Sexual anatomy and response

Erogenous zone

Body part that can give sexual pleasure when stimulated, subjective!

Characteristics of erogenous zones

More nerve endings/tactile nerves/vascularization (blood flow), learned associations, psycho factors, sociocultural norms, context!

Sexual anatomy development timeline

6 wks: same; 12 wks: partial dev; 12+ wks: fully M/F anatomy

Homologous organs

Organs from same embryonic tissue (clit and penis, foreskin and prepuce)

Analogous organs

Organs with similar functions (NOT clit and penis)

Female anatomy - vulva

External genital structure

Female anatomy - inner labia

Very sensitive, + vascularization, engorge if aroused

Female anatomy - vestibule

Area with urethral opening + fourchette

Female anatomy - Bartholin glands

Produce small amount of lubrification

Female anatomy - clitoris

Glans (tip), shaft, 2 cavernous bodies, 1 spongy body, vestibular bulbs (engorge)

= mostly internal

Function of clitoris

ONLY sexual pleasure

Female anatomy - hymen

Flexible membrane at vaginal opening (VARIABLE - fissure if activity), no clear bio purpose

Hymen myths (virginity and bleeding)

/= virginity, bleeding deps on capillaries
Nervousness = less lubrification = micro-tears = discomfort/bleeding

Most tactile nerves are at the ENTRANCE of the vagina, not…

inside

Female anatomy - anus

Many tactile nerves + vascularization, no natural lube = sphincter must relax

Why is there a higher STI risk from anal sex

No natural lube = micro-tears + fecal bacteria risk for male urethra

Male anatomy - penis

2 cavernous bodies and 1 spongy body (urethra)

Male anatomy - tunica albuginea/drosal vein

Fibrous sheath limiting expansion; dorsal vein traps blood during erection

Penis size is determined ONLY by _________, and erection is the great ________

genetics, equalizer

Circumcision (cultural/religious)

Removal of foreskin, STI risk slightly less, same sensitivity

Physiology of erection

Arteries dilate + veins constrict = blood trapped
Smooth muscles relax (involontary!) = erection

Nervous system control (PARAsympathetic sn = dilation)

Sensory input = spinal cord = brain = erection

Viagra mechanism

Prevents smooth muscle contraction = maintains dilation

Scrotal changes during male arousal

Testes elevate and skin thickens/tenses

Cowper’s gland

Clears urethra of urine acidity, lubricates, may contain small amount of sperm

Composition of sperm

Sperm cells = .1%
Seminal vesicles = 60%
Prostate secretions = 40% (milky color)

Masters & Johnson — 4 stages

Excitement = Plateau = Orgasm = Resolution

2 physiological processes in sexual response

Vasocongestion (blood flow) + myotonia (muscle contraction)

Ejaculation - stage 1

Emission: fluids in ejaculatory duct, internal sphincter closes, point of no return

Ejaculation - stage 2

Expulsion: rhythmic contractions expel semen

Orgasm vs ejaculation

Orgasm /= ejaculation BUT ejaculation /= erection
Orgasm = limbic synapses BUT ejaculation = muscular

Refractory period (women do not have one!)

Post-ejaculation recovery, longer with age

Male excitement phase

Erection, vasodilation, Cowper’s secretion, testes elevate

Male plateau phase

Sustained erection, more muscle tension

Male orgasm phase

Emission and expulsion, contractions

Male resolution phase

Loss of erection and refractory period

Female excitement phase

Clit enlarges, uterus elevates, vaginal lube = filtered plasma/estrogen-dep

Female plateau phase

Inner vagina expands, clitoris retracts, inner labia darken

Female orgasm phase

Uterus/orgasmic platform/anal sphincter contract

Female resolution phase

Structures return to baseline

_______% of women need clitoral stimulation for orgasm

70-92

G-spot - internal clitoral complex!!

Internal stimulation of vestibular bulbs of clitoris, may produce orgasm

Skene glands

Female prostate, homologous to male prostate, may expel fluid

Female expulsion/ejaculation - clitoral complex

Fluid may be from Skene glands OR bladder (10-40% of women)