medical physiology

1. The parasympathetic
nervous system

2. Functional anatomy:
 As in the sympathetic nervous system, parasympathetic pathways are composed of
preganglionic and postganglionic neurons.
 The preganglionic nerve fibers originate in cranial nerve nuclei in the brainstem
and in the lateral horn of the spinal cord between cord segments S2 and S4
(craniosacral origin).
 These fibers pass uninterrupted all the way to the effector organ.
 In the wall of the effector organ, the preganglionic fibers synapse with very short
postganglionic fibers, which in turn affect the function of the organ.

5. Functions of parasympathetic nervous
system
 [I] Oculomotor (3rd cranial) nerve
 Origin:
 Edinger -Westphal nucleus in mid brain.
 Relay:
 The ciliary ganglion.
 Functions:
 1) Motor to the constrictor pupillae muscle ---- Pupil constriction (miosis).
 2) Motor to the ciliary muscle --- accommodation for near vision.

7. [II] Facial (7th carnial) nerve
 Origin:
 1) Superior salivary nucleus (SSN) in lower part of pons 􀂟 Chorda tympani.
 2) Lacrimal center close to SSN 􀂟 Greater superficial petrosal nerve.
 Relay:
 1) Chorda tympani --- (the submandibular ganglion).
 2) Greater superficial petrosal nerve (the pterygopalatine ganglion).
 Functions:
 (I) Chorda tympani:
 1) Secretory & VD to the submandibular & sublingual salivary glands 􀂟 large amount of watery saliva poor in
enzymes.
 2) VD to blood vessels of the anterior 2/3 of tongue.
 (II) Greater superficial petrosal nerve:
 Secretory & VD to lacrimal & nasal glands.

8. [III] The glossopharyngeal (9th carnial) nerve
 Origin:
 Inferior salivary nucleus (ISN) in medulla oblongata.
 Relay:
 The otic ganglion.
 Functions:
 1) Secretory & VD to parotid salivary gland --- large amount of watery saliva poor
in enzymes.
 2) VD to blood vessels of the posterior 1/3 of the tongue.

9. [IV] The vagus (10th carnial) nerve
 Origin:
 Dorsal vagal nucleus in medulla oblongata.
 Relay:
 The terminal ganglia in the organs which it supplies.
 Functions:
 (1) Heart:
 Inhibition all cardiac properties; 􀂟 contractility (-ve inotropic), decrease excitability,
decrease rhythmicity (-ve chronotropic),decrease conductivity (-ve dromotropic).

10.  (2) Lungs:
 Bronchoconstriction.
 increase Bronchial mucous secretion.
 (3) GIT:
 a- Motor to plain muscles in wall of esophagus, stomach, small intestine & proximal
large intestine but inhibitory to their sphincters:
 increase Evacuation of food from GIT.
 increase Motility (peristalsis).
 b- Secretory to glands of stomach, intestine, pancreas & liver.
 (4) Gall bladder (GB):
 Motor to GB wall & inhibitory to sphincter of oddi ----- evacuation of GB.

11. [V] The sacral autonomic = pelvic nerve
 Origin:
 The autonomic motor nuclei in sacral spinal cord segments (S2-4).
 Relay:
 The terminal ganglia in organs of supply.
 Functions:
 (1) Defecation: (nerve of defecation)
 Constriction of the wall of the distal part of large intestine & rectum & relaxation of
internal anal sphincter.

12.  (2) Micturition: (nerve of micturition)
 Contraction of the wall of the urinary bladder (detrusor muscle) &
relaxation of internal urethral sphincter.
 (3) Erection: (nerve of erection = nervous erigentes)
 VD of the blood vessels of the pelvic viscera & the external genetalia
erection of penis & clitoris.
 (4) Secretion:
 Secretory to seminal vesicles & prostate.

13. Anatomical & physiological Differences between the
sympathetic & parasympathetic division

15. The main effects of the SNS & PNS on
target structures