TOB S9 - Nerves and the ANS

Question 1

Describe the structure of a peripheral nerve bundle

Answer 1

Entire nerve surrounded by connective tissue called Epineurium

Nerve fascicles surrounded by Perineurium

Individual axons surrounded by Endoneurium

Question 2

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.

Answer 2

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

Question 3

what surrounds peripheral nerve axons?

Describe the structure of this layer

Answer 3

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

Question 4

What are nodes of Ranvier?

What process does they support?

Answer 4

Gaps in the myelin sheath (neurolemma) of an axon

Saltatory conduction

Question 5

What special stain might be used to stain a myelin sheath and why is it used?

Answer 5

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.

Question 6

What cells produce myelin in the CNS?

What is the difference in their coverage of an axon as compared to Shwann cells?

Answer 6

Glial cells called oligodendrocytes.

They can coat up to 250 axons each, as opposed to only covering one axon partially as in Shwann cells

Question 7

Describe the distribution of myelinated and un-myelinated neurones in the Autonomic and Somatic nervous systems.

Answer 7

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

Question 8

Where do synaptic connections occur?

Answer 8

Between axon terminals and dendrites or another axon

Question 9

What is released by excitatory neurones?

Answer 9

Glutamate/aspartate neurotransmitter

Question 10

What is released by Inhibitory neurones?

Answer 10

Glycine/GABA (Gamma-amino butyric acid) neurotransmitter

Question 11

Why does demyelination of an axon cause a drop in conduction velocity?

Answer 11

The impulse has further to travel along the plasmalemma due to inhibition of saltatory conduction/propogation

Question 12

Give an example of a case where demyelination of axons may occur.

Explain the result of this.

Answer 12

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

Question 13

What are some of the specialised structures of a neurone?

List them and explain the function of each

Answer 13

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.

Question 14

Explain the process of saltatory conduction

Answer 14

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.

Question 15

List the types of Glial cells.

What is the general function of Glial cells?

Answer 15

Astrocytes
Oligodendrocytes
Microglia
Shwann cells
Satellite cells

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

Question 16

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

Answer 16

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

Found in the CNS

Question 17

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

Answer 17

Myelination of CNS neurones, up to 250 axons per cell

Found in the CNS

Question 18

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

Answer 18

Immune and inflammatory functions

Found in the CNS and PNS

Question 19

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

Answer 19

Myelination
1 axon per cell

Found in the PNS

Question 20

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

Answer 20

Physical support of peripheral neurones (afferent and efferent)

Found in the PNS

Question 21

what are the Two functional branches of the nervous system?

Answer 21

Autonomic and Somatic nervous system

Question 22

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

Answer 22

Sympathetic
Parasympathetic
Enteric

Question 23

What is the anatomical composition of the ANS?

What is a ganglion?

Answer 23

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

Question 24

How do neurones of the Autonomic nervous system exert action?

Answer 24

Via smooth muscles, viscera and secretory glands

Question 25

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

Answer 25

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

Question 26

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

Answer 26

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.

Question 27

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

Answer 27

The para-vertebral ganglion chain

Question 28

Where are ganglia of the sympathetic nervous system found?

Answer 28

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

Question 29

What are the functions of the sympathetic nervous system?

Answer 29

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 Hyperventilation ```

Question 30

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

Answer 30

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

Question 31

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

Answer 31

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

Question 32

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

Answer 32

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

Question 33

How do drugs affecting the ANS exert their effect?

Answer 33

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