CHAPTER 29 Summary

• The nervous system senses and responds to signals from the environment and coordinates bodily actions, including moving, breathing, and thinking.
• The central nervous system (CNS) consists of the brain and the spinal cord, a thick bundle of nerves extending from the base of the brain to the lower back; the peripheral nervous system (PNS) consists of all the nerves extending from the spinal cord to the limbs and internal organs.
• The PNS senses and responds to information both inside and outside our bodies. It includes the sensory receptors of our sensory organs, such as the eyes, ears, and skin, as well as the effectors, such as the muscles, that respond to signals sent from the CNS.
• Neurons are specialized cells that consist of a cell body, branched dendrites, and a long axon. Neurons conduct electrical signals known as action potentials.
• The coordinated movement of positively charged ions across the axon membrane initiates an action potential. When an action potential reaches the end of a neuron, it causes the neuron to release neurotransmitters.
• Neurotransmitters are chemical signaling molecules released from neuron axon terminals into the synaptic cleft of a synapse and bind to the receptors of other cells (for example, neurons, muscle cells, and endocrine gland cells). Important neurotransmitters include dopamine, serotonin, and acetylcholine.
• Dopamine is a neurotransmitter that produces feelings of pleasure. It is one of the primary neurotransmitters involved in addiction.
• Neurotransmitters bind to receptors on their target cells. The number of receptors can be down-regulated in response to persistently high levels of a neurotransmitter.
• Different parts of the brain coordinate different functions. The four main regions of the brain are the cerebellum, brain stem, diencephalon, and cerebrum. The brain’s limbic system, composed of subregions in the diencephalon and cerebrum, includes the brain’s “pleasure center” and has been implicated in addiction.
• All organisms have ways of sensing and responding to their environment, but not all have a central nervous system with a brain and spinal cord.

• MORE TO EXPLORE

  • National Institute of Drug Abuse http://www.drugabuse.gov/
  • Volkow, N. D., et al. (2011) Addiction: beyond dopamine reward circuitry. Proceedings of the National Academy of Sciences 108(37):15037–15042.
  • Kringelbach, M. L., and Berridge, K. C. (2010) The functional neuroanatomy of pleasure and happiness. Discovery Medicine 9(49):579–587.
  • Proctor, R. N. (2011) Golden Holocaust: Origins of the Cigarette Catastrophe and the Case for Abolition. Berkeley: University of California Press.
  • Olds J. (1956) Pleasure centers in the brain. Scientific American 195:105–116.