Chapter 4- Biology of Behaviour 12/1/2011 6:13:00 PM
The Brain and its Components
Helper Cells take care of important support and housekeeping functions.
Pierre Flourens- emphasized that different parts of the nervous system were responsible for
Donald Hebb- provided the foundation for a better understating… he considered how
individual nerve cells are organized into larger units. Proposed specific principles of
organization by which these units were structurally organized.
Nerve cells in the brain are organized into modules – clusters of nerve cells that communicate
with each other. Particular modules have particular functions
Structure of the Nervous System
The brain has 3 major functions: Controlling behavior, processing and retaining the
information we receive from the environment, and regulating the bodies physiological
The nervous system is composed of two parts:
- The Central Nervous System: The brain and the Spinal cord (Long, thing collection of
nerve cells attached to the base of the brain and running the length of the spinal column.)
- The Peripheral Nervous System: the cranial and spinal nerves (bundles of fibers that
transmit information in and out of the central nervous system), that part of the nervous
system peripheral to the brain and spinal cord
Information from the head and neck region (eyes, ears, nose, tongue) reaches the brain and
spinal cord. Information from the head and neck region reaches the brain through the cranial
Sensory information from the rest of the body reaches the spinal cord through the spinal
The cranial nerves and spinal nerves also carry information away from the central nervous
system. The brain controls muscles, glands, and internal organs by sending messages to
these structures through these nerves.
Brain has 3 main parts: the brain stem, the cerebellum, and the cerebral hemispheres
The Brain Stem: it primarily controls physiological functions and automatic behaviours
Cerebral Hemispheres: largest part of the human brain, are involved in Behaviours of
particular interest to psychologists
Cerebellum: attached to the back of the brain stem, looks like a miniature version of cerebral
hemispheres. Primary function is to control and coordinate movements.
Vertebrae: one of the bones that encase the spinal cord and constitute the vertebral column.
Meninges- Three layered set of membranes that enclose the brain and spinal cord. The brain and spinal cord never come into direct contact with the bones of the skull and
vertebrae. Cerebrospinal fluid (CSF)- the liquid in which the brain and spinal cord float;
provides a shock absorbing cushion. Fills space between the meninges
Blood-Brain barrier- A barrier between the blood and the brain produced by the cells in the
walls of the brain‟s capillaries; prevents some substances from passing from the blood into
Cerebral Cortex- the outer layer of the vertebral hemispheres of the brain, approx. 3 mm
Grey Matter- the portions of the central nervous system that are abundant in cell bodies of
neurons rather than axons. The colour appears grey relative to white matter.
In the cerebral cortex, perceptions take place, memories are stored, plans are formulated and
White matter- a layer of nerve fibers that connect cells in the vertebral cortex to other parts of
The human cerebral cortex has bulges which are separated by grooves. The bulges are called
gyri or gyrus (plural), the grooves are called fissures. Fissures and gyri increase the surgace
area of the cortex and the number of nerve cells it can contain
The Peripheral nervous system consists of the nerves that connect the central nervous system
with sense organs, muscles and glands.
- sense organs detect changes in the environment, send signals to central nervous system.
Brain sends signals to muscles and glands (producing adjustments in internal physiological
Cells of the Nervous System
Neurons- Bring sensory information to the brain, store memories, reach decisions, control
activity of muscles
- A nerve cell; consists of a cell body with dendrites and an axon who‟s branches end in
terminal buttons that synapse with muscle fibers, gland cells, or other neurons.
- contain structures specialized for processing, receiving, processing, transmitting
Glia cells- aid the neurons. Guide new neuron cells, provide neurons with essential
chemicals, absorb harmful chemicals, or form protective insulation.
Dendrites- Tree-like part of a neuron on which other neurons form synapses
A Synapse is a junction between two nerve cells, consisting of a minute gap across which
impulses pass by diffusion of a neurotransmitter.
Dendritic Spines- small protuberances on the surface of a neurons synapses Soma- cell body. Largest part of the neuron, contains the mechanisms that control the
metabolism and maintenance of the cell.
Axon- aka nerve fiber, carries messages away from the soma to towards the cells with which
the neuron communicates. These messages are called action potentials, consist of brief
changes in the electrical charge of the axon.
Terminal Button- the rounded swelling at the end of the axon of a neuron, releases a
neurotransmitter (a chemical)
Myelin insulates many axons. The white matter gets its colour from the myelin sheaths
around the axons that travel through the cerebral cortex. The main function of it is to insulate
axons from one another and to prevent the scrambling of messages.
- we can see how important it is through multiple sclerosis: attacks a protein in the myelin
sheaths of axons, causing them to wear away and the axons not to function problem
Neurotransmitter- a chemical secreted by terminal buttons whenever an action potential is
sent down the axon (whenever the axon fires).
The Excitable Axon: The Action Potential
Axon potential- the message carried by the axon – involves an electrical current.
- Axons transmit information at less than 30 meters/second.
Membrane of axons are electrically charged. When no action potential is occurring (its
resting), the inside is charged at -70 millivolts (thousandths of a volt).
An Action potential in an abrupt, short-lived reversal in the electrical charge of an axon.
Axons are electrically charged because of an unequal distribution of +ve and –ve particles
inside the axon and surrounding fluid
Ion- a positive or negatively charged particle; produced when many substances dissolve in
The axonal membrane has special submicroscopic proteins act as ion transporters.
Ion Channels- A special protein molecule located in the membrane or a cell, controls the
entry or exit of a particular ion. Two types of Ion channels: Sodium Channels and Potassium
Ion Transporters- A special protein molecule located in the membrane of a cell; actively
transports ions into or out of the cell.
While in a resting state, outside of the axon membrane is positively charged, and the inside is
negatively charged. Atm the ion channels are closed.
An action potential is caused by the opening of some ion channels at the end of the axon
nearest the soma. An action potential is a brief reversal of the membranes electrical charge. Once the change
reverses, the ion channels close and another set opens for a short time, letting +ve potassium
ions out of the axon. Action potentials resemble “the wave”.
Ion transporters pump sodium ions out of the axon and pump potassium ions back in,
restoring the normal balance
All-or-None law- The principle that once an action potential is triggered in an axon, it is
propagated, without getting smaller, to the end of the axon. All the same size
Sensory neurons- A neuron that detects changes in the external or internal environment and
sends information about these changes to the central nervous system.
Motor neurons- A neuron whose terminal buttons form synapses with muscle fibers. When
an action potential travels down its axon, the associated muscle fibers will twitch.
A single action potential is not the basic element of information. Quantitative information is
represented by an axon‟s rate of firing. Ex. Bright lights (strong stimuli) trigger a high rate of
firing in axons of sensory neurons. High rate of firing in axons of motor neurons causes
strong muscular contractions.
A Synapse- The junction between the terminal button of one neuron and the membrane of a
muscle fiber, a gland or another neuron.
Presynaptic neuron- A neuron whose terminal buttons form synapses with and excite or
inhibit another neuron. The one that sends the message.
The neuron that receives the message is called the Postsynaptic Neuron- A neuron with
which the terminal buttons of another neuron form synapses and that is excited or inhibited
by that neuron.
Excitatory synapses- when the axon fires, terminal buttons release a neurotransmitter that
excites the postsynaptic neurons with which they form synapses. They raise the likelihood
that the axons of the postsynaptic neurons will fire.
Inhibitory Synapses- LOWER the likelihood that the axons of the postsynaptic neurons will
Rate at which a particular axon fires is determined by the activity of all synapses on the
dendrites and soma of the cell.
If the excitatory synapses = more active axon fires at higher rate
If the Inhibitory synapses = more active Axon fires at a low rate or not at all
When an action potential reaches a terminal button, it causes the terminal button to release a
small amount of a neurotransmitter into the Synaptic Cleft- A fluid-filled space between the presynaptic and postsynaptic membranes. The terminal button releases a neurotransmitter
into this space.
Neurotransmitter causes reations in the postsynaptic membrane called Neurotransmitter
Receptors- A Special protein molecule located in the membrane of the postsynaptic neuron
that responds to molecules of the postsynaptic neuron that responds to molecules of the
Myasthenia gravis- “grave muscle weakness”. Attacks the neurotransmitter receptor found
in muscle fibers.
Reuptake- the process by which a terminal button retrieves the molecules of a
neurotransmitter that it has just released; terminates the effect of the neurotransmitter on the
receptors of the postsynaptic neuron.
The rate at which the terminal button takes back the neurotransmitter determines how
prolonged the effects of the chemical on the postsynaptic neuron will be.
Drugs and Behavior
Effects of Drugs on Synaptic Transmission
Stimulating or Inhibiting the Release of Neurotransmitters
Some drugs stimulate certain terminal buttons to release their neurotransmitter continuously,
even when the axon is not firing. Other prevent terminal buttons from releasing their
neurotransmitter when the axon fires. Effects of a drug are generally specific to one
Stimulating or Blocking Postsynaptic Receptors
Some drugs mimic the effects of some neurotransmitters by directly stimulating some kinds
ex. Lock and Key analogy- effects of a neurotransmitter on a recptor- drug works like a
master key, turning on receptor without the neurotransmitter. (fig. 4.15)
Some drugs bind w. receptors, blocking receptors. Neurotransmitters cant reach them, which
inhibits synaptic transmission. Plugs up the lock(receptor) so key (neurotransmitter) cant fit.
Some drugs inhibit the process of reuptake (stopping the stimulation of receptors in the postsynaptic
membrane) which means the neurotransmitter continues to stimulate the postsynaptic receptors for a
long time. This increases the effect of the neurotransmitter.
Neurotransmitters, Their Actions, and Drugs that Affect them Two general effects of neurotransmitters on postsynaptic membranes- excitatory or inhibitory
Most synaptic communication in the brain is done by two neurotransmitters: Glutamate
(excitatory) and GABA (inhibitory)
Glutamate- the most important excitatory neurotransmitter in the brain and spinal cord
GABA- the most important inhibitory neurotransmitter in the brain. Stands for gamma-amino
Glycine- another neurotransmitter found in the lower brain stem and the spinal cord.
All the other NTs generally have modulating effects rather than information transmitting
effects. Release of these either activates or inhibits entire circuits of neurons that are involved
in brain functions. Ie. Facilitation of learning, control of wakefulness and vigilance,
suppression of impulsive Behaviour, and suppression or enhancement of anxiety.
Most important excitatory NT in the brain. Is the major excitatory neuron in the spinal cord.
All sensory organs transmit information to the brain through axons whose terminals release
glutamate (except neurons detecting painful stimuli)
NMDA receptor plays critical role in the effects of environmental stimulation on the
developing brain. Is responsible for many changes in synaptic connections that are
responsible for learning.
Partially deactivated by alcohol
Drugs causing depression, relaxation, sedation or even loss of consciousness usually have an
affect on a particular type of GABA receptor (the GABAa receptor)
Barbiturates acts this way- a drug that causes sedation; one of several derivatives or
In high doeses: difficulty walking, talking, unconsciousness, coma and death.
Most common used depressed drug is ethyl alcohol, acts on the GABAa receptor. Very
Antianxiety drugs- A „tranquilizer‟ which reduces anxiety are members of a family called
Benzodiazepines- A class of drug having anxiolytic (tranquilizing) effects, such as
diazepam… includes valium.
Act on this receptor as well as a region involved in fear and anxiety.
Acetylcholine “A NT found in the brain, spinal cord, and parts of the peripheral nervous system;
responsible for muscular contraction. (ACh)
primary NT secreted by axons of motor neurons. People with myasthenia gravis have
immune systems that attack acetylcholine receptors.
3 systems have been focused on the most by neuroscientists:
- One system activates the brain mechanisms responsible for REM sleep occurs.
- Another activates neurons in the cerebral cortex and facilitating learning, especially
- third controls the functions of the hippocampus, involved in learning.
Botulinum toxin- a drug that prevents the release of acetylcholine by terminal buttons.
Black Widow spider venom- drug that stimulates the release of acetylcholine by terminal
Acetylcholine is not deactivated by reuptake, instead by an enzyme called
acetylcholinesterase. This can be inactivated by drugs like Neostigmine- Drug that enhances
the effects of acetylcholine by blocking the enzyme that destroys it.
Nicotine affects acetylcholine receptors the best. It binds with and stimulates acetylcholine
receptors, mimicking the effects of this neurotransmitter.
Curare- blocks acetylcholine receptors. This causes paralysis. U=often used during surgery
because is paralyses, ensuring muscles don‟t contract when being cut.
“A category of neurotransmitters that includes dopamine, norepinephrine and serotonin.”
- Includes Dopamine, norepinephrine and serotonin.
Monoamines are produced by several systems of neurons in the brain. Monaminergic
neurons serve to modulate the function of widespread regions of the brain, increasing or
decreasing the activities of particular brain functions.
Dopamine – “a monoamine NT involved in control of brain mechanisms of movement,
attention, learning and reinforcement.”
Parkinson‟s Disease- “A neurological disorcer characterized by tremors, rigidity of the limbs,
poor balance, and difficulty in initiating movements; caused by degeneration of a system of
dopamine- secreting neurons.”
- given a drug called l-DOPA. Taken by surviving DA neurons in the brain and is converted
to dopamine. This alleviates symptoms.
Clozaril and Thorazine help relieve symptoms of schizophrenia
Amphetamine and cocaine inhibit reuptake of dopamine. Dopamine plays a large role in
reinforcement. The second monoamine is Norepinephrine (NE) –“a monoamine neurotransmitter involved in
alertness and vigilance and control of REM sleep”
Third monoamine NT is Serotonin- “A monoamine NT involved in the regulation of mood;
control of eating, sleep, arousal and in the regulation of pain.” Drugs like Prozac inhibit the
reuptake of serotonin, can be used to treat depression, anxiety disorder, obsessive compulsive
LSD- lysergic acid diethylamide; hallucinogenic drug that blocks a category of serotonin
receptors. Produces distortions of visual perceptions, stimulates one category of serotonin
“A category of NTs and neuromodulators that consist of two or more amino acids, linked by
Neuromodulators – “A substance secreted in the brain that modulates the activity of neurons
that contain the appropriate receptors.” Some neurons release chemicals that get into the
general circulation of the brain and stimulate receptors on many thousands of neurons. Called
Can be thought of as the brains own drugs.
Most neuromodulators are peptides.
Best known family of peptide bonds are Endogenous opioids- “A neuromodulator whose
action is mimicked by a natural of synthetic opiate, such as opium, morphine or heroin.”
Opiates reduce pain because they have a direct effect on the brain.
-stimulate special opioid receptors located on neurons in several parts of the brain.
decreased pain sensitivity, tendency to persist in on going Behaviour.
Opioid refers to endogenous chemicals, opiate refers to drugs.
Naloxone- “a drug that binds with and blocks opioid receptors, preventing opiate drugs or
endogenous opioids from exerting their effects.” Reverses opiate intoxication, blocks the
effects of heroin.
Other peptide neuromodulators play roles in behaviours important to survival like control of
eating and metabolism, drinking, mineral balance, mating, parental care, social bonding.
Tetrehydrocannabinol (THC) – principal ingredient in the resin produced by cannabis sativa,
affects perception and behavior
THC mimics the effects of Endogenous Cannabinoids- “A neuromodulator whose action is
mimicked by THC and other drugs present in marijuana.” THC- produces analgesia, sedation, stimulates appetite, reduces nausea, relieves asthma
attacks, decreases pressure in the eyes in patients with glaucoma, etc.
- interferes with concentration, memory, alters visual and auditory perception, distorts
perception of passing time.
Most important endogenous cannabinoid: fat like substance called anandamide.
Cannabinoid receptors are found on terminal buttons of neurons the secrete glutamate,
GABA, acetylcholine, dopamine, norepinephrine and serotonin.
* See chart pg 104- table 4.1 *
Study of the Brain
the brain changes in response to disease of accident, shows electrical and chemical responses
and it responds to the instructions encoded in its genes.