The menace response is one of three forms of
blink reflex. It includes the reflexive blinking that occurs specifically in response to the rapid approach of an object.
The menace response comprises blinking of the
eyelids, in order to protect the eyes from potential damage, but may also include turning of the head, neck, or even the trunk away from the optical stimulus that triggers the response.
Stimulating the menace response is used as a diagnostic procedure in veterinary medicine, in order to determine whether an animal's visual system, in particular the cortical nerve, has suffered from nerve damage. Cortical damage, particularly cerebral lesions, can cause loss of the menace response while leaving the other blink reflexes, such as the dazzle reflex, unaffected.
The presence or absence of the menace response, in combination with other reflexes, indicates a locus of damage. For example, an animal with
polioencephalomalacia will lack the menace reflex, but will still have the pupillary light reflex. Polioencephalomacia damages the visual cortex, impairing the menace response, but leaves the
optic nerve
In neuroanatomy, the optic nerve, also known as the second cranial nerve, cranial nerve II, or simply CN II, is a paired cranial nerve that transmits visual system, visual information from the retina to the brain. In humans, the optic nerve i ...
,
oculomotor nucleus
The fibers of the oculomotor nerve arise from a nucleus in the midbrain, which lies in the gray substance of the floor of the cerebral aqueduct and extends in front of the aqueduct for a short distance into the floor of the third ventricle. F ...
, and
oculomotor nerve
The oculomotor nerve, also known as the third cranial nerve, cranial nerve III, or simply CN III, is a cranial nerve that enters the orbit through the superior orbital fissure and innervates extraocular muscles that enable most movements o ...
intact, leaving the pupillary light reflex unaffected. Contrastingly, an animal with ocular hypovitaminosis-A will suffer from degeneration of the optic nerve, and such an animal presents with a lack of both reflexes.
Care must be taken when testing the menace response. Waving an object close to an animal's eyes or face does not necessarily demonstrate a functioning menace response, in part because the animal can sense such objects and react to them via senses other than sight. Clinical testing of the menace response usually involves precautions such as waving an object from behind a sheet of glass, so as to shield the animal from any drafts caused by the motion of the object through the air, which it might otherwise sense. Such reactions to non-visual stimuli are a widespread cause of false positives and false negatives when pet owners test their own animals for the presence of the menace response.
The neural pathway of the menace response comprises the
optic (II) and
facial (VII) nerves. It is mediated by tectobulbar fibres in the rostral
colliculi of the
midbrain
The midbrain or mesencephalon is the uppermost portion of the brainstem connecting the diencephalon and cerebrum with the pons. It consists of the cerebral peduncles, tegmentum, and tectum.
It is functionally associated with vision, hearing, mo ...
passing from the
optic tract to accessory nuclei, and thence to the
spinal cord
The spinal cord is a long, thin, tubular structure made up of nervous tissue that extends from the medulla oblongata in the lower brainstem to the lumbar region of the vertebral column (backbone) of vertebrate animals. The center of the spinal c ...
and lower
motor neuron
A motor neuron (or motoneuron), also known as efferent neuron is a neuron whose cell body is located in the motor cortex, brainstem or the spinal cord, and whose axon (fiber) projects to the spinal cord or outside of the spinal cord to directly o ...
es that innervate the head, neck, and body muscles affected by the response. The facial nerve is mediated through a corticotectopontocerebellar pathway.
References
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