PSYC 1100 – Principals of Behaviour
Chapter 3 – Psychology: Biological Foundations of Behaviour
This chapter is all about how our brain controls our experience, behaviour and how the cells function
and communicate with one another.
NEURONS: Specialized Cells; are the building blocks of the nervous system. At birth, the brain
contained about 100 billion neurons. But at the process of cell death that accompanies aging, about
10,000 of them are lost each day of our lives. (Filogamo, 1998)
Each neuron has three main parts: A cell body or soma, Dendrites and an Axon.
CELL BODY: Contains the biochemical structures needed to kepp neurons alive, and its nucleus
carries genetic info. that determines how the cell develops and functions.
DENDRITES: These are like antennas that collect messages from neighbouring neurons and send
them to the cell body. There the incoming info. is combined and processed.
AXON: Conducts electrical impulses away from the cell body to other neurons, muscles, or glands.
Axon branches out at its end to form a number of AXON TERMINALS.
Neurons are supported in their work by GLIAL CELLS. Glial cells surround neurons and hold them
in place. It also manufactures nutrient chemicals, and absorbs toxins and waste materials.
BLOODBRAIN BARRIER: A specialized barrier that prevents many substances, including a wide
range of toxins, from entering the brain.
NERVE CONDUCTION: AN ELECTROCHEMICAL PROCESS
Neurons perform two important things:
1) They generate electricity
2) They release chemicals.
Neurons are surrounded by a salty liquid environment. This environment consists of a high
concentration of sodium carriers a positive electrical charge, some positively charged potassium ions
and many other ions that carry a negative charge.
An Action Potential is a sudden reversal in the neuron’s membrane voltage from 70 millivolts (inside) to
The shift from negative to positive voltage is called DEPOLARIZATION.
The depolarization process occurs when the dendrites of the cell are stimulated resulting in small shifts
in the cell membrane’s electrical potential. This small shift is called GRADED POTENTIAL. If the graded potential is large enough to reach the Action Potential Threshold, an action potential
occurs. The action potential obeys the AllorNone Law; it either occurs with maximum intensity or does
not occur at all.
ION CHANNELS: These are tiny protein structures that are activated when a neuron is stimulated.
Sodium ions channels allow positively charged sodium ions to enter the interior of the cell, leading to the
process of Depolarization.
Immediately after an impulse passes any point on the Axon, a time period called a REFRACTORY
PERIOD occurs, during which another action potential cannot occur.
THE MYELIN SHEATH: A fatty, whitish tube like insulation layer derived for glial cells during
development covering some axons in the brain and spinal cord.
HOW NEURONS COMMUNICATE: SYNAPTIC TRANSMISSION
Neuron system acts as a giant communications network, with action of transmission of nerve impulse
from one neuron to another. It communicates through synaptic transmission.
SYNAPSE: A functional (but not physical) connection between a neuron and its target.
SYNAPTIC CLEFT: A tiny gap or space between the axon terminal of one neuron and the dendrites
of the next neuron. The neuron as wrote earlier on produces chemical substances. These substances
are known as NEUROTRANSMITTERS.
NEUROTRANSMITTERS: Chemical substances stored in the synaptic vesicles that carry
messages across the synapse, bind to receptor sites and inhibit their firing.
This process of communication involves five steps: synthesis, storage, release, binding and
deactivation. One method of deactivation is REUPTAKE; in which the transmitter molecules are taken
back into the presynaptic neuron.
There are many types of neurotransmitters and their effects. See the table on page 89 of the text.
THE NERVOUS SYSTEM
There are three major types of neurons in the nervous system: i)SENSORY (ii) MOTOR and (iii)
SENSORY NEURONS: Carry input messages from the sense organs to the spinal cord and brain.
MOTOR NEURONS: Transmit output impulses from the brain and spinal cord to the body’s muscles
INTERNEURONS: Perform connective or associative functions within the nervous system.
The nervous system is broken down into two major divisions where are; CENTRAL NERVOUS
SYSTEM and PERIPHERAL NERVOUS SYSTEM. CENTRAL NERVOUS SYSTEM (CNS)
This is the division of the system consisting of all the neurons in the brain and spinal cord. This system
distinguishes us from other creatures. It contains the spinal cord and the brain.
A) SPINAL CORD: Most nerves enter and leave the CNS via the spinal cord. This is a structure
that in a human adult is 40 to 45 centimetres long and about two and a half centimetres In diameter that
are protected by the vertebrae.
SPINAL REFLEXES: Some simple stimulusresponse sequences such as pulling away from a hot
stove typically that don’t involve the brain.
B) THE BRAIN: The three pounds of protein, fat and fluid that you carry around inside your skull is
the real “you”.(Looks like a grapefruitsize mass of tissue that feels like jelly and looks like a greyish
gnarled walnut). The brain is the most complex structure in the universe and it is the only one that can
wonder about itself. Your brain is the most active energy consumer of all your body organs. It consumes
about 20% of the oxygen you use in a resting state.
Psychologists have used a number of methods of studying the brain.
UNLOCKING THE SECRETS OF THE BRAIN (PAGE 94)
Neuropsychological Tests: measure verbal and nonverbal behaviours that are affected by particular
types of brai