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 present in females of most

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

s including

rodents Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia ( ), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are n ...

elephants Elephants are the Largest and heaviest animals, largest living land animals. Three living species are currently recognised: the African bush elephant (''Loxodonta africana''), the African forest elephant (''L. cyclotis''), and the Asian ele ...

, and

cats The cat (''Felis catus''), also referred to as the domestic cat or house cat, is a small domesticated carnivorous mammal. It is the only domesticated species of the family Felidae. Advances in archaeology and genetics have shown that the ...

. 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 describe unambiguously the anatomy of humans and other animals. 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 elongated section at the rear end of a bilaterian animal's body; in general, the term refers to a distinct, flexible appendage extending backwards from the midline of the torso. In vertebrate animals that evolution, evolved to los ...

. During lordosis, the spine curves dorsoventrally 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 The pelvis (: pelves or pelvises) is the lower part of an Anatomy, anatomical Trunk (anatomy), trunk, between the human abdomen, abdomen and the thighs (sometimes also called pelvic region), toge ...

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 (; : penises or penes) is a sex organ through which male and hermaphrodite animals expel semen during copulation (zoology), copulation, and through which male placental mammals and marsupials also Urination, urinate. The term ''pen ...

. It is commonly seen in female mammals during

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

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

Neurobiology

The lordosis

reflex arc A reflex arc is a neural pathway that controls a reflex. In vertebrates, most sensory neurons synapse in the spinal cord and the signal then travels through it into the brain. This allows for faster reflex actions to occur by activating spinal mo ...

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

vertebrae Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal ...

(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 The brainstem (or brain stem) is the poste ...

and the

cerebellum The cerebellum (: cerebella or cerebellums; Latin for 'little brain') is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid fishes it may be as large as it or eve ...

, 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 (: hypothalami; ) is a small part of the vertebrate brain that contains a number of nucleus (neuroanatomy), nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrin ...

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 (also spelled oestrogen in British English; see spelling differences) is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three ...

) simultaneously induce

ovulation Ovulation is an important part of the menstrual cycle in female vertebrates where the egg cells are released from the ovaries as part of the ovarian cycle. In female humans ovulation typically occurs near the midpoint in the menstrual cycle and ...

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 American and British English spelling differences#-ise, -ize (-isation, -ization), spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give ...

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

perineum The perineum (: perineums or perinea) in placentalia, placental mammals is the space between the anus and the genitals. The human perineum is between the anus and scrotum in the male or between the anus and vulva in the female. The perineum is ...

and the rump of the female are transmitted via the

sensory nerve A sensory nerve, or afferent nerve, is a nerve that contains exclusively afferent nerve fibers. Nerves containing also motor fibers are called mixed nerve, mixed. Afferent nerve fibers in a sensory nerve carry sensory system, sensory information ...

s in the

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue that extends from the medulla oblongata in the lower brainstem to the lumbar region of the vertebral column (backbone) of vertebrate animals. The center of the spinal c ...

. In the spinal cord and lower

brainstem The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is conti ...

, they are integrated with the information coming from the brain, and then, in general, a

nerve impulse An action potential (also known as a nerve impulse or "spike" when in a neuron) is a series of quick changes in voltage across a cell membrane. An action potential occurs when the membrane potential of a specific Cell (biology), cell rapidly ri ...

is transmitted to the

muscle Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...

s via the

motor nerve A motor nerve, or efferent nerve, is a nerve that contains exclusively efferent nerve fibers and transmits motor signals from the central nervous system (CNS) to the effector organs (muscles and glands), as opposed to sensory nerves, which transf ...

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

hormone A hormone (from the Ancient Greek, Greek participle , "setting in motion") is a class of cell signaling, signaling molecules in multicellular organisms that are sent to distant organs or tissues by complex biological processes to regulate physio ...

estradiol Estradiol (E2), also called oestrogen, oestradiol, is an estrogen steroid hormone and the major female sex hormone. It is involved in the regulation of female reproductive cycles such as estrous and menstrual cycles. Estradiol is responsible ...

, induces sexual receptivity by the

neuron A neuron (American English), neurone (British English), or nerve cell, is an membrane potential#Cell excitability, excitable cell (biology), cell that fires electric signals called action potentials across a neural network (biology), neural net ...

s in the ventromedial nucleus, 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 ...

, and other areas of the

brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

. The ventromedial hypothalamus sends impulses down

axon An axon (from Greek ἄξων ''áxōn'', axis) or nerve fiber (or nerve fibre: see American and British English spelling differences#-re, -er, spelling differences) is a long, slender cellular extensions, projection of a nerve cell, or neuron, ...

s synapsing with neurons in the periaqueductal gray. These convey an impulse to neurons in the medullary

reticular formation The reticular formation is a set of interconnected nuclei in the brainstem that spans from the lower end of the medulla oblongata to the upper end of the midbrain. The neurons of the reticular formation make up a complex set of neural networks ...

which project down the reticulospinal tract 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 cause-and-effect by demonstrating what outcome occurs whe ...

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 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

While lordosis behavior has not been observed in humans, positions similar to lordosis can be seen in those being mounted from behind, with the autonomous lordosis reflex replaced by a conscious decision to expose the vulva for penetration.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 (p. 2301) 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 An anthropologist is a scientist engaged in the practice of anthropology. Anthropologists study aspects of humans within past and present societies. Social anthropology, cultural anthropology and philosophical anthropology study the norms, values ...

Helen Fisher also speculated that when a human female wears high-heeled footwear the buttocks thrusts out and the back arches into a pose that simulates lordosis behavior, which is why high heels are considered "sexy". Recent evidence has also supported the perception of sexual receptivity in women when arching the back in supine and quadruped poses. Researchers have found that women perceive other women exhibiting this posture as a potential threat to their romantic relationship.

References

{{DEFAULTSORT:Lordosis Behavior Ethology Mammalian sexuality Physiology Sex positions Sexual intercourse Sex

Description

Neurobiology

Hormonal and cerebral regulation

In humans

See also

References