Clinical Application of Somatosensation Flashcards
Somatosensation is essential for what?
The accurate control of movements and protection against injury
What are the 4 pathways necessary to test for somatosensation?
- Discriminative touch
- Conscious proprioception
- Fast pain
- Discriminative temperature
What does quick screening for sensory impairment consist of?
Testing proprioception and vibration in the fingers and toes and testing past pain sensation in the limbs, trunk, and face with a pinprick
Do somatosensory tests test the ability to use somatosensation to prepare for and during movements?
No, they only require that the patient has conscious awareness and cognition
What is one way you can reveal the location of nerve pathologies?
recording electrical activity from nerves
What are 2 methods of examining sensory nerve function?
- Nerve conduction studies (NCSs)
- Somatosensory-evoked potentials (SEPs)
What do nerve conduction studies evaluate?
The function of peripheral nerves
How are NCS and SEP applied?
Electrical stimulation is applied to the peripheral nerve so that all axons are depolarized simultaneously
Nerve conduction studies only measure the performance of ___-diameter axons
large
Conduction velocity is slowed in what types of nerves?
demyelinated ones
What are the 3 numeric values that are compared in order to determine whether a NCS is normal
- Distal latency
- Amplitude of the evoked potential
- Conduction velocity
What is distal latency?
the time required for the depolarization evoked by the stimulus to reach the distal recording site
What do somatosensory-evoked potentials evaluate?
The function of the pathway from the periphery to the upper spinal cord or to the cerebral cortex
What are SEPs used to verify?
Subtle signs and locate lesions of the dorsal roots, posterior columns, and brainstem
What is ataxia?
Incoordination that is not the result of weakness
What are the 3 types of ataxia?
- sensory
- vestibular
- cerebellar
What test is used to distinguish between cerebellar ataxia and sensory ataxia?
Romberg test
What is neuropathy?
A general term for dysfunction or the pathologic condition of one or more peripheral nerves
What does complete severance of a peripheral nerve result in?
Lack of sensation in the distribution of the nerve, pain may occur, and sensory changes are accompanied by motor and reflex loss
What does compression of a peripheral nerve result in?
Decreased sensation or a feeling of a limb “falling asleep”
Describe the order in which sensory loss proceeds
1) Conscious proprioception and discriminative touch
2) Cold
3) Fast pain
4) Heat
5) Slow pain
What occurs when compression is relieved?
Sensations are returned in the reverse order that they were lost. Thus, aching pain occurs first, then a sensation of warmth, then sharp, stinging sensations, then cold, and finally a return of discriminative touch and conscious proprioception
What are the 3 common causes of dysfunction of the spinal region?
- Trauma to the spinal cord and complete or partial severing of the cord
- Disease that compromises the function of specific areas in the spinal cord
- Virus that infects the dorsal root ganglion
Describe sensory and motor loss following a complete severing of the spinal cord
All sensation is lost at one of two levels below the lesion and all voluntary motor control is lost below the lesion
Describe sensory loss following a hemisection of the spinal cord
- There is reduced sensation of pain and temperature on the contralateral side two to three dermatomes below the level of the lesion
- There is reduced sensation of discriminative touch and conscious proprioception on the ipsilateral side of the lesion
- There is a zone of complete loss of sensation on the ipsilateral side of the lesion, just below it
What sensations are lost in posterior column lesions?
Conscious proprioception, two-point discrimination, and vibration sense are lost below the level of the lesion
What occurs immediately after a posterior column lesion?
Movements are ataxic
What may occur in a posterior column lesion above C6?
The individual may be unable to recognize objects by palpation because ascending information from the hand has been lost
Infection of a dorsal root ganglion or a cranial nerve ganglion causes what?
Varicella zoster (aka shingles)
What is the major symptom of shingles?
severe pain
Do brainstem lesions causes ipsilateral and contralateral signs?
A mix of the two because the axons that carry sensory information from the body and face cross the midline at various levels
A lesion at what point in the brainstem will sensory loss be entirely contralateral?
In the upper midbrain after all discriminative sensation tracts have crossed the midline
A lesion of trigeminal nerve proximal axons or of the trigeminal nerve nuclei causes what?
An ipsilateral loss of sensation from the face
Lesions in the brainstem often cause mixed sensory impairments, affecting the _____ body and ____ face
contralateral
ipsilateral
What do thalamic lesions result in?
Decreased or lost sensation from the contralateral body or face
Do those who experience thalamic lesions (stroke) have severe pain in the contralateral body or face?
They rarely do
What does a lesion of the somatosensory cortex result in?
Contralateral sensory effects that include decreased or loss of discriminate sensations such as conscious proprioception, two-point discrimination, stereognosis, and localization of touch and pinprick (nociceptive) stimuli
When is the only time in which somatosensory cortex lesions are evident?
When symmetrical body parts are tested bilaterally, so that the person neglects stimuli on one side of the body when the other side of the body is stimulated simultaneously (unilateral neglect)
What is pain often associated with?
tissue damage or potential tissue damage, although it can be experienced independently of tissue damage
Even though nociceptors signal injury, their activity is insufficient to cause pain because pain is a ______.
perception
When nociceptors are stimulated by biochemicals released from tissue that is injured or ischemic they become excessively reactive to stimuli, what is this called?
peripheral sensitization
Unlike superficial pain, when does deep pain usually occur?
After the tissue has been damaged
What is the function of deep pain?
To encourage rest of the damaged tissue
What is referred pain?
Pain that is perceived as coming from a site distinct from the actual site of origin
When does referred pain occur?
When branches of nociceptive fibers from an internal organ and branches nociceptive fibers from the skin converge on the same second-order neurons in the spinal cord or in the thalamus, and the central neurons become sensitized
What does the pain matrix consist of?
Brain structures that process and regulate pain information and are capable of creating pain perception in the absence of nociceptive input
What brain structures does the pain matrix include?
parts of the brainstem, amygdala, hypothalamus, thalamus, and areas of the cerebral cortex
What is the experience of pain strongly linked to?
emotional, behavioral, and cognitive phenomena
What does the discriminative aspect of pain refer to?
The ability to localize the site, timing, and intensity of tissue damage or potential tissue damage
What does the motivational-affective aspect of pain refer to?
The effects of the pain experience on emotions and behavior, including increased arousal and avoidance behavior
What does the cognitive-evaluative aspect of pain refer to?
The meaning that the person ascribes to the pain
Describe the gate theory of pain
If low-threshold mechanical afferents are more active than nociceptive afferents, mechanoreceptive information is transmitted and nociceptive information is inhibited.
According to the gate control theory of pain where is pain transmission blocked?
in the dorsal horn of the spinal cord
What theory incorporates findings from research stimulated by the gate theory?
The Counterirritant Theory
What are the 4 states of dorsal horn processing?
- Normal
- Suppressed
- Sensitized
- Reorganized
Describe the mechanism of suppressed sensory processing in the dorsal horn
Touch, pressure, and vibration information is transmitted normally, but pain impulses are inhibited
Describe the mechanism of sensitized sensory processing in the dorsal horn
There are changes in neurotransmitters and receptors
Describe the mechanism of reorganized sensory processing in the dorsal horn
The structure of the dorsal horn has changed owing to cell death, degeneration of nociceptive axon terminals, and the sprouting of new terminals that synapse with neurons in the nociceptive pathways
Of the 4 states of dorsal horn processing, which are neuropathic (pain causing)?
Sensitized and Reorganized
What does neuropathic pain result from?
changes in neuronal activity, thus by neuroplasticity not by stimulation of nociceptors.
What is Antinociception?
the suppression of pain in response to stimulation that would normally be painful
What are the substances that activate antinociceptive mechanisms?
Endorphins
Endorphins bind to what kind of receptor?
Opiate receptors
The phenomenon of antinociception is summarized by a ___-level model
five
Where does level 1 of antinociception occur?
in the periphery
Where does level 2 of antinociception occur?
in the dorsal horn
What is level 3 called?
The fast-acting neuronal descending system, involving PAG, the rostral ventromedial medulla, and the locus coeruleus
What is level 4 called?
the hormonal system, involving the PVG in the hypothalamus, the pituitary gland, and the adrenal medulla
Level 5 is the _____ level
cortical
At what level do superficial heat and high-rate TENS act on?
Level 2
At what level does low-rate TENS act on?
Level 4
What is pronoception?
The biological amplification of pain signals
What is the mechanism of pronoception?
Edema and endogenous chemicals sensitize free nerve endings in the periphery intensifying pain signals
What causes acute pain?
Threat or actual tissue damage
How does a client report acute pain?
They give a clear, description of location, pattern quality, frequency, and duration of pain
What is the function of acute pain?
Acts as warning of tissue damage to enforce rest of healing tissue
What are the causes of chronic pain?
- Continuing tissue damage
- Environmental factors
- Sensitization of nociceptive pathway neurons
- Dysfunction of endogenous pain control systems
How does a client report chronic pain?
They give very vague descriptions
What is the function of chronic pain?
If tissue damage is not continuing, there is no biological benefit, but there may be a social or psychosocial benefit
What is nociceptive chronic pain due to?
continuing stimulation of nociceptive receptors
What is an example of nociceptive chronic pain?
Chronic pain that results from a vertebral tumor pressing on nociceptors in the meninges surrounding the spinal cord
The chemical changes that occur in chronically damaged tissues activates peripheral nociceptors which leads to what?
Primary hyperalgesia which is an excessive sensitivity to stimuli in the injured tissue
