Autonomic Nervous System: Horner’s Syndrome

The autonomic nervous system runs Automatically. It requires sympathetic and parasympathetic components. The higher center for the ANS is the Hypothalamus. It helps the ANS maintain internal homeostasis. The Sympathetic nervous system is known to have Thoracolumbar flow because Sympathetic neurons run in the thorax and the lumbar region of the spinal cord from T1 - L2 spinal segments. The Parasympathetic Nervous System has Craniosacral flow because it Constitutes of cranial nerves (3, 7, 9, 10) and sacral nerves (S2 - S4).

The autonomic nervous system operates through a complex network of fibres. Preganglionic fibres, originating from the central nervous system, and postganglionic fibres, which are part of the autonomic motor ganglia, play crucial roles in this system. Preganglionic fibres from CNS enters the parasympathetic or sympathetic ganglion, which then sends the postganglionic fibres reaching the target organs;

• Smooth muscles
• Cardiac muscles
• Glands

Comparatively parasympathetic ganglia are closer to target organs than sympathetic ganglion. Thus the postganglionic fiber length is short in the parasympathetic ganglia and Preganglionic fibers of sympathetic ganglion are short. For Example, the Vagus nerve is the longest cranial nerve (preganglionic fibers) in the parasympathetic nervous system.

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Comparison Between Parasympathetic and Sympathetic Nervous System 

The parasympathetic nervous system is activated during resting and digesting. It is mainly used for the conservation of energy and is Anabolic in nature. The Neurotransmitter in the parasympathetic nervous system is Acetylcholine.

The Sympathetic system is activated during emergency situations like Fight or flight response. It requires a short burst of energy and is Catabolic in nature.

The Neurotransmitter is Adrenaline (Mostly) and Acetylcholine in Skin.

Now, let us discuss the main disorder of the autonomic nervous system—Horner's Syndrome. This syndrome has a special triad of clinical features: Ptosis, Miosis, and Anhydrosis(which may or may not be seen). The T1 sympathetic fibers are affected in Horner’s syndrome. As these symptoms are an important topic for the NEET-PG and FMGE exams, one should know about them in detail.

Partial ptosis is seen because of Paralysis of the superior tarsal muscle (part of the muller muscle). The eyelid is elevated. The Superior tarsal muscle is compromised as it is supplied by T1 sympathetic fibers.

One can also observe Miosis because the Dilator pupillae is supplied by the paralyzed T1 sympathetic fibers as well.

In a few cases of Horner's syndrome, Exophthalmos occurs because Orbitalis pushes the eyeball out of the socket. The Paralyzed eyeball appears to be sunken.

Some other very common features of Horner's syndrome are Nasal congestion, redness of the face, and conjunctival congestion resulting from Vasodilation due to hyperemia.

Horner syndrome is caused by damage to a certain pathway in the sympathetic nervous system. The nerve pathway affected by Horner syndrome is divided into three groups of nerve cells (neurons):

These pathways have three main pathologies, which are important not only for theoretical exams but also in clinical practice.

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Wellenberg Syndrome

• Lateral medullary ischemia 
• Lesion: 1st order neuron injury
  • Ptosis
  • Miosis 
  • Anhidrosis: Loss of sweating on the same side of the face
    • Face will become dry, red: Vascular congestion
    • Pathways controlling the sweat glands are compromised
• 3rd order neuron: Follows internal carotid artery and external carotid artery
  • The sweat glands in the face are affected:
    • Sympathetic vasoconstriction: Skin or mucosa 
    • Forms plexus around the sympathetic carotid artery

Pancoast Tumor

• Apical lung cancer in right side lead to right sided horner's syndrome 
• Injury at the level of sympathetic chain 
• Injury of preganglionic fibers
  • Miosis
  • Partial ptosis
  • Anhidrosis
  • Vascular congestion

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Right Sided Cavernous Sinus

• Internal carotid artery dissection
  • At the Levels of the internal carotid artery are separated 
  • 3rd order neuron injury 
• Features
  • Anhidrosis
  • Vascular congestion is not observed 
• Only distal parts are compromised 

This material does feel like a lot of things need to be remembered, but when it is watched in the PrepLadder app with the teacher, it becomes much easier to understand. It is recommended that such topics that require a lot of reading should always be studied with the app.

Also Read: Inguinal Canal & Spermatic Cord - NEET PG

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