1. The Biological Basis of Behavior
Psychobiology: the study of how biological processes affect our behavior

2. The Human Nervous System
One of the most complex structures in the living world
Consists of the Central Nervous System (CNS) brain, spinal cord
and the Peripheral Nervous System (PNS)
Basic building blocks of the nervous system: nerves, neurons, neurotransmitters, and glial cells

3. Neurons The functional unit of the brain
Cells which process and transmit information in the nervous system
100 billion in the brain- more in other parts of the body
Communication between neurons is the foundation for brain function and controls changes in cognitive processes and behavior

4. Neuron

5. Neurons, cont.
Neurons enable people to think, move, maintain homeostasis, and feel emotions
Neurons are specialized cells that produce different actions because of its precise connection with other neurons, sensory receptors, and muscle cells
A typical neuron has four parts (regions):
the cell body, dendrites, axons, presynaptic terminals

6. Parts of the neuron

7. Cell Body Also called the SOMA The metabolic center of the neuron
The nucleus is located in the cell body and most of the cell’s protein synthesis occurs in the cell body

8. Dendrites
A neuron has multiples fibers, or dendrites, that extend from the cell body
They branch out somewhat like tree branches and serve as the main apparatus for receiving input into the neuron from other nerve cells

9. Axon
The part of the neuron that is specialized to carry messages away from the cell body and to relay messages to other cells
Varying lengths- may be up to a meter in length
Some large axons are surrounded by a fatty insulating material called myelin, which enables electrical signals to travel down the axon at higher speeds

10. Presynaptic terminals
Near the end, the axon divides into many fine branches that have specialized presynaptic terminals
These presynaptic terminals end in close proximity to the dendrites of another neuron
The dendrite of one neuron receives the message sent from the presynaptic terminal of another neuron

11. Neuron

12. Synapse
The site where a presynaptic terminal ends in close proximity to a receiving dendrite
The cell that sends out information is called the presynaptic neuron, and the cell that receives the information is called the post synaptic neuron

13. Synaptic Space
The synapse is not a physical connection between the two neurons
The intercellular space between the presynaptic and postsynaptic neuron is called the synaptic space
An average neuron forms approximately
1,000 synapses with other neurons- this dynamic change in neuronal connections forms the basis of learning

15. How do neurons pass and receive information?
The billions of neurons that makeup the brain coordinate thought, behavior, homeostasis- how?
1. Neurons convey information by transmitting messages to other neurons or other types of cells, such as muscles.
2. Neurons employ electrical signals to relay information from one apart of a neuron to another.

16. Cont.
3. The neuron converts the electrical signal to a chemical signal in order to pass this information to another neuron.
4. The target neuron then converts the message back to an electrical impulse to continue the process.

17. Action Potential
The electrical impulse that occurs when a neuron is stimulated.
Moves along the neuron axon or dendrite
Enable signals to travel very rapidly along the neuron fiber
Last less than 2 milliseconds
Result from the flow of ions across neuronal cell membranes

18. Resting Membrane Potential
Neurons, like all cells, maintains a balance of ions inside the cell that differs from the balance outside the cell
This uneven distribution of ions creates an electrical potential across the cell membrane
This resting potential is assigned a negative (-) number because the inside of the neuron is more negatively charged than the outside environment of the neuron
The negative charge is the result of unequal distribution of sodium , potassium and chloride ions

19. Action Potential- revisited
A stimulus occurring at the end of a nerve fiber starts an electrical change that travels like a wave over the length of the neuron
This electrical change, the action potential, results from a change in the permeability of the neuronal membrane
Sodium ions rush into the neuron, and the inside of the cell becomes more positive
This rush of sodium ions in the neuron starts a similar change in the adjoining segment and the impulse moves from one end of the neural fiber to the other

20. All-or-none phenomenon
Action potentials are an all-or-none phenomenon
The action potential either occurs or it doesn’t
The response of the neuron to an action potential depends on how many action potentials it transmits and the time interval between them

21. Neurotransmitters
Electrical signals carry information within a single neuron
Communication between neurons is a chemical process
When the neuron is stimulated, the electrical signal (action potential) travels down the axon to the axon terminals
When the electrical signal reaches the end of the axon, it triggers a series of chemical changes in the neuron
Calcium (+) flows in to the neuron and initiates the release of a neurotransmitter

22. continued
A neurotransmitter is a molecule that is released from a neuron to relay information to another cell
Neurotransmitter molecules are stored in membranes called vesicles in the axon terminal 9thousands of molecules of neurotransmitters)
These molecules are released into the synaptic space to the postsynaptic neuron

23. Receptors
Receptors are membrane proteins that are able to bind to a specific chemical substance, such as a neurotransmitter
The interaction of a receptor and neurotransmitter can be thought of as a lock and key for regulating neuronal function
Just like a lock and key- a neurotransmitter binds only with a specific receptor

24. continued
If an action potential is triggers, the communication process continues
After the neurotransmitter molecule binds to its receptor on the postsynaptic neuron, it releases from the receptor and diffuses back into the synaptic space
The releases neurotransmitter is either degraded (dissolved) by enzymes or taken back into the presynaptic axon terminal through a reuptake pump

26. Glial Cells Second type of cells in the brain
10 to 50 X more glial cells than neurons in the CNS
Their purpose is not as clear as the purpose of neurons
Some guide movement of neurons, others help to insulate and separate groups of neurons