Changes

===Innervation===

===Innervation===

The bladder receives sympathetic and parasympathetic nerve supply.

The bladder receives sympathetic and parasympathetic nerve supply.

*Parasympathetic supply: This comes from S1-S3, synapses within the '''pelvic plexus''', continues as the '''pudendal nerve''' and is excitatory to the destrusor muscle. Parasympathetic dominance allows emptying of the bladder.

*'''Parasympathetic supply''': This comes from S1-S3, synapses within the '''pelvic plexus''', continues as the '''pudendal nerve''' and is excitatory to the destrusor muscle via release of Acetylcholine which binds muscarinic acetylcholine receptors. Parasympathetic dominance allows emptying of the bladder.

*Sympathetic Supply: This comes from L1-L4, synapses within the '''caudal mesenteric ganglion''' before entering the '''pelvic plexus. It then continues as the '''hypogastric nerves''' which terminate on beta 2 receptors within the detrusor muscle. It has inhibitory action on muscular contraction, therefore enabling bladder filling.

*'''Sympathetic Supply''': This comes from L1-L4, synapses within the '''caudal mesenteric ganglion''' before entering the '''pelvic plexus'''. Postganglionic fibres continue as the '''hypogastric nerves''', which terminate on beta 2 receptors within the detrusor muscle. It has inhibitory action on muscular contraction, therefore enabling bladder filling.

==Urethra==

==Urethra==

===Muscles of the Urethra===

===Muscles of the Urethra===

The '''''urethralis''''' muscle runs the entire length of the urethra and forms the '''external urethral sphincter'''. Unlike the [[Urinary Bladder - Anatomy & Physiology#Internal Urethral Sphincter|internal sphincter]], the external sphincter is composed of striated muscle fibres which are under the voluntary control of the somatic nervous system.  

The '''''urethralis''''' muscle runs the entire length of the urethra and forms the '''external urethral sphincter'''. Unlike the [[Urinary Bladder - Anatomy & Physiology#Internal Urethral Sphincter|internal sphincter]], the external sphincter is composed of striated muscle fibres which are under the voluntary control of the somatic nervous system.  

=====Somatic Motor Supply - External Urethral Sphincter=====

===Innervation of the External Urethral Sphincter===

* S1-S2

The ''urethralis'' muscle receives somatic innervation originating from S1-S3 and continuing via the '''pudendal nerve'''. This releases the neurotransmitter Acetylcholine, which binds to nicotinic Acetylcholine receptors and mediates skeletal muscle contraction of the external urethral sphincter. This is important in urine retention.

 

* Innervates the urethral skeletal muscle - external urethral sphincter

* Function is to contract and retain urine

===Vascular Supply===

===Vascular Supply===

Blood Supply comes from the '''Urethral Artery''', which is a branch of the '''vaginal artery''' which in turn is a branch of the '''internal pudendal''' which is a branch of the '''internal iliac'''.

Blood Supply comes from the '''Urethral Artery''', which is a branch of the '''vaginal artery''' which in turn is a branch of the '''internal pudendal''' which is a branch of the '''internal iliac'''.