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Chapter 2
Biological Basis of
Behavior
THE NERVOUS SYSTEM
The Nervous System
The Nervous System
Central Nervous System (CNS)
Brain
Peripheral Nervous System (PNS)
Spinal Cord
•
Motor Neurons
Somatic Nervous System
voluntary movements via
skeletal muscles
Sympathetic
- “Fight-or-Flight” responses
•
Sensory Neurons
Autonomic Nervous System
organs, smooth muscles
Parasympathetic
- maintenance
THE NERVOUS SYSTEM
•A physical organ system like any other. It
is the sensory and control apparatus
consisting of a network of nerve cells.
•Composed of 2 main kinds of cells
 Neurons
 Glia cells (ganglia)
GLIAL CELLS
• Support neurons (literally,
provide physical support, as
well as nutrients)
• Cover neurons with myelin
• Clean up debris
• “Housewives”
• Regulate external environment
(ions, etc.)
• Most abundant glial cells are
the ASTROCYTES
NEURONS
 Basic units of the nervous system
 Receive, integrate, and transmit
information
 Operate through electrical impulses
 Communicate with other neurons
through chemical signals
 Neurons conduct impulses from one part of
the body to another.
Three Types of Neurons
 Sensory Neurons (Afferent)
sensitive to various non-neural stimuli
 Inter-neurons (Connecting)
provide connections between sensory and motor
neurons, as well as between themselves
 Motor Neurons (Efferent)
stimulate muscle cells and glands throughout the
body
Sensory (Afferent) vs. Motor (Efferent)
sensory (afferent) nerve
e.g., skin
Neurons that send signals from the senses,
skin, muscles, and internal organs to the CNS
motor (efferent) nerve
Neurons that transmit commands from the
CNS to the muscles, glands, and organs
Gray’s Anatomy 38 1999
e.g., muscle
Specific Parts: The Neuron
Structure
Neural Anatomy/ Parts
Dendrites
the bushy, branching extensions of a neuron that
receive messages and conduct impulses toward the cell
body
 It is primarily the surfaces of the dendrites that receive
chemical messages from other neurons.
Axon
the extension of a neuron, ending in branching terminal
buttons, through which messages are sent to other
neurons or to muscles or glands
transmit an electro-chemical signal to other neurons,
sometimes over a considerable distance.
Myelin Sheath
• Fatty material made by glial cells
• Insulates the axon
• Allows for rapid movement of
electrical impulses along axon
• Nodes of Ranvier: gaps in myelin
sheath where action potentials
are transmitted
• Speed of neural impulse Ranges
from 2 – 200+ mph
 Axon Ending
• Goes by a variety of names
such as the terminal button,
the synaptic knob, the axon
foot, and so on
• It is there that the electrochemical signal that has
travelled the length of the
axon is converted into a
chemical message that travels
to the next neuron.
Specific Parts: The Neuron
Function
1.
3.
2.
Neurons = 3 functions: Reception, Conduction, Transmission
Action Potential
 When chemicals contact the surface of a neuron, they change the
balance of ions (electrically charged atoms) between the inside and
outside of the cell membrane. When this change reaches a threshold
level, this effect runs across the cell's membrane to the axon. When it
reaches the axon, it initiates the action potential, which is a rapidly
moving exchange of ions.
When dendrites are stimulated, the delicate balance is
altered
Membrane breaks down
Positively charged ions rush in (depolarization)
Charge inside becomes less negative
Causes release of chemicals from terminal buttons
Synapse
junction between the
axon tip of the sending
neuron and the
dendrite or cell body of
the receiving neuron
tiny gap at this junction
is called the synaptic
gap or cleft
For every neuron, there
are between 1000 and
10,000 synapses.
COMMUNICATION
• Impulse releases
neurotransmitter from
vesicles
• Neurotransmitter enters
synaptic gap
• Neurotransmitter binds
to receptors sites on the
receiving neuron
GLIAL CELLS
• Support neurons (literally,
provide physical support, as
well as nutrients)
• Cover neurons with myelin
• Clean up debris
• “Housewives”
• Regulate external environment
(ions, etc.)
• Most abundant glial cells are
the ASTROCYTES
NEUROTRANSMITTERS
chemicals which allow the transmission of
signals from one neuron to the next across
synapses
when released by the sending neuron,
neurotransmitters travel across the synapse
and bind to receptor sites on the receiving
neuron, thereby influencing whether it will
generate a neural impulse
Kinds of Neurotransmitters
•Acetylcholine (ACh)
• 1st to be discovered (1921)
• Otto Loewi
• It is responsible for much of the stimulation of muscles,
including the muscles of the gastro-intestinal system. It is also
found in sensory neurons and in the autonomic nervous system,
and has a part in scheduling REM (dream) sleep.
• Links motor neurons and muscles (contract or relax)
• e.g. curare vs black widow spider
• Also involved in memory, learning, sleep, dreaming
• there is a link between acetylcholine and Alzheimer's
disease: There is something on the order of a 90% loss of
acetylcholine in the brains of people suffering from Alzheimer's,
which is a major cause of senility.
Kinds of Neurotransmitters
• Norepinephrine
• Discovered in 1946
• Ulf von Euler
• Formerly known as noradrenalin
• strongly associated with bringing our nervous systems into "high
alert."
• prevalent in the sympathetic nervous system, and it increases
our heart rate and our blood pressure
Kinds of Neurotransmitters
• Dopamine
• Discovered in 1950’s
• Arvid Carlsson
• It is an inhibitory neurotransmitter, meaning that when it finds
its way to its receptor sites, it blocks the tendency of that
neuron to fire.
• If it feels good, dopamine neurons are probably involved
• Drugs like cocaine, opium, heroin, and alcohol increase the
levels of dopamine, as does nicotine.
• schizophrenia has been shown to involve excessive amounts of
dopamine in the frontal lobes, and drugs that block dopamine
are used to help schizophrenics
• too little dopamine in the motor areas of the brain are
responsible for Parkinson's disease, Carlsson also figured out
that the precursor to dopamine (called L-dopa) could alleviate
some of the symptoms of Parkinson's. He was awarded the
Nobel Prize in 2000.
Kinds of Neurotransmitters
• GABA (gamma aminobutyric acid)
• Discovered in 1950
• Eugene Roberts
• It is an inhibitory neurotransmitter and acts like a brake to the
excitatory neurotransmitters that lead to anxiety
• People with too little GABA tend to suffer from anxiety
disorders, and drugs like Valium work by enhancing the effects
of GABA.
• If GABA is lacking in certain parts of the brain it will result to
epilepsy.
Kinds of Neurotransmitters
• Glutamate
• Discovered in 1994 as a neurotransmitter
• Peter Usherwood
• It is an excitatory neurotransmitter
• It is the most common neurotransmitter in the central nervous
system and is especially important with regards to memory.
• Curiously, glutamate is actually toxic to neurons, and an excess
will kill them.
Kinds of Neurotransmitters
• Serotonin
• Discovered in 1954 as a neurotransmitter
• John Welsh
• It is an inhibitory neurotransmitter
• found to be intimately involved in emotion and mood.
• Too little serotonin has been shown to lead to depression, problems
with anger control, obsessive-compulsive disorder, and suicide.
• Too little also leads to an increased appetite for carbohydrates (starchy
foods) and trouble sleeping, which are also associated with depression
and other emotional disorders.
• Prozac and other recent drugs help people with depression by
preventing the neurons from "vacuuming" up excess seratonin, so that
there is more left floating around in the synapses.
• It is interesting that a little warm milk before bedtime also increases
the levels of serotonin.
• also plays a role in perception; hallocinogens such as LSD, mescaline,
psilocybin, and ecstasy work by attaching to serotonin receptor sites
and thereby blocking transmissions in perceptual pathways.
Kinds of Neurotransmitters
• Endorphine
• Discovered in 1973
• Solomon Snyder and Candace Pert
• Endorphin is short for "endogenous morphine."
• It is structurally very similar to the opioids (opium, morphine,
heroin, etc.) and has similar functions: Inhibitory,
• It is involved in pain reduction and pleasure, and the opioid
drugs work by attaching to endorphin's receptor sites.
• It is also the neurotransmitter that allows bears and other
animals to hibernate.