PNS diseases Flashcards
What are Negative manifestation?
Negative Manifestations
Partial or complete loss of normal function→Less of something
What are positive manifestations?
Positive Manifestations
Excess of normal function→More of something
What are the negative manifestations of PNS diseases?
Negative Manifestations • Paresis or paralysis Paresis: Partial or incomplete paralysis Paralysis: Loss of voluntary muscle movement • Hyporeflexia or areflexia Hyporeflexia: Reduced deep tendon reflexes Areflexia: Absence of these reflexes • Anhidrosis Absence of sweating
Numbness
Partial or complete loss of sensations
What are the positive manifestations?
Positive Manifestations • Fasciculations Involuntary contractions or twitching of groups (fascicles) of muscle fibers • Paresthesia Subjective report of abnormal sensations, such as tingling, or what is colloquially described as “pins and needles” • Pain Such as brief attacks of severe, sharp, shooting facial pain in trigeminal neuralgia
Describe assessment of patients with PNS disease
Things to consider in the assessment of the patient with signs and symptoms of a peripheral nervous system disease:
• Onset and progression Acute versus chronic
• Parts of the nervous system affected Sensory, motor or sensorimotor (both), autonomic
• Number of nerves affected Mononeuropathy: single nerve Polyneuropathy: multiple nerves
• Histopathology
Small fibers versus large fibers, myelinated versus unmyelinated
-electrophysiological consequences
Demyelination, axonal damage, and nerve conduction studies
What are patch clamp recordings?
- Patch Clamp Recordings
- Primarily used in research labs
- Measure electrical current running through small membrane patches of neurons and the ion channels located within these patches
What are intracellular recordings?
- Intracellular Recordings
- Primarily used in research labs
- Measure changes of the electrical potential (resting potential, graded potential, action potential) of a single neuron
What are extracellular recordings?
Extracellular recordings
Frequently used in clinical medicine
- Examples are electroencephalogram (EEG) and nerve conduction studies (NCS)
- Measure electrical potential changes of several cells surrounding the recording electrodes
- Signals from individual cells overlap, and the recording shows the sum of the electrical activity of all of these cells
What causes Carpel tunnel syndrome?
- Occurs due to reduction in tunnel size, such as swelling of tendon sheaths or swelling of soft tissue due to edema.
- Occurs spontaneously often in middle- aged women, during pregnancy and with hypothyroidism.
- Pain and/or tingling sensation in the cutaneous distribution of the thumb, index and middle fingers.
- Difficulty in handling small objects, due to muscle weakness of thenar eminence
What happens after Wallerian Degeneration?
Regeneration begins after Wallerian degeneration is complete. Schwann cells play a major role in promoting axonal regeneration.
Describe axonal sprouting after axonal injury/regeneration
Axonal sprouting may occur. The sprouts may use the myelin debris as guiding tubes for regrowth.
In some instances, cells may survive the axonal injury, but sprouting axons make navigational errors, re-growing to the wrong targets, yielding aberrant motor output during attempts at volitional movement (e.g., blinking instead of smiling,
salivating instead of sweating).
Describe axonal regrowth
Nerve growth factor (released from Schwann Cells), laminins and adhesion molecules promote regrowth. The probability of successful regrowth is higher when the site of injury is closer to the original target
When does remyelination occur?
After regrowth of axons
Describe the reinnervation of the muscle
Reinnervation of the Muscle depends on Basal Lamina
• Basal lamina intact – axon reinnervates muscle at same point
- Basal lamina lost – No reinnervation
- Critical components of the basal lamina are laminins and agrin.
- Laminin 11 – expressed at synaptic junction, prevents Schwann Cell invasion
Describe regeneration in the CNS after axonal injury
When axons in the central nervous system are cut or badly crushed, they rarely regenerate over a significant length because:
• Oligodendrocytes do neither release nerve growth factor, nor do they guide regenerating axonal sprouts.
• Astrocytes multiply in regions of trauma and form glial scar tissue, which acts as a mechanical barrier to sprouting axons. This process is called gliosis.
• There is an inhibitory chemical messenger released within the central nervous system that opposes axonal regeneration in the adult
