BIOM20002 Lecture Notes - Lecture 2: Extracellular Fluid, Dorsal Root Ganglion, Tight Junction
○
Myelination allows impulse to jump between nodes. Myelating doesn’t actually help thin
axons. Better for thicker axons
○
•
A bundle of axons in CNS is called a tract, in PNS is called a nerve
•
Axons in the periphery cluster together to form nerves - collections of thousands of individual
axons within a common external connective tissue sheath (epineurium). Within the nerve
axons are sub-grouped into fascicles surrounded by a perineurial sheath
•
HSF Page 8
•
Nerves have much connective tissue for protection.
•
Epineurium: connective tissue (fibroblasts etc.)
•
Perineurium: connective tissue around a group of axons
•
Endoneurium: connective tissue around a single nerve fibre
•
Astroglia: (astrocytes) a type of glial cell. Have numerous functions including recycling of
neurotransmitters and maintaining the ionic composition of the extracellular fluid. A
supporting role. Highly branched
•
•
Blood brain barrier: a property of CNS endothelial cells conferred by astrocytes. Nothing to do
with meningies.
•
HSF Page 9
Document Summary
A bundle of axons in cns is called a tract, in pns is called a nerve. Axons in the periphery cluster together to form nerves - collections of thousands of individual axons within a common external connective tissue sheath (epineurium). Within the nerve axons are sub-grouped into fascicles surrounded by a perineurial sheath. Perineurium: connective tissue around a group of axons. Endoneurium: connective tissue around a single nerve fibre. Have numerous functions including recycling of neurotransmitters and maintaining the ionic composition of the extracellular fluid. Blood brain barrier: a property of cns endothelial cells conferred by astrocytes. Endothelial cells that make up capillaries form tight junctions. This means nothing leaks out of vessels unless it is small enough. So lipid soluble things (o2 and co2) and small molecules like glucose can pass through the endothelia to the brain. The structure of nerves cells reveals their penchant for connectivity.
