Transcript Chapter 3: The Nervous System

Drugs and the Nervous System
Chapter 3
 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
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
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
Synapse
Synapse
(Gk., to clasp or join)
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Multiple types of synapses
Multiple patterns of connectivity
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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)
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
Cholinergic system (Acetylcholine)
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.
Dopamine
DOPAMINE (DA)
•Dopamine (DA) is an inhibitory
neurotransmitter.
•It is implicated in movement control,
attention, and learning.
▫ Parkinson’s Disease
•Dopamine excess may be involved in
Schizophrenia.
•Most importantly, it is involved in the
“reward system of the brain.”
Noradrenergic system (Norepinephrine)
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).
Serotonergic System (Serotonin)
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.
Endorphins
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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)…
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/antianxiety
• Many drugs target this system
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
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
The Nervous System
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
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
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
Neuroscience and the Divisions of the
Brain (cont.)
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 longterm memory storage
Limbic System
• Limbic System
▫ Cortical and subcortical
structures that are in part
responsible for emotional
arousal
 Hippocampus
 Amygdala
 Hypothalamus