These reflexes are built naturally into the body, and they exist at birth and change as we grow older. Reflexes are kind of like safety features for survival that allow us to move in response to something in the environment.
Reflexes can act to protect you in many ways, including removing your hand from a hot or sharp object, or ducking when a loud and sudden sound occurs.
These fast actions are reflex responses! The fact that these responses are automatic shows that reflexes occur at a rate that is far too fast for the brain to be involved with the response. Actions that occur without the involvement of the brain are called involuntary actions, while planned actions from the brain, like throwing a ball or strumming a guitar, are called voluntary actions. After the reflex action has happened, the brain does become aware and tells you what happened.
At this point, the brain might even add to the action. For example, you might have ducked as an involuntary response to a very loud noise, but when the brain becomes involved you learn why you ducked down and the brain sends the voluntary action to respond—maybe to stand back up.
In order for reflexes to work, messages need to move around the body. These messages are action potentials , and they travel along the neurons and send messages, special parts of the neurons are involved. The neuron has three different parts that allow signals to be sensed, to travel, and then move to another neuron or muscle. These three parts are called the dendrites, the axon, and the nerve ending Figure 1. The dendrites receive information from the sensor or other neurons.
This information then moves to the axon, which travels to or from the spinal cord. The action potential travels from the nerve endings at one end of the neuron to the next neuron.
Many reflexes start at the muscle or skin and go to the spinal cord. When the action potential reaches the nerve ending, the signal is transferred to another neuron, such as an interneuron or motor neuron.
The action potential then travels outside the spinal cord to a muscle. But the neurons do not touch each other in the spinal cord and do not touch at the muscle. There are tiny spaces called synapses that the action potential must jump across.
Doctors will perform a test to make sure reflexes are working properly because reflexes can change if you are sick and as you grow. Imagine you are sitting up on the exam table and the doctor taps you just below the knee with a rubber hammer. Hopefully, the doctor moved out of the way! A common example of this reflex is the knee jerk reflex that is elicited by a rubber hammer striking against the patellar tendon, such as during a physical exam.
When the hammer strikes, it stretches the tendon, which pulls on the quadriceps femoris muscle. Along with the monosynaptic activation of the alpha motor neuron, this reflex also includes the activation of an interneuron that inhibits the alpha motor neuron of the antagonistic muscle. This aspect of the reflex ensures that contraction of the agonist muscle occurs unopposed. Recall from the beginning of this unit that when you touch a hot stove, you reflexively pull your hand away.
Sensory receptors in the skin sense extreme temperature and the early signs of tissue damage. To avoid further damage, information travels along the sensory fibers from the skin and into the posterior dorsal horn of the spinal cord.
Once in the spinal cord, the sensory fibers synapse with a variety of interneurons that mediate the responses of the reflex. These responses included a strong initial withdrawal of the flexor muscle caused by activation of the alpha motor neurons , inhibition of the extensor muscle mediated through inhibitory interneurons , and sustained contraction of the flexor mediated by a spinal cord neuronal circuit. Because the integration center in this reflex arc has many synapses, it is a polynaptic reflex.
And as already discussed, the sensory information will also travel to the brain to develop a conscious awareness of the situation such that conscious decision-making can take over immediately after the reflex occurs. If rolling over, sitting up, or any of the other motor reflex schemes do not emerge when expected, do not mature at the typical rate, or seem challenged in anyway regardless of age , underlying primary infant motor reflexes should be assessed.
If any one or combination of underlying reflexes has not integrated, MNRI techniques can be used to facilitate maturation and integration. Once integrated, the function of innate motor reflex schemes often improves. As already discussed, a learned motor response that has been mastered and occurs automatically without conscious thought or control when a particular stimulus is presented is considered an acquired reflex.
While motor responses that have not been mastered and do not occur automatically are reflexive in nature, they are not reflexes.
If the basic reflexive neurosensorimotor circuitry outlined for the reflex arc is not functioning, a motor activity cannot occur. In fact, when someone sustains brain damage, whether through congenital issues, trauma or disease, lost motor function is due to the damage sustained some place within the neurosensorimotor circuitry.
Alexander Luria , among others, demonstrated that when function is lost due to brain damage, restorative techniques can improve and sometimes even restore function to damaged neural pathways by activating inhibited neural pathways or by establishing new pathways either within the damaged brain area or within alternative brain areas related to the function. We use cookies to help us understand how visitors interact with our site, and to provide media playback functionality.
By using masgutovamethod. The official site of the Masgutova Method. Svetlana Masgutova Educational Institute. About Svetlana Masgutova, Ph. Treatment Options Testimonials. The somatic nervous system manages four general types of reflexive motor responses: Innate 1.
Identify maturationally inappropriate reflexes -- not actively present when they should be or actively present when they should not be. Think back to the last time you had a sports physical or a routine physical examination. Why did the doctor tap your leg just below the knee?
What information can he possibly gather from this simple procedure? The magic of examining reflexes comes from the phenomenon that, under normal circumstances, a specific stimulus will elicit a predictable response. In the case of the knee-jerk reflex the expected response is extension of the leg at the knee. If the reflex is greater than expected hyperactive , less than expected hypoactive or totally absent, that suggests potential pathology.
Now let's look at how the stretch reflex works. Muscle spindles are specialized proprioceptors that monitor muscle length.
They are bundles of modified skeletal muscle fibers with extensive sensory and motor innervation. These fibers, called intrafusal fibers , run parallel to the contractile skeletal muscle fibers called extrafusal fibers that make up the bulk of skeletal muscle. Muscle spindles are scattered throughout skeletal muscle, but they occur in the highest density near tendinous insertions and in muscles involved in fine motor control i.
Intrafusal fibers are only capable of contraction at their tapered ends where they are innervated by gamma motor neurons. The contraction is too weak to contribute to gross movement but is important in maintaining the sensitivity of the muscle spindle while the muscle is either shortened or lengthened.
Sensory neurons innervate the noncontractile central region of the intrafusal fibers. If stretched, the sensory fiber associated with the muscle spindle will be activated and result in stimulation of an alpha motor neuron a type of lower motor neuron in the anterior horn of the spinal cord. The alpha motor neurons directly innervate the skeletal muscle where the muscle spindle is located. This is an example of a monosynaptic reflex because the sensory neuron synapses directly with the motor neuron and occurs without any input from the upper motor neuron.
Imagine stepping out of the driver's seat of your car onto a patch of ice in the parking lot. As your weight transfers to your left foot and starts to slide out from under you, what happens? The muscle spindles in your left inner thigh adductors are quickly stretched and send a message to your alpha motor neurons in the spinal cord begging for help. The alpha motor neurons then cause contraction of the same inner thigh muscles adductors that were stretched, and you narrowly avoid the pain of a groin injury.
All of this happens so fast signals are sent at speeds around miles per hour that you have already recovered by the time you are aware that you were in trouble. When a muscle is stretched, the muscle spindles are stimulated and thus increase the frequency of action potentials sent to the lower motor neurons in the CNS. The increased action potential frequency causes alpha motor neurons to rapidly fire, resulting in muscle shortening.
This reflexive contraction, in the direction directly opposite to the initial stretch, protects skeletal muscle from damage due to overstretching. The same process that we described above also relates to other very common situations.
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