The menace response is one of three forms of

blink reflex The corneal reflex, also known as the blink reflex or eyelid reflex, is an involuntary blinking of the eyelids elicited by stimulation of the cornea (such as by touching or by a foreign body), though it could result from any peripheral stimulus. ...

. It is the reflex blinking that occurs in response to the rapid approach of an object. The reflex comprises blinking of the

eyelids An eyelid is a thin fold of skin that covers and protects an eye. The levator palpebrae superioris muscle retracts the eyelid, exposing the cornea to the outside, giving vision. This can be either voluntarily or involuntarily. The human eyel ...

, 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 reflex. Stimulating the menace reflex 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 reflex while leaving the other blink reflexes, such as the dazzle reflex, unaffected. The presence or absence of the menace reflex, in combination with other reflexes, indicates a locus of damage. For example, an animal with

polioencephalomalacia Polioencephalomalacia (PEM), also referred to as cerebrocortical necrosis (CCN), is a neurological disease seen in ruminants that is caused by multiple factors, one of which is thiamine depletion in the body. Thiamine (vitamin B1) is a key chemic ...

will lack the menace reflex, but will still have the pupillary light reflex. Polioencephalomacia damages the visual cortex, impairing the menace reflex, 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. From ...

, 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 of ...

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. Testing the menace reflex has to be done with care. Waving an object close to an animal's eyes or face does not necessarily demonstrate a functioning menace reflex, in part because the animal can sense such objects and react to them via senses other than sight. Clinical testing of the menace reflex 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 reflex. The neural pathway of the menace reflex 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 forward-most portion of the brainstem and is associated with vision, hearing, motor control, sleep and wakefulness, arousal (alertness), and temperature regulation. The name comes from the Greek ''mesos'', " ...

passing from the

optic tract In neuroanatomy, the optic tract () is a part of the visual system in the brain. It is a continuation of the optic nerve that relays information from the optic chiasm to the ipsilateral lateral geniculate nucleus (LGN), pretectal nuclei, and supe ...

to accessory nuclei, and thence to the

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the spi ...

and lower

motor neuron A motor neuron (or motoneuron or 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 or indirectl ...

es that innervate the head, neck, and body muscles affected by the reflex. The facial nerve is mediated through a corticotectopontocerebellar pathway.

References

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