The Nervous System What did you learn at school today? Neurophysiology!
The Nervous System Controls heart rate, emotions, memories, consciousness, and much more. The most intricate and beautifully complex of all the systems. Connects all other organ systems together Protects you using reflexes. (eg. stove)
Spinal and Cranial Nerves Spinal Nerves: Nerves that originate from the spinal cord Cranial Nerves: Nerves that originate from the brain
Organization of the Nervous System
Afferent vs. Efferent Afferent: Neurons that transmit action potentials (an electrical signal) from the sensory organs to the CNS (brain and spinal cord). Efferent Neurons: Neurons that transmit action potentials from the CNS to the effector organs.
The Cellular Level of Neurons (the axon) Nerves: The body s communication system Dendrite: Tiny extensions that help neurons communicate with each other Soma: The cell body of the neuron Axon: The long extension that carries electrical signals (action potentials). Axon Terminal: Exactly what we learned about in module 5
The structure of a nerve is incredibly similar to the structure of a muscle!
Classification of Neurons (Page 202) Unipolar: One process that carries action potentials away from its cell body Bipolar (interneurons): Two process. Multipolar: Many processes
Neuroglia (neural glue) The connective tissue of the nervous system There are about 9 neuroglia for every nerve Nerves cannot reproduce, but neuroglia can Without these, the function of the nervous system would not be possible
Neuroglia 1. 2. 3. 4. 5. Oligodendrocytes: Binds together and insulates the CNS neurons Schwann Cells: Insulates PNS neurons Microglia: Fight infection with phagocytosis Astrocytes: Form the blood-brain barrier (more on this later) Ependymal Cells: Move and secrete cerebrospinal fluid (more on this later)
Action Potential: How the nerves send this electrical signal that tells just about everything in our body what to do and when to do it.
There s an app for that Single electrical impulses are responsible for setting everything your body does into motion. There is no such thing as a more powerful action potential. The frequency changes but the intensity does not. - Seeing a tiger inside a cage vs. being inside the cage with the tiger
The Action Potential Chart
Sodium (+) and Potassium (+) Responsible for causing this electrical signal! Your neuron is like a battery with a positive and negative charge on each side of the membrane. Both sodium and potassium are positive. The concentration gradient and the proteins make the inside (-) NATURE HATES GRADIENTS: Sodium potassium pump makes the inside have a negative charge
(1) Resting Potential -70mv Potential Difference: Measure of the charge across the cell membrane. At rest the cell is polarized meaning it is negative with a measure of -70mv of electricity. NATURE HATES GRADIENTS. The -70 charge is only possible by the sodium potassium pump.
The different channels in the cell membrane
(2) Stimulus Build up This can happen when something causes some of the smaller sodium channels to open allowing a small amount sodium to come inside the cell making it less negative. What causes this Build Up?-> Graded Potentials.
(3) Threshold is reached. DROP THE BASS! Action Potential begins. Neurons work in something called an all-or-nothing phenomenon. -55mv is the magic number. Once -55mv is reached, all the sodium gates open up! -55 mv
4: DEPOLARIZATION of the membrane The sodium channels of the cell open when the threshold is reached. Most of the sodium travels inside the cell and the membrane potential rises steadily until it goes from -70 to about +30 mv. This occurs along the entire axon and is the electrical signal that your body uses for everything.
(5) Saturation reached. Potassium channels open. At +30mv, the sodium channels close and sodium stops coming into the cell Now both sodium and potassium are crammed inside of the cell Potassium gets uncomfortable with sodium invading its space. Potassium channels open and potassium now begins to leave the cell.
(6) REPOLARIZATION The potassium leaves the cell rapidly through the potassium channels and the membrane potential steadily drops again. Now potassium is on the outside and sodium is on the inside.
(7 and 8) Hyperpolarization and Potassium Gates Shut Because SO much potassium leaves the inside of the cell, the membrane potential drops to about -75 or -80mv. The potassium gates shut and potassium stops flooding out of the cell.
(9) Back to normal Here is a link that illustrates the entire process. https://www.youtube.com/watch?v=y Q-wQsEK21E What is wrong now? The potassium is on the outside and the sodium is on the inside. The Sodium Potassium Pump restores everything back to normal by bringing 3 sodium out of the cell and 2 potassium into it. After a while, everything goes back to the way it was before.
This entire process occurs down the entire axon and it is the cornerstone for understanding how the nervous system works!
Absolute and Relative Refractory Periods Action Potentials can only fire at a certain rate. Think of a toilet. After one flush you cannot immediately flush it again. Repolarization can only happen so fast
Myelinated Axon vs. Unmyelinated Myelin (Schwann Cell): A fatty sheath that covers an acon and speeds up the action potential drastically. Unmyelinated axons are much slower When you get a cut, there is a sharp pain followed by a dull ache. The initial pain is from the myelinated axons and the dull ache later is from the unmyelinated. Cattle can stand right after birth because most of their axons are instantly myelinated. Humans develop it later.
How do nerves communicate with each other? Similar to neuromuscular junction See page 223
Homework By 12 tonight all of the homework will be listed Watch the lecture for module 8 and familiarize yourself with the brain by completing the study guide! Next week we have the brain dissection Start working on your essay Take module 8 quiz (open book, online)