Lecture 1 - Micturition

Where are the preganglionic and postganglionic sympathetic neurons in the bladder?

-Preganglionic: from spinal cord to caudal mesenteric ganglion

-Postganglionic: From caudal mesenteric ganglion to bladder wall and sphincter

What is the result of sympathetic neurons to the bladder and what are the receptors?

-Bladder filling

-a1 - constricts internal sphincter

-B3 - relaxes detrusor muscle

Where are the preganglionic and postganglionic neurons in the bladder?

-Preganglionic: from S1-3 to pelvic plexus

-Postganglionic: pelvic plexus to bladder wall

What is the result of sympathetic neurons to the bladder and what are the receptors?

-Bladder releasing (micturition)

-M3 - contract detrusor muscle

What are the steps in micturition (including spinal reflex vs brainstem)?

1. Stretch receptors in bladder wall send signals to the spinal cord (pelvic plexus → pelvic n.)

2. TWO OPTIONS:

   1. Spinal reflex (micturition reflex) activates preganglionic parasympathetic neurons

   2. Sensory info travels to the micturition center in the brainstem (awareness) and signal is sent to preganglionic parasympathetic neurons

3. Efferent info is sent through pelvic n. and synapses on pelvic plexus

4. Postganglionic parasympathetic neurons synapse on detrusor muscle causing contraction

What are the steps in urine storage?

1. Sympathetic preganglionic fibers from L1-4/5 synapse on caudal mesenteric ganglion

2. Postganglionic sympathetic fibers in hypogastric n. synapse with detrusor muscle and sphincter muscle

3. Urine accumulates in the bladder

What are the steps to consciously hold urine?

1. Urine leaking activates stretch receptors in sphincter

2. Signal ascends pudendal n. activating motor neurons in the sacral region

3. Causes constriction around urethral neck

Where could a lesion to a lower motor neuron to the bladder occur?

-Sacral spinal cord

-Pudendal nerve

-Pelvic

What is the result of a lower motor neuron lesion in the bladder?

-Loss of parasympathetic neurons to the bladder (loss of micturition reflex and constriction of detrusor muscle)

-Loss of external sphincter tone

What are the signs of a lower motor injury to the bladder?

-Overdistension of bladder (detrusor muscle unable to contract)

-Bladder is full and overflow incontinence but animal cannot void

Where could a lesion to an upper motor neuron to the bladder occur?

Cranial to sacral spinal cord

What is the result of a upper motor neuron lesion in the bladder?

-Parasympathetic innervation to detrusor muscle remains intact (micturition reflex exaggerated)

-Pudendal n. activated (cannot be inhibited)

What are the signs of a upper motor injury to the bladder?

-Full, turgid bladder

-Difficulty to express urine

Where are the preganglionic and postganglionic sympathetic neurons in the descending colon/rectum?

-Preganglionic: L1-4/5 (splanchnic n.) to caudal mesenteric ganglion

-Postganglionic: Hypogastric n. to nerve plexus

What is the result of sympathetic innervation to the descending colon and rectum? What are the receptors?

-B2 - inhibition of secretion and peristalsis

-a1 - contraction of internal anal sphincter

Where are the preganglionic and postganglionic parasympathetic neurons in the descending colon and rectum?

-Preganglionic: spinal cord to pelvic nerve

-Postganglionic: pelvic plexus to descending colon/rectum

What is the result of parasympathetic innervation to the descending colon and rectum? What are the receptors?

M3 - stimulate peristalsis and secretion

How is somatic innervation of the descending colon/rectum achieved? What does it innervate?

-Pudendal n.

-Innervates striated m. of external anal sphincter

How is conscious awareness achieved in the descending colon/rectum?

Sensory input from organ walls, rectum walls, sphincters, and perineum reach cortex