Lecture 10 - ANS Flashcards
What centrally controls the autonomic NS?
ANS is part of the peripheral NS
Hypothalamus
Structure of the autonomic NS
Preganglionic nerve
Autonomic ganglion - sympathetic chain
Postganglionic nerve
Target tissues of the autonomic NS
Smooth muscle
Cardiac muscle
Glands - lacrimal, mucosal and salivary
Sympathetics
Vasoconstriction
Opens eyelids - tarsal muscle (small contribution)
Pupil dilation - dilator pupillae in iris
Sweat glands
Arrector pilli muscles
Decreases secretions from salivary and lacrimal glands (smaller volume but more viscous)
Parasympathetics
Pupil constriction - sphincter pupillae (CN III)
Increased secretions from:
- lacrimal glands - (CN VII greater petrosal)
- Salivary glands (CN IX and VII chorda tympani)
- Mucosal glands (CN VII greater petrosal)
Bronchodilation
Increased digestion GI tract
Craniosacral outflow
Parasympathetic
- Cranial - CN III, VII, IX, X
- Sacral (splanchnic) - S2, 3, 4
Thoracolumbar outflow
- Sympathetic
- T1- L2
- Cell bodies in the lateral horn of grey matter of spinal cord
How do the sympathetics travel to target tissues?
The postganglionic sympathetic nerves follow the external surface of blood vessels in the head and neck (CCA)
What are the 3 cervical ganglion
Superior - head
Middle - neck and chest
Inferior
Describe the route of sympathetic nerves
- The hypothalamus stimulates a sympathetic nerve between T1 - L2
- The preganglionic sympathetic nerve travel through the sympathetic chain without synapsing
- At the superior cervical ganglion where the postganglionic cell bodies are found, it synapses.
- The postganglionic sympathetic nerve travels along the common carotid artery.
- If it supplies the face or sweat glands - ECA
If it supplies the eye, eyelid or iris - ICA - opthalmic artery
Horner’s syndrome
Conditions that affect the CCA can affect the sympathetic nerves:
Partial ptosis (tarsal muscle)
Miosis - unopposed parasympathetic innervation
Anhydrosis (sweat glands)
Causes of Horner’s syndrome
Pancoast tumour - in apex of lung
Aneurysm
Which cranial nerves carry parasympathetics?
CN III
CN VII
CN IX
CN X
Structure of the parasympathetics
- Preganglionic parasympathetic nerves arise from the brainstem from parasympathetic nuclei
- They travel along the respective cranial nerve to the parasympathetic ganglion
- The postganglionic parasympathetic nerve then travels on the branches of CN V except the vagus nerve to the target tissue
[Note: very short postganglionic course]
4 parasympathetic nuclei
Edinger Westphal - pupillary light reflex
Superior salivary
Inferior salivary
Dorsal motor
4 parasympathetic ganglia
Ciliary
Submandibular
Pterygopalatine
Otic
Describe the parasympathetics of the occulomotor nerve
- The Edinger Westphal nucleus and the nucleus of the occulomotor fibres both exit the brain stem together
- The preganglionic parasymathetic fibres synapse at the ciliary body
- The postganglionic parasympathetic fibres travel to the sphincter pupillae and ciliary body muscles to constrict the pupil
Impingement of CN III
The parasympathetics are located on the periphery of the occulomotor nerve so affected first - partial ptosis
If persists: occulomotor nerve affected causing complete ptosis
Pupillary light reflex
- Optic nerve detects the light stimulus.
- Sends sensory afferents to the optic chiasm and to the mid brain.
- The Edinger Westphal nucleus and occulomotor nucleus is stimulated by both the left and right eye.
- The pre-ganglionic parasympathetic fibres leave the brainstem with the CN III and synapse at the ciliary ganglion.
- The postganglionic parasympathetic nerve travels to the sphincter pupillae muscle of the iris to constrict the pupil and the ciliary body muscle for the accommodation reflex
Direct light reflex
Eye in which the light is shone
Consensual light reflex
Constriction of the opposite pupil
Anisocoria
Unequal size of the pupils
Parasympathetics with the facial nerve
- PS exit the brainstem with the facial nerve axons
- The preganglionic PS nerve synapses at the pterygopalatine ganglion and the submandibular ganglion.
- The post-ganglionic PS reach the target tissue via the greater pertrosal and chorda tympani nerve.
- Run with distal branches of the trigeminal Vc lingual nerve
Parasympathetics with the glossopharyngeal nerve
- PS fibres arise from the brainstem and exit with CN IX
- Exits through the jugular foramen and splits into branches.
- PS fibres run with the tympanic branch of CN IX initially
- Exit the middle ear as the lesser petrosal nerve
- Synapse in the otic ganglion in the infratemporal fossa
- PS then travel with the auriculotemporal nerve (from CN Vc)
- Enters the parotid gland
Parasympathetics with the vagus nerve
- PS from the medulla of the brainstem exit with the axons of CN X
- Preganglionic PS nerve runs within CN X and its branches
- Meets ganglion at or within the target tissue
What are the target tissues for vagus nerve parasympathetics?
- Mucosal glands in the pahrynx and larynx
- Smooth muscles of the oesophagus and trachea
- Smooth muscle and mucosal glands of the resp system and GI tract
- Cardiac muscle
