Lecture 38 4/12/24

Question 1

What are the two main steps of micturition?

Answer 1

-bladder progressively fills until the tension in its walls rises above a threshold level
-nervous reflex known as the micturition reflex causes a conscious desire to urinate

Question 2

What type of nervous reflex is the micturition reflex?

Answer 2

autonomic spinal cord reflex

Question 3

What are the two main parts of the urinary bladder?

Answer 3

-the body, where the urine collects
-the neck, which is funnel shaped and connects with the urethra

Question 4

What is the posterior urethra?

Answer 4

the lower part of the bladder neck

Question 5

What is the detrusor muscle?

Answer 5

-smooth muscle component of the bladder
-extends in all directions
-increases bladder pressure when contracted

Question 6

How is the detrusor muscle able to contract the bladder all at once?

Answer 6

the smooth muscle cells are fused together to allow for low-resistance electrical pathways; action potentials easily spread from cell to cell

Question 7

How is the trigone identified?

Answer 7

it has smooth mucosa, in contrast to the folded mucosa elsewhere in the bladder

Question 8

What are the characteristics of the ureters entering the bladder?

Answer 8

-course obliquely through the detrusor muscle
-pass 1 to 2 centimeters beneath the bladder mucosa before emptying into bladder

Question 9

What is the internal sphincter?

Answer 9

-involuntary smooth muscle composed of detrusor muscle interlaced with elastic tissue
-prevents bladder emptying until threshold is reached

Question 10

What is the external sphincter?

Answer 10

-in urogenital diaphragm
-voluntary skeletal muscle
-consciously prevents urination

Question 11

Which nerves provide the main parasympathetic supply to the bladder?

Answer 11

pelvic nerves

Question 12

Which spinal cord segments do the pelvic nerves connect to?

Answer 12

segments S2 and S3 via sacral plexus

Question 13

What is the function of the sensory fibers in the pelvic nerves?

Answer 13

detect the degree of stretch in the bladder wall

Question 14

What is the function of the motor fibers in the pelvic nerves?

Answer 14

innervate the detrusor muscle

Question 15

What is the function of the skeletal motor fibers of the pudendal nerve?

Answer 15

innervate and control the voluntary skeletal muscle of the external sphincter

Question 16

Which nerves provide the main sympathetic supply to the bladder?

Answer 16

hypogastric nerves

Question 17

Which segment of the spinal cord do the hypogastric nerves connect to?

Answer 17

L2

Question 18

What are the functions of the hypogastric nerve fibers?

Answer 18

-stimulate the blood vessels
-provide sensations of fullness and possibly pain

Question 19

What happens when a ureter becomes blocked?

Answer 19

-reflex constriction occurs, which is associated with severe pain
-pain leads to constriction of the renal arterioles, which reduces urine output from kidney (ureterorenal reflex)

Question 20

What are the characteristics of the ureter walls?

Answer 20

-contain smooth muscle
-innervated by sympathetic and parasympathetic nerves
-intramural plexus of neurons and nerve fibers extends along entire length

Question 21

What are the steps of urine transport to the bladder?

Answer 21

-urine flows from collecting ducts into the renal pelvis; no more compositional changes
-calyces stretch and stimulate peristaltic contractions; urine flows towards bladder
-detrusor muscle tone holds ureters shut during bladder contraction to prevent backflow

Question 22

What are micturition waves?

Answer 22

periodic acute increases in pressure that last from a few seconds to more than a minute and are caused by the micturition reflex

Question 23

What is the threshold amount of urine in the bladder before the pressure begins to rise rapidly?

Answer 23

300 to 400 mL

Question 24

What does it mean for the micturition reflex to be self-regenerative?

Answer 24

initial contraction of the bladder activates stretch receptors to cause a greater increase in sensory impulses from the bladder and posterior urethra, which causes further increase in reflex contraction of the bladder

Question 25

What occurs in a complete cycle of the micturition reflex?

Answer 25

-progressive and rapid increase in pressure
-period of sustained pressure
-return of pressure to basal tone

Question 26

What happens if the micturition reflex becomes too powerful?

Answer 26

it can cause a reflex which inhibits the pudendal nerve control over the external sphincter, causing involuntary urination

Question 27

Which centers in the brain are involved in the inhibition or facilitation of the micturition reflex?

Answer 27

-pons
-cerebral cortex

Question 28

What happens when the sensory nerve fibers from the bladder to the spinal cord are destroyed?

Answer 28

-micturition reflex contraction cannot occur
-stretch signals from bladder are not transmitted
-individual loses bladder control; bladder fills to capacity and overflows a few drops at a time

Question 29

What happens when the spinal cord is damaged above the sacral region?

Answer 29

-micturition reflexes can still occur, but are no longer controlled by the brain
-periodic but unannounced bladder empyting occurs

Question 30

What is uninhibited neurogenic bladder?

Answer 30

-partial damage in spinal cord or brain stem interrupts most of the inhibitory signals
-results in frequent, relatively uncontrolled micturition