Body processes

Reflexes – function, task and diseases


Innate and acquired reflexes accompany us throughout life. If they are disturbed, this can indicate serious illnesses or be a consequence of natural aging . A reflex is always the same reaction to a certain stimulus.

What is a reflex?

Biology distinguishes between self-reflexes, external reflexes and conditioned reflexes. They are innate and controlled by the spinal cord . They serve to protect the living being. This is the only way to react quickly in the event of danger.

Reflexes are coordinated by nerve cells . Each reflex involves a receptor and an effector. These are connected by nerves to form a reflex arc.

A reflex that I am sure everyone is familiar with is the hamstring reflex. If the kneecap receives a light blow, the leg makes an involuntary movement forward. The person concerned cannot prevent the seesaw at all. The reaction occurs without the brain being able to control it.

When a physical or chemical stimulus hits a sensory cell, it is converted into an electrical signal. The impulses are conducted via afferent nerve fibers into the spinal cord, where the stimulus is processed (afferent = leading to the central nervous system).

The stimulus reaches the muscle cells via an efferent, i.e. leading away nerve fiber. They represent the effector. The electrical excitation is transmitted from the nerve fibers to the muscle through the motor endplate .

The whole process is so fast that we are not even aware of it. The brain cannot influence or control innate reflexes.

function & task

Both receptor and effector are classified according to their location in the organism. The number of synapses present in the reflex arc also plays a role in the categorization. The receptor is located in the periphery, for example in the muscle spindle in the case of the patillary tendon reflex . If this is stimulated, the reaction is transmitted in a reflex arc via the spinal nerve , the spinal ganglion and the hinterland to the spinal cord. Here is the reflex center. The stimulus moves on to the anterior horn, where it is switched to an action potential and sets the motor system in motion. It comes to the recognizable reflex. 

In the case of intrinsic reflexes, the excitation and response to the stimulus take place in the same organ. Examples of this are the described patillar tendon reflex and the radioperiosteal reflex at the elbow. In the case of an extraneous reflex, the sites of stimulus triggering and stimulus response are in different organs. An example of this is touching the hot stove. The excitation reaches the human organism via the skin on the finger and is passed on via afferent pathways to the reflex center in the spinal cord.

Early childhood reflexes are innate, but are lost after the first few months of life. As the brain develops, these early reflexes are lost. They all have the goal of protecting the infant from injuries and dangers or making it easier to eat.

For example, the baby has a grasping reflex. It automatically grabs at the touch of his palm. A swimming reflex is also innate at this early age and can be observed in baby swimming courses. Babies will automatically start paddling forward in the water like small dogs do. Infants also have a searching reflex. If the corner of the mouth is touched, they automatically turn their head in the appropriate direction. This is important in order to be able to find the mother’s breast blindly.

Diseases & Ailments

While early childhood reflexes are lost over time, and this is a healthy process, many reflexes are also affected by illness or accidents. For example, liver disease Wilson’s disease is common in children and causes muscle weakness , sensory and reflex disturbances, and a loss of intelligence . 

concussion , like a persistent vitamin B6 deficiency, can noticeably disturb the reflexes. Hyperactive children also often suffer from reflex disturbances and exhibit muscle twitching , often associated with insomnia , headaches and abdominal pain , loss of appetite and weight loss .

In the case of nerve or brain damage, pathological reflex disorders occur. The Babinski reflex is the best known of the pathological reflexes. If you stroke the sole of the foot of a sick person , the big toe stretches while the other toes bend down. It is one of the early childhood reflexes and usually disappears on its own after a year. However, after a stroke or brain haemorrhage , this reflex can reappear. Then it is the indication of clear brain damage.

In order to be able to assess a reflex response on the legs and arms, the doctor must always examine both sides. Only in comparison can it be determined whether a disease may be present. Then there is a one-sided weakening or strengthening of the reflex.

If the muscles are paralyzed after a stroke, there is often an increase in the muscle’s own reflexes. The most extreme form of this increased muscle movement is clonus, in which a muscle twitches rhythmically without a break after a stimulus. Clonus is the result of damage to the cerebrum.

Parkinson’s disease is also a typical example of disturbances in sustained reflexes and creates balance problems . The disease manifests itself in the early stages as an olfactory disorder , and in the second stage there is a typical sleep disorder that affects the deep sleep phase.

With advancing age, many reflexes weaken. It is a natural process and cannot be influenced much. This relaxation is usually bilateral and is not limited to one organ or muscle.

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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.