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Erection & Ejaculation ENDOCRINE PHYSIOLOGY: Note #1. 1 of 3
> 1.
# ERECTION & EJACULATION
Male Reproductive System | Erection & Ejaculation Medical Editor : Ilia -Presiyan Georgiev
OUTLINE
I) ERECTION
II) EJACULATION
III) REVIEW QUESTIONS
IV) REFRENCES
I) ERECTION (1) The penis
consists of of
o Bulb
o Shaft
o Glans penis
The tip
Most of the penis consists of the corpora cavernosum
(CC)
o A.k.a. erectile tissue
o Spongy connective tissue
o Riddled with a lot of blood vessels
The corpora spongiosum
o Connective tissue lining the urethra
o Keep the urethra open during ejaculation
(2) The first stimulus
for an erection may be
o Sight of erotic stimuli
o Thought of erotic stimuli
o Tactile stimuli
Touching of the genitals or specific areas of the skin that activate erotic sensations
o Smell
Specific areas in the brain are activated
The S2-S4 area of the sacral region in the spinal column is activated
Parasympathetic neurons come out as the pelvic nerve and innervates specific area in the penis the corpora cavernosum
(3) The pelvic nerve
innervates
o A lot of blood vessels within the corpora cavernosum
o A few blood vessels within the corpora spongiosum
The parasympathetic neurons secrete specific chemical
acetylcholine
o Binds to receptors on the endothelial cells of the blood vessels
(4) Acetylcholine
triggers an intracellular pathway that activates an enzyme - nitric oxide synthase (NOS)
NOS triggers the conversion of the amino acid arginine
into citrulline and nitric oxide (NO)
The NO flows into the smooth muscle cells of the vessels
o The smooth muscle cells have specific enzyme embedded in their cell membrane Guanylyl cyclase
NO stimulates Guanylyl cyclase to convert GTP into
cyclic GMP (cGMP)
The cGMP activates other enzymes that activate K+ channels
o The K + leave the cell
o The cell hyperpolarizes
(5) This leads to vasodilatation
The smooth cells relax
o the vessels will become bigger
o the erectile tissue expands
As it expands the corpora cavernosum presses the veins responsible for the draining of the blood
o Stops the draining
The penis gets engorged with blood
o The erection is triggered
Nice to know!
Phosphodiesterase type 5 (PDE5) degrades cGMP
Viagra (Sildenafil) inhibits PDE5
o cGMP remains abundant
o The cell continues to release K+
o The smooth muscle cells remain relaxed
o Vasodilatation persists
The erection persists
Figure 1 Erection.
Remember! Erection is controlled by the Parasympathetic system. Point .
Ejaculation is controlled by the Sympathetic system. Shoot .Last edited: 9/9/2021 2 of 3 ENDOCRINE PHYSIOLOGY : Note # 1. Erection & Ejacula tion
II) EJACULATION (1) There is large parasympathetic influx
due to the erection
The cerebral cortex eventually stops it from happening
o It sends descending fibers that
Inhibit the parasympathetic nervous system (PSNS)
Stimulate the sympathetic nervous system (SNS)
It causes the ejaculation
(2) Descending fibers
stimulate the cell bodies in the lateral grey horn of the spinal cord
o On level T12-T2
The axons come out and synapse on the inferior mesenteric ganglion (IMG)
o Contains cell bodies of postganglionic motor neurons
o Their axons make up the hypogastric plexus and go to different places.
(3) When the peak point
of the erection is reached the SNS activates.
The sperm is
o Created in the seminiferous tubules in the testes
o Stored and matures in the epididymis
A C-shaped structure on top of the testes
When an individual is about to ejaculate
o The adrenergic fibers of the postganglionic motor neurons release norepinephrine (NE)
o NE stimulates the adrenergic receptors on the smooth muscle cells
Causes them to contract
o They squeeze the sperm out of the epididymis and into the vas deferens
There are adrenergic receptors on the vas deferens smooth muscle cells
o Activated by NE
o The cells contract continuously
o Squeezing the sperm onwards
At the end of the vas deferens is the ampulla
o A dilated region
(4) The seminal vesicle
produce many different chemicals that make up the
seminal fluid
There are adrenergic receptors on the seminal vesicle
o Activated by NE
o The seminal vesicle contracts and expels the seminal fluid into the common ejaculatory duct (CED)
Formed from the fused vas deferens and a duct from the seminal vesicle
There seminal fluid is combined with sperm to make semen
The CED goes through the prostate and merges with the prostatic urethra
o The semen is pushed in the prostatic urethra
(5) The bladders epithelium
is made up of transitional epithelial cells
On the outside there is a smooth muscle layer - the
detrusor
On the beginning of the urethra there is a continuation of the detrusor - the internal urethral sphincter
There are adrenergic receptors on the internal urethral sphincter
o Activated by NE
o The sphincter contracts
Prevents the reflux of the semen into the bladder
(6) There are cell bodies
in the anterior grey horn in the sacral region of the spinal cord
o Level S2-S4
Their axons come out as the pudendal (somatic) nerve
o Innervates the skeletal muscles
Bulbospongiosis (main muscle)
Ishciocavernousus
Superficial transverse peroneus
o Secretes acetylcholine
Causes an influx of Na+
Causes these muscles to start contracting
Thus propelling the semen through the urethra at 11 miles an hour
The muscles also provide a lot of pleasure
(7) The ejaculation
is the peak point of the orgasm
o A.k.a. the climactic point
Right after ejaculation
o The SNS turns on
o The PSN turns off
The smooth muscle cells of the vessels inside the corpus cavernosum will return to their normal size
The erectile tissue to decrease in size
The drainage veins open and the blood starts flowing out of the penis, rendering it flaccid.
> Figure 2 Ejaculation.
Erection & Ejaculation ENDOCRINE PHYSIOLOGY: Note #1. 3 of 3
III) REVIEW QUESTIONS
The erectile tissue is?
a. Shaft b. Corpora cavernosum c. Corpora spongiosum d. Urethra
What is the purpose of the corpora spongiosum?
a. Protects the urethra b. Initiates the erection c. Initiates ejaculation d. Keeps the urethra open
What chemical is secreted by the parasympathetic neuron?
a. Acetylcholine b. Norepinephrine c. Arginine d. Cyclic GMP
Which enzyme embedded in the smooth muscle cells of the vessels?
a. Nitric oxide synthase b. Guanylyl cyclase c. Phosphodiesterase type 5 d. Adenylate cyclase
Which enzyme degrades cyclic GMP?
a. Nitric oxide synthase b. Guanylyl cyclase c. Phosphodiesterase type 5 d. Adenylate cyclase
Which structure is not part of the sympathetic nervous system?
a. Pelvic nerve b. Inferior mesenteric ganglion c. Hypogastric plexus d. Postganglionic motor neurons
Where does the sperm matures?
a. Corpus cavernosum b. Vas deferens c. Seminal vesicle d. Epididymis
Which is the main muscle responsible for ejaculation?
a. The detrusor b. Bulbospongiosis c. Ishciocavernousus d. Superficial transverse peroneus
Which nerve innervates the skeletal muscles that cause the ejaculation?
a. Pelvic b. Hypogastric plexus c. Pudendal d. Inferior mesenteric ganglion
The influx of which ions cause the skeletal to initiate ejaculation
a. K +b. Ca ++ c. Cl -d. Na +
CHECK YOUR ANSWERS