Mint Properties

[jackrob15]

I posted a question recently about a garlic and lemon investigation. My sheet aslo asked about mint which we found to have no antibacterial properties, however, our worksheet did say that it numbs gums and is why it is used in toothpaste. Is this true and how does it do this? Does it contain a particular chemical? Thnx a lot!!

[JustSia]

The chemical you are looking for is Menthol.

You can read up on it here, http://en.wikipedia.org/wiki/Menthol.

S.

[theprof]

JustSia is correct - It is the menthol that exerts the local anaesthetic action on gums when using toothpaste. The menthol present in toothpaste is synthesised synthetically nowadays due to enormous demand, but it can be purchased as a natural product which has been derived from mint oil.

Mint oil and other extracts of the mint family are sold in the USA for the emergency home treatment of dental cavities and toothache in the same way that clove oil is popular in the UK.

Menthol itself has been used as a cutaneous antiseptic and local anaesthetic for years by homeopathic vets, but there are ethical issues involved as to whether it is a "true" homeopathic treatment.

It has also been used to some degree as an ingredient in proprietary counter-irritants to help relieve muscular aches and pains etc in humans although there is no conclusive evidence that it is very effective alone.

If you still need to know the precise method by which menthol acts as a local anaesthetic, let me know as its quite complicated to fully understand.

[jackrob15]

Once again thanks for the information, it is proving very helpful. Any more information you have on how menthol acts as a local anaesthetic would be great. I will try and get my head round the complicated stuff.

Also do you have any more detailed information on how natural oils in lemon act as an antiacterial agent. I have tried researching quite a bit on the internet, however at present it is mainly herbal claims, and not much science that I could find. No worries if not, and thanks again!!

[theprof]

You asked for it!

Sensory nerve fibres in mammals can be stimulated by extreme conditions to signal pain. Pain receptors are known as nociceptors.
There are two types of sensory nerve fibres that transmit signals that the mammalian brain interprets as pain:

� A fibres: These fibres transmit signals rapidly and are responsible for acute pain. They act as a warning when you touch a hot surface for example. These A fibres transmit signals rapidly.
� C fibres: These are responsible for the transmission of chronic pain such as pain of cancerous origin etc. Removing the stimulii cannot abate this type of pain. The fibres do not possess myelin and transmit signals slowly.

These fibres are part of the peripheral nervous system and their axons enter the dorsal root ganglion (where the cell body is located), and then into the grey matter of the spinal cord where they join with interneurons.

(Continued)

[theprof]

(continued)

In mammalian tissue there are C noniceptors that are extremely sensitive to menthol. This manifests itself as a signifant burning sensation when raw menthol is rubbed into the skin and the skin reddens quite rapidly due to both irritation and increased blood flow. In addition, these C nonireceptors can be sensitised to cold stimuli. Recent work suggests that menthol sensitive C nonireceptors may belong in a sub-class of their own.

Cold sensation ( analgesia in extremis) is conducted via the myelinated A fibres which eventually enter the local ganglion. This is known as an afferent. These cold- specific A fibre afferents are directly affected at the molecular level by menthol causing a change in transmission rate � menthol sensitises cold-specific A fibres often leading to prolonged activity. This is why the analgesia remains for some time following removal of the stimulus. In addition, research on the effect of menthol on dorsal root ganglia and trigeminal nerves, seems to show that menthol potentiates responses by moving the thermal activation thresholds to higher temperatures.

It may be seen that although menthol can act as an irritant to mammalian tissue, it can also act as a local anaesthetic by decreasing the cold-pain threshold.

[theprof]

The exact reasons why lemon oil has such remarkable bactericidal properties is not know - that's why you won't see the answer on herbal websites.

There has been some research done on the effect of lemon oil on bacterial surface lipids and it does appear that the lemon oil may affect the solubility of the surface lipids which in turn leads to bacterial lysis due to destuction of the cell membrane.

Lemon fruit have an additional bactericide present in the form of citric acid. Bacterial exposure to lemon juice will destroy a large number of the most common pathogens within minutes due to the low pH of the acid. Once again, bacterial lysis occurs.