External reflex

A reflex is an involuntary, automatic reaction of a body part or organ to a stimulus. A External reflex describes a certain type of reflex within it and is also called polysynaptic reflex designated.

What is a foreign reflex?

In contrast to the self-reflex, the external reflex receptor and effector are not in the same organ. This means that the perception of a stimulus and the action of the body directed towards it take place in different organs.

A receptor is a cell or a group of cells that can translate chemical or physical stimuli into a neuronal form. The sensory cells in the eye or in the ear and the sensitive cells of the skin are examples of receptors.

An effector is a group of cells that can pick up neuronal signals and then produce a response. The organ belonging to the effector is also called the success organ.

Function & task

The path that the stimulus takes from the receptor to the effector is also known as the reflex arc. The stimulus is first registered by the receptor. There it triggers an excitation in the nerve cells. This excitation is transmitted to the central nervous system (CNS) via so-called afferent nerve fibers.

Afferents are nerve fibers that lead from the periphery, for example from the extremities, to the CNS. Most of the reflexes travel from their receptor to the spinal cord via afferent fibers. The spinal cord is part of the central nervous system and runs in the vertebral canal of the spine. In the spinal cord, the stimulus is then transmitted from the afferent sensory nerve pathways to a motor nerve pathway. The motor nerve pathway in the anterior horn of the spinal cord is an efferent, which means that the nerve pathway runs from the spinal cord into the periphery to the successor organ. There the stimulus then triggers a corresponding reaction.

Reflexes enable people to react quickly to different living conditions in their fairly constant environment. Reflexes occur automatically, schematically and stereotypically and thus enable a very short reaction time.

Innate reflexes facilitate survival. They have been tried and tested by previous generations and thus offer an increase in adaptation and survivability from birth. Many external reflexes serve as protection. For example, the eyelid closing reflex protects the eye from foreign bodies and the swallowing reflex enables fluid and food to be consumed while protecting the airways and lungs.

In addition to the eyelid closing and swallowing reflexes, the physiological reflexes also include the abdominal skin reflex and the cremaster reflex. In the abdominal skin reflex, the abdominal wall muscles contract when you stroke the abdomen from the flank side in the direction of the navel. The cremaster reflex is the lifting of the testicle by brushing the inside of the thigh.

The pupillary reflex is also a physiological external reflex. As a result, the pupils adapt to different lighting conditions. Both pupils always narrow or widen, even if only one of the pupils is illuminated. The gag reflex occurs when fluid or other foreign bodies enter the windpipe. Also spoiled or very bitter foods can trigger the gag reflex. Just like the swallowing reflex, this reflex is a protective reflex. In babies, the sucking reflex and the plantar reflex also belong to the physiological reflex repertoire. However, the plantar reflex, also known as the Babinski reflex, is pathological in adults.

Illnesses & ailments

Pathological external reflexes are involuntary body reactions that do not occur in healthy people. As a rule, they provide evidence of diseases of the central nervous system. In the Babinski reflex, the outer edge of the foot is painted. Toes spread in healthy infants and in diseases of the central nervous system. The big toe pulls towards the back of the foot. If this toes is spread, one speaks of a positive Babinski reflex. A positive Babinski reflex provides an indication of damage to the pyramidal tract. The fibers of the so-called motor neurons run in the pyramidal tract. They supply the body's muscles.

The Chaddock reflex is also one of the pyramidal orbit signs, i.e. one of the pathological external reflexes that indicate damage to the pyramidal orbit. Similar to the Babinski reflex, pressure on a point on the foot triggers a toe spread. The Gordon reflex is also a pyramid orbit sign. Here, the toes are spread apart and the big toe is pulled in by applying pressure to the calf muscles. Other pathological external reflexes that are caused by damage to the pyramidal tract are the Bechterew-Mendel reflex, the Oppenheim reflex and the Rossolimo reflex.

A well-known disease in which pathological external reflexes occur is multiple sclerosis. The meylin sheaths of the nerves are damaged by autoimmune processes.

In addition to pathological external reflexes, missing or weakened physiological external reflexes also provide information on possible diseases. A missing or weakened abdominal skin reflex is just like the Babinski or Oppenheim reflex a sign of multiple sclerosis.

If the cremaster reflex does not occur when the inside of the thigh is swept, this indicates a testicular rotation or damage to the spinal cord segments L1 and L2. A missing anal reflex in turn indicates damage to the spinal cord segments S3-S5.

If there is damage to the afferent or efferent nerve fibers in the area of ​​the eye or if the facial nerve is paralyzed, the eyelid-closing reflex does not occur. Disturbances in the blink reflex can indicate damage to the optic nerve as well as disturbances of the motor fibers in the area of ​​the eye. If the optic nerve is damaged, the pupillary reflex fails when the eye is illuminated; however, when the healthy eye is illuminated, the pupillary reflex can be triggered in both eyes. If, on the other hand, the motor part of the eye is damaged, the pupil reflex can no longer be triggered in the affected eye, even when the healthy eye is illuminated.