UNIT II: THE HUMAN BRAIN

How many cells are in the human brain?

• 1 trillion!• Two categories:– Glial Cells– Neurons

1/15

Glial Cells• Three Functions: – Provide scaffolding to support

both developing and mature neurons.

– Wrap around neurons to form insulation from electrical signals

– Releasing chemicals that influence neuron growth

• Make up 90% of cells in brain!

2/15

Neurons• 100 billion cells - both sends and receives messages and

signals (up to 268 mph!)

• Allows us to:– Receive sensory information– Control muscle movement– Regulate digestion– Release hormones– Complete mental processes (thinking, etc.)

3/15

Neurons (cont)

• Each neuron has hundreds of connections– Approximately 100 trillion neural connections in

the brain• Which is more: the world’s communications,

or the brain’s?• 0.00005%

4/15

Neuron Growth

• Humans born with all our neurons that slowly die over our lifetime.

• What two areas of the brain does new research suggest can regrow?– Hippocampus and olfactory bulb

• Humans do have the ability to rewire our brains -> recover from traumatic event

5/15

Alzheimer’s Disease• Excessive buildup of protein amyloid destroys

neurons faster than body can repair them.• All people produce amyloid, Alzheimer’s patients

cannot get rid of it– Teeth plaque

• Only “cure” right now is to slow or stop amyloid buildup

6/15

Neurons – Structure and Function

1. Cell body – egg-shaped structure that provides fuel, manufactures chemicals, maintains working order in the neuron, contains neurons DNA

7/15

Neurons – Structure and Function

2. Dendrites – Branchlike extensions; receive signals from cells or other neurons and pass them to the cell body.

8/15

Neurons – Structure and Function3. Axon – single threadlike structure, carries

messages to other neurons, organs, or muscles. Can be the length of the width of a human hair, or over 3 feet!

9/15

Neurons – Structure and Function

4. Myelin Sheath – looks like separate tube-like segments composed of fatty tissue. Prevents interference from other electrical signals and helps signals travel faster.

10/15

Neurons – Structure and Function

5. Terminal bulbs – look like tiny bubbles at the end of axon’s branches. Acts like a tiny container that stores neurotransmitters. Do not actually touch any neighboring organs, muscles, or cells.

11/15

Neurons – Structure and Function

6. Synapse – Infinitely small gap between terminal bulb and its neighboring organ, muscle, or other neural cells. Terminal bulbs eject neurotransmitters into the synapse to send messages.

12/15

What’s Wrong Here?

13/15

Reattaching Limbs

• Limbs can be reattached because of something we call nerves.

• In whole body except brain/spinal cord• String-like bundles of axons and dendrites• Carry messages from senses, skin, muscles,

and organs

14/15

Reattaching Limbs

• Nerves (but not neurons) have the ability to regrow • Gives us the ability to reattach limbs• Difference between nerve and neuron:– Neuron is individual cell– Nerve is a group of neurons

• Think of nerves as the superfast lane of highway neurons use to get signals to your brain

15/15