87. Nerve fibres Flashcards
what are the main components of the PNS
nerves, ganglia, nerve endings
in peripheral nerves, what are axons covered by
Schwann cells or neurolemmocytes
the sheath may or may not form myelin around the axon
how is the thick myelin sheath formed in myelinated nerve fibres
the plasma membrane of each Schwann cells fuses around axon at a area called mesaxon.
moves circumferentially and wraps around axon many times
multiple layers of schwann cell membrane forms myelin sheath- which is a lipoprotein complex
Difference between nerves in PNS and CNS
CNS: axons enclosed in sheaths of glial cells (oligodendrocytes)
PNS: axons sheathed by schwann cells or neurolemmocytes
Difference between oligodendrocyte and schwann cells
oligo in CNS and may myelinate many axons at once
each schwann cell myelinate only one axon
The myelin sheath can be seen under high mag on TEM. What are the layers called
major dense lines
at what bit along myelin sheath does the major dense line disappear in order for movement of cytoplam for membrane maintenence
myelin clefts
How does schwann cells helps the function of the myelin sheath
membranes of schwann cells have a high proportion of lipids
myelin sheaths insulate axons and maintain constant ionic microenvornment suitable for action potential
What are the gaps between myelin sheath
nodes of Ranvier
has a higher conc of voltage gated Na+ channels at the nodes
saltatory conduction- faster transmission of action potentials
has unmyelinated nerves got faster conduction or slower conduction than myelinated
why
slower
no saltatory conduction bc no nodes of ranvier
evenly distributed Na+ voltage gated channels
they still have Schwann cells however they dont undergo multiple wrapping of it to form myelin sheath
why do nerves have a whitish glistening appearance
bc of their myelin and collagen content
nerve fibers are surrounded by eoisonphillic connective tissue sheaths.
what are these sheaths and what do they cover
axon is surrounded by endoneurium ( reticular fibers, scattered fibroblasts capillaries)
Bundles of nerve fibres covered by thicker perineurium (layers of this form blood nerve barrier)
The entire peripheral nerve is covered by the epineurium
peripheral nerves contains both afferent and efferent fibres
what is the difference
afferent fibres carry info to CNS
efferent fibres carry impulses from CNS to effector organs
Nerves possessing only sensory fibers are
called sensory nerves; those composed only of fibers carrying impulses to the effectors are called motor nerves. Most
nerves have both sensory and motor fibers and are called
mixed nerves, usually also with both myelinated and unmyelinated axons
What are ganglia?
Ganglia are typically ovoid structures containing neuronal
cell bodies and their surrounding glial satellite cells supported by delicate connective tissue and surrounded by a
denser capsule.
serves as relay stations to transmit impulses
the direction of the nerve impulse determines whether the ganglion is sensory or autonomic.
What is sensory ganglia
Sensory ganglia receive afferent impulses that go to the CNS.
they are asscociated with cranial ganglia and spinal ganglia
The neural cell body is associated with satellite cells
The neurons of these ganglia are
pseudounipolar and relay information from the ganglion’s
nerve endings to the gray matter of the spinal cord via synapses with local neurons.
