Many creatures have mana sensing and mana absorbing organs so that they make take mana out of the air for use in their bodies. For Draken, this organ would be the Third Eye Gem. The vessel leads to an organ near the stomach. This organ stores mana to be used later, and they often require mana to perform certain bodily functions. If charged mana particles were unavailable for an extended period of time - say, about three days straight - a Draken would die. For Nyulop, it is their whiskers, though it is more difficult to mana-starve them and can live without whole whiskers and brows.

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Dead Mana

When the charge of a mana particle (or a collection of mana particles) is used up, it becomes “dead mana”. Dead mana simply refers to any mana particle that is no longer charged with magic. 

A mana particle is completely stripped of it’s magical charge when used to cast a powerful magic spell (any magic that is tier 7 through 10 might do it.) A dead mana particle will take time to recycle and regain it’s magical charge, but a creature known as the Drakesprite are known to be able to recycle dead mana instantly. It is said that certain Drakesprites can even generate new charged mana particles. 

Attempting to cast a spell with dead mana will result in Mana Burn, as the lack of energy in the air will force the user to pull energy from the body instead. 
How is Mana used?
In-taking and using mana in bodily processes is involuntary in Draken, and will only stop if a serious illness or injury prevents the organ from working. An illness or injury of this magnitude is fatal. 

When casting a spell, or using magic in any general sense, the charged mana particles required for an action are condensed into a usable form, where the caster can then manipulate them in any which way they want. Novice casters take a bit longer to condense the mana particles necessary to cast a spell, but some experienced casters can do this near instantly. 
For small spells (such as spells in the tiers 1-4 range), magic charged particles can be used multiple times. It is especially useful to use the charge in mana particles to keep a spell sustained (such as a fireball.) They will eventually lose their charge, but they can last long enough that a skilled caster would be able to keep an active spell sustained for about an hour. 

Mid-range spells (such as tiers 5 and 6) require a bit more energy to cast, it is estimated that a mid-range spell can be cast up to two times in quick succession before the mana loses its charge and needs to be recycled. 
High tier spells (tiers 7-10) require an incredible amount of energy to cast, and will sap all of the charge of mana particles in close proximity to the user. It is very dangerous to try and cast more than one or two high level spells in quick succession, and will likely result in mana burn. 

Manabind

How to cut off mana flow

Though few know of the origin of this condition, there exist spells in this world that can cut off the flow of mana to one person completely. This condition is called Manabind, and it is incredibly dangerous to sustain this condition for too long. For example, because it cuts off the flow of mana to an individual completely, a Draken would only be able to live for three days under this condition. 
It is incredibly rare, and no known elemental skills or class skills can cause it - meaning the origin of the condition is very mysterious. 

Someone who is affected by this condition is manabound, and cannot cast spells. While their bodies retain the mana that already entered their system before the condition was placed upon them, no new mana may be taken in. This effectively runs anyone completely dry of mana, which may render them mana burned whether they attempted to cast a spell or not. 
Attempting to cast a spell when you are manabound will result in anywhere from minor to severe mana burn, depending upon the severity of the spell.