Reflex Pathway

Reflex Pathway:

Receptors: Rods and cones in the retina Afferent limb: Optic nerve

Efferent limb: Oculomotor nerve

The afferent fibres involved travel in the optic nerve and leave it before the lateral geniculate body to enter thestem in the pretectal region. These fibres synapse in the Edinger Westphal nucleus (para sympathetic nucleus of oculomotor nerve). The fibres then travel along the oculomotor nerve to the ciliary ganglion in the orbit. Post ganglionic fibres pass via, short ciliary nerves to the sphincter pupillae muscles.

Indirect light reflex (Consensual reflex):

Ask the subject to look at a distant object. Make a partition in front of the nose using a book or his own hand to avoid light falling into the other eye. Throw light into one eye and observe the pupil of other eye.lt will constrict.

The decussation of fibres in the optic chiasma as well as in the pretectal region of the mid brain accounts for the consensual light reflex.

Accommodation reflex:

Accommodation is the process by which the eye adapts to near vision.

During accommodation, the following changes occur,

(a) Convergence of eye balls

(b) Constriction of pupils

(c) Increase in anterior curvature of the lens

Procedure: Seat the subject comfortably. Ask the subject to keep his index finger in front of his nose. He is instructed to look at a distant object. Then ask him to suddenly shift his gaze on to the finger. Observe the eyes and pupils. The eye balls converge and pupils constrict.

Pathway for accommodation reflex:

Receptor : Rodsand cones

Afferent : Optic nerve

Centre : Oculomotor nucleus

Efferent Oculomotor nerve

Effector (1) Constrictor pupillae

(2) Ciliary muscles

(3) Extrinsic muscle of eye ball (Medial rectus)

Rods and cones of retina —* Optic nerve —* Optic chiasma —* Optic tract —* Lateral geniculate body —* Optic radiation —* Occipital cortex —* Premotor cortex (Frontal eye field) —* (Area 8) —* Edinger Westphal nucleus —* Third cranial nerve —* Ciiiary ganglion —* Ciliary muscle and sphincter pupillae muscles.

Muscles of eye ball

Oculomotor nerve Constrictor pupillae

L* Ciliary muscle

In Argyll Robertson pupil, light reflex is sluggish or lost, but accommodation reflex is intact. This is seen in Neurosyphilis involving pretectal region.

(4) Palatine reflex:

Ask the subject to open his mouth widely and then touch the mucous membrane covering the palate using a spatula. This produces reflex contraction of the palatal muscles which results in sudden elevation of the palate.

Reflex pathway:

Receptors : Touch receptors of the palatal mucosa

Afferent limb : Glossopharyngeal nerve and Trigeminal nerve

Centre : Vagus nucleus in the medulla

Efferent limb : Vagusnerve

Effector : Palatal muscle

(5) Pharyngeal reflex: [Pharyngeal gag reflex]

Touch the posterior pharyngeal wall or fauces with a spatula. Elevation and contraction of the Pharynx results.

Afferent limb : Glossopharyngeal nerve

Centre : Vagal nucleus in the medulla

Efferent limb : Vagus nerve

Effector : Middle constrictor of pharynx

 

 

 

 

Reference on Medicinal plants  Part I

Reference on Medicinal plants Part II

 

reference on  Indian medicinal plants and its treatments.