A structure at the front of a sperm that contains enzymes and receptors required for penetration of the zona pellucida of an ovum.
action potential
An electrochemical signal that travels rapidly along an axon.
afferent
Carrying signals toward the CNS.
autonomic ganglion
A cluster of autonomic neurons outside the CNS.
autonomic nervous system
The portion of the nervous system that controls smooth muscles and glands without our conscious involvement.
axon
The extension of a neuron that conveys impulses, usually in a direction away from the cell body. Also called nerve fiber.
balanitis
Inflammation of the glans of the penis.
basal ganglia
Deep non-cortical structures of the forebrain.
benign prostatic hypertrophy
An enlarged but noncancerous prostate gland.
brainstem
The region of the brain between the forebrain and the spinal cord.
bulbospongiosus muscle
A muscle that attaches to the base of the penis or clitoris and assists with erection and (in men) ejaculation.
bulbourethral glands
Two small glands near the root of the penis whose secretions (“pre-cum”) may appear at the urethral opening during sexual arousal prior to ejaculation. Also known as Cowper’s glands.
cell body
The part of a neuron where the nucleus is located.
central nervous system (CNS)
The brain and spinal cord.
cerebral cortex
Convoluted, layered gray matter that covers most of the brain.
cerebral hemispheres
The uppermost and largest portion of the brain, divided into left and right halves.
chronic pelvic pain syndrome
An alternative, more-inclusive term for chronic prostatitis.
corona
The rim of the glans of the penis.
corpus callosum
A band of axons interconnecting the left and right cerebral hemispheres.
corpus cavernosum (pl. corpora cavernosa)
Either of two elongated erectile structures within the penis or clitoris, which also extend backward into the pelvic floor.
corpus spongiosum
A single midline erectile structure. In both sexes it fills the glans; in males it extends backward along the underside of the penis, surrounding the urethra.
cortex
The outer portion of an anatomical structure, as of the cerebral hemispheres or the adrenal gland.
cremaster muscle
A striated muscle that wraps around the spermatic cord and the testis.
dartos
A sheet of smooth muscle underlying the skin of the scrotum, which when contracted causes the skin to become thick and wrinkled.
dendrites
The extensions of a neuron that receive incoming signals from other neurons.
dorsal horn
The rear portion of the gray matter of the spinal cord: It has a sensory function.
dorsal root
A bundle of sensory axons that enters a dorsal horn of the spinal cord.
efferent
Carrying signals away from the CNS.
ejaculatory duct
Either of the two bilateral ducts formed by the junction of the vas deferens and the duct of the seminal vesicle. The ejaculatory ducts empty into the urethra within the prostate.
emission
The loading of the constituents of semen into the posterior urethra immediately before ejaculation.
epididymis (pl. epididymides)
A structure attached to each testis through which sperm must pass before entering the vas deferens.
epididymitis
Inflammation of the epididymis.
fascia
A tough sheet or sheath of connective tissue.
fibrin
A protein responsible for the coagulation of body fluids.
fibrinogen
The precursor to fibrin.
flagellum
A whip-like fiber extending from a spermatozoon or other cell that confers motility.
forebrain
The cerebral hemispheres and basal ganglia.
foreskin
The loose skin that partially or completely covers the glans in males who have not been circumcised.
frenulum
A strip of loose skin on the underside of the penis, running between the glans and the shaft.
fructose
A simple sugar (monosaccharide) present in semen.
ganglia
Collections of neurons outside the central nervous system.
genital end-bulbs
Specialized nerve endings found in erogenous zones, which probably detect the mechanical stimulation associated with sexual activity.
glans
The terminal knob of the clitoris or penis.
gray matter
A region of the central nervous system containing the cell bodies of neurons.
hydrocele
A collection of fluid around a testicle.
hypothalamus
A small region at the base of the brain on either side of the third ventricle; it contains cell groups involved in sexual responses and other basic functions.
inguinal canal
A short canal passing through the abdominal wall in the region of the groin in males.
interneuron
A neuron whose connections are local.
ischiocavernosus muscle
One of the muscles that attaches to the internal portions of the penis and clitoris. It assists with erection and (in men) ejaculation.
koro
A social panic based on the fear that the penis will retract and disappear, causing death.
Leydig cells
Cells located between the seminiferous tubules in the testis that secrete steroids. Also called interstitial cells.
locus coeruleus
A nerve center in the pons that helps regulate the state of consciousness.
medulla
The portion of the brainstem closest to the spinal cord.
midbrain
The region of the brainstem between the pons and the thalamus.
midpiece
The portion of the tail of a sperm that is closest to the head, containing mitochondria.
motor neuron
A neuron that triggers the contraction of muscle fibers.
neuromuscular junction
A synapse between an axon and a muscle fiber.
neuron
A single nerve cell with all its extensions.
neurotransmitter
A compound released at a synapse that increases or decreases the excitability of an adjacent neuron.
nitric oxide
A dissolved gas that functions as a neurotransmitter in erectile tissue.
nocturnal orgasm
Orgasm during sleep.
nucleus
In neuroanatomy, a recognizable cluster of neurons in the central nervous system.
Onuf’s nucleus
A sexually dimorphic group of motor neurons in the sacral segments of the spinal cord that innervates striated muscles associated with the penis and clitoris.
orchiectomy
Surgical removal of one or both testicles.
orchitis
Inflammation of a testicle.
paraphimosis
Entrapment of the retracted foreskin behind the corona.
parasympathetic nervous system
A division of the autonomic nervous system; among other functions, its activity promotes erection of the penis and clitoris.
pelvic nerves
Nerves that convey parasympathetic signals from the lower spinal cord to the genitalia and other organs.
penile bulb
An expansion of the corpus spongiosum at the root of the penis.
penis
The erectile, erotically sensitive genital organ in males.
peripheral nervous system
The motor and sensory connections between the central nervous system and peripheral structures such as muscles and sense organs.
Peyronie’s disease
Pathological curvature of the penis.
phimosis
A tightening of the foreskin, preventing its retraction from the glans.
pons
A region of the brain above the medulla.
postganglionic neuron
A neuron with cell body in an autonomic ganglion and an axon that innervates glands or smooth muscles in a peripheral organ such as the genitalia.
preganglionic neuron
An autonomic motor neuron in the spinal cord.
prostate cancer
Cancer of the prostate gland.
prostate gland
A single gland at the base of the bladder, surrounding the urethra; its secretions are a component of semen.
prostate-specific antigen (PSA)
An antigen characteristic of cells of the prostate gland, whose presence at high levels in the blood is suggestive of, but not diagnostic of, prostate cancer.
prostatitis
Inflammation of the prostate gland; may be acute or chronic.
pudendal nerves
Peripheral nerves supplying the external genitalia.
radical prostatectomy
Surgical removal of the entire prostate gland and local lymph nodes.
rete testis
A network of spaces between the testis and epididymis, through which sperm must pass.
scrotum
The sac behind the penis that contains the testicles.
semen
The fluid, containing sperm and a variety of chemical compounds, that is ejaculated from the penis at male sexual climax.
seminal plasma
The noncellular constituents of semen.
seminal vesicles
Two glands situated to either side of the prostate; their secretions are a component of semen.
seminiferous tubules
Convoluted microscopic tubes within the testis; the site of spermatogenesis.
Sertoli cell
A type of cell within the seminiferous tubules that nurtures developing sperm and secretes hormones.
sexual dimorphism
An anatomical difference between the sexes.
sinusoids
A vascular space, such as within erectile tissue, capable of being expanded by filling with blood.
smegma
A whitish, greasy secretion that builds up under the prepuce of the penis or clitoris.
sperm
A male gamete, produced in the testis.
spermatic cord
Either of two bilateral bundles of structures, including the vas deferens, blood vessels, and the cremaster muscle, that pass through the inguinal canal to the testis.
spermatogenesis
The production of sperm.
spinal cord
The portion of the central nervous system within the vertebral column.
spinal reflex
A reflex mediated by neurons in the spinal cord, requiring no participation by the brain.
subincision
A form of male circumcision in which a cut is made along the underside of the penis, exposing the urethra.
superincision
An unusual form of male circumcision in which the upper part of the foreskin is incised but not removed.
suspensory ligament
A ligament that connects the root of the penis to the pubic symphysis.
sympathetic nervous system
A division of the autonomic nervous system; among other functions, its activity inhibits penile erection but helps trigger ejaculation.
synapse
A junction where signals are transmitted between neurons or from neurons to muscle fibers.
synaptic cleft
The narrow space between two neurons at a synapse.
testicle or testis
The male gonad: one of the two glands within the scrotum that produce sperm and secrete sex steroids.
thalamus
The uppermost region of the brainstem.
trabeculae
Connective tissue partitions separating the sinusoids of erectile tissue.
tunica albuginea
A fibrous capsule surrounding the corpora cavernosa.
urethral meatus
The opening at the tip of the penis (in males) or in front of the vagina (in females).
varicocele
Enlargement of the veins that drain the testis.
vas deferens (pl. vasa deferentia)
Either of the two bilateral ducts that convey sperm from the epididymis to the ejaculatory duct.
ventral horn
The portion of the gray matter of the spinal cord nearer to the front of the body, where motor neurons are located.
ventral root
A bundle of motor axons that leaves a ventral horn of the spinal cord.
white matter
A region of the central nervous system that contains bundles of axons but no neuronal cell bodies.
