October 24, 12
PSYCH – Week 7 Online Readings
Week 7: The Biology of Behaviour
Focus Question: How does the structure of the nervous system determine behaviour?
This area of science is called neuroscience. Neuroscience involves collaborations
between psychologists, neuroanatomists, neurologists, biochemists,
neuroendocrinologists, biologists, engineers, and computer scientists.
Neuroscientists attempt to determine the relationship between behaviours, including
thoughts and feelings, and activity in the brain and hormonal systems.
The Nervous System
1. Central nervous system (CNS)
b. Spinal cord
2. Peripheral nervous system (PNS)
a. Skeletal nervous system
i. Sensory or afferent
ii. Motor or efferent
b. Autonomic nervous system
CNS is composed of two broad classes of cells: neurons and glia.
The glia, neuroglia, or glial cells are supporting cells. There are different
kinds of glia (beyond the scope of this course) and they serve supportive
and protective functions – helping the neurons to do their work.
The PNS is divided into skeletal and autonomic portions.
• The skeletal portion controls the various muscles (e.g., your leg muscles),
relaying motor commands from the brain.
• The autonomic nervous system (ANS) controls “involuntary” muscles (e.g., heart
and diaphragm) and many internal organs (e.g., the viscera). It is especially
important in maintaining homeostasis
Homeostasis can be described as the tendency of an animal to regulate its
internal conditions (e.g., temperature, glucose levels, osmotic pressure of
cells) by a system of feedback controls (like hunger and eating; thirst and
drinking; shivering and putting on a sweater) so as to optimize health and
The autonomic nervous system (ANS) is subdivided into two parts:
• The sympathetic division, which promotes the ‘fightorflight’ response, involves
high arousal/alertness, mobilizes the body for rapid energy expenditure, and
• The parasympathetic division, which promotes the ‘restanddigest’ response,
enhancing the internal processes related to the digestion of food. October 24, 12
A “prototypical” neuron has several distinct features:
• Cell body – contains structures that maintain cell health and metabolism
• Nucleus – contains genes (DNA) and makes the proteins that “run” the cell
• Dendrites – look similar to trees and receive information
• Axon – transmits information from the neuron (analogous to a telephone wire)
• Myelin – a sheath or covering that makes the axon faster and more efficient
• Axon terminal or synaptic terminal – sends information across a synapse
• Synapse – the gap between two neurons
The word “neuron” refers to an individual neural (or nerve) cell. Each neuron is
comprised of a cell body and a long fibre called an axon. “Nerve” always refers to a
bundle of axon fibres. Nerves that are entirely within the brain and spinal cord (i.e., the
CNS) are called tracts.
Neurons can be classified by function into three distinct groups:
Sensory neurons – Detect information from the physical world and pass that information
to the brain (e.g., light receptor neurons in the eye or touch receptor neurons in the skin).
Sensory neurons are often called afferent neurons because they send signals from the
body to the brain.
Motor neurons – Direct muscles to relax or contract, producing movement. They are
efferent neurons, sending information from the brain to the body (opposite of afferent
Interneurons – Basically, any neuron that is not a sensory or motor neuron. They link
sensory/motor neurons and work to integrate and communicate information, rather than
to transmit information from the body to the brain or from the brain to the body. October 24, 12
Spinal reflex: doesn’t involve the brain, pretty primitive, and help to move the body away
from painful sensations.
Synapses and Connections
A synapse is the conjunction of a terminal button of one neuron and the membrane of
another. The terminal button is on the neuron sending the message, or the presynaptic
neuron, and the postsynaptic neuron received the message. The space between the two is
called the cleft, or gap. Neurotransmitters act like bridges or ferry boats to carry messages
across the cleft from one neuron to the next.
There are two types of synapses: excitatory synapses and inhibitory synapses.
• Excitatory synapses are activated when a terminal button releases a transmitter
substance that excites the postsynaptic neurons on the other side of the synapse.
This excitation makes it more likely the postsynaptic neuron will fire.
• Inhibitory synapses, on the other hand, lower the likelihood that the axons of the
postsynaptic neurons will fire when they are activated.
• The effects of these synapses on the postsynaptic neuron are sometimes referred
to as excitatory postsynaptic potential and inhibitory postsynaptic potential,
respectively. These postsynaptic electrical potentials, whether excitatory or
inhibitory, are graded potentials.
Sending a Pain Signal
How neurons transmit information about pain: Dendrites receive information (from
another neuron or from a specialized receptor that has transduced, or converted, the
energy of external stimulation into an electrical signal), the cell body “analyzes” it, and
the axon transmits it. The information is passed on to the next neuron at the axon terminal
until it reaches the spinal cord.
Eventually the signal is sent to the muscles through spinal reflex, and the body
withdraws from pain. The signal is also sent to the brain itself, which interprets the
sensation as painful.
Action Potential October 24, 12
The action potential is an “allornone” event. If a neuron is sufficiently depolarized (i.e.,
if it reaches the threshold of activation), it will generate an action potential. There are no
large or small action potentials. If it does not reach the threshold of activation, the
impulse will decay rapidly and will not reach the end of the axon.
Communication Between Neurons
The binding of a neurotransmitter to a receptor can trigger an action potential in the
postsynaptic neuron. Graded potentials are generated in the dendrites and travel to the
cell body, which sums and compares the potentials, then ‘decides’ to fire an action
potential down the axon or not. If the decision is to fire an action potential, that message
is then transmitted to the end of the neuron that contains the terminal buttons.
Action potential Electrical signal that reflects ‘decision’ of cell body to send
information to the neurons with which it communicates. Action
potential either occurs or it does not: allornone.
Neurotransmitter Chemical released by the terminal buttons that causes the
postsynaptic neuron to generate a graded potential (excitatory or
Axon Nerve fibre that carries messages away from the cell body toward
the cells with which the neuron communicates
Dendrite Treeshaped structures branching from the body of a nerve cell that
take input from other neurons.
Synapse Junction between the terminal button of one neuron and the
membrane of a muscle fibre, a gland, or another neuron.
Need to remember > many drugs and chemicals affect the body’s nervous system by
interfering with some aspect of the release, uptake, or reuptake of one or more
Neurotransmitters can be classified into three ‘families’ based on their chemical structure:
the amines, the amino acids, and the peptides. The members of each of these three
‘families’ have similar properties and functions.
The amines include dopamine, epinephrine and norepinephrine, serotonin, and
The amino acids include glutamate and gammaaminobutyric acid (GABA).
Peptides are a large family of neurotransmitters. Some peptides modulate emotions, and
others are involved in the perception of pain, while others regulate responses to stress.
The bestknown group of peptides are the opioids. October 24, 12
Neurotransmitters and Disorders
Many behaviours are linked to specific types of neurotransmitters. We can usually tell
that a behaviour is linked to a neurotransmitter system when a drug known to affect a
neurotransmitter also affects a behaviour.
Dysregulation of neurotransmitter systems plays a significant role in the abnormal brain
function of mental disorders. The drugs used for pharmacotherapy work in one of three
• They can act on presynaptic neurons to either facilitate or inhibit release of the
neurotransmitter, thereby affecting the amount of neurotransmitter that enters the
• They can act in the cleft to either facilitate or inhibit the processes that normally
terminate the action of the neurotransmitter once it has been released, either
prolonging or shortening the amount of time that the neurotransmitter remains in
the cleft and exerts its effects.
• They can act directly on postsynaptic binding sites, either producing the same
effect as the neurotransmitter or blocking the neurotransmitter from producing its
Any drug that affects behaviour does so by changing the nature of neurotransmitter
activity at the synapse. Generally in one of three ways. The substances can:
• Ldopa is a dopamine agonist – it increases the synthesis of dopamine and is used
to treat Parkinson’s disease.