UNIT II: THE HUMAN BRAIN

How many genes are in the human bod? 20,000-25,000! 1/15

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? % 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 Function 3.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

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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

Neurotransmission Action Potential (tiny electrical current that propels the message through the neuron) travels down the pre-synaptic neuron to terminal bulbs. 1/7

Neurotransmission (cont.) Action Potential cannot cross synapse. To send message, AP causes vesicles to move to membrane of terminal. 2/7

Neurotransmission (cont.) Vesicles attach to membrane and release its contents (neurotransmitters, or NT) into synapse. 3/7

Neurotransmission (cont.) Binding of NT to post-synaptic neuron causes AP to activate in next cell. 4/7

Neurotransmission (cont.) Once message is received, NT release from the receptors. Some are broken down by enzymes in synapse, others are sucked back into pre-synaptic neuron by transporter proteins. This is called “reuptake”. 5/7

Neurotransmission (cont.) This process repeats itself every time a signal is sent, at speeds well over 200 mph! No wonder you are tired at the end of the day! 6/7

Neurotransmitters Definition: any of about a dozen chemicals that are made by neurons and used to communicate to other neurons during physical or mental activities. 12 kinds? Don’t they get confused where to go, like a traffic jam? Each neurotransmitter has a specific chemical key which allows it open or close a receptor like a lock in a door NT can be either excitatory (open lock and turn on neuron) or inhibitory (close lock and turn off neuron) 7/7