TOB S9 - Nerves and the ANS Flashcards Preview

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Flashcards in TOB S9 - Nerves and the ANS Deck (33):

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?

Shwann cells
Satellite cells

Main function of Glial cells is to support neurones, they also help maintain homeostasis and form myelin.


What is the specific function of an Astrocyte and where can they be found in the nervous system?

Form the blood brain barrier
Assist in transfer of nutrients and waste

Found in the CNS


What is the specific function of an Oligodendrocyte and where can they be found in the nervous system?

Myelination of CNS neurones, up to 250 axons per cell

Found in the CNS


What is the specific function of a Microglia and where can they be found in the nervous system?

Immune and inflammatory functions

Found in the CNS and PNS


What is the specific function of a Shwann cell and where can they be found in the nervous system?

1 axon per cell

Found in the PNS


What is the specific function of a satellite cell and where can they be found in the nervous system?

Physical support of peripheral neurones (afferent and efferent)

Found in the PNS


what are the Two functional branches of the nervous system?

Autonomic and Somatic nervous system


The Autonomic nervous system has three branches, what are they?



What is the anatomical composition of the ANS?

What is a ganglion?

ANS is comprised of many series of 2 neurones

One pre ganglionic (White Rami Communicantes)
One post ganglionic (Grey Rami Communicantes)

A ganglion is a collection of cell bodies in the PNS


How do neurones of the Autonomic nervous system exert action?

Via smooth muscles, viscera and secretory glands


How is the difference between sympathetic and parasympathetic nervous system reflected anatomically?

Sympathetic nerves exit the spinal cord at the Thoraco-lumbar outflow
Short pre-ganglionic fibres and long post ganglionic fibres

Parasympathetic nerves exit the spinal cord at the Cranio-sacral outlow
Long pre-ganglionic fibres and short post-ganglionic fibres


Where might the synapse of a sympathetic pre-ganglionic to post-ganglionic nerve be located?

May synapse at a ganglion at the same level as origin (para-vertebral origin)

May synapse at a ganglion of different level than origin

May not synapse in the para-vertebral ganglion chain.


What structure is formed by ganglia present immediately laterally of the spinal cord?

The para-vertebral ganglion chain


Where are ganglia of the sympathetic nervous system found?

In all 12 thoracic levels and the first 2 lumbar levels of the spinal cord.


What are the functions of the sympathetic nervous system?

Fight/Flight/Fright response

Diversion of blood to muscles and heart
Reduce blood flow to GI tract and skin
Increase heart rate
Increase blood pressure


What are the functions of the para-sympathetic nervous system?


Reduce heart rate and force of contraction
Promotes digestion
Promotes bodily functions such as passing urine
Promotes sleep


Describe the in detail the neurotransmitters involved at synapses of the sympathetic nervous system.

Pre-ganglionic neurones are cholinergic (secrete acetylcholine)
Post ganglionic nerve express nicotonic acetylcholine receptors

Post ganglionic neurones are noradrenergic (secrete noradrenaline)
Effectors express Alpha (1 or 2) or Beta (1 or 2) receptors
Exception: Perspiration and ejaculation pathways are cholinergic


Describe in detail the neurotransmitters used at synapses of the para-sympathetic nervous system.

Pre-ganglionic neurones are cholinergic (secrete acetylcholine)
Post-ganglionic neurones express nicotonic acetylcholine receptors

Post-ganglionic neurones are cholinergic


How do drugs affecting the ANS exert their effect?

Through modulation of neurotransmitter release and binding to receptors or by imitating the action of neurotransmitters