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Unit 3 - PNS Pain (Pain
An unpleasant sensory/emotional experience…
Unit 3 - PNS Pain
Pain
- An unpleasant sensory/emotional experience associated with actual/potential injury
- Subjective
Pain Threshold
- Lowest intensity which a stimulus is perceived as pain
- Doesn't really vary in the same person over time
- Intense pain at one location may increase threshold in another location (Perceptual Dominance)
Pain Tolerance & Expression
- Max intensity/duration that a person is willing to endure
- Varies, and depends on conditions (like emotion and stress)
Types of Pain
Acute Pain
- From tissue injury
- Gone when injury heals
Clinical Manifestations
- SNS activation
- Pallor, sweating, nausea, anxiety
- Pacing, grimacing, crying, moaning
Chronic Pain
- Could be d/t disease process
- Lasts longer than expected healing time (>6 months)
Clinical Manifestations
- Depression
- Insomnia
- Changes in appetite
Cutaneous Pain
- Skin or subcutaneous structures
- Sharp pain with burning quality
- Abrupt or slow onset
- Accurately located
Visceral Pain
- Pain from some organs
- Diffuse
- From ischemia, stretching, distension
- Can be referred pain
Phantom Limb Pain
- After amputation
- 70% of amputees
- Spinal nerves fire d/t loss of sensory input
- Begins as tingling, heat/coldm heaviness, then burning, cramping, or shooting pain
Pain in Children & Elderly
- Children experience & remember pain
- Pain is NOT normal with aging
Spinal Cord Injury (SCI)
- Damage to vertebrae, nerves, & supporting ligaments of spinal cord
- Compressed, transected, contused
- Complete/incomplete
- Young males 3-4x likely
- Hyperflexion, hyperextension, compression
Hyperextension
- Sudden bend
eg: Hitting chin on desk when falling
Compression
- Squished
eg: Diving down too fast, head hits rock, spine compressed and crushed
Hyperflexion
- Sudden stretch
eg: car crash, head lurches forward
Autonomic Dysreflexia (AD)
- Life-threatening condition in people with SCI at T6 or above
Pathphysiology
- Visceral stimulus activates sympathetic reflexes below injury
- Peripheral nerves carry impulse to spinal cord
- Stimulates thoracolumbar sympathetic nerves
- Causes vasoconstriction
- HTN stimulates baroreceptors in neck (CN 10)
- Reduces HR (bradycardia) and induces vasodilation, sweating, headache ABOVE injury
- Baroreceptor signaling can't descend past injury, so no reduction in vasoconstriction/HTN BELOW injury
- Continued dangerous positive feedback cycle until stimulus is removed
Etiology
- Visceral stimulus
- Distended bladder (most common)
- Full rectum
- Pressure sore
- Ingrown toenail
- Infection
- etc.
Clinical Manifestations
- HTN with SBP > 20 mm Hg above baseline or >300 mm Hg
- Pale, cool, most skin BELOW injury
- Vasodilation/sweating/headache ABOVE injury
Treatment
- Remove stimulus whiel monitoring BP
- Place in upright position & remove restictive clothing to allow venous pooling (lowers BP)
- Patients must have regular bowel/bladder routines
Types of Neurons
1st Order Neurons
- Transmits sensation from periphery to CNS
-
3rd Order Neurons
- Transmit informations from thalamus to cerebral
Nociceptor
- Receptor at end of sensory neurons
Nociception (4 stages)
- Transduction
- Damaged cell releases neurotransmitter & makes an AP
- Transmission
- Movement of AP from nociceptor to CNS
- Perception
- Brain recognizes and responds to pain
- Modulation
- Descending pathways inhibit pain transmision
Transmission
- Dorsal horn --> interneurons --> cross to anterolateral tract
- Nociceptors terminate in spinal cord
Anterolateral tract to...
- Neospinothalamic tract A-delta fibers --> thalamus
or...
- Paleospinothalamic tract C fibers --> RAS --> Thalamus
Thalamus to...
- Limbic cortex (emotional cortex)
or...
- Orimary somesthetic cortex (location,intensity) --> Cortical centers (cognition)
Perception
- Recognizing & defining painful stimuli
3 factors
- Frequency of AP = intensity of stimulus
- More activated receptors = more intense stimulus
- Location of stimuli (sensory homunculus)
Modulation
- Efferent pathways to control pain response
- Impulses from brain --> brain stem --> down spinal cord
Endogenous Analgesic Mechanisms
- Opioid receptors & synthesized opioid peptides in afferent neurons
- 3 families of opioid peptides
- Enkephalins
- Endorphins
- Dynorphins
- All reduce Ca2+ to block pain transmission
Gate Control Theory
- Pain signals have neurological gates in spinal cord
- Non-painful stimulation of Alpha-Beta fibers (eg: rubbing, touching) can close the gate and suppress pain
2 Types of Neurons
A-Delta
- 10%
- Large, myelinated
- Fast pain
- Sharp
- Thermal, mechanical
C-Fiber
- 90%
- Small, unmyelinated
- Slow
- Burning, aching, throbbing
Bell Palsy
- Idiopathic neuropathy of CN 7
- Paralysis of one side
- Virus causing inflammation around nerve
Clinical Manifestations
- Develops rapidly over 24-48hrs
- Unilateral facial weakness
- Facial droop/diminished eye blink
- Hyperacusis (intolerance of everyday sound)
- Decreased lacrimation