The sneezing reflex is one of the protective reflexes and corresponds to a “fake” foreign reflex. Sneezing clears the upper airways of nasal secretions and foreign-body substances to ensure free breathing. Disturbances of the sneezing reflex occur mainly after damage to the nervous tissue involved peripherally and centrally, which includes the respiratory and gustatory centers of the brain and, in particular, the spinal cord.
What is the sneezing reflex?
The sneezing reflex is one of the protective reflexes and corresponds to a “fake” foreign reflex. Sneezing clears the upper airways of nasal secretions and foreign-body substances to ensure free breathing. Every human being has reflexes. The first instance of each reflex arc is a sensory perception. The perceived stimulus is directed via afferent nerves toward the central nervous system, where the reflex arc is wired to specific motor nerves. Through this circuitry, the nerve excitation travels efferently toward the body periphery, where it triggers a motor response from the body. This motor response usually corresponds to an uncontrollable muscle contraction. Reflexes are thus bodily reactions that the organism executes involuntarily in response to certain stimuli. An extraneous reflex is the sneezing reflex, whose affectors and effectors are located in different organs. In the first place of the reflex arc are the mechanoreceptors and chemoreceptors of the nasal mucous membranes. These sensory cells of the skin sense register touch such as pressure and bind to chemical signals. For the sneezing reflex, a stimulus registered in this way forms the first instance of the reflex arc. The sneezing reflex is a “fake” reflex because the stimulus response can be suppressed under certain circumstances. The effectors of the reflex include the respiratory, laryngeal, oral and pharyngeal muscles. The main function of the motor reflex response is to clear the upper airway. Thus, the sneezing reflex corresponds to a protective reflex that clears the nasal mucosa of microorganisms such as bacteria, among other things.
Function and task
Researchers recognize the sneezing reflex as an opportunity for a fresh start, which an overworked nose allows itself due to air filtration problems. The sneeze reflex is triggered by mechanoreceptors and chemoreceptors in the nasal mucosa. These sensory cells register, for example, pressure stimuli caused by endogenous substances such as nasal secretions, foreign substances and microorganisms. In addition, these sensory cells are located in the pharynx (throat), bronchi and lungs. In addition to touch stimuli, the receptors register chemical substances, fragrances and temperature stimuli. They transport these impulses via primary fibers of the vagus nerve and secondary fibers of the trigeminal nerve to the nucleus tractus solitarii in the rhomboid fossa of the brainstem. In addition, impulses reach the respiratory center of the formatio reticularis and the spinal cord via the fibers. The spinal cord contains the nerve cells that control the execution organs of the sneezing reflex via motor nerves. The execution organs include the diaphragm and the intercostal musculature as well as the abdominal musculature. The nerve fibers involved in the sneezing reflex have different qualities. When the receptors involved are stimulated, a motor response is involuntarily triggered, beginning with a reflex deep inhalation. This is followed by a spasmodic exhalation. The soft palate is tightened in such a way that the air escapes mainly through the nose. The sneeze reaches speeds of more than 150 kilometers per hour. The sneezing reflex cleanses the upper respiratory tract of endogenous secretions and foreign bodies to ensure unobstructed breathing. By cleansing foreign body substances, the sneezing reflex in the extended definition can be understood as a protective function against infections. The sneezing reflex can also be triggered in some people by light stimuli and sexual arousal. In the case of light stimuli, this is referred to as a photopic sneezing reflex.
Diseases and disorders
Sneezing accompanies many diseases, such as infections like the flu. The fact that people with influenza have to sneeze more often is partly due to the accumulated nasal secretions and partly due to the foreign-body bacteria that are in the nose after the infection. The sneezing reflex seeks to clear the upper respiratory tract of both. Allergies are also associated with a symptomatic sneezing reflex, which in turn aims to drive allergens out of the upper airways.An increased sneezing reflex thus has pathological value and can refer to various diseases such as infections and allergies. The sneezing reflex is disturbed in people with sinusitis. The inflammation is also called sinusitis and makes patients sneeze more often than is actually necessary. The sneezing is related to biochemical signals that show an influence on the activity of the cilia in the paranasal sinuses. These cilia of the nose transport the secretion of the mucous membranes together with unwanted particles out of the paranasal sinuses. This removal is affected by disturbances in patients with sensitus. Not only an increased, but also a decreased or failed sneezing reflex may have pathological value. These phenomena occur mainly after nerve damage. If the individual nerves of the reflex arc are impaired in their conductivity due to inflammation, traumatic events or compression, a reduction in the reflex response occurs. Inflammation and other types of lesions in the spinal cord or brain can also impair the sneezing reflex. In the brain, lesions in the area of the nucleus solitarius or the formatio reticularis play a role in this context. Damage in these areas usually affects the coordination of the sneezing reflex in particular. Lesions in the formatio reticularis can cause general impairment of breathing and occur mainly in the context of damage to the right cerebral hemisphere. Those in the nucleus solitatius are associated primarily with impairments of the sense of taste. The sneezing reflex may also be affected by such phenomena as a diaphragmatic herniation or other diseases of the effector organs.
