is the brain involved in reflex actions?

[paul]

when a doctor taps your knee to test your reflex, a signal is sent from the neurons in the knee to the spinal cord; does a signal then go straight back to the knee from the spinal cord; or does it first go from the spinal cord to the brain (to be 'processed') befor a signal goes from the brain to the knee?

[ecoli]

answer to the thread title, "No" ... look up the "pateller reflex".

[iNow]

It does ultimately go to the brain for interpretation, but the reaction happens MUCH before the signal every gets there.

 

These may help:

http://www.unmc.edu/physiology/Mann/mann15.html

http://en.wikipedia.org/wiki/Reflex_arc

[Mokele]

It depends. Some reflexes, such as the patellar reflex or pulling back from a burnt finger, are spinal, involving no brain input whatsoever.

 

Other reflexes, such as the optomotor reflex (where the eyes will stay fixed in inertia space if the body is moved by an external force), involve the brain strongly.

 

Mokele

[jimmydasaint]

OK guys, what about the blinking response?

[Mokele]

It'd have to involve the brain - the muscles involved in blinking are innervated by a different cranial nerve from those associated with sensing contact with the eye, so the signal would have to pass through the brain.

[jimmydasaint]

So, in answer to the OP, you would have to say that some reflex responses do involve the brain. Would I be correct also when thinking of the ducking response and the response of salivary glands etc...to a nicely prepared meal?

[Mokele]

Yep. Spinal reflexes, which don't involve the brain, are usually things like the patellar reflex, pulling your hand away from a hot stove - very simple actions in which neither the stimulus nor response requires any great degree of processing or control.

 

However, some actions are complex, yet still mostly governed below the brain, in the spinal cord. Walking, for instance. You can take a cat (I have no idea why they're the animal subject of choice for these experiments), cut the spinal cord in the back, and when given a simple series of pulses from an external generator, the hind limbs will walk, and do so well enough for simple, unobstructed, straight movement. The cat can even pick up it's feet higher if they bump into a short obstacle to avoid tripping. Turning, balancing on a narrow surface, all the more complex stuff cannot be done without the brain, but the basic control circuits for many movements are in the spine, not the brain. I even recall hearing of how a decapitated alligator swatted a scalpel on the back of its neck away with its forelimb. Mammals, and humans in particular, seem to have opted for a lot more brain-based control, but the spine is far from a passive wire bundle.

 

Mokele