How Your Brain Works

1. How Your Brain Works

2. Overview of Your Brain • About the size of a small head of cauliflower. • Controls body temperature, heart rate, blood pressure and your breathing. • Constantly is being flooded with information from your senses. • It controls all physical movement. • It allows you to think, dream, reason and experience emotions.

3. Structure of the Neurons • Made up of 100 billion nerve cells, called neurons • Act like the gates and wires in a computer • Have three basic parts: cell body, axon and dendrites • Like other body cells but they have electrochemicals that allows them to transmit information over long distances

4. Neurons Differ from Other Cells Soma – the number of extensions from the cell body • Neurons have specialized extensions called dendrites and axons. • Dendrites bring information to the cell body • Axons take information away from the cell body • Neurons communicate with each other through an electrochemical process • Neurons contain some specialized structures (for example, synapses) and chemicals (for example, neurotransmitters)

5. Cell Body • This main part has all of the necessary components of the cell, such as: • the nucleus - contains DNA • endoplasmic reticulum and ribosomes - for building proteins • Mitochondria - for making energy • If the cell body dies, the neuron dies.

6. Axon • This long, cable-like projection of the cell carries the electrochemical message (action potential) along the length of the cell. • Depending upon the type of neuron, axons can be covered with a thin layer of myelin, like an insulated electrical wire. • Myelin is made of fat, and it helps to speed transmission of a nerve impulse down a long axon. • Myelinated neurons are typically found in the peripheral nerves (sensory and motor neurons). • Non-myelinated neurons are found in the brain and spinal cord.

7. Dendrites • Dendrites- small, branch-like projections of the cell make connections to other cells and allow the neuron to talk with other cells or perceive the environment. • Dendrites can be located on one or both ends of the cell.

8. Basic Neuron Types • Neurons come in many sizes. • For example, a single sensory neuron from your fingertip has an axon that extends the length of your arm, while neurons within the brain may extend only a few millimeters. • Neurons have different shapes depending on what they do. • Motor neurons that control muscle contractions have a cell body on one end, a long axon in the middle and dendrites on the other end; • Sensory neurons have dendrites on both ends, connected by a long axon with a cell body in the middle.

9. Types of Neurons Motor neurons: send information AWAY from the central nervous system to muscles or glands. Sensory neurons: send information from sensory receptors (e.g., in skin, eyes, nose, tongue, ears) TOWARD the central nervous system. Interneurons: send information between sensory neurons and motor neurons. Most interneurons are located in the central nervous system.

10. Action Potential Overview • Neurons send messages electrochemically. • This means that chemicals cause an electrical signal. • Chemicals in the body are "electrically-charged" -- when they have an electrical charge, they are called ions. • The important ions in the nervous system are sodium, potassium, calcium and chloride. There are also some negatively charged protein molecules as well. • It is also important to remember that nerve cells are surrounded by a membrane that allows some ions to pass through and blocks the passage of other ions. This type of membrane is called semi-permeable.

11. Ions related to Action Potential Chloride - passes through membrane, but not as easy as potassium Protein – can’t pass through membrane Potassium – crosses through membrane easily; lives inside the neuron (+) Sodium – can’t pass through membrane as easy; lives outside of the neuron (+)

12. Action Potential • An action potential occurs when a neuron sends information down an axon, away from the cell body. • The action potential is an explosion of electrical activity that is created by a depolarizing current. • If the neuron does not reach the critical thresholdlevel (-55 mV), then no action potential will fire. • For any given neuron, the size of the action potential is always the same. • The neuron either does not reach the threshold or a full action potential is fired - this is the "ALL OR NONE" principle.

13. Action Potential In order for action potential to occur, the cell needs to depolarize (or become more positive). To make the cell more positive, we need to add sodium from the outside of the cell. The sodium channel will open its gate and allow positively-charged sodium ions to enter. The sodium depolarizes one piece of the axon at a time, moving an action potential down the axon into the axon terminal. It spits out tiny droplets of neurotransmitters that the dendrites of the next neuron can taste. The cell will want to return to its negative charge eventually; therefore, it will open its potassium gate and let positively-charged potassium ions leave. This is called repolarization (becoming more negative again).

14. Today’s Resources • Neuron Video • http://outreach.mcb.harvard.edu/animations/actionpotential.swf • How the Brain Works Article • http://health.howstuffworks.com/human-body/systems/nervous-system/brain.htm • Quiz! • http://curiosity.discovery.com/topic/cognitive-neuroscience/brain-quiz.htm • Mrs. Comunale’sWikispace for Resources • https://misssparks.wikispaces.com