pns Flashcards
What are the 4 types of peripheral neuropathy?
- Mononeuropathy: damage to a single nerve
- Polyneuropathy: damage to more than one nerve
- Radiculopathy: damage to affecting a spinal nerve
- Plexopathy: damage to one of theplexuses
Mononeuropathy vs polyneuropathy origin
mono- mechanical injury
poly- systemic/metabolic pathology- longest fibers are affected first
dysthesia:
abnormal sensations whether provoked by stimuli or not
hypoesthesia
a decrease in sensory perception
hyperesthesia
an increase in sensory perception
paresthesia
unusual feelings, such as pins and needles without any stimulus
hyperalgesia
normally painful stimuli are perceived as even more painful than usual
Allogynia
previously non painful stimuli are now painful (bed sheets on feet)
What are the 3 different levels of severity for a peripheral nerve injury?
- Neuropraxia- mild– axon remains intact myelin is just mildy effected
- Axonotmesis- severe, damage to axon but myelin is intact; can recovery slowly
- Neurotmesis- damage to myelin and axon; no myelinated path for the neuron to regrow
what are the clinical implications for a dymylenating peripheral injury in terms of : weakness, reflexes, distribution, infection, conduction velocity, symptom progression.
- weakness more diffuse
- early loss of reflexes
- non length dependant distribution
- rapid ascending symptoms
- preceding infection
- conduction velocity decreased
what are the clinical implications of an axonal peripheral injury in terms of: weakness, reflexes, distribution, symptom progression and conduction amplitude.
- weakness is more distal
- reflexes are less affected
-length dependant distribution - usually chronic progression
conduction amplitude decreased
What are the clinical implications of GBS (motor, sensory, autonomic)
- it is a demyelinating condition usually following a recent infection
- Sensory: numb/tingling feet that ascends; sometimes neuropathic pain in face and trunk; large fiber> small fiber impairment
- Motor: distal> proximal weakness, ascends; opthalomoplegia and/or ptosis in 5-15%
- Autonomic: hypertension/hypotension; cardiac arrhythmia
What causes diabetic neuropathy?
Due to axonal damage
stocking and glove symptoms because distal axonal damage is first (lack of blood supply to neurons due to blood damage)
What part of the spinal cord does poliomyelitis effect?
anterior horn of cell bodies (LMN)
What part of the spinal cord does Tabes Dorsalis effect?
dorsal column damage due to neurosyphillis
What is the neuroanatomical basis of ALS
chronic progressive disease of corticospinal tracts and neurons of anterior grey horn
Syringomyelia
tube like enlargement of the central canal due to buildup of CST
How many pairs of spinal nerves?
31
how many pairs of cranial nerves?
12
What is a nerve plexus? examples?
a reorganization of nerves- you end up with mixed terminal nerves that can do a variety of functions
Brachial plexus (C5-T1) Lumbar plexus (T1-L4)
what is the endoneurium of a peripheral nerve?
fills the space between a bunch of axons
what is the perineurium of a peripheral nerve? what does it form?
surrounds a bunch of neurons with the endoneurium around them
nerve fasicle- same modality- carrying either sensory or motor neurons
what is the epineurium of the PNS? what does it form?
surrounds a bunch of fasicles and forms a proper peripheral nerve
In terms of peripheral fibre types, earlier numbers and letters are what?
larger and more likely to be myelinated, therefore have faster conduction
The different sensory receptors differ in which 4 ways?
Adaptability
Speed
Sensitivity
size of receptor field
What are dermatomes?
an area of skin supplied by a single spinal nerve
What do we mean when we say there is overlap between dermatomes?
There is significant overlap of dermatomes, especially for pain sensation, so for complete loss of sensation to occur three or more adjacent segments of the spinal cord would need to be damaged or disconnected from the brain.
what is a motor unit?
a single alpha motor neuron and the muscle fibers it innervates.
what does the number of muscle fibres per neuron in a motor unit depend on?
how much precise control is required
What is the neuromuscular junction or motor end plate?
similar to a synapse, except the post synaptic site is a muscle fiber and not another neuron
what is the NT at the NMJ/motor end plate?
achetylcholine
What are myotomes
areas of muscle that are innervated by one nerve root
Why are myotomes difficult to test individually? What helps this?
myotomes contribute to many different muscles so they are difficult to test individually
some spinal levels contribute to certain muscle groups to a greater degree than others
you need to test several myotomes to hone in on where there may be damage
What is the process of skeletal muscle inntervation at the motor end plate (6 steps)
- AP signal comes down
- Voltage gated Ca+ channels open
- Ca+ influx causes NT filled vesicles to fuse with cell membrane
- ACh is released into the synaptic cleft and binds to receptors , causing the ion channels to open
- ACh binds to the post synaptic receptors and causes influx of Na+, which depolarizes the cell
- post synaptic cell depolarizes, causing the opening of voltage-gated Ca+ channels, initiating muscle contraction.
which peripheral neuropathy is more likely due to mechanical damage as opposed to pathology ?
axonal- demyelinating damage is likely due to a systemic pathology.
what are the clinical implications for myathenia gravis
an autoimmune condition where antibodies attack the acetylcholine receptors at the NMJ.
how many cervical SC segments are there?
8
How many thoracic SC segments are there?
12
how many lumbar SC segments are there?
5
how many sacral SC segments are there?
5
How many coccygeal SC segments are there?
1 (usually)
What is the cauda equina?
combination of all the lumbar rootlets
what is the conus medullaris?
the end of the spinal cord
