Adrenaline response

[Rye]

A question I was wondering:

I was tought that to get the adrenaline flowing, something happens in the brain, a crisis is recognised, like when a kid jumps in front of your car. Once that happens, the petuitary gland fires up, with hormones that will set off the adrenaline secretors, then your heart will beat faster, and the other effects.

Is this correct? If so, how on earth does it work so fast? Realisation of a crisis can occur in a split second, like with the kid in front of your car example, it's suddenly just there, you weren't aware of it before and BANG, you're prepared for the crisis. The petuitary gland didn't have the time, as far as I know to secrete the needed hormones and have them suffuse the bloodstream as far as the adrenaline secretors, did it? And yet you're there, ready for quick action.

So how does this work, exactly? Does the brain have a "rapid fire" crisis mode that flies off whenever there's the starts of a crisis while the hormones get going, triggered by the same recognition of danger, but something distinct?

[Gunhead]

It's not the adrenaline that makes you react fast. In the car instance your reflexes take over and you jump on the brake, only your brain doesn't realize it until you've already done it. Adrenaline comes after it making you ready for the next surprise.
It takes the brain few seconds to see-comprehend-act. That's why we have reflexes, because in most cases the brain would be too slow for us to act.
Reflexes come from the spine, and the brain gets the message after action has already taken place.
Another example would be that you put your hand on a hot plate without knowing it's hot. Your reflexes tell you to pull out your hand and the adrenaline helps with the pain so you don't pass out.

-Gunhead

[j1j2j3]

In the car instance your reflexes take over and you jump on the brake, only your brain doesn't realize it until you've already done it. Reflexes come from the spine, and the brain gets the message after action has already taken place. -Gunhead

I wouldn't say that breaking for a kid in your car is a spine only reflex. It may be a conditioned response but it definately involves your brain making a decision.

[Admiral Valdemar]

This is quite a technical topic, but I'll summarise.

The CNS and PNS of the Human body are quite adept at controlling bodily functions without any concious input (they have to, else you die when you think about what 5x6 is rather than breathing). Because of this, there are certain subsystems that automatically take control of specific functions when a situation arises: fight or flight is one of them.

This involves the parasympathetic and sympathetic nervous systems.

In the sympathetic nervous system, you get actions that help in this "fight or flight" response. The release of adrenaline in the bloodstream from such a reaction does everything from constrict unnecessary blood vessels to dilating pupils and stimulating the heart. The parasympathetic nervous system does the exact opposite via different pathways such as the vagus nerve which directly controls the projectile vomit reaction (nice).

The adrenal medulla secretes the hormone when stress levels are reached that permit it to do so. Since many organs have such chemical receptors on their tissues (the liver has many for instance to let it know to release more glucose from the glycogen stores) then it is fast acting throughout the body and has a positive feed-back mechanism until the parasympathetic nervous system comes into play. I haven't got my books with me right now, but there's already a supply of adrenaline in a proto state much like insulin has another form that is easily converted to an active form when needed quickly. That along with the density of adrenergic recptors allows for the body to go into this mode so quickly.

[Admiral Valdemar]

It's not the adrenaline that makes you react fast. In the car instance your reflexes take over and you jump on the brake, only your brain doesn't realize it until you've already done it. Adrenaline comes after it making you ready for the next surprise.
It takes the brain few seconds to see-comprehend-act. That's why we have reflexes, because in most cases the brain would be too slow for us to act.
Reflexes come from the spine, and the brain gets the message after action has already taken place.
Another example would be that you put your hand on a hot plate without knowing it's hot. Your reflexes tell you to pull out your hand and the adrenaline helps with the pain so you don't pass out.

-Gunhead

Such responses are far too complex to bypass the brain. They may be learnt until they are, like riding a bike, part of the implicit memory core, but they are not like reflex reactions. The best they do is a quick movement of an affected limb, say, placing you hand in a fire. The pain is detected and the reflex arc fired since it's simply a case of going "MOVE!" which needn't have the brain co-ordinate actions.

Additionally, adrenaline can take effect in milliseconds once adequately pumped into the bloodstream. If it took much longer it'd be entirely useless.

[The Grim Squeaker]

a possible Adrenaline effect is a dominance of lower brain functions,
i.e blocking a punch.