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The Nervous System – Understanding Addiction

  • Homeostasis = Balance
    •  Maintained by the release of endogenous regulatory chemicals such as neurotransmitters and hormones.  Many drugs affect these substances and change the function of the nervous or endocrine system.
  • There are two main types of cells in the nervous system: glia and neurons.
    • Glia cells out-number neurons but cannot process information like neurons.  Glia cells make up the blood-brain barrier that protects the brain from toxic chemicals in the blood.
  • All nervous systems consist of neurons, axons and receptors.
  • Activation of receptors by neurotransmitters cause a change in activity of the target cell and many of the effects of psychoactive drugs are due to the ability to alter neurotransmitters.
  • Neurons are the basic structural unit of the nervous system that are responsible for analyzing and transmitting information.  There are more the 100 billion neurons in the nervous system.
  • The typical point of communication is the synapse.  The gap between neurons is called the synaptic cleft.
  • The two types of synapses are the excitatory synapse and the inhibitory synapse. The receiving region is called the dendrite.
  • The receptors are proteins that help regulate activity of cells in the nervous system and throughout the body.
  • Some specific drugs and natural neurotransmitters can activate the same receptors.
  • Communication is accomplished through a specific, precise rapid method. The message is transmitted along a neuron’s axon.   Neurotransmitters are released so the communication can happen from one neuron to the other.
  • There are agonistic and antagonistic effects on receptors.
  • Agonistic drugs interact with the receptor and produce a response, whereas antagonistic drugs interact with the receptor but prevent a response.
  • Selective blocking of some channels prevents the communication between the neurons.  An example of this would be cocaine and other local anesthetics.
  • Neurotransmitters most likely altered by drug abuse include acetylcholine (ACh), epinephrine, dopamine, serotonin, and the endorphins.
  • The somatic nervous system carries sensory information from outside the body into the CNS and motor information out.
    • These voluntary movements come from large cells with long axons.  The seven senses are produced from this system.
  • The autonomic nervous system (ANS) cell bodies are located within the brain or spinal cord but their axons project outside the CNS to involuntary muscles.
  • The ANS is divided into two components that contest each other
    1. the sympathetic –Fight or Flight– and
    2. the parasympathetic –Rest and Digest– branch.
  • Like amphetamines and other sympathomimetic drugs, the sympathetic branch speeds up both heart and breathing rates, and is a vasoconstrictor.
  • The parasympathetic branch releases the neurotransmitter ACh and has essentially the opposite effects of sympathetic.
  • The central nervous system contains the brain and spinal cord.
  • The cerebral cortex receives sensory input, interprets visual information, as well as processes auditory information.  Reasoning and language occur here.
  • The basal ganglia are the primary centers for involuntary movement and are hidden from external view underneath the cerebral cortex.
  • The hypothalamus integrates information from many sources and is the control center for the autonomic nervous system.
    • The hypothalamus is a small structure near the base of the brain that is involved in sex drive, hunger, body temperature and others.
  • The limbic system regulates emotional activities, memory, and modulation  of basic hypothalamic functions, mating, procreation, and caring for young.
  • The neurotransmitters most associated with psychoactive drugs are dopamine, acetylcholine, norepinephrine, serotonin, GABA, glutamate and endorphins.
  • There can be positive or negative effects from drugs on these neurotransmitters.
  • Some drugs help misfiring neurotransmitters or help to increase the amount of them when a body is naturally low.  Others, however, do harm by doing the same action in a user who already has a natural level of neurotransmitters.
  • Precursors are the building blocks of neurotransmitters that are found circulating in the blood.
  • After they are synthesized the neurotransmitters are stored in vesicles waiting to be released.  The release happens in microseconds in less than 1/10,000th of an inch of space to several thousand neurotransmitters.
  • GABA is called an inhibitory neurotransmitter.  Many sedatives are dependent upon their binding to theGABA receptors.
  • One way neurotransmitters molecules are removed from the synapse is that some molecules have specific transporters built into their terminals. This brings the neurotransmitters molecules back into the releasing neuron.   Other neurotransmitters have enzymes in the synapse that metabolize molecules.
  • In Positron Emission Tomography (PET) a radioactively labeled chemical is injected in the bloodstream then a computer tracts it as it flows through the brain.
  • Magnetic Resonance Imaging (MRI) uses strong magnetic fields and  measures the energy coming from molecules as the field is collapsed.

Re-blogged from LCDC Exam Review (WordPress)

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