Reflexes: Function, Task & Diseases

Congenital and acquired reflexes accompany us throughout life. If they are disturbed, this can indicate serious diseases or be a consequence of natural aging. A reflex is the response to a particular stimulus that is always the same.

What is a reflex?

One reflex that I’m sure everyone is familiar with is the hamstring reflex. If the kneecap receives a slight blow, the leg makes an involuntary movement forward. Biology distinguishes between intrinsic reflexes, extrinsic reflexes and conditional reflexes. They are innate and are controlled by the spinal cord. They serve to protect the living being. This is the only way to react quickly in case of danger. Reflexes are coordinated by nerve cells. A receptor and an effector are involved in each reflex. These are connected by nerves to form a reflex arc. One reflex that I’m sure everyone is familiar with is the hamstring reflex. If the kneecap receives a slight blow, the leg makes an involuntary forward movement. The person concerned cannot prevent the bobbing 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 transmitted via afferent nerve fibers to the spinal cord, where the stimulus is processed (afferent = leading to the central nervous system). Via an efferent nerve fiber, i.e. leading away, the stimulus reaches the muscle cells. They represent the effector. The electrical excitation is transmitted from the nerve fibers to the muscle through the motor end plate. The whole process is so fast that we are not even aware of it. The brain cannot influence or control innate reflexes.

Function and task

Both receptor and effector are classified according to their location in the organism. Similarly, the number of synapses present in the reflex arc plays a role in categorization. The receptor is located in the periphery; in the patillary tendon reflex, for example, it is located in the muscle spindle. If this is stimulated, the reaction is transmitted in a reflex arc via the spinal nerve, the spinal ganglion and via the hinterland to the spinal cord. This is where the reflex center is located. The stimulus travels on to the anterior horn, where it is switched to action potential and sets the motor system in motion. The result is a recognizable reflex. In intrinsic reflexes, the excitation and the response to the stimulus occur in the same organ. Examples of this are the patillary tendon reflex described above and the radieoperiosteal reflex at the elbow. In extraneous reflexes, the sites of stimulus initiation and stimulus response are in different organs. An example of this is touching the hot stove top. The excitation enters the human organism via the skin on the finger and is transmitted 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 brain development progresses, these early reflexes are lost. They all aim to protect the infant from injury and danger or to facilitate feeding. For example, the baby has a grasping reflex. It automatically reaches out when its palm is touched. A swimming reflex is also innate at this early age and can be observed in baby swimming classes. Babies automatically begin to paddle forward in the water, just as small dogs do. Infants also have a search reflex. If the corner of their mouth is touched, they automatically turn their head in the appropriate direction. This is important in order to be able to find their mother’s breast, even blindly.

Diseases and complaints

While early infant reflexes are lost over time and this is a healthy process, many reflexes are also affected by disease or accidents. For example, Wilson’s disease of the liver is common in children and causes muscle weakness, sensory and reflex disturbances, and loss of intelligence. A concussion can noticeably disrupt reflexes, as can persistent vitamin B6 deficiency. It is also not uncommon for hyperactive children to suffer from reflex disorders and exhibit muscle twitching, often associated with insomnia, headaches, abdominal pain, loss of appetite and weight loss. Pathological reflex disorders occur when there is nerve or brain damage. The Babinski reflex is the best known of the pathological reflexes. If one strokes the sole of the foot of a diseased person, the big toe stretches while the other toes bend downward.It belongs to the early childhood reflexes and usually disappears by itself after one year. However, after a stroke or a brain hemorrhage, this reflex may reappear. Then it is the indication of a clear brain damage. In order to assess a reflex response in the legs and arms, the doctor must always examine both sides. Only by comparison can it be determined whether a disease is perhaps present. If so, a one-sided weakening or strengthening of the reflex will be evident. If the muscles are paralyzed after a stroke, there is often an increase in the muscle’s own reflexes. The most extreme form of these increased muscle movements is clonus, in which a muscle twitches rhythmically without pause after a stimulus. Clonus is the result of cerebral damage. Parkinson’s disease is also a typical example of disorders of maintained reflexes and produces balance problems. Already in the early stages, the disease is manifested by an olfactory disorder; in the second stage, a typical sleep disorder is added, which affects the deep sleep phase. With advancing age, many reflexes weaken. It is a natural process and can be influenced little. This weakening usually occurs on both sides and is not limited to one organ or muscle.