PNS fiber classification (Quiz 5) Flashcards
The formal boundary between the CNS and PNS is hard to see, but is a line where….
oligodendrocytes change to Schwann cells
Nerves are large bundles of axons, subdivided into….
fascicles
What is the epineurium mainly composed of?
collagen (strong, unbranched, fibers go in 1 direction) and fibroblasts (cells that form new CT)
The epineurium is a loose sheath that surrounds peripheral nerves. It is thicker and more substantial around nerve trunks and closer to the spinal cord, and gets thinner at the ends of small branches and terminations. Peripheral nerves have a high tensile strength due to the collagen. What is continuous with the epineurium centrally?
dura mater
The perineurium is a thin layer of concentrically arranged cells that has some collagen fibers interspersed. What is the perineurium continuous with centrally?
arachnoid mater
The perineurium has perineural cells that have tight cell junction. What does this isolate?
epineural space and endoneural space
The perineurium wraps fascicles. Each bundle is associated with a blood vessel. The endothelium of the capillaries are connected by tight junctions. This is a functional equivalent of the arachnoid BBB. This is called the ____________________. It shares many structural features with the BBB with the exception of astrocytes and the glial limiting membranes formed by astrocytes. In order to reach the endoneurial extracellular space, molecules need to cross the perineurium that surrounds the nerve fascicle.
blood nerve barrier (BNB)
At the distal ends of a nerve, the perineurium continues, forming _________ of pacinian, meissners corpuscles, muscle spindles, and golgi tendon organs
capsules
The _______________ is a loose connective tissue sheath within the perineurium. It surrounds individual fibers and provides isolation
endoneurium
The endoneurial tube is a distensible _________ structure containing some matrix of the collagen tissue. It has a nutritive and protective function with properties analogous to the BBB.
elastic
The endonerium plays an important role in fluid pressure. By maintaining a light positive pressure in the endoneurial space, it guarantees a constant environment for the nerve. Within the endoneurium, individual nerve fibers are surrounded by a liquid called the ___________________. It is similar to CSF in the CNS. During nerve irritation or injury, the amount of fluid may increase at the site of damage
endoneurial fluid
The 3 distinct speeds recorded after peripheral stimulation have been named….
A, B, and C
The fibers for the A tracing are A fibers and are myelinated sensory, motor, or both?
both
B fibers are myelinated __________ fibers
visceral
C fibers are myelinated or unmyelinated?
unmyelinated
The other classification system is based on direct measurement of the axonal diameter. The axons are subdivided into….
I, II, III, and IV
The other classification system is based on direct measurement of the axonal diameter. What are the myelinated fibers?
I, II, and III
note: I is larger than II, and III has the smallest diameter
The other classification system is based on direct measurement of the axonal diameter. What are the unmyelinated fibers?
group IV
Both PNS fiber classification systems are used by unmyelinated fibers are generally called….
C fibers not IV
The A fibers can be further divided into….
alpha, beta, delta, gamma
A alpha fibers are the largest diameter and the fastest
A delta are the slowest
The large axons innervating fibers of skeletal m. are….
A alpha (usually will just say alpha)
The smaller axons innervating intrafusal muscle fibers are….
A gamma (usually will just say gamma)
Preganglionic ANS fibers are in their own category and are called ______ fibers
test q
B
The I fibers are all myelinated afferent. The largest group in I are found in muscle nerves and are split between 2 subdivisions. What are they?
1a= spindle primary fibers
1b= golgi tendon organ fibers
Fibers in group II correspond with which group from the other classification system?
A beta
Fibers in group III are small myelinated afferents, these are free nerve endings and transmit info on cold, sharp pain, hair movement, and visceral mechanoreception. These fibers correspond with which group from the other classification system?
A delta (usually just called delta fibers)
Where are muscle spindles found?
within belly of muscles between extrafusal muscle fibers
The specialized fibers that constitute the muscle spindle are known as ______________ and are stretch receptors that primarily detect changes in the length of the muscle. They contribute to fine motor control and providing axial and limb position info
intrafusal fibers
What is the purpose of muscle spindles and the stretch reflex?
protect the body from injury caused by over-stretching and to maintain muscle tone
Golgi tendon organs are proprioceptors that are specialized sensory receptors located within….
joints, muscles, and tendons
Golgi tendon organs are sensitive to what?
tension and pressure
As tension in the muscle increases, discharge of the golgi tendon organs ____________
increases
