TOB S9 - Nerves and the ANS Flashcards
Describe the structure of a peripheral nerve bundle
Entire nerve surrounded by connective tissue called Epineurium
Nerve fascicles surrounded by Perineurium
Individual axons surrounded by Endoneurium
What are the 3 basic nerve cell types and how do their structures differ from one another?
Show some appreciation of their distribution in the body i.e. where they might appear.
Unipolar - No dendrites, one axon
Eg. Primary sensory neurones
Bipolar - One axon and one Dendrite, originate from opposite ends of the soma (cell body)
Eg. Rare, mostly found in the retina
Multipolar - Multiple dendrites originating from distinct locations on the soma, one distinct axon.
Eg. Most neurones
what surrounds peripheral nerve axons?
Describe the structure of this layer
Surrounded by a layer of Shwann cells (neurolemma)
The Shwann cells wrap themselves around the plasmalemma in several concentric layers. When this occurs the axon is said to be myelinated
What are nodes of Ranvier?
What process does they support?
Gaps in the myelin sheath (neurolemma) of an axon
Saltatory conduction
What special stain might be used to stain a myelin sheath and why is it used?
Osmium tetroxide
Due to a myelin sheath being an accumulation of plasmalemma of mostly lipid composition they stain poorly with routine histological processing using lipid solvents.
What cells produce myelin in the CNS?
What is the difference in their coverage of an axon as compared to Shwann cells?
Glial cells called oligodendrocytes.
They can coat up to 250 axons each, as opposed to only covering one axon partially as in Shwann cells
Describe the distribution of myelinated and un-myelinated neurones in the Autonomic and Somatic nervous systems.
The autonomic nervous system contains myelinated nerves in the CNS and un-myelinated nerves in the PNS
The somatic nervous system contains only myelinated neurones
Where do synaptic connections occur?
Between axon terminals and dendrites or another axon
What is released by excitatory neurones?
Glutamate/aspartate neurotransmitter
What is released by Inhibitory neurones?
Glycine/GABA (Gamma-amino butyric acid) neurotransmitter
Why does demyelination of an axon cause a drop in conduction velocity?
The impulse has further to travel along the plasmalemma due to inhibition of saltatory conduction/propogation
Give an example of a case where demyelination of axons may occur.
Explain the result of this.
In Multiple Sclerosis
Myelin sheath is removed from axon and replaced by scar tissue
Oligodendrocytes and axons can also be damaged.
The conduction velocity slows down as saltatory conduction is impaired. Scar tissue doesn’t permit conduction therefore axon is useless
What are some of the specialised structures of a neurone?
List them and explain the function of each
Nissl Substance - Aggregations of RER for protein synthesis
Axon Hillock - Contains a large amount of Nissl Substance and Voltage gated ion channels for protein synthesis and initiation of action potential respectively
Axon - transmission of an action potential
Dendrite - A branched cellular extension specialised for receiving input from axons of other neurones.
Explain the process of saltatory conduction
Due to Shwann cells high lipid content they do not conduct electricity.
this allows action potentials to jump between nodes of ranvier, hence decreasing the distance they must travel across the plasmalemma.
List the types of Glial cells.
What is the general function of Glial cells?
Astrocytes Oligodendrocytes Microglia Shwann cells Satellite cells
Main function of Glial cells is to support neurones, they also help maintain homeostasis and form myelin.
