Autonomic Innervation of the Head and Neck Flashcards
What part of the nervous system is the autonomic nervous system?
The autonomic nervous system is part of the peripheral nervous system and controls smooth muscle and glands. There is also some central control from the hypothalamus
Describe how sympathetic neurones in the head and neck leave the spinal cord and reach their target tissues
Sympathetic preganglionic fibres arise from the T1 - L2 (T1 and T2 for head and neck) level and travel superiorly up the sympathetic chain to synapse with the upper cervical ganglia (majority go to superior cervical ganglia). The post ganglionic fibres from this ganglion reach their target tissues by hitch hiking onto blood vessels forming a carotid plexus up the internal and external carotid arteries.
Where do sympathetic fibres on the internal carotid artery go to?
Postganglionic fibres on the internal carotid artery end up at the eye by following the ophthalmic artery. These innervate the tarsal muscle in the eyelid causing them to contract (wide eyed) and the iris (dilator pupillae) causing it to dilate. To get to the eyelid from the artery they hitch hike on cranial nerves i.e. oculomotor nerve for tarsal muscle and trigeminal nerve for dilator pupillae.
Where do sympathetic fibres on the external carotid artery go to?
Post ganglionic fibres on the external carotid artery innervate structure in the face such as sweat glands and smooth muscle.
How can the sympathetic fibres in the head and neck become damaged?
Pathologies involving any of the structures they travel pn or pathology of the apex of the lung can cause palsies of these sympathetic fibres. E.g. smokers for apex of lung and dissection of the carotid artery leading to neck pain.
How would palsies of the sympathetic fibres at the head and neck present and what is this known as?
Ptosis – droopy eyelid
Myosis – excessive constriction of the pupil
Anhydrosis – lack of sweating
Collectively known as Horner’s syndrome
Describe how parasympathetic neurones in the head and neck leave the brainstem and reach their target tissues
Parasympathetic fibres originate in the brainstem, the nuclei (collections of preganglionic parasympathetic cell bodies) of these fibres lie near to that of the cranial nerves which they then hitch hike onto when leaving the brainstem. Rather than having a chain of ganglia like the sympathetic nervous system the parasympathetic has 4 discrete ganglia in the head and neck: ciliary (oculomotor), pterygopalatine (facial) found in the pterygopalatine fossa, submandibular (facial) and the otic ganglia (glossopharyngeal).
Which nerves do the parasympathetic nerves hitch hike on?
The ganglia are reached by hitch hiking onto 4 cranial nerves: III (oculomotor), VII (trigeminal), IX (glossopharyngeal) and X (vagus). Upon reaching their ganglia the postganglionic neurones associate themselves only with the trigeminal nerves. The exception is those associated with the Vagus nerve which carry on down into the thorax and abdomen until they reach their ganglia, within or close to their target tissues.
Which ganglia and target tissue do parasympathetic fibres associated with the occulomotor nerve go to?
Preganglionic neurones travelling with the oculomotor nerve synapse at the ciliary ganglion. Postganglionic neurones from the ciliary ganglia go to the eye innervating the sphincter pupillae and the ciliary body
Which ganglia and target tissue do parasympathetic fibres associated with the facial nerve go to?
Preganglionic neurones travelling with the facial nerve synapse at the pterygopalatine and the submandibular ganglions. Post ganglionic neurones from the pterygopalatine ganglion innervate the lacrimal gland, nasal/oral cavity (mucosal glands). Post ganglionic neurones from the submandibular ganglia innervate the salivary glands – sublingual and submandibular
Which ganglia and target tissue do parasympathetic fibres associated with the glossopharyngeal nerve go to?
Preganglionic neurones travelling with the glossopharyngeal nerve synapse at the otic ganglion. Postganglionic neurones from the otic ganglia innervate the parotid gland.
Which ganglia and target tissue do parasympathetic fibres associated with the vagus nerve go to?
Post ganglionic neurones associated with the vagus nerve innervate glands in the larynx, respiratory tract/GI/Heart etc. The ganglia for these nerves are found within or next to the target tissues.
Describe the Path of Parasympathetic fibres associated with CN III
Leave the medulla with the oculomotor nerve pass through the cavernous sinus and then through the superior orbital fissure at which point it joins the ciliary ganglion.
Describe the Path of Parasympathetic fibres associated with CN VII
In the petrous bone the facial nerve splits into 3 fibres. The parasympathetic fibres join 2 of these: the chorda tympani which also contains taste for anterior 2/3 of tongue and the greater petrosal which only contains parasympathetic fibres.
Chorda tympani joins with the submandibular ganglia and the greater petrosal enter the pterygopalatine ganglia. These hitch hike onto the trigeminal nerve branches to reach their targets.
How does the location of a trauma to the petrous bone affect which parasympathetic fibres are affected?
Pathology at or before the geniculate ganglion (sensory ganglion where the nerve first splits) may involve all parasympathetic functions carried with CN VII. Pathology after geniculate gland will not involve greater petrosal nerve.
