The so-called genital end bulbs are also observed.·

The involvement of neuroendocrine reflex mechanisms in a
variety of reproductive functions is implied by a number of observations. In
reflex ovulators such as the rabbit, cat, and ferret, stimuli applied to the
external genitalia result in pituitary gonadotropin release and ovulation,
whereas in some spontaneous ovulators such as the rat and mouse, this same
stimulus causes pseudopregnancy. Olfactory stimuli supplied by strange male
mice block pregnancy. The degree of dependence of reproductive activity upon
external stimuli, however, shows considerable species variation.·        
Despite
obvious gross anatomical differences between the genders, neuroanatomical
pathways within the pelvis, spinal cord, and the brain also show a great deal
of resemblance·        
Afferent
terminations of the penis are free nerve endings (FNE) of thin myelinated Ag, and unmyelinated C fiber type.·        
They
penetrate the epidermis and end in the stratum granulosum.·        
Pacinian
corpuscles, Ruffini’s corpuscles, and so-called genital end bulbs are also
observed.·        
The
brain and spinal cord also receive sensory information from mechanoreceptors
located in the urethra, muscle spindles/golgi tendons of ischiocavernosus
(ICM), bulbospongiosus (BCM) and external urethral sphincter (EUS) muscles,
tunica albuginea (TA), and corpora·        
This
sensory input is crucial in the central regulation of micturition, erection,
and ejaculation.·        
Afferent
receptors converge and form bundles that enter the main branch of the pudendal
nerve (PN) via dorsal (DNP) (dorsal surface of the penis) and perineal (PerN)
nerves (ventral surface and frenulum of the penis). ·        
Lateral
arborizing fibers of the DNP innervate the distal urethral lumen, and the PerN
supplies the proximal bulbar and membranous urethra·        
The
female equivalent of the DNP is the dorsal nerve of the clitoris, and the PerN
branches out to become the posterior nerves of labia majora and labia minora.
These nerves join to become the PN.·        
Both
the DNP and PerN join and become the PN nerve at the ICM and BCM junction. The
latter enters the spinal cord through S2-S4 roots to terminate on spinal
neurons and interneurons in the gray commissure and central region of the
lumbosacral segment. ·        
Spinothalamic
and spinoreticular pathways relay sensory information (pain, touch,
temperature, etc.) from the spinal cord to the thalamus, hypothalamus, medial
reticular formation (MRF), sensory cerebral cortex, and other centers.·        
In
addition, penile afferent nerves interact with autonomic centers located in the
sacral intermediolateral cell columns to modulate reflexogenic erection and
micturition. The Role of Peripheral Nerves in Reproductive Processes in
the Male·        
The
glans penis are important sources of sensory information to the CNS for
induction and maintenance of sexual and micturition reflexes. ·        
In
fact, desensitization of the glans of rats severely impairs erectile ability
and successful penile intromission. ·        
The
most numerous genital receptors of both sexes are free nerve endings (FNE)·        
FNE
are known to express polymodality, which implies their ability to perceive
different stimuli, such as temperature, mechanical (touch, pressure, stretch,
vibration), and pain. ·        
This
physiologic capacity is called “dissociated sensibility”·        
FNE
receptors can translate multiple sensory inputs to excitatory signals. This
information is rapidly transmitted by genital afferents to the spinal cord and
higher centers to produce sexual arousal, erection, ejaculation, and pleasure.·        
External
urethral sphincter activity after PN stimulation appears to be frequency
dependent. ·        
In
a nonspinal male cat study, high frequency (1–10 kHz) electrical stimulation
(ES) of PN causes reversible block of External Urethral Sphincter contractions
(EUS). ·        
In
another cat study, ES of the dorsal nerve of penis (DNP) either inhibits (low
frequency) or activates (high frequency) detrusor contractions, promoting
storage or emptying, respectively. ·        
Evoked
electromyographic (EMG) activity of the EUS after DNP electrical stimulation
was also observed. ·        
Can
sensory stimulation of a nerve with both sensory and motor function lead to
contraction of striated muscles supplied by it? o  
The
PN appears to have this special characteristic. This functional coupling was
studied in the cat. ES of the PN lead to vaginal dilation and anal sphincter
contraction. The Role of Peripheral Nerves in Reproductive Processes in
the Female·        
Abundant
evidence indicating an important role of afferent stimuli on reproductive
processes in the female of many species·        
For
example, ovulation in the rabbit is induced by the act of coitus or vaginal
stimulation with a glass rod.·        
Ovulation
in response to coitus, however, appears not to be dependent solely upon genital
receptors, since local anesthesia of the vulva and vagina, denervation of the
genital region, abdominal sympathectomy, hysterectomy, and extirpation of the
proximal half of the vagina does not affect the response.·        
It
seems likely that a variety of receptors and afferent pathways capable of
activating the release of a pituitary ovulating hormone exist.·        
In
rat and mouse, pseudopregnancy can be induced by mechanical or electrical
stimulation of the cervix or by sterile mating.·        
It
could be due to convergence of afferent impulses on the hypothalamus, causing
the release of prolactin which activates the corpora lutea to secrete
progesterone.·        
The
length of the pseudopregnant period is determined by the functional life of the
corpora lutea and is approximately 12-13 days or about one-half the length of
the normal gestation period.Modification of Gonadal Function by Manipulation of the Genital
Tract·        
Effects
of Uterine Distention:o  
Uterine
distention is accompanied by an alteration of the estrous cycle length in some
species. o  
This
effect has been attributed to a neurogenic stimulus from the distended horn
acting by way of the hypothalamopituitary pathway to influence the release of
hormones controlling the persistence or regression of corpora lutea.o  
In
sheep the insertion of a plastic beads in utero during the early luteal phase
shortened the cycle by several days, similar effect has been reported in cow
and guinea pig§  due to afferent impulses from uterine
receptors, since denervation of the segment containing the bead results in
essentially normal cycles.o  
Presence
of a mechanical irritant in the magnum portion of the oviduct of laying hens
suppresses ovulation.o  
Alterations
in the secretion of anterior pituitary gonadotropic hormones by uterine
distention have not been reported, but the secretion of oxytocin following
genital stimulation is well documented, particularly in ruminants.o  
Injection
of oxytocin early in the estrous cycle inhibits the development of the corpus
luteum and produces a precocious estrus. o  
On
the other hand, when a similar treatment was given to hysterectomized animals,
the induction of estrus did not occur. o  
It
is that the stimulation of the uterus by injections of oxytocin or distention
results either in an inhibition of a pituitary luteotropic factor by way of
neural pathways or alternatively by the production of a uterine luteolytic
factor.·        
Intrauterine
Foreign Bodies:o  
Plastic
devices Inserted in utero for contraceptive purposes in humans to prevent
pregnancy.o  
Studies
on the effect of loosely placed sutures in the uterine horn of laboratory
rodents – implantation fails to occur in the operated horn  ·        
Effects
of Removal of Uteruso  
Removal
of the uterus causes a significant prolongation of the life span of corpora
lutea in the guinea pig, cow, sheep, pig, rat, mouse and rabbit but not in
ferret, monkey or human.§  Luteolysis by PGF2? is secreted by
endometricum Exteroceptive Stimuli Influencing Reproductive Processes·        
Olfactory
Stimuli:o  
When
male domestic animals are exposed to a receptive female, most display a
somewhat stereotyped behavioral pattern. o  
This
includes smelling and licking the vulva, tasting the urine, and an occasional
lifting of the head, curling the lip, and expanding the nares (Flehman
response).o  
The
role of olfactory stimuli in mating behavior due to the odor emanating from the
urine or vaginal secretions of the female in estrus.o  
In
most laboratory rodents, olfaction does not appear to be important for
copulation as long as other sensory capacities remain active.o  
Rabbits
and rats show no alteration in sexual behavior after removal of the olfactory
bulbs as long as the neocortex is intact.o  
Complete
ablation of the olfactory bulbs of sexually mature sows causes a permanent
anestrus, a reduction in uterine weight, ovarian atrophy.·        
Visual
Stimuli:o  
Bulls
show an increased interest in the nonestrous heifer if first an estrous cow has
been led past the stanchion.o  
An
increased uterine motility can be demonstrated in heifers at the sight of a
bull.o  
In
young female pigs the presence of a male apparently triggers a release of
pituitary gonadotropins which precipitates first estrus. o  
Visual
stimuli have marked effects on reproduction in birds. §  An example of a purely visual
stimulus affecting reproductive processes is the observation that the pigeon
will ovulate when she sees another pigeon or an image of herself in a mirror.§  Many birds display definite courtship
performances such as a type of dance. o  
It
has been proposed that these sexual displays and the presence of other animals
serve to cause afferent stimulation of the hypothalamus and in turn activation
of the pituitary.·        
Auditory
Stimuli:o  
Ringing
of bell 1 out of every 10 minutes persistently – after 1 week female rats
develop prolonged and more or less persistent estrus.o  
Rabbits
react to auditory stimuli by forming large hemorrhagic ovarian follicles
similar to those found in a positive pregnancy test.o  
In
trials where estrous sows were exposed to combined auditory and olfactory
stimuli from a boar, 90% responded to manual pressure on the back with an
immobilization reflex in contrast to 50% in the absence of these stimuli and
81% of those exposed to olfactory stimuli alone.o  
Dairy
bulls who have refused to mount a cow for a long time have been induced to
mount it again when stimulated by specific calls of cows recorded and playedSummary

Evidence for the role of a variety of
exteroceptive stimuli in reproductive processes seems irrefutable. It is
difficult to prove that one sensory modality or one afferent pathway is of
primary importance over another; rather, it would seem that all the senses are
involved and to some degree interrelated, no one sense being absolutely
essential. The impulses apparently impinge upon neurons of the hypothalamus and
thereby affect pituitary gonadotropin secretion.

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