domingo, 27 de marzo de 2011

Voluntary and involuntary actions

There are two main kinds of actions that our body carries out:

  • Voluntary actions,

  • Involuntary actions or reflex actions.
Both actions involve stimuli, an impulse, neurons and effectors. However they are differents.
Voluntary Actions:
A voluntary action is basically an action which you yourself initiate by your own conscious. Your cerebral cortex (brain) sends impulses from it to the effectors (muscles or glands) via the spinal cord with relay neurons and finally a motor neurons. This action is under the control of the will thus is known as a voluntary action.
Involuntary Actions (Reflex Actions):
Involuntary actions as their name suggest, are total opposites of voluntary actions, a reflex action is not under the control of the will. In this case, your spinal cord takes total control, without your own conscious. Reflex actions controlled by the spinal cord, example scratching, are called spinal reflexes. There are also cranial reflexes, example blinking, that are controled by de brain but not by the cerebral cortex. Brushing, sneezing and salivation are also reflex actions however, salivation is also known an conditioned reflex action which we will be discussing later. In this webpage Kidshealth you can read and listen to a explanation of different reflex actions.
This table compares the two types of actions:

Voluntary actionsReflex actions
Iniated in cerebral cortex of brain - due to thoughIniated by stimulation of receptor
Impulses passes from the motor area in cerebral cortes down spinal cord to:Impules pases sensory neuorns and relay neurone in grey matter of spinal cord which passes impulse to:
Motor neurone carries impulse to effector (muscle) with contracts and produces actionMotor neurone carries impulse to effector (muscle) with contracts and produces action
Impulses passes over to oppsite side of the bodyStimulus, neurones,
actions all on same side of body
Many cells and synapses, and longer pathway – therefore slow.Only 3 cells, 2 synapses – therefore quicker.
Secondary information passes up spinal cord to brain, so subject is aware after event.

In a reflex actions a receptor pick up the stimulus. Impulses are produced and travel along the sensory neurons to the spinal cord.. The reflex actions are very rapid and they are designed to prevent injury. So they are automatic, you do not have to think about them.

In a reflex action a sensory receptor is stimulated by a stimulus, signals pass from it along a sensory neuron ( afferent neuron) to the spinal cord. The impulse passes through a relay neuron, directly to the motor neuron (efferent neuron) that transmites the impulse to the effector (e.g., a muscle or a gland), which acts accordingly. Such a pathway is called a reflex arc.

This videos is another way of learn it.
Conditioned Reflex:

A conditioned reflex action is a special kind of reflex action which results from the learning from past experiences. For example, many people salivate at the smell of good food as they had learnt from past experiences that such smell are associated with good food and they have to urge to want to eat them, hence salivary glands are stimulated and saliva is produced and secreted.

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