PS268 Chapter Notes - Chapter 4: Limbic System, Methamphetamine, Autonomic Nervous System
Module I: Introduction to Psychoactive Drugs, Behaviour, and the Brain
(Chapter Four
−
How Drugs Work: The Nervous System)
4.1 − Homeostasis
- Psychoactive drugs can influence homeostasis
o Homeostasis: can be loosely translated as staying the same
o Describes the fact that many biological factors are maintained at or near certain
levels
4.2.a − Components of the Nervous System
- The nervous system is composed of two types of cells:
o Glial Cells (Glia)
o Nerve Cells (Neurons)
- Glia
o Communicate with neurons and modulate their activity
o A function of glia is to create the blood-brain barrier, a barrier between the blood
and fluid that surrounds neurons
o This semipermeable structure protected the brain from potentially toxic chemicals
circulating in the blood
o Lipophilic: the extent to which chemicals can be dissolved in oils and fats
- Neurons
o Primary elements of the nervous system responsible for analyzing and transmitting
information
o 100 billion neurons in the nervous system
o Each neuron has 4 morphologically defined regions:
▪ Cell Body
▪ Dendrite
▪ Axon
▪ Presynaptic Terminal
o Dendrites: tree-like features extending from the cell body
▪ Contain within their membranes the specialized structures (receptors) that
recognize and respond to specific chemicals’ signals
o Axon: long and slender, extends from the cell body
▪ Responsible for conducting the electrical signal to the presynaptic terminals
o Presynaptic Terminals: bulbous structures located at the end of the axon where
chemical messengers are stored in small, round packages called vesicles
4.2.b − Neurotransmission
- Neurotransmission
o Action Potential: electrical signal that initiates a chain of events that allows one
neuron to communicate with another through the release of neurotransmitters
▪ Occurs as a result of opening ion channels that allow electrically charged
particles (ions) to access the inside of the cell
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o This change moves the cell’s membrane away from its resting potential, to a more
positively charged voltage
o Hyperpolarization: the state that occurs when the membrane potential of a cell is
pushed below the resting potential
o Action potential occurs when the neuron’s membrane is depolarized to the
threshold of excitation
▪ During the time Na+ channels open, allowing Na+ ions to move across the
membrane intracellularly and further depolarize adjacent regions of the
neuron
4.3 − The Peripheral Nervous System
- Made up of the nerves outside the brain and spinal cord
o Consists of the somatic and autonomic nervous system
- Somatic Nervous System
o The Somatic System: the nerves that are on the front lines interacting with the
external environment
▪ The cranial nerves that relate to vision, hearing, taste, smell, chewing, and
movements are included as spinal nerves carrying information from the skin
and joints and controlling movements of the arms and legs
▪ Acetylcholine: the neurotransmitter at neuromuscular junctions in the
somatic system
• Acts on receptors that excite the muscle
- Autonomic Nervous System
o Autonomic Nervous System: monitors and controls the body’s internal environment
▪ Regulates the visceral or involuntary functions of the body, such as heart
rate and blood pressure
▪ Where chemical neurotransmission was first studied
o Many psychoactive drugs have simultaneous effects in the brain and on the ANS
o Divided into sympathetic and parasympathetic braches
▪ The inhibition of the heart rate by valgus nerve is an example of
parasympathetic branch
- Central Nervous System
o Consists of the brain and spinal cord
▪ These two structures form a central mass of nervous tissue with sensory
nerves coming in and motor nerves going out
4.4 − The Brain
- Major Structures
o Some areas of the cortex are known to be involved in processing visual information
▪ Other areas are involved in processing auditory or somatosensory
information
o Relatively smaller cortical areas are involved in the control of muscles (motor
cortex) and large areas are referred to as association areas
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Document Summary
Module i: introduction to psychoactive drugs, behaviour, and the brain (chapter four how drugs work: the nervous system) Psychoactive drugs can influence homeostasis: homeostasis: can be loosely translated as (cid:498)staying the same(cid:499, describes the fact that many biological factors are maintained at or near certain. 4. 2. a (cid:498)components of the nervous system(cid:499) levels: glial cells (glia, nerve cells (neurons) The nervous system is composed of two types of cells: Made up of the nerves outside the brain and spinal cord: consists of the somatic and autonomic nervous system. Central nervous system: consists of the brain and spinal cord, these two structures form a central mass of nervous tissue with sensory nerves coming in and motor nerves going out. Equilibrium develops quickly for most drugs, so drugs" concentration in the brain is about equal to that in the blood, and the number of molecules leaving the blood is equal to the number leaving the brain: ex.
