Homeostatic Systems and Drugs Chapter 4

Homeostasis Internal and external changes in the environment Body self-regulates via nervous system and endocrine system Equilibrium

Homeostasis – Example with Blood Glucose The continual adjustment brought about by homeostasis (autoregulation) help to maintain the physiological balance of blood glucose by way of counter regulatory hormones

Introduction to Nervous Systems All nervous systems consist of specialized nerve cells called neurons and glia (supporting cells). Glia are supporting cells that are critical for the health and maintenance of the neurons Neurons are responsible for conducting the homeostatic functions of the brain and other parts of the nervous system by receiving and sending information. Sending and receiving information is an electrochemical process.

Transfer of Messages by Neurons The receiving region of the neuron is affected by a chemical message that either excites or inhibits it. Neuronal message: Impulse moves from the receiving region (dendrites or cell body) of the neuron down the axon to the sending region (terminal). Chemical messengers (neurotransmitters) are released.

Transfer of Messages by Neurons (continued) Neurotransmitters travel and attach to receiving proteins called receptors on target cells. Activation of receptors causes a change in the activity of the target cell; the target cells can be other neurons or cells that make up organs, muscles, or glands. (see Figure 4.1, next slide)

Sending Messages by Neurons

Neurons and Neurotransmitters Neurons can send discrete excitatory or inhibitory messages to their target cells. Neurons are distinguished by the type of neurotransmitter they release. Neurotransmitters represent a wide variety of chemical substances and functions. Example: Dopamine activates the pleasure center.

Neurons and Neurotransmitters Many of the desired (and undesired) effects of psychoactive drugs are due to their ability to alter the neurotransmitters associated with neurons. Thus, the addictive properties of these substances relate to their ability to alter the actions of these neurotransmitters (See Table 4.1, p.138, next slide)

Neurons and Neurotransmitters

Think About it… Read aloud with your small group the information presented: “Family Matters: What about Genes?”. Prepare with your group a response to the following: 1) Should we use genetic screening to identify if an individual is more susceptible to any particular addiction? Why or Why not? 2) Because of the enormous expense of addictions on our society, should screenings be conducted to hold individuals accountable to addictive behaviors (ie. Someone screens high risk, and still chooses to use an addictive substance that has been previously identified through screening). Why or Why not?

Neurons – Basic Structure / Function Dendrites are the receiving regions of a neuron’s cell body. Each neuron in the central nervous system is in close proximity with other neurons. Although they are close, neurons never actually touch. Synapse is the point of communication between one neuron and another. Synaptic cleft is the gap between neurons at the synapse.

Neurons (continued)

Synapses Excitatory synapse initiates an impulse in the receiving neuron when stimulated, causing release of neurotransmitters or increasing activity in target cell. Inhibitory synapse diminishes likelihood of an impulse in the receiving neuron or reduces the activity in other target cells.

Synapses (continued) A receiving neuron or target cell may have many synapses. Final cellular activity is a summation of these many excitatory and inhibitory synaptic signals.

Drug Receptors The chemical messengers from glands and neurons exert their effects by interacting with special protein regions in membranes called receptors. Receptors only interact with molecules that have specific configurations. The receptors are also targets for specific types of neurotransmitters, hormones, and drugs (see opiate receptors example in text, p. 141) If the drug is the proper shape and size, it may substitute for the endogenous messenger substance and activate the receptor protein by causing it to change its shape, or conform. This activity gives insight to the addictive quality of a particular drug.

Drug Receptors (continued)

Drug Receptors (continued) Agonists: Substances or drugs that activate receptors Antagonists: Substances or drugs that attach to receptors and prevent them from being activated

Drug Receptors (continued) End of PPT Series 4A