Micturition Pathway & Physiology

Micturition Pathway & Physiology

Anatomy of Bladder

Function of Bladder: Storage and evacuation of urine

Anatomical components that are important in mictirition:

1. Detrusor muscle of the bladder
2. Internal sphincter
3. External sphincter

Innervation of Bladder

1. Sympathetic from T12-L2 via hypogastric nerve
     mainly on internal sphincter and urethral smooth muscle
     receptor: Alpha
     Activation causes inhibition of parasympathetic system & contraction of  internal sphincter and   .     urethral smooth muscle

2.  Parasympathetic from Sacral plexus (S2-4) via Pelvic nerve
     innervation on the bladder detrusor and internal sphincter
     Receptor:  M2 and 3 on Detrusor muscles; Nicotinic receptor on Internal sphincter
     Activation leads to contraction of the detrusor muscle and relaxation of internal sphincter

3. Somatic innervation via Pudendal nerve (S2-4) arising from Onuf's nucleus
     Innervation on the external sphincter on the urogenital diaphragm  
     Receptor: ACh
     Action: Relaxation of external sphincter   

Nerve	Type of receptor	Action
Sympathetic (Hypogastric nerve)	Alpha 1 receptor	Contraction of internal sphincter & inhibition of parasympathetic
Parasympathetic (Pelvic nerve)	M2 & M3 receptor Nicotinic receptor	Contraction of detrusor muscle Relaxation of internal sphincter
Somatic (Pudendal nerve)	Ach receptor	Contraction of external sphincter (voluntary)

  Mah Joon Kooi.

Preganglionic parasympathetic detrusomotor neurons are located in the intermediolateral cell column of the sacral cord S2 and have axons traveling in the pelvic nerve to peripheral ganglion cells in the wall of the bladder, where acetylcholine is released. 

sphincteromotor nucleus of Onuf is located in the ventral horn at LaminaIX, just medial to the motoneurons of the hind limb and lateral to those of the trunk and axial musculature.



(Berthil, 2002. Central pathway controlling micturition. Urology. )

Voiding reflex:  ranzcog.net/publications/document-library/.../166-cu-model-saq.html

• The central pathways controlling lower urinary tract function are organised as simple on-off switching circuits (1 mark) that maintain a reciprocal relationship between the urinary bladder and urethral outlet (1 mark)
  
• Urine storage reflexes: During the storage of urine distention of the bladder produces low level vesical afferent firing (1 mark), which in turn stimulates:
  

(1) the sympathetic outflow to the bladder outlet (base and urethra) (1 mark); and
(2) pudendal outflow to the external urethral sphincter (1 mark)

• Voiding reflexes: during elimination of urine intense bladder afferent firing activates spinobulbospinal reflex pathways passing through the pontine micturition centre, (1 mark) which stimulate the parasympathetic outflow to the bladder and internal sphincter smooth muscle (1 mark) and inhibit the sympathetic and pudendal outflow to the urethral outlet. (1mark)
  
• The expulsion phase consists of an initial relaxation of the urethral sphincter followed in a few seconds by a contraction of the bladder, an increase in bladder pressure and the flow of urine (1 mark). Relaxation of urethral smooth muscle is mediated by activation of the parasympathetic pathway to the urethra, that triggers the release of nitric oxide, an inhibitory transmitter (1 mark) and by removal of adrenergic and somatic cholinergic excitatory inputs to the urethra. (1 mark)
  

• The storage phase of the urinary bladder can be switched to the voiding phase, either involuntarily (reflexly [human infant]) or voluntarily.
  (1 mark)
  
• Intravesical pressure measurements during bladder filling reveal low and relatively constant bladder pressures when bladder volume is below the threshold for inducing voiding (1 mark) (intrinsic properties of the vesical smooth muscle, and quiescence of the parasympathetic efferent pathway).
  
• Lower urinary tract is innervated by three sets of peripheral nerves (1 mark):
  (1) pelvic parasympthatic nerves, which arise at the sacral level of the spinal cord, excite the bladder and relax the urethra;
  (2) lumbar sympathetic nerves inhibit the bladder body, modulate transmission in the bladder parasympthatic ganglia and excite the bladder base and urethra; and
  (3) pudendal nerve excites the external urethral sphincter.
  These nerves contain afferent (sensory) axons as well as efferent pathways.
  
• The switching system is modulated by various neurotransmitters and is sensitive to a variety of drugs. (1 mark)
  

Accesory Nerve

It has 2 parts, the cranial component and the accessory component

The cranial accessory nerve arise from the nucleus ambuguus at the tegmentum of medulla oblongata posterior to the olive. It received bilateral innervation from the cortoticonuclear fibers.

The spinal accessory nerve arise from the ventral horn of  C1-6.  The SCM receives ipsilateral corticospinal innervation, whilst the Trapezius receive contralateral corticospinal innervation.

The cranial accessory nerve exit the medulla oblongata at the post olivary sulcus below vagus nerve and fluocullus and enter jugular foramen.

Within the jugular foramen it stay with vagus to form vagus accessory complex, which is separated from the glossopharyngeal nerve via a fibrous band / bony crest.

It converge with the spinal accessory nerve briefly eventually merge with vagus nerve.

The spinal accessory nerve arise from the ventral horn of C1-6. The motor nerve ascends to reach the infratentorial fossa via foramen magnum and merge with vagus nerve briefly (as just mentioned) before taking a posteroinferior course to supply the upper surface of SCM C1-2. Then it travels posterolaterally  to the posterior triangle of the neck and finally supply trapezius C2-4. 

In posterior triangle the accessory nerve is embedded in between 2 deep cervical facia within the loose connective tissue.

The spinal accessory nerve was found within 3.6 cm (mean, 1.43 cm) above Erb’s point. 

Erb’s point is where the bundle of sensory nerves from the cervical plexus emerges from the posterior border of the sternocleidomastoid muscle, midway between the mastoid process and the clavicle. 

The distance between the spinal accessory nerve entering the trapezius muscle and the clavicle was between 2 To 7 cm (mean, 4.5 cm)

Previous study  in Caucasians shows the spinal accessory nerve exits within 2 cm above the posterior border of the muscle.

In study done on thai people, the nerve was found below Erb’s point in  one neck, and at or above Erb’s point

Studies in Caucasion shows that the point where accessory nerve innervates the trapezius muscles can be found 2-4 cm away from clavicle. But in thai people, the measurement ranges 2-7cm. 

(Dr Pitchit, Chiang Mai University, 2005. Identification of Accessory Nerve in Posterior triangle)

 

 

Vagus nerve

Intro

1.     Vagus nerve is the longest cranial nerve, from brainstem till splenic flexure of colon

2.     Aka Pneumogastric nerve or the wanderer

3.     Mixed motor and sensory nerve

4.     Bilateral lesion to the X cranial nerve is fatal since it causes

a.     Loss of parasympathetic supply to heart à Tachyarrhythmias

b.      Laryngeal muscle paralysis -à Asphyxia

Component	Nucleus	Ganglion	Peripheral Nerve and target organs	Function
Branchial efferent	Ambigus		Pharyngeal nerve à Uvula, tensor veli palatini, Stylopharyngeus, Styloglossus Sup Laryngeal nerveà Cricothyroid muscle  (stretch vocal folds) Recurrent Laryngeal nerveà PosteriorCricoarythenoids (abduct VC) Lateral Cricoarythenoids (adduct VC) Arythenoids Thyroarythenoids	Swallowing Speech
Para sympathetic Efferent	Dorsal motor nucleus of X		Esophagus, cardiac, pulmonary, gastric, celiac plexus SA node of Atrium Carotid sinus(Baro)/ Body (Chemo) The sm and glands of GIT	Peristalsis Heart rate and rhythm BP regulation
Visceral sensation	Solitary nucleus	Inferior ganglion (Nodusum)	..	..
Special sensation	Solitary nucleus	Inferior ganglion	Epiglottis and Taste buds	Taste
General sensation	Trigemina	Superior Ganglion (jugular)	Posterior meninges, External ear, auditory meatus,	Cutaneous sensation

 

Course of Vagus nerve

1.It exit the medulla oblongata at the post olivary sulcus between olive and inferior cerebellar peduncle inferior to the flocculus’ (Cisternal portion)

2. Together with cranial portion of accessory nerve, it forms the vagua accessory nerve complex to enter jugular foramen

This complex is divided from the more superiorly located glossopharyngeal nerve by the fibrous band or a bony crest.

3. The vagus nerve enter its superior ganglion in the jugular fossa of the petrous temporal bone.

The auricular nerve arises from the superior ganglion. It travels in the mastoid cannaliculus lateral to the jugular foramen. Later on it exit the skull base via tympanomastoid suture to supply the posterior aspect of pinna and external auditory meatus.

1cm distal to the superior ganglion, the vagus nerve meets the inferior ganglion of nodusom, which has a larger size since it contains the cell bodies of the visceral and special sensory afferent nerve supplying the viscera.

1.   Upon exiting the jugular foramen, the glossopharyngeal nerve and vagus accessory complex is separated by dura sheath, but the branchial motor nerves soon rejoin their effector at the pharynx. The pharyngeal nerve is therefore formed and penetrate the middle constrictor muscles before supplying the uvula, and the pharyngeal musculatures. Tensor veli palatini, palatoglossus, palatopharyngeus by Vagus nerve; Stylopharyngeus by Gloospharyngeal nerve

6. In the neck the vagus nerve run together with IJV posterolaterally and ICA anteromedially within the carotid sheath

It joints with the glossopharyngeal nerve to form nerve of Hering to supply the carotid sinus and body

It gives off superior laryngeal nerve to supply Cricothyroid muscle, which is responsible to stretch the vocal fold.

It also gives out branches to reach the superior and inferior cardiac plexus which is mainly the right vagus nerve function. Vagus nerve stimulation is only performed on its left counterpart to avoid cardiac complication (This is my understanding at this moment, but I found books stating that the SA node is by the R vagus nerve; VA node by L vagus nerve.. Puzzled.. somebody help to clear my doubt, please??)

7.The right vagus nerve and its left counterpart take a slightly different course while descending from the neck to the abdominal cavity.

8. The right vagus nerve runs lateral to the CCA and cross anterior to the proximal part of subclavian artery to reach the thoracic cavity. At this juncture, it gives rise to right recurrent laryngeal nere which loop around the subclavian artery before ascending to supply the laryngeal muscles with the exception of cricothyroid muscle. (Posterior cricoarythenoid to abduct VC whilst Lateral cricoarythenoid to adduct VC)

9. The left vagus nerve runs in between the left CCA and L Brachiocephalic artery and cross in front of aortic arch. The Left recurrent laryngeal loops below the aortic artery and ascend lateral to the trachea to supply the larynx

10. 

10. The vagus nerve pierces the esophageal hiatus and gives rise to the gastric nerves, celiac plexus and etc.

The right Vagus nerve is distributed in the anterosuperior surface of abdominal viscera e.g. fundus, liver, omentum

Left vagus nerve assume a posteroinferior distribution.