Physiology of Peripheral Nerves Flashcards
What is the
- Epineurium
- Perineurium
- Endoneurium
- Surrounds entire nerve
- Encapsulates fasicles
- In the perineurium, surrounds axons
Where is the blood-nerve barrier?
Between the inner perineurium and endothelial cells of microvasculature within the endoneurium
2 types of Schwann cells associated with axons
Myelinating
Ensheathing
2 main variables that influence AP propagation rate
Fiber diameter (larger = faster) Myelin (greater the thickness and length = faster)
A, B, C designation is based on…
Conduction velocity
A is fastest, C is slowest (unmyelinated)
I, II, III, IV designation is based on…
Diameter
Used exclusively for sensory neurons
I is fastest, IV is slowest
Motor unit definition
An alpha motor neuron and all the muscle fibers it innervates
The alpha MN can branch many times, and each branch innervates a single muscle cell
What is the function of junctional folds on the post synaptic membrane?
To provide a large surface area for ACh receptor activation
Perijunctional zone
The site of muscle AP initiation
Segmental demyelination
Mildest form of nerve damage
The Schwann cells are compromised
Reduction in myelin thickness = slower AP propagation = prolonged M wave latency
Several adjacent segments lost = AP failure = reduced M wave amplitude
How does remyelination occur?
Requires trophic factors and cytokines released by damaged Schwann cells and affected axons
Triggers the proliferation of undifferentiated Schwann cells
Can differentiate into myelinating cells and wrap around bare axon
M wave
A compound muscle action potential (CMAP_
Evoked by peripheral nerve stimulation of alpha MN
Generated during muscle contraction
Amplitude = number of motor units activated
Latency = time to propagate
If you see
1. Decreased M wave with no change in latency
2. Decreased M wave and decreased latency
what does that mean?
- Axon problem
2. Myelin problem
