Drugs and the Nervous System

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Drugs and the Nervous System

• Chapter 3

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• The nervous system is an electro-chemical
  communication system that regulates all
  physiological systems
• Psychotropic drugs exert effects through the
  alteration of nervous system activity
• Understanding drugs means understanding the
  nervous system

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The Basis of the Nervous System

• Neurons Single cell unit of the nervous system
• 10 billion in the brain alone
• Receives, processes and transmits information
• Each neuron in the brain received signals from
  thousands of other neurons.
• Synapses Small gaps that separate neurons
• The site of neurotransmission
• Neurotransmission

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The Neuron

• Parts
• Soma Cell body
• Dendrites Branches that receive messages from
  other neurons
• Axon Trunk of neuron that sends messages to
  other neurons
• Myelin Sheath Fatty layer protects and speeds
  conduction
• Axon terminals Buds at end of axon from which
  chemical messages are sent
• Types
• Sensory
• Motor
• Interneurons All CNS neurons

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Synapse

• Synapse
• (Gk., to clasp or join)

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Multiple types of synapses

• Multiple patterns of connectivity
• Axodendritic
• Axoaxonic
• Axosomatic
• Dendrodendritic

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Neurotransmission

• Transmission Involves Multiple Steps
• Mediated by neurotransmitters
• Functions of Neurotransmitters
• Substances that enhance, inhibit or modulate
  neuron firing
• Most drugs enhance or inhibit neurotransmission
• Main Types and Functions of Neurotransmitters
• Acetylcholine
• Dopamine
• Norepinephrine
• Serotonin (5HT)
• Endorphins
• Gamma aminobutyric acid (GABA)

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Steps in Synaptic Transmission

• Synthesis
• Occurs in soma
• Transport
• Transmitter moves down neuron
• Storage
• Vesicles in axon terminals
• Release
• Stimulated by action potential
• Inactivation
• Reuptake
• Degradation

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Cholinergic system (Acetylcholine)
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ACETYLCHOLINE (ACh)

• Acetylcholine (ACh) is a neurotransmitter
  substance that is found in both the CNS and in
  the PNS.
• In the PNS, it is the NT released at synapses on
  skeletal muscles and is also found in the cell
  bodies of the autonomic nervous system.
• In the brain, it appears to be involved in
  learning/memory, attention as well as sleeping
  and dreaming.

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Dopamine
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DOPAMINE (DA)

• Dopamine (DA) is an inhibitory neurotransmitter.
• It is implicated in movement control, attention,
  and learning.
• Parkinsons Disease
• Dopamine excess may be involved in Schizophrenia.
• Most importantly, it is involved in the reward
  system of the brain.

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Noradrenergic system (Norepinephrine)
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NOREPINEPHERINE (NE)

• NE is not synthesized in the cell body, but the
  dopamine synthesized there is converted into NE
  inside the synaptic vesicles.
• Like ACh, NE is found in the autonomic nervous
  system. Here it has an excitatory role.
• Leads to release of adrenalin (HR BP)
• In the brain, NE is inhibitory and is primarily
  involved in control of alertness/vigilance.
• Also involved in the control of eating
  (stimulates eating).

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Serotonergic System (Serotonin)
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SEROTONIN

• At most synapses, serotonin (5HT) is an
  inhibitory neurotransmitter.
• Facilitates and regulates motor behavior
• It plays a role in the regulation of mood,
  producing sedation or relaxation.
• It also has a role in the control of eating,
  sleep and arousal. In addition, it can regulate
  pain.

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Endorphins

• Generally inhibitory
• Modulate the experience of pain
• Controls breathing and heart rate
• Controlling cough reflex as well as nausea and
  vomiting
• Involved in feelings of euphoria and reward
• Sensory motor integration
• Olfaction
• Endocrine functions (eating, temp control)

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GABA

• Most prevalent inhibitory neurotransmitter in the
  brain
• GABA secreted by local interneurons all over
  the brain.
• Works as an off switch.
• Implicated in relaxation/anti-anxiety
• Many drugs target this system

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Glutamate

• The workhorse of the neurotransmitters
• Most prevalent excitatory NT.
• Involved in everything, but especially important
  in the formation of memories.
• Can be highly toxic when out of control

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Putting it Together

• PRESYNAPTIC neuron releases neurotransmitter into
  the synapse
• POSTSYNAPTIC neuron dendrites receive signal
  through interaction with RECEPTORS
• Cell body sums signal. If enough signal is
  generated then neuron depolarizes
• ACTION POTENTIAL then propagates down axon.
  Sodium potassium pump.
• At the axon terminal VESICLES move and fuse at
  the end and neurotransmitter is released into the
  synapse
• The process continues

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The Nervous System
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Peripheral Nervous System

• Somatic Branch of PNS
• Controls voluntary muscles and movement
• Autonomic Branch of the PNS
• Sympathetic and parasympathetic branches of the
  ANS
• Regulates cardiovascular system body
  temperature
• Also regulates the endocrine system and aids in
  digestion
• Sympathetic NS Fight/Flight

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The Central Nervous System

• The CNS is the BRAIN and the SPINAL CHORD
• It is the site of all psychoactive drug action
• Made up of internuerons
• The BRAIN is divided into numerous divisions
• Subcortical
• Cortical

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Divisions of the Brain

• Hindbrain
• Medulla Heart rate, blood pressure, respiration
• Pons Regulates sleep
• Cerebellum Involved in physical coordination
• Midbrain
• Coordinates movement with sensory input
• Inferior and superior colliculi
• Substantia nigra
• Forebrain (Cerebral cortex)
• Location of most sensory, emotional, and
  cognitive processing
• Two specialized hemispheres (left and right)
  joined by the corpus callosum

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Neuroscience and the Divisions of the Brain
(cont.)
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Cerebral Cortex

• Lobes of cerebral cortex
• Frontal Thinking and reasoning abilities,
  memory, executive function
• Parietal Touch recognition
• Occipital Integrates visual input
• Temporal Recognition of sights and sounds and
  long-term memory storage

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Limbic System

• Limbic System
• Cortical and subcortical structures that are in
  part responsible for emotional arousal
• Hippocampus
• Amygdala
• Hypothalamus