1. Physiological Basis of Behaviour
Psychology 100
Josée L. Jarry, Ph.D., C.Psych.
Department of Psychology
University of Toronto
May 14, 2003

2. Nervous system
Coordinates and directs the body’s action in the environment
Receives information about the environment
Organises and integrates information with already stored information
Uses integrated information to send messages to the body to respond
Provides the basis for conscious experience

3. Central and Peripheral Nervous Systems
Central nervous system
Brain and spinal cord
Peripheral nervous system
Nerves extending from the central nervous system
Nerves
bundles of axons of many neurons that connect the central nervous system to the body’s muscles, glands, and sensory organs.

4. The Neuron (1) Carry information rapidly
Integrate information from various sources
Cell body
Contains the cell nucleus and all the basic structures common to all cells.
Dendrites
Thin extensions branching out from the cell body
Increase the surface of the cell to facilitate receipt of signals from other neurons

5. The Neuron (2) Axon Thin, tube like extension
Carries signals from the cell body to other cells
Branches into the terminal arborisation
Each branch ends with a small swelling called the axon terminal or terminal button
Axon terminals release chemical substances onto other cells, either other neurons, muscle cells, or glands

6. Myelin sheet Many neurons are surrounded by a myelin sheath
Casing made of the membranes of fatty cells wrapped tightly around the axon
It is designed to insulate the neuron such that its electrical impulses are not lost before reaching the axon terminal
Forms a tube made of segments with small gaps called nodes de Ranvier.

8. Three functional classes of neurons (1)
Sensory neurons
Carry information from the sensory organs to the central nervous system.
2 or 3 million
Motor neurons
Carry information from the central nervous system to the body’s muscles and glands

9. Three functional classes of neurons (2)
Interneurons
Within the central nervous system
Relay information from one set of neurons to the other
Organise and integrate information
100 billion to a trillion

10. Glial cells Are the cushioning of the nervous system
Constitute half of the volume of the central nervous system
Several functions
myelin sheet
surround blood vessels in the brain to protect the neurons from certain toxic substances
clean up waste products and dead neurons
provide nutrients to neurons.

12. Neural impulse or Action Potential
signals or messages sent down the axon
electrical bursts that starts at one end of the axon and travel in one direction only toward the axon terminals
All or nothing
an action potential is always the same strength or magnitude
retains its full strength all the way down the axon

13. Molecular Basis of the Action Potential
Intracellular fluid
water solution inside of the cell
Extracellular fluid
water solution that bathes the outside of the cell
It is the flow of these fluids through the membrane that produces the action potential.

14. Chemicals in the Intra and Extra cellular fluid
Protein anion(-)
large and trapped in the intracellular fluid
Potassium (K+)
more concentrated in the intracellular fluid than in the extracellular fluid
Sodium (Na+)
more concentrated in the extracellular fluid
Chloride (Cl-)

16. Resting potential Sodium-potassium pumps
constantly pump sodium outside of the neuron, and potassium inside the neuron
Sodium channels
prevent sodium from entering the membrane
Potassium channels
prevent potassium from flowing out of the membrane
The balance of the ions on both sides of the membrane results in a negative charge inside the cell of approximately -70 millivolts

17. Diffusion & Electrostatic Pressure
Resting potential
Na+ is attracted inside the cell by the forces of diffusion and electrostatic pressure
K+ is attracted outside the cell by the forces of diffusion but not electrostatic pressure
Action Potential
Na+ rushes inside the cell by the forces of diffusion and electrostatic pressure
K+ rushes outside the cell by the forces of diffusion and electrostatic pressure

18. Depolarization & Repolarization
Depolarization phase
Na+ channels open causing sodium to rush inside
The electrical charge across the membrane reverses itself
The inside of the cell becomes temporarily positive
Repolarization phase
Na+ channels close, and K+ channels open causing potassium to rush out
the sodium-potassium pumps then proceed to move potassium back inside and sodium outside the cell.

21. Conduction of the Action Potential
The action potential triggers the opening of the sodium channels in the area just ahead of it
In myelinated axons, the action potential regenerates itself at the nodes de Ranvier
Between nodes, travels by passive cable properties
Allows faster conduction with less energy expenditure

22. Synaptic transmission (1)
Synaptic cleft
Space that separates two neurons
Presynaptic membrane
The membrane of the neuron from which the signal arrives
Postsynaptic membrane
The membrane of the neuron that receives the signal

23. Synaptic transmission (2)
Vesicles
Tiny globes containing a chemical substance called neurotransmitter
Neurotransmitter
Released by the presynaptic neuron in the synaptic cleft
Transmits signals to the postsynaptic neuron

25. Excitatory & Inhibitory Synapses
Excitatory synapse
increases the rate of firing of the postsynaptic neuron
transmitter causes the sodium gates to open, allowing sodium to enter the cell
Inhibitory synapse
decreases the rate of firing of the postsynaptic neuron
transmitter causes potassium to leave the cell or
Cl- to enter the cell
makes the inside even more negative
makes the neuron less susceptible of firing.

27. Integration of Excitatory & Inhibitory Inputs
Depolarizations and hyperpolarizations spread passively across the cell body
Affect the electrical charge at the junction of the cell body and the axon
If reaches critical value, the axon will increase its rate of action potential
The greater the depolarization, the greater the number of AP per second
The rate of firing reflects the integration of all excitatory and inhibitory input

28. The Cerebral Cortex: Brain Bark
Frontal lobe
Motor cortex
Parietal lobe
Somatosensory cortex
Occipital lobe
Visual cortex
Temporal lobe
Auditory cortex
Association areas

32. Topographical Organization
The entire body is mapped on the sensory and motor areas of the cortex
Adjacent parts of the body are connected to adjacent parts of the cortex
Fine sensation and motor control have the largest representation
These areas have a certain degree of plasticity

34. Asymmetry of Higher Functions
Sensory and motor areas are quite symmetrical
Equally represented in the right and left hemisphere
Less symmetry in the association areas
Most evident for language and non-verbal, visual-spatial analysis of information