Parasympathetics

Parasympathetics

Feature	Sympathetic NS	Parasympathetic NS
Summary of responses	Fight or flight	Rest and digest
Spinal cord distribution	Thoracolumbar	Craniosacral
Preganglionic neurone	Short	Long
Preganglionic neurotransmitter	Acetylcholine (Ach, cholinergic)	Acetylcholine (Ach, cholinergic)
Postganglionic neurone	Long	Short
Postganglionic neurotransmitter	Noradrenaline (NA, adrenergic) in most cases*	Acetylcholine (Ach, cholinergic)

*Sweat being an exception 

Efferent i.e. motor

Afferent i.e. towards the CNS so sensory 

Parasympathetic motor efferents—This system is divided into cranial and sacral components, and parasympathetic efferents only synapse with postganglionic cells close to or within target viscera (allowing local discrete responses)

4 main parasympathetic nuclei (III, VII, IX, X) with synapses in 4 ganglia (NB ganglia are outside CNS)

NB Most ganglia are associated with some sensory and sympathetic nerves – these do not synapse in the ganglia, they merely travel through it. 

1. Cilliary (parasympathetic eye) 

Supplied by fibres from Edinger-Westphal nucleus (a/w CNIII) 

Function: pupil constriction and accommodation 

2. Pterygopalatine Ganglion (aka sphenopalatine) in pterygopalatine fossa (cries/lubricates nasopharynx) 

Supplied by superior salivatory nuclues (a/w CN VII)  via GSPN and Vidian nerve. 

Function: secretomotor innervation to lacrimal gland, mucous glands of nasal cavity, nasopharynx and palate. 

3. Submandibular ganglion (salivates) 

Suspended from lingual nerve 

Supplied by superior salivatory nucleus (a/w CN VII) 

Function: Secretomotor innervation to the submandibular and sublingual salivary glands 

4. OTic Ganglion (parOTid - salivates) 

Inferior to foramen ovale 

Supplied by inferior salivatory nuclues (a/w CN IX)

Innervates parotid 

NB Vagus (X) does not innervate head and neck structures - only thorax and abdomen. 

Nucleus	Pre-ganglionic	Ganglion	Post-ganglionic	Target organs
Edinger-Westphal (Oculomotor nerve)	Travels with the motor root of the oculomotor nerve	Ciliary ganglion	Travels via the short ciliary nerves	Sphincter pupilliae Ciliary muscles
Superior salivatory nucleus (Facial nerve) NB VII above IX hence sup and inf (both salivate)	Travels with the greater petrosal nerve and the nerve of the pterygoid canal	Pterygopalatine ganglion	Hitchhikes on branches of the maxillary nerve	Lacrimal gland Nasopharynx Palate Nasal cavity
	Travels within the chorda tympani, a branch of the facial nerve	Submandibular ganglion	Fibres travel directly to target organs	Sublingual and submandibular glands
Inferior salivatory nucleus (Glossopharyngeal nerve)	Travels within the lesser petrosal nerve	Otic ganglion	Hitchhikes on the auriculotemporal nerve	Parotid gland
Dorsal vagal motor nucleus (vagus nerve)	Travels within the vagus nerve	Many – located within the target organs	n/a	Smooth muscle of the trachea, bronchi and gastro-intestinal tract

Neuro-embryology

The Medulla

Medulla

1. Surface anatomy

Ventral:

Gracilis (lower limb- graceful-) medial to cuneatus (upper limb). Generally when standing straight your legs are medial to arms. 

Floor of 4th ventricle:

Cranial nerves:

ff

Axial views through medulla

1. At level of pyramidal decussation (most caudal)

2. At level of sensory decussation (of medial lemnisci). 

Purple lines represent the internal arcuate fibres as they form the medial lemniscus  

3.  At level of olives (most cranial) NB Open Medulla i.e. above obex of 4th ventricle 

Vasculature:

Vessels that supply the medulla include: the anterior spinal, the posterior spinal, the PICA, AICA, and vertebral arteries

From the above it is possible to surmise the effects of lateral medullary (PICA) syndrome: 

Features are ipsilateral except for loss of contralateral pain and sensation over the body. Also NB Picachew i.e. dysphagia mnemonic.