Reflex activities of brain stem

REFLEX ACTIVITIES OF BRAIN STEM

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.

neural_pathway1

Corneal reflexes

  • Corneal blink reflex
    • It 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
    • It 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.

Last modified: Wednesday, 23 May 2012, 9:16 AM