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 the brain stem 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 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

(6) Abdominal reflex:

Make the subject lie down comfortably on a bed in the supine position. Uncover the abdomen and see that his abdominal muscles are well relaxed. With a blunt object gently stroke on the abdominal skin from lateral to the medial aspect in all the four quadrant. Observe the contraction of the abdominai muscles resulting in deviation of umbilicus towards the area stimulated. In children, obese persons and multi-parous women the reflex may be absent normally.

Thoracic 7th -12th segments are involved. This reflex helps to assess the level of lesion in paraplegia.

(7) Plantar reflex:

The patient is made to lie supine on the bed. Make sure that the muscles of the lower limb are well relaxed. Keep the ankle joint firmly fixed by one hand. To stimulate nociceptor, use an object like a keyte stroke the lateral border of the sole of the foot from the heel to the root of the little toe and then extend it medially to the base of the big toe.


Plantar flexion of the big toe with plantar flexion and adduction of other toes. This reflex is centered at the L5 S1 segments of the spinal cord. The afferents and efferents go through the tibial nerve.

Abnormal Plantar reflex:

This is usually seen in pyramidal tract disease. There is dorsiflexion of the big toe with extension and fanning out of other toes. This is also called extensor plantar response or Babinski sign.

(8) Cremasteric reflex:

Gently stroke the skin at upper inner aspect of the thigh. This results in the upward movement of testicle on that side due to the contraction of crem aster muscle.

Reflex pathway:

Afferent limb : Femoral nerve

Centre : L1 2segments

Efferent : Gènito fem oral nerve

B) DEEP REFLEXES: They are stretch reflexes. They are monosynaptic reflexes. They are elicited by stimulation of muscle spindles, for which the muscle has to be passively stretched prior to the elicitation of the reflex.

I . Jaw jerk:

Ask the subject to keep the mouth slightly open. The examiner’s left index finger is placed over the chin of the subject and gently tap the index finger with the tip of the right middle finger. Reflex contraction of the jaw muscles resulting in sudden closure of the mouth. Normally this reflex is very sluggish or even may be absent. Upper motor neuron lesion above the 5th cranial nerve nucleus may cause exaggerated jaw jerk.

The afferents and efferents go through the Trigeminal nerve and the centre is in the pons.

2. Biceps jerk:

Keep the elbow flexed at right angle and forearm in semiprone position supported on the forearm of the examiner. The examiner’s thumb is placed on the biceps tendon and strike on the thumb with a knee hammer.


Contraction of biceps which can be seen or felt by palpation resulting in flexion of elbow.

Centre: Cervial 5th and 6th segments are involved.

3. Triceps jerks:

Elbow is kept flexed at 900 and the forearm supported at the wrist. Tap the triceps tendon just proximal to the olecranon process. Contraction of the triceps results in extension of the elbow.

Centre: Cervical 5th & 6th segments.

4. Supinatorjerk:

Keep the elbow semiflexed. Support the forearm. Tap over the tendon on the styloid process of the radius. Flexion of elbow results due to contraction of brachioradialis.

Centre: Cervical 5th and 6th segments 5. Knee jerk:

Make the subject sit on the couch with his knee flexed and leg hanging freely from the edge of the couch. Muscles of the limb should be relaxed. Gently tap on the patellar tendon (quadriceps tendon).






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