Bladder and Micturition

Question 1

Overview the primary functions of the urinary bladder (storage, emptying)
Detail the parasympathetic and sympathetic innervation to the lower urinary tract
Overview the micturition cycle
Categorize the types of incontinence in men/women
Overview common causes of urinary tract obstruction.

Answer 1

focus on the first three

Question 2

Describe the bladder

Answer 2

The bladder is a hollow, elastic sac of muscular and connective tissue. The layer of smooth muscle is called the detrusor muscle.

Question 3

Describe the bladder neck in women vs men.

Answer 3

Bladder neck consists of fine bundles of muscle fibers. In women, these slant downwards and into the urethra and are instrumental in maintaining continence. In men, the bladder neck consists of bundles that ring the neck. Together with the smooth muscle fibers of the prostate, they form the urethral sphincter.

Question 4

Does the bladder reside in the peritoneum?

Answer 4

No. It resides in the retroperitoneal space inferior to the peritoneum. It can extend into the peritoneum when full.

Question 5

Name the female sphincters and state whether they are under voluntary or involuntary control.

Answer 5

The external rhabdosphincter (external sphincter) is under voluntary control. It is the one that clenches when someone walks in when you’re peeing (voluntary control).

The intrinsic sphincter (comprised of bladder neck muscle fibers and the mid urethral complex) is responsible for continence. It is under involuntary parasympathetic control.

Question 6

Name the male sphincters and state whether they are under voluntary or involuntary control.

Answer 6

The external rhabdosphincter (external sphincter) is under voluntary control. It is the one that clenches when someone walks in when you’re peeing (voluntary control).

The intrinsic sphincter (bladder neck muscle, sm of PROSTATE and membranous urethra)

Question 7

The _____ is the most important innervation, followed by the ____, then the ____

Answer 7

Parasympathetic
Sympathetic
Skeletal (motor)

Question 8

Which nerves innervate the detrusor muscle?

Answer 8

Parasympathetic and sympathetic. Parasympathetic activation results in detrusor muscle contraction and micturition. This is what is activated when you pee.

Sympathetic activation inhibits detrusor contraction and increases tension in the smooth muscle sphincters, preventing micturition until parasympathetic stimulation occurs. This is activated when you sit on your ass, not wetting your pants. Like you’re doing now.

Question 9

S 2,3,4 keeps the ______.

Answer 9

penis off the floor.

So the S2-4 motor (somatic) nerves innervate the bladder, penis, (responsible for erection, hence the mnemonic), pelvic floor, urethral sphincter.

** Sensations of bladder fullness or stretch are conveyed through long neurons from the spinal cord to the pons.

Question 10

HIGH YIELD

Describe the sympathetic innervation to the bladder. Name the nerve, the vertebral levels from which the nerve arises, and the effect of nerve activation.

Answer 10

T10-L2
Hypogastric nerve
Sympathetic innervation to the urethra and trigone
Stimulation is inhibitory to micturition.

**TSH (Thoracolumbar, Sympathetic, Hypogastric)

Question 11

HIGH YIELD

Describe the parasympathetic innervation to the bladder. Name the nerve, the vertebral levels from which the nerve arises, and the effect of nerve activation.

Answer 11

S2-S4
Pelvic nerves
Parasympathetic innervation

**SPP (Sacral, Parasympathetic, Pelvic nerves)

Question 12

HIGH YIELD

Describe the somatic innervation to the bladder. Name the nerve, the vertebral levels from which the nerve arises, and the effect of nerve activation.

Answer 12

S2-S4
Pudendal nerves
Somatic
Motor impulse to the pelvic floor and external sphincter (voluntary control)

**SSP (Sacral, Somatic, Pudendal)

Question 13

The CNS “chooses” when to void. Which part of the brain, and how?

Answer 13

The frontal cortex is your “inner voice.” Should I urinate right now? Loss of cortical inhibition (parkinsons, dementia, stroke)

Question 14

HIGH YIELD

Describe the afferent response.

Answer 14

Afferent activity is generated by filling of the bladder. Signal goes through the sacral cord DORSAL ROOT GANGLION, and then up to the frontal cortex.

Dysfunction occurs when these afferents are unmyelinated or injured.

Question 15

What’s the deal with storage?

Answer 15

Bladder should change volume readily but not pressure. (compliant)

If this is dysfunctional, you get urinary frequency, urgency, and urge incontinence.

Question 16

HIGH YIELD

Describe the efferent response.

Answer 16

Efferent responses to bladder filling are controlled at supraspinal levels by activating somatic (pudendal) motor neurons in the ANTERIOR HORN of the sacral spinal cord. These are associated with inhibition of the detrusor (cortical inhibition of detrusor activity).

Frontal lobe lesions can impair this inhibitory input resulting in detrusor overactivity.

Question 17

HIGH YIELD

Name the 5 steps of micturition (urination) IN ORDER.

Answer 17

1) Increase in bladder wall tension
2) Afferent input overcomes pontine micturition center threshold
3) Pudendal nerve activity ceases, external sphincter/pelvic floor muscles relax, detrusor neurons are freed and discharge
4) Proximal urethra opens
5) Bladder immediately contracts.

** any defect can mean hesitancy, weak stream, incomplete emptying, retention

Question 18

Name the result
Cortical brain lesion
Spinal cord injury
Overactive bladder
Sacral cord/nerve root/nerve lesion

Answer 18

Cortical brain lesion = hyperactive
Spinal cord injury= hyperactive
Overactive bladder= hyperactive
Sacral cord/nerve root/nerve lesion = can’t urinate (areflexia)

Question 19

Stress incontinence

Answer 19

Involuntary, sudden loss of urine during increase in intra-abdominal pressure. Putting physical stress on the bladder. (Sneezing, laughing, coughing, exercising).

NOT EMOTIONAL STRESS.

Question 20

Urge incontinence

Answer 20

You have a sudden, intense urge to urinate followed by an involuntary loss of urine. You may need to urinate often, including throughout the night. Urge incontinence may be caused by a minor condition, such as infection, or a more severe condition such as neurologic disorder or diabetes.

Question 21

Oxybutynin

Answer 21

Drug for overactive bladder. Blocks Ach. Dries you out (dry eyes, constipation, etc).

Question 22

How common is BPH?

Answer 22

80% of 80 year olds (microscopic evidence). But only 50% have symptoms.