Reactions

Physiology

Reactions

There are 3 main kinds of reaction: simple reaction; discrimination reaction; choice reaction.

Simple reaction — person responses with a certain action to some predefined signal, e.g., red light flashes on the fire safety board and the firewatcher switches on the siren. Simple reaction is especially important in competitions, for example, when the sprinter must quickly react to the starting shot and spring forward.

Discrimination reaction — person responds only to one signal out of several accidental ones, e.g., a good mom will always hear her child tossing and turning in the adjacent room even if it’s noisy around.

Choice reaction — person reacts to several or all various signals with various actions, e.g., work of traffic-controller, who must give various correct directions to all road users.

Neuron Metabolism

The main feature of neuron metabolism is its high speed and predominance of aerobic processes. The brain’s demand for oxygen is extremely high (at rest it consumes about 46 ml of oxygen per minute) and even though the brain makes up only 2% of total body weight, the brain uses 25% of the oxygen consumed by an average adult person at rest and 50% of the oxygen consumed by an infant. Even a short break in the delivery of oxygen through the bloodstream to the brain can cause irreversible changes in nervous cell activity.

Brain Energy

Glucose is the main source of energy for the human brain which requires around 115g of glucose daily. Due to the low percentage of glucose present in brain cells, it is constantly being delivered to the brain through the bloodstream.

Nervous Cells Vascular Supply

Neurons are supplied with oxygen and glucose via intensive blood flow. Blood flows through the brain, with its abundance of blood vessels, 5–7 times faster than through other resting muscles. The cerebral cortex has the densest vascular network (about 10% of the cortex). Physical activity causes the vasodepression of brain arteries and physical or intellectual fatigue can tone up arteries causing less blood flow through the nervous tissues.

Why Can't I Change My Voluntary Reaction Physiology?

For example, let’s consider eye’s reaction to bright light (shutting.) Turn on the light! Photons reach your eye receptors — in 60 ms photochemical reactions in your retina turn into nervous impulses. Your receptors send a nervous impulse to your cerebral cortex. Cerebral cortex assesses them in the current context in 60 ms. After that your cerebral cortex sends a signal to the motor brain center, which sends an order to your muscles. Your muscles response in 100 ms. Thus, a simple reaction to light takes about 150-225 ms and you cannot speed it up, because you can’t change your body chemistry without causing it any harm.

What Slows Down Reaction?

As a rule, a tired person acts slowly. Weariness does not affect simple reactions so much as it impacts the complex ones, which leads to more mistakes.

  • Alcohol, nicotine and drugs slow down your reaction.
  • Your psychical state also has a drastic effect on reaction, e.g., negative emotions slow down all kinds of reaction, while positive ones accelerate them.
  • People aged 8-40 have fastest reaction, which decelerates as they get older.
  • The fastest motor reaction is in the middle of the day.