Hormones and Behavior

Type of psychology: Biological bases of behavior
Fields of study: Auditory, chemical, cutaneous, and body senses;
endocrine system
Hormones are chemical messengers, usually of protein or steroid content, that are produced
in certain body tissues and that target specific genes in the cells of other body tissues,
thereby affecting the development and function of these tissues and the entire organism.
By exerting their influences on various parts of the body, hormones can affect
behavior.

Key concepts

• endocrine gland
• hormone
• human growth hormone (HGH)
• hypothalamus
• melatonin
• oxytocin
• pheromone
• pituitary
• steroid
• vasopressin

Cell-to-cell communication among the trillions of cells that make up multicellular
animals relies primarily upon the specialized tissues of the nervous
and endocrine systems. These two systems are intricately connected, with
the former having evolved from the latter during the past five hundred million
years of animal life. The endocrine system consists of specialized ductless
glands located throughout the animal body that produce and secrete
hormones directly into the bloodstream. Hormones are chemical messengers
that usually are composed of protein or steroid subunits. The bloodstream
transports the hormones to various target body tissues, where the
hormones contact cell membranes and trigger a sequence of enzyme reactions
which ultimately result in the activation or inactivation of genes located
on chromosomes in the cell nucleus.

A gene is a segment of a chromosome that is composed of deoxyribonucleic
acid (DNA). The DNA nucleotide sequence of the gene encodes a
molecule of messenger ribonucleic acid (mRNA) which, in turn, encodes a
specific protein for the given gene. If the control sequence of a gene is activated,
then ribonucleic acid (RNA) and protein will be produced. If the control
sequence of a gene is inactivated, then RNA and protein will not be produced.
Hormones target the genes in specific cells to start or stop the
manufacture of certain proteins. Within cells and the entire organism, proteins
perform important functions. Therefore, hormones control the production of proteins by genes and, as a result, control many activities of the
entire animal.

The nervous system, which in vertebrate animals has evolved to become
more elaborate than the endocrine system, consists of billions of neurons
(nerve cells) that conduct electrical impulses throughout the body. Neurons
transmit information, contract and relax muscles, and detect pressures,
temperature, and pain. Neuron networks are most dense in the brain
(where there are one hundred billion neurons) and spinal cord, where
much of the electrical information is centralized, relayed, and analyzed.
Neurons must communicate electrical information across the gaps, or synapses,
which separate them. To accomplish this goal, the transmitting neuron
releases hormones called neurotransmitters, which diffuse across the
synapse to the receiving neuron, thereby instructing the receiving neuron
to continue or stop the conduction of the electrical message. There are
many different types of neurotransmitters, just as there are many different
types of regular hormones.