Home » Life Science » Reactions and Reflexes. Figure 1 Schematic representation of the sensorimotor pathway for a volunatry response to a stimulus. Reflexes and reactions are often confused, but important differences exist.
Reactions are voluntary responses whereas reflexes are involuntary or unintentional and not subject to conscious control in most cases. Each type of response is initiated by a sensory stimulus that may be visual, audible, tactile, olfactory, or gustatory in nature.
Once activated, the receptors propagate nerve impulses that travel toward the brain along sensory afferent nerve tracts. The speed of a reflex is greater than that of a voluntary reaction, due largely to the relative complexity of the neural pathway for a reaction Fig. An effective way to help your students differentiate reactions and reflexes is by leading them through a scenario involving a familiar sport. For example, you can describe the events that occur when a baseball player is at bat.
The ball will travel from his hand to the plate in approximately 0. That is all the time the batter will have to respond by either swinging the bat or allowing the ball to pass by.
Many hours of practice have provided him with an uncanny ability to judge how the pitch should be played. When he launches a home run over the left field fence, the announcer praises his "unbelievable reflexes. The batter's eyes close involuntarily as he reacts by ducking sideways to avoid being hit. Again the announcer applauds the player's "terrific reflexes," and this time he is at least partially correct. Although reflexes are automatic and predictable, they have value in the avoidance of injury.
At the same time, he responded to the danger by utilizing voluntary movement to get out of the way. How much time? Figure 2 Generalized reflex arc. Reaction time is the amount of time required for an individual to perceive and respond to a sensory stimulus such as the act of swinging a bat at a baseball.
The average reaction time for a visual stimulus is to ms; for hearing, to ms; and for touch, to ms. Reaction time improves somewhat through repetition, which is a beneficial result of the many hours of practice that athletes endure.
Ultimately, however, the speed at which a nerve impulse travels along a neural pathway called nerve conduction velocity limits reaction time. The diameter of the nerve and the amount of myelination can affect nerve conduction velocity.
The simplest, least expensive way for students to measure reaction time is with a reaction time ruler. This device is similar to a yardstick, except its scale is in milliseconds ms to correspond with the progressive acceleration of a falling object. The subject sits with his thumb and forefinger poised opposite a designated point near the bottom of the ruler while the experimenter holds the ruler vertically. The experimenter allows the ruler to drop and the subject stops it as quickly as possible without moving his hand upward or downward.
Students can design their own experiments, testing the effects of distraction, fatigue, caffeine, and other factors on their performance. These experiments can be an excellent introduction to the fundamental procedures used in scientific data collection and analysis.
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Hence, this is another difference between reaction and reflex. The below infographic shows more details on the difference between reaction and reflex. Reaction and reflex are two ways of responding to a detectable stimulus generated both externally and internally. Reflex is a much instantaneous process that takes place involuntarily. Comparatively, the reaction is a much slow voluntary process.
During a reaction, information from the stimulus reaches the brain, but during a reflex, it does not. Thus, this is the key difference between reaction and reflex.
However, both processes are important in maintaining the body homeostasis. Phillips, Harry. Available here 2. Available here. Samanthi Udayangani holds a B. Degree in Plant Science, M. Your email address will not be published. Figure Reaction. It is polysynaptic, and causes the stimulation of sensory, association, and motor neurons. When a person touches a hot object and withdraws his hand from it without thinking about it, the heat stimulates temperature and danger receptors in the skin, triggering a sensory impulse that travels to the central nervous system.
The sensory neuron then synapses with interneurons that connect to motor neurons. Some of these send motor impulses to the flexors to allow withdrawal. Some motor neurons send inhibitory impulses to the extensors so flexion is not inhibited—this is referred to as reciprocal innervation. Although this is a reflex, there are two interesting aspects to it:. Golgi tendon organ : The Golgi tendon organ, responsible for the Golgi tendon reflex, is diagrammed with its typical position in a muscle left , neuronal connections in spinal cord middle , and expanded schematic right.
The tendon organ is a stretch receptor that signals the amount of force on the muscle and protects the muscle from excessively heavy loads by causing the muscle to relax and drop the load.
Privacy Policy. Skip to main content. Peripheral Nervous System. Search for:. Components of a Reflex Arc A reflex arc defines the pathway by which a reflex travels—from the stimulus to sensory neuron to motor neuron to reflex muscle movement.
Learning Objectives Describe the components of a reflex arc. Key Takeaways Key Points Reflexes, or reflex actions, are involuntary, almost instantaneous movements in response to a specific stimulus. Reflex arcs that contain only two neurons, a sensory and a motor neuron, are considered monosynaptic. Examples of monosynaptic reflex arcs in humans include the patellar reflex and the Achilles reflex. Most reflex arcs are polysynaptic, meaning multiple interneurons also called relay neurons interface between the sensory and motor neurons in the reflex pathway.
Key Terms motor neuron : A neuron located in the central nervous system that projects its axon outside the CNS and directly or indirectly control muscles.
There are two types of reflex arcs: autonomic reflex arc affecting inner organs and somatic reflex arc affecting muscles. Spinal Reflexes Spinal reflexes include the stretch reflex, the Golgi tendon reflex, the crossed extensor reflex, and the withdrawal reflex.
Learning Objectives Distinguish between the types of spinal reflexes. Key Takeaways Key Points The stretch reflex is a monosynaptic reflex that regulates muscle length through neuronal stimulation at the muscle spindle.
The alpha motor neurons resist stretching by causing contraction, and the gamma motor neurons control the sensitivity of the reflex. The stretch and Golgi tendon reflexes work in tandem to control muscle length and tension.
Both are examples of ipsilateral reflexes, meaning the reflex occurs on the same side of the body as the stimulus. The crossed extensor reflex is a contralateral reflex that allows the body to compensate on one side for a stimulus on the other.
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