Reflex activities of brain stem
Brain stem exhibits reflex activities-
Light reflexes – Pupillary light reflex
When light strikes the retina of either eye both the pupils constrict to reduce the amount of light passing through the pupil.
Receptor organ is retina
Sensory fibres pass via optic nerve that terminate in the pre tectal nucleus.
This nucleus lie between the mid brain and thalamus.
The fibre synapse with internuncial neurons of the pre tectal nucleus from here the fibre project to occulomotor nuclei to cause excitatory post synaptic potential.
The induced stimulus on occulomotor nerve causes generation of action potential in the circular smooth muscles of the iris-effector organ.
Pupillary construction is the effect produces by this reflex.
Corneal blink reflex
Corneal blink reflex is a protective reflex preserving cornea from injurious foreign material. Receptor organ is the cornea. Sensory fibres passes via opthalmic division of trigeminal nerve.
It involves internuncial neurons located within the BSRF. Motor neurons are the alpha motor neurons of the facial nucleus that supply muscles of orbicularis oculi, that cause closure of the eyelid.
In most occasion blink reflex is acccompanied with lacrimation reflex. If not associated with lacrimation it is known as palpebral blink reflex.
Lacrimation reflex
Lacrimation reflex is a protective reflex preserving cornea from drying and preserves vision. Afferent fibres or through opthalmic division of trigeminal nerve.
Internuncial neurons are involved. Cell bodies are located within the reticular formation of the brain stem. The efferent neurons comprise a portion of rostral salivatiry nucleus.
These neurons are parasympathetic pre ganglionic fibres to the lacrimnal gland. The efferent fibres pass via facial nerve from BSRF joint to the petrosal nerve.
At this point the synapse with pterygopalantine ganglian. From here fibres are projected to lacrimnal gland. This reflex modify the rate of lacrimal flow and aids the removal of foreign material from the surface of the cornea.