The Snout reflex (also orbicularis oris reflex
) or a "Pout" is a pouting or pursing of the lips that is elicited by light tapping of the closed lips near the midline. The contraction of the muscles causes the mouth to resemble a
snout
A snout is the protruding portion of an animal's face, consisting of its nose, mouth, and jaw. In many animals, the structure is called a muzzle, rostrum, or proboscis. The wet furless surface around the nostrils of the nose of many mammals is c ...
.
This
reflex
In biology, a reflex, or reflex action, is an involuntary, unplanned sequence or action and nearly instantaneous response to a stimulus.
Reflexes are found with varying levels of complexity in organisms with a nervous system. A reflex occurs ...
is tested in a
neurological exam
A neurological examination is the assessment of sensory neuron and motor responses, especially reflexes, to determine whether the nervous system is impaired. This typically includes a physical examination and a review of the patient's medical hist ...
and if present, is a sign of
brain damage
Neurotrauma, brain damage or brain injury (BI) is the destruction or degeneration of brain cells. Brain injuries occur due to a wide range of internal and external factors. In general, brain damage refers to significant, undiscriminating t ...
or dysfunction. Along with the "suck",
palmomental reflex The palmomental reflex (PMR) or Marinesco-Radovici Sign or Kinn reflex or Marinesco Reflex is a primitive reflex consisting of a twitch of the chin muscle elicited by stroking a specific part of the palm. It is present in infancy and disappears as t ...
es and other reflexes, snout is considered a
frontal release sign
Frontal release signs are primitive reflexes traditionally held to be a sign of disorders that affect the frontal lobes. The appearance of such signs reflects the area of brain dysfunction rather than a specific disorder which may be diffuse, such ...
. These reflexes are normally inhibited by
frontal lobe
The frontal lobe is the largest of the four major lobes of the brain in mammals, and is located at the front of each cerebral hemisphere (in front of the parietal lobe and the temporal lobe). It is parted from the parietal lobe by a groove betwe ...
activity in the brain, but can be "released" from inhibition if the frontal lobes are damaged. They are normally present in infancy, however, and until about one year of age, leading to the hypothesis that they are primitive or archaic reflexes.
Frontal release signs are seen in disorders that affect the frontal lobes, such as
dementia
Dementia is a disorder which manifests as a set of related symptoms, which usually surfaces when the brain is damaged by injury or disease. The symptoms involve progressive impairments in memory, thinking, and behavior, which negatively affe ...
s,
metabolic encephalopathies,
closed head injuries, and
hydrocephalus
Hydrocephalus is a condition in which an accumulation of cerebrospinal fluid (CSF) occurs within the brain. This typically causes increased intracranial pressure, pressure inside the skull. Older people may have headaches, double vision, poor ...
. All of these disorders produce diffuse cerebral damage, usually involving many areas and systems in addition to the frontal lobes and
pyramidal system
The pyramidal tracts include both the corticobulbar tract and the corticospinal tract. These are aggregations of efferent nerve fibers from the upper motor neurons that travel from the cerebral cortex and terminate either in the brainstem (''cort ...
, so the frontal release signs are not sufficient for a diagnosis.
References
{{Refend
Sources
Walker, Hall and Hurst. ''Clinical Methods: The history, physical and laboratory examinations, 3rd ed.'' Reflexes