2. Biological Bases
of Behavior

3. Everything psychological is biological.

4. The human brain is not solid
The human brain is not solid. It’s soft and squishy similar to the consistency of soft tofu or soft gelatin. And it’s very fragile.

5. Makes up 2% of body’s weight
Uses 20-25% of total energy and oxygen intake.

6. Brain is 73% water
Just 2% dehydration impairs attention, memory, and other cognitive skills.

7. Weights around 3 pounds
60% fat

8. Weights around 3 pounds
60% fat

9. While awake, the brain produces enough electricity to power a dim lightbulb.

10. The average brain is believed to generate around 50,000 thoughts per day. Disturbingly, it’s estimated that in most people 70% of these thoughts are negative.

11. Brain cells cannibalize themselves as a last ditch source of energy to ward off starvation. So in very real ways dieting can force your brain to eat itself.

12. Your brain’s storage capacity is considered virtually unlimited
Your brain’s storage capacity is considered virtually unlimited. It doesn’t get “used up” like RAM in your computer.

13. There is no such thing as a left-brain or right-brain personality type
There is no such thing as a left-brain or right-brain personality type. We are not left-brained or right-brained; we are “whole brained.”

14. Human brains contain approximately 400 miles of capillaries.

15. When you are severely drunk, your brain is incapable of forming memories.

16. Think you’re in control of your life. Think again
Think you’re in control of your life? Think again. 95% of your decisions take place in your subconscious mind.

17. Over 140 proteins in the brain are negatively impacted by exposure to electromagnetic frequencies — the kind emitted by your cell phone and other electronic devices.

18. Although pain is processed in your brain, your brain has no pain receptors and feels no pain. This explains how brain surgery can be performed while the patient is awake with no pain or discomfort.

20. Human brain contains approximately
Neuron:
Nerve cell
Human brain contains approximately
100 billion
Each neuron connects with tens of thousands of other neurons, forming neural networks.

21. A piece of brain tissue the size of a grain of sand contains 100,000 neurons and 1 billion synapses all communicating with each other.

22. Cell Body (Soma)

23. Dendrites
Receive messages and conduct impulses toward cell body

24. Dendrites (detect messages; listen)
Information collectors (what is new?)
Receive inputs from neighboring neurons
Inputs may number in thousands
If enough inputs (electrical signals) the cell’s AXON may generate an output
Key words: dendrite
Interesting facts:
- The word DENDRITE comes from the Greek word for tree. This may serve as a useful analogy in discussing the dendrites for several reasons:
1. The dendrites branch repeatedly from the cell body (to increase the surface area of the cell to better allow the cell to receive incoming information). These radiations from the cell body are often referred to as a dendritic tree.
2. In terms of function, the dendrites function similiarly to the roots of a tree. Just as the roots take water and other nutrients from the soil and carry them to other parts of the tree, the dendrites collect information and and spread it to other parts of the neuron.

25. Dendritic Growth Mature neurons generally can’t divide
But new dendrites can grow (learn)
Provides room for more connections to other neurons
New connections are basis for learning
Key words: dendrite
Interesting facts:
- The word DENDRITE comes from the Greek word for tree. This may serve as a useful analogy in discussing the dendrites for several reasons:
1. The dendrites branch repeatedly from the cell body (to increase the surface area of the cell to better allow the cell to receive incoming information). These radiations from the cell body are often referred to as a dendritic tree.
2. In terms of function, the dendrites function similiarly to the roots of a tree. Just as the roots take water and other nutrients from the soil and carry them to other parts of the tree, the dendrites collect information and and spread it to other parts of the neuron.
Dendrites grow – and can reach more neurons

26. Axon
Carries info away from cell body toward other cells

27. Myelin Sheath
Fatty tissue that protects axon and speeds up impulses

28. Terminal Buttons
Store neurotransmitters that release and attach to the dendrites of other neurons.

29. Glial cells (glia)
Form myelin and provide support, nutritional benefits, and protection for neurons.
10 glial cells for every 1 neuron

30. Gray Matter: Mostly cell bodies and dendrites
White Matter: Mostly axons connecting neurons to one another.

31. Action Potential!

32. Resting potential: Inside of axon is negatively charged.

33. Ion channels: gates in the axon that allow ions to flow in and out of the cell.
Closed during resting potential

34. When dendrites receive input from other neurons they transmit signals to the cell body.

35. Impulses cause ion channels to open and positively charged ions to flow inside the axon.
Depolarization

36. All-or-nothing principle:
Once the electrical impulse reaches a certain level of intensity called its threshold, it fires (triggers an action potential) and moves all the way down the axon.
If the threshold is not met, an action potential is not triggered.

38. A strong stimulus can trigger more neurons to fire, and to fire more often, but it does not affect the action potential’s strength or speed.
It’s all or nothing.
One-size-fits all!

40. Reuptake
Once the neighboring neuron receives the message, the neurotransmitters are reabsorbed back into the axon of the sending neuron.

41. Refractory Period
The recovery time during which another stimulus given to the neuron (no matter how strong) will not lead to a second action potential.
“Recovery period”

42. Types of Neurons

43. Body ------> Spinal cord/Brain
Sensory neurons
(Afferent neurons)
Neurons that carry incoming information from the sensory receptors in the body to the spinal cord and brain for processing.
Body > Spinal cord/Brain

44. Spinal cord/Brain ------> Body
Motor neurons
(Efferent neurons)
Neurons that carry outgoing information from the brain and spinal cord to the muscles and glands.
Spinal cord/Brain > Body

45. Interneurons Neurons that act as a middle man between other neurons.
Neurons that act as a middle man between other neurons.
They allow efferent neurons, afferent neurons, and other interneurons to communicate with one another.
Afferent N --> Interneuron --> Efferent N
Efferent N --> Interneuron --> Afferent N

47. Mirror Neurons
Neuron that fires both when someone acts and when someone observes the same action performed by another. Thus, the neuron "mirrors" the behavior of the other, as though the observer were itself performing the action.
May help explain feelings of empathy.