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Human Sexual Response A. Signs of arousal 1. physical signs a. increased cardiovascular activity increased : respiration blood pressure heart rate b. increased blood flow to: penis (male) erection clitoris, vagina and vulva (female) 2. generalized hormal changes during arousal a. epinephrine(E) and norepinephrine (NE) “sympathetic adrenal hormones” produced and secreted by adrenal glands norepinephrine Divisions of the Nervous System released as neurotransmitter I. CNS (central nervous system) from neurons in II. PNS (peripherial nervous system) sympathetic A. Somatic nervous system nervous system voluntary/skeletal muscle control i. cardiovascular B. Autonomic nervous system activity because acts on smooth muscle, cardiac muscles, and glands metabolic rate 1. parasympathetic ii. inhibit many nonsends signals to conserve and store energy immediately 2. sympathetic essential sends signals to expend energy activities (fight or flight response) such as digestion and blood flow to penis/clitoris Notes: E and NE return to normal when stimulus removed NE released when anxious, afraid, or cold NE inhibits erection: by binding to specific receptors (α-adrenoreceptors) in penis erection only possible/maintained if antagonists present antagonists bind to and block α-adrenoreceptors b. slight of lutenizing hormone (LH) role in arousal unknown general functions: stimulates production of estrogens in females androgens in males c. slight of testosterone role in arousal unknown d. of prolactin only if climax sexual response notes 1 B. Pathways to arousal/erection 1. the non-aroused state flaccid – low blood flow to penis (5ml/min) a. muscles in penis are contracted allows blood to enter and leave b. brain sends signals that inhibit erection inhibit “erection generating center” (EGC) in spinal cord through sympathetic nerves – release serotonin – inhibits EGC (Note: inhibition is turned off during REM sleep) c. anything that stimulates the sympathetic n.s. (or increases E & NE) inhibits EGC by sympathetic neuron activity 2. A reflex arc – the spinal erection reflex general stimulus receptors sensory (afferent) neuron integrating center in spinal cord motor (efferent) neuron effector - muscle specific tactile receptors in genitals erection generating center (EGC) parasympathetic (excitatory) neurons in penis 3. the erection process a. stimulation of excitatory parasympathetic neurons in penis b. parasympathetic neurons release neurotransmitters: acetylcholine stimulates endothelial cells in penis to release NO nitric oxide (NO) NO causes in production of cGMP cGMP causes smooth muscles to relax blood vessels dilate blood flow (penis/clitoris) spongy tissue fills with blood veins compressed blood can’t leave (more enters than exits) erection 4. Sources of stimulation = pro-erectile messages. signals initiate in… a. tactile receptors i. in genitals – requires direct stimulation signal sent to reflex arc ii. in other areas signal sent to hypothalamus b. other sensory organs/receptors -smell -images -tastes -sounds signals sent to brain sexual response notes 2 c. brain areas interconnected -cerebral cortex signals that originate in cortex and limbic system sent to hypothalamus -limbic system - other areas i-hypothalamus organizes and integrates signals from many sources if releases oxytocin parasympathetic neurons stimulated erection/arousal if releases something other than oxytocin sympathetic neurons stimulated inhibits erection/arousal ii-learning and memory can have a strong influence on erections cues: fetish objects iii-mood can effect pro-erectile messages 5. the effect of some chemicals on the pathway a. parasympathetic neurons release nitric oxide (NO) NO causes in production of cGMP cGMP is normally broken down by the enzyme, phosphodiesterase Viagra blocks phosphodiesterase cGMP causes smooth muscles to relax papaverine injected induces smooth muscle relaxation blood vessels dilate blood flow spongy tissue fills with blood veins compressed blood can’t leave erection b. sympathetic neurons release norepinephrine (NE) pentolamine, injected into penis, blocks NE NE inhibits erection sexual response notes 3 C. Orgasm A reflex general stimulus receptors sensory (afferent) neuron integrating center motor (efferent) neuron effectors sexual response notes specific physical or mental in penis or clitoris and G-spot in spinal cord sympathetic neurons glands secrete (emission in males) organ secretes sperm vas deferens% prostate fluid prostate % seminal fluid seminal vesicles % Skenes glands & muscles contract males females muscles in pelvic region penis uterus parts of vagina (causes ejaculation) 4