Chapter 3: Neuroscience and Behaviour • In many neurons, axon is covered by a myelin sheath- an
insulating layer of fatty material which is composed of glial cells
Prosopagnosia: an inability to recognize familiar faces.
which are support cells found in the nervous system.
Neurons: The Origin of Behaviour:
• Myelin sheath allows the axon to transmit information more
• 100 billion cells in the brain perform a variety of tasks to allow efficiently (think about the water heater pipes being insulated;
the functioning of human beings. the water stays hotter and the heater works efficiently).
• Neurons: cells in the nervous system that communicate with
one another to perform information-processing tasks.
Discovery of How Neurons Function: • In Multiple sclerosis (demyelinating disease), myelin sheath
deteriorates, slowing the transmission of information from one
neuron to another loss of feeling in the limbs, partial
• Santiago Ramon y Cajal was the first to see that each neuron
was composed of a body with many threads extending outward blindness and difficulties in coordinated movement and
toward other neurons.
• Saw that the threads of each neuron did not actually touch each
other. • Synapse: the junction/gap/region b/w the axon of one neuron
and the dendrites or cell body of another.
Components of the Neuron:
Three basic parts: Major Types of Neurons:
1. Cell body: (soma) the largest component of the neuron that 1. Sensory neurons: receive information from the external world
coordinates the information-processing tasks and keeps the cells and convey this information to the brain via the spinal cord.
alive. • Have specialized endings on their dendrites that receive
• Protein synthesis, energy production and metabolism takes
signals for light, sound, touch, taste and smell.
place in the cell body 2. Motor neurons: carry signals from the spinal cord to the
• Contains a nucleus, the structure that houses chromosomes muscles to produce movement.
that contain DNA (the genetic blueprint of who you are!) 3. Interneurons: (most of the nervous system) connect sensory
• Surrounded by a porous cell membrane that allows neurons, motor neurons or other interneurons.
molecules to flow into and out of the cell. • carry information from the sensory neurons into the
2. Dendrites: receive information from other neurons and relay it nervous system
to the cell body. • carry information from the nervous system to motor
3. Axon: transmits information to other neurons, muscles, or neurons
glands. • perform information-processing tasks (identify the location • The concentration of (K+) inside and outside an axon is
of a sensory signal or recognize a familiar face). controlled by channels in the axon membrane that allow
molecules to flow in and out of the neuron.
Neurons Specialized by Location: • In the resting state, the channels that allow K+ molecules to flow
• Purkinje cells- type of interneuron that carries information from freely across the cell membrane are open and the channels that
the cerebellum to the rest of the brain and spinal cord. allow the flow of Na+ and the other ions are closed.
• Pyramidal cells • When the K+ ions flow out, the inside of the neuron is left –vely
• Bipolar cells- type of sensory neuron found in the retinas of the charged. (-70mV)
eye. The action potential:
The electrochemical actions of neurons: information processing:
• An electric signal that is conducted along a neuron’s axon to a
The communication of information within and between neurons synapse.
• When an electric charge is raised to the threshold value, the K+
happens in two stages:
channels briefly shut down and it opens the Na+ channels,
1. Conduction of an electric signal over relatively long distances allowing the Na+ ions to rush in and increase the positive charge
within neurons, from the dendrites, to the cell body, then
inside the axon.
throughout the axon. • The membrane channels return to their original state once the
2. Transmission of chemical signals b/w neurons over the synapse. action potential reaches its maximum (+40mV).
Electrical signalling: conducting information within a neuron: • The ions are imbalanced until the axon returns to its resting
potential and during this period, the neuron cannot initiate
• The neuron’s cell membrane which is porous allows small another action potential refractory period- the time following
electrically charged molecules, ions, to flow in and out of the an action potential during which a new action potential cannot
• The flow of molecules across a cell membrane enhances the • The imbalance in ions from the action potential is reversed by an
transmission of information in the nervous system. active chemical “pump” in the cell membrane that moves Na+
ions outside the axon and moves K+ ions inside the axon the
The resting potential: neuron can generate another action potential.
• Difference in electric charge b/w the inside and outside of a Nodes of Ranvier: the break points in the myelin sheath. As an electric
neuron’s cell membrane.
current passes down the length of a myelinated axon, the charge seems
• In a resting state, there is a high concentration of (K+) ion and a to “jump” from node to node rather than having to traverse the entire
protein (A-) inside the neuron’s cell membrane. axon saltatory conduction- helps speed the flow of information down
• There is a high concentration of (Na+) and (Cl-) outside the the axon.
neuron’s cell membrane. Chemical Signaling: Transmission between Neurons: Types and functions of neurotransmitters:
• Axons usually end in terminal buttons- knoblike structures that 1. Acetylcholine- involved in voluntary motor control.
branch out from an axon. • Found in neurons of the brain and in the synapses where
• Terminal button is filled with tiny vesicles that contain axons connect to muscles and body organs (heart).
neurotransmitters- chemicals that transmit information across • Activates muscles to initiate motor behaviour and
the synapse to a receiving neuron’s dendrites. contributes to the regulation of attention, learning, sleeping,
• The dendrites of the receiving neuron has receptors-parts of the dreaming and memory.
cell membrane that receive neurotransmitters and either initiate • Alzheimer’s disease- a medical condition involving severe
or prevent a new electric signal. memory impairments associated with the deterioration of
Synaptic transmission: Ach-producing neurons.
2. Dopamine- regulates motor behaviour, motivation, pleasure
and emotional arousal.
Presynaptic neuron (resting potential)(action potential)travels
through the axon to terminal buttons stimulates the release of • High levels schizophrenia.
• Low levels Parkinson’s disease.
neurotransmitters into the synapsereceptor sites on the dendrites
of a postsynaptic neuron a new electric potential initiates and the 3. Glutamate- major excitatory neurotransmitter involved in
same process continues. information transmission throughout the brain.
• High levels overstimulation of the brain; causes seizures.
• Lock-and-key system: specific neurotransmitters bind to specific 4. GABA (gamma-aminobutyric acid)- primary inhibitor
receptors on a dendrite. neurotransmitter in the brain; stop the firing of neurons.
After the neurotransmitters relay the chemical message, they aren’t • Low levels can cause neurons to become overactive (just
just left in the synapse: 5. Norepinephrine- influences mood and arousal.
1. Reuptake- neurotransmitters are reabsorbed by the terminal • Particularly involved in states of vigilance and heightened
buttons of the presynaptic neuron’s axon. awareness of dangers in the environment.
2. Enzyme deactivation- neurotransmitters can be destroyed by • Low levels mood disorders.
enzymes in the synapse. 6. Serotonin-involved in the regulation of sleep and wakefulness,
3. Neurotransmitters can bind to the receptor sites called eating and aggressive behaviour.
autoreceptors on the presynaptic neuron- detect the release of • Low levels mood disorders.
neurotransmitters and signal the neuron to stop releasing if an 7. Endorphins- chemicals that act within the pain pathways and
excess is present. emotion centres of the brain. “Runner’s high”. Dull the
experience of pain and elevate moods. How Drugs Mimic Neurotransmitters • Amphetamine and cocaine- stimulates the release of
norepinephrine and dopamine. Increases in either
Agonists: drugs that increase the action of a neurotransmitter.
neurotransmitters result in euphoria, wakefulness and a burst of
Antagonists: drugs that block the function of a neurotransmitter.
• Drug called L-dopa was developed to treat Parkinson’s disease, • Overdose: causes the heart to contract so rapidly that,
a movement disorder characterized by tremors and difficulty heartbeats do not last long enough to pump blood
initiating movement and caused by the loss of neurons that use effectively, leading to fainting and sometimes to death.
Regular cocaine users have trouble recognizing expressions of fear.
• Ingesting L-dopa elevates the amount of itself in the brain and
spur the surviving neurons to produce more dopamine. The size of brain structure, amygdala- which is important in recognizing
• L-dopa agonist for dopamine.
the expressions of fear- reduces in cocaine users.
• The effectiveness of L-dopa typically decreases when used over
a long period of time, so many long-time users experience some The organization of the Nervous System:
symptoms of the disease :( • Neurons are the building blocks that form nerves, or bundles of
• Prozac- used to treat depression. Blocks the reuptake of axons and the glial cells that support them.
• Nervous system: an interacting network of neurons that
serotonin more serotonin remains in the synapse longer and
produces greater activation of serotonin receptors, elevates conveys electrochemical information throughout the body.
mood and helps relieve depression. Divisions of the Nervous System:
• Beta Blockers- obstruct a receptor site for norepinephrine in the 1. Central Nervous System: composed of the brain and the spinal
heart heart rate slows down (helpful for disorders that cause cord.
irregular and fast heart beats; reduces agitation racing heart and • Receives sensory information from the external world,
processes and coordinates information and sends
nervousness associated w/ stage fright.
commands to the skeletal and muscular systems for action.
• MPTP- antagonist for dopamine; destroys dopamine-producing • Brain (at the top of the CNS) contains structures that
neurons. support the most complex perceptual, motor, emotional
and cognitive functions of the nervous system.
• The spinal cord branches down from the brain; nerves that
• Methamphetamine- affects pathways for dopamine, serotonin
and norepinephrine at the neurons’ synapses. Might cause process sensory information and relay commands to the
hallucinations. body connect to the spinal cord. 2. Peripheral Nervous System: connects the nervous system to the 1. The Hindbrain
body’s organs and muscles. • An area of the brain that coordinates information coming
a. Somatic Nervous System: a set of nerves that conveys into and out of the spinal cord.
information into and out of the CNS.