Lordosis behavior (), also known as mammalian lordosis (Greek lordōsis, from ''lordos'' "bent backward") or presenting, is the naturally occurring body posture for sexual receptivity to

copulation Sexual intercourse (or coitus or copulation) is a sexual activity typically involving the insertion and thrusting of the penis into the vagina for sexual pleasure or reproduction.Sexual intercourse most commonly means penile–vaginal penetra ...

present in females of most mammals including rodents, elephants, and cats. The primary characteristics of the behavior are a lowering of the forelimbs but with the rear limbs extended and hips raised,

ventral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

arching of the spine and a raising, or sideward displacement, of the

tail The tail is the section at the rear end of certain kinds of animals’ bodies; in general, the term refers to a distinct, flexible appendage to the torso. It is the part of the body that corresponds roughly to the sacrum and coccyx in mammal ...

. During lordosis, the spine curves

dorsoventral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

ly so that its apex points towards the abdomen.

Description

Lordosis is a reflex action that causes many non-primate female mammals to adopt a body position that is often crucial to reproductive behavior. The posture moves the

pelvic tilt Pelvic tilt is the orientation of the pelvis in respect to the thighbones and the rest of the body. The pelvis can tilt towards the front, back, or either side of the body. Anterior pelvic tilt and posterior pelvic tilt are very common abnorma ...

in an anterior direction, with the posterior pelvis rising up, the bottom angling backward and the front angling downward. Lordosis aids in copulation as it elevates the hips, thereby facilitating penetration by the

penis A penis (plural ''penises'' or ''penes'' () is the primary sexual organ that male animals use to inseminate females (or hermaphrodites) during copulation. Such organs occur in many animals, both vertebrate and invertebrate, but males d ...

. It is commonly seen in female mammals during

estrus The estrous cycle (, originally ) is the set of recurring physiological changes that are induced by reproductive hormones in most mammalian therian females. Estrous cycles start after sexual maturity in females and are interrupted by anestrous ...

(being "in heat"). Lordosis occurs during copulation itself and in some species, like the cat, during pre-

copulatory Sexual intercourse (or coitus or copulation) is a sexual activity typically involving the insertion and thrusting of the penis into the vagina for sexual pleasure or reproduction.Sexual intercourse most commonly means penile–vaginal penetra ...

behavior.

Neurobiology

The lordosis

reflex arc A reflex arc is a neural pathway that controls a reflex. In vertebrates, most sensory neurons do not pass directly into the brain, but synapse in the spinal cord. This allows for faster reflex actions to occur by activating spinal motor neurons w ...

is hardwired in the spinal cord, at the level of the lumbar and sacral

vertebrae The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristi ...

(L1, L2, L5, L6 and S1).Pfaff D. W. , Schwartz-Giblin S., Maccarthy M. M., Kow L-M (1994). "Cellular and molecular mechanisms of female reproductive behaviors", in Knobil E., Neill J. D. ''The physiology of reproduction'', Raven Press, 2nd edition. In the brain, several regions modulate the lordosis reflex. The

vestibular nuclei The vestibular nuclei (VN) are the cranial nuclei for the vestibular nerve located in the brainstem. In Terminologia Anatomica they are grouped in both the pons and the medulla in the brainstem. Structure Path The fibers of the vestibular n ...

and the cerebellum, via the vestibular tract, send information which makes it possible to coordinate the lordosis reflex with postural balance. More importantly, the ventromedial

hypothalamus The hypothalamus () is a part of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrine system via the pituitary gland. The hypothalamu ...

sends projections that inhibit the reflex at the spinal level, so it is not activated at all times. Sex hormones control reproduction and coordinate sexual activity with the physiological state. Schematically, at the breeding season, and when an ovum is available, hormones (especially

estrogen Estrogen or oestrogen is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogenous estrogens that have estrogenic hormonal ac ...

) simultaneously induce

ovulation Ovulation is the release of eggs from the ovaries. In women, this event occurs when the ovarian follicles rupture and release the secondary oocyte ovarian cells. After ovulation, during the luteal phase, the egg will be available to be fertilize ...

and

(heat). Under the action of estrogen in the hypothalamus, the lordosis reflex is uninhibited. The female is ready for copulation and

fertilization Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Proce ...

. When a male mammal mounts the female, tactile stimuli on the flanks, the

perineum The perineum in humans is the space between the anus and scrotum in the male, or between the anus and the vulva in the female. The perineum is the region of the body between the pubic symphysis (pubic arch) and the coccyx (tail bone), includi ...

and the

rump Rump may refer to: * Rump (animal) ** Buttocks * Rump steak, slightly different cuts of meat in Britain and America * Rump kernel, software run in userspace that offers kernel functionality in NetBSD Politics *Rump cabinet * Rump legislature * Ru ...

of the female are transmitted via the

sensory nerve A sensory nerve, or afferent nerve, is a general anatomic term for a nerve which contains predominantly somatic afferent nerve fibers. Afferent nerve fibers in a sensory nerve carry sensory information toward the central nervous system (CNS) fro ...

s in the

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the sp ...

. In the spinal cord and lower brainstem, they are integrated with the information coming from the brain, and then, in general, a

nerve impulse An action potential occurs when the membrane potential of a specific cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells, ...

is transmitted to the muscles via the

motor nerve A motor nerve is a nerve that transmits motor signals from the central nervous system (CNS) to the muscles of the body. This is different from the motor neuron, which includes a cell body and branching of dendrites, while the nerve is made up of ...

s. The contraction of the longissimus and transverso-spinalis muscles causes the ventral arching of the vertebral column.

Hormonal and cerebral regulation

Sexual behaviour is optimized for reproduction, and the

is the key brain area which regulates and coordinates the physiological and behavioural aspects of reproduction.Plant T., Zeleznik A. (Eds).
Knobil and Neill's Physiology of Reproduction
'. Academic Press, 4th edition, 2015 Most of the time, the

ventromedial nucleus The ventromedial nucleus of the hypothalamus (VMN, also sometimes referred to as the ventromedial hypothalamus, VMH) is a nucleus of the hypothalamus. "The ventromedial hypothalamus (VMH) is a distinct morphological nucleus involved in terminati ...

of the hypothalamus (VMN) inhibits lordosis. But when environmental conditions are favorable and the female is in estrus, the

hormone A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are require ...

estradiol Estradiol (E2), also spelled oestradiol, is an estrogen steroid hormone and the major female sex hormone. It is involved in the regulation of the estrous and menstrual female reproductive cycles. Estradiol is responsible for the development o ...

, induces

sexual receptivity Animal sexual behaviour takes many different forms, including within the same species. Common mating or reproductively motivated systems include monogamy, polygyny, polyandry, polygamy and promiscuity. Other sexual behaviour may be reproduc ...

by the

neuron A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. ...

s in the

, the

periaqueductal gray The periaqueductal gray (PAG, also known as the central gray) is a brain region that plays a critical role in autonomic function, motivated behavior and behavioural responses to threatening stimuli. PAG is also the primary control center for d ...

, and other areas of the

brain A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a ve ...

. The ventromedial hypothalamus sends impulses down

axon An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action p ...

s synapsing with neurons in the periaqueductal gray. These convey an impulse to neurons in the medullary reticular formation which project down the

reticulospinal tract The reticular formation is a set of interconnected nuclei that are located throughout the brainstem. It is not anatomically well defined, because it includes neurons located in different parts of the brain. The neurons of the reticular formatio ...

and synapse with the neurobiological circuits of the lordosis reflex in the

(L1–L6). These neurobiological processes induced by estradiol enable the tactile stimuli to trigger lordosis. The mechanisms of regulation of this estrogen-dependent lordosis reflex have been identified through different types of

experiment An experiment is a procedure carried out to support or refute a hypothesis, or determine the efficacy or likelihood of something previously untried. Experiments provide insight into Causality, cause-and-effect by demonstrating what outcome oc ...

s. When the VMN is lesioned lordosis is abolished; this suggests the importance of this cerebral structure in the regulation of lordosis. Concerning hormones, displays of lordosis can be affected by ovariectomy, injections of estradiol benzoate and progesterone, or exposure to

stress Stress may refer to: Science and medicine * Stress (biology), an organism's response to a stressor such as an environmental condition * Stress (linguistics), relative emphasis or prominence given to a syllable in a word, or to a word in a phrase ...

during puberty. Specifically, stress can suppress the hypothalamic-pituitary-gonadal (HPG) axis and therefore decrease concentrations of gonadal hormones. Consequently, these reductions in exposure to gonadal hormones around puberty can result in decreases in sexual behavior in adulthood, including displays of lordosis.

In humans

Lordosis behavior is non-functional in humans, although lordosis-like positions can be observed in women being mounted from behind.Pfaus, J. G.; Flanagan-Cato, L. M.; Blaustein, J. D. "Female sexual behavior". in Plant T., Zeleznik A. (Eds). ''Knobil and Neill's Physiology of Reproduction''. Academic Press, 4th edition, 2015 In a 2017 study, using 3D models and eye-tracking technology it is shown that the slight thrusting out of a woman's hips influences how attractive others perceive her to be and captures the gaze of both men and women. The authors argue "while reflexive lordosis posture is not exhibited by human females and receptivity is not passive or obligatory for them, a manifestation of lumbar curvature might serve as a vestigial remnant of proceptivity-/receptivity-communicative signal between men and women". Previously, anthropologist Helen Fisher also speculated that when a human female wears

high-heeled footwear High-heeled shoes, also known as high heels, are a type of shoe with an angled sole. The heel in such shoes is raised above the ball of the foot. High heels cause the legs to appear longer, make the wearer appear taller, and accentuate the ...

the buttocks thrusts out and the back arches into a pose that simulates lordosis behavior, which is why high heels are considered "sexy". Nonetheless, recent evidence has extended the effect of lordosis pose beyond a standing posture and high-heels, as it is indicated a sexual receptivity signal in other than standing postures of quadruped and supine in women.

References

{{DEFAULTSORT:Lordosis Behavior Animal sexuality Ethology Mammalian sexuality Physiology Sex positions

Description

Neurobiology

Hormonal and cerebral regulation

In humans

See also

References