinth within petrosal bone affected, associated with head tilt
What is central vestibular syndrome
Brain stem is affected, associated with paresis, hemiparesis, gait and posture effects
How can a middle ear infection cause vestibular signs
Infection leads to pressure on the round/oval window of the cochlea and leads to head tilt.
Pressure difference causes unbalanced AP frequency
What are 4 very common signs of vestibular syndrome
Head tilt, nystagmus, ataxia, loss of balance
