Chapter 8 Visual Summary

Hormones are chemicals that are secreted by endocrine glands into the bloodstream and are taken up by receptor molecules in target cells. Unlike neurotransmitters in neuronal signaling, hormones spread more slowly and act throughout the body. Review Figure 8.1, Figure 8.2, Figure 8.3, Table 8.1, Activity 8.1, Animation 8.2, Animation 8.3

Most hormones act on receptors in a wide variety of cells, coordinating influences throughout the body. Peptide hormones and amine hormones bind to receptor molecules at the surface of the target cell membrane and activate second-messenger molecules inside the cell. Steroid hormones pass through the membrane and bind to receptor molecules inside the cell, ultimately regulating gene expression. Review Figure 8.4, Figure 8.5, Figure 8.6, Figure 8.7, Animation 8.4

Negative feedback systems control hormone secretion. Neuroendocrine cells in the hypothalamus send axons down the pituitary stalk to the posterior pituitary, releasing two hormones—oxytocin and vasopressin—into the bloodstream. Release of the hormones is regulated by synaptic influences on those neuroendocrine cells. Review Figure 8.8, Figure 8.9, Figure 8.10

Other hormones are controlled by a releasing hormone from the hypothalamus that stimulates the anterior pituitary to release tropic hormones, which in turn control the secretion of hormones by endocrine glands. The endocrine gland hormone then provides negative feedback to the hypothalamus and pituitary. Review Figure 8.11, Figure 8.12, Figure 8.13, Animation 8.5

Many behaviors require the coordination of neural and hormonal components. Messages may be transmitted in the body via neural-to-neural, neural-to-endocrine, endocrine-toendocrine, or endocrine-to-neural links. There are continual, reciprocal influences between the endocrine system and the nervous system: experience affects hormone secretion, and hormones affect behavior and therefore future experiences. Review Figure 8.14, Figure 8.15, Figure 8.16

In animals, reproductive behaviors are regulated by hormones. In female rats, a steroid-sensitive lordosis circuit extends from the ventromedial hypothalamus (VMH) to the spinal cord. In male rats, medial preoptic area (mPOA) neurons integrate inputs from the vomeronasal organ (VNO) and medial amygdala, and they project axons widely to regulate copulatory behavior. Review Figure 8.17, Figure 8.18, Figure 8.19, Figure 8.20

In humans, very low levels of testosterone are required for either men or women to display a full interest in sex, but additional testosterone has no additional effect. In animals, hormones significantly influence maternal behavior by acting on the same brain regions that are important for sexual behavior (mPOA, VMH). Review Figure 8.18 and Figure 8.21, Figure 8.22, Figure 8.23

Sex chromosomes (XX or XY) control whether the indifferent gonads of an individual develop as testes or ovaries, the beginning of the process of sexual differentiation. Then, hormonal secretions from the testes masculinize the rest of the body in males. This means that some people, for example, women who carry a Y chromosome but have androgen insensitivity syndrome (AIS), may be masculine in some parts of the body but feminine in others. Review Figure 8.24, Figure 8.25, Figure 8.26, Figure 8.27, Figure 8.28

In animals, androgens also organize the developing brain, masculinizing regions such as the sexually dimorphic nucleus of the preoptic area (SDN-POA) and the spinal nucleus of the bulbocavernosus (SNB). There is evidence that prenatal androgens also masculinize the human brain. Review Figure 8.29, Figure 8.30, Figure 8.31, Figure 8.32, Animation 8.6

Several regions of the human brain are sexually dimorphic, but we do not know whether these dimorphisms are organized by fetal steroids or by sex differences in the social environment. Research demonstrates that human sexual orientation is affected by prenatal influences and is not simply a matter of individual choice. Review Figure 8.33, Figure 8.34, Figure 8.35, Figure 8.36

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