This week, you will learn about advanced physiology of the human nervous system. Topics include development; growth, and the structure and physiology of neurons and associated cells, the brain, and the brainstem. You should already have a foundation in human anatomy and physiology from prior education and experiences. The lessons and readings this week will enhance and strengthen your foundation in nervous system structure and function. They will also prepare you for the advanced Pathophysiology units in this course.
Complex and fascinating, the human nervous system has puzzled and intrigued people through the ages. As you can see from the photo on the right, we have proof of early people’s fascination with the brain. Note the holes in this ancient Egyptian skull, a practice known as trepanning.If Egyptians came to the conclusion that the brain had something to do with our spirit, soul, personality, and abilities, priorcivilizations probably had similar thoughts. Wouldn’t it be amazingto be one of those first people to discover the power of what’s between our ears? On second thought, for the subjects involved, the discovery probably didn’t occurunder favorable circumstances. But let’s back up a moment and take a look, not just at the brain, but at all the components of the human nervous system.(Nervous system image location: http://commons.wikimedia.org/wiki/File:Eustachi_nervous_system.jpg Image is in public domain)(Skull with holes image location: http://commons.wikimedia.org/wiki/File:Trepanated_skull,_Bronze_Age.JPG)
Our nervous system is our control center. Without it, we wouldn’t be able to taste, smell, hear, see, think, dream, breath, sleep, laugh, move, feel pain or pleasure, or anything else that is vital to our existence. (mouse click to display additional image) The central nervous system is made up of the brain and spinal cord, and (mouse click) the peripheral nervous system is made up of an enormous network of nerves threading through our bodies. These include cranial and spinal nerves and the ganglia associated with these nerves. These nerves transport information to and from the central nervous system, via (mouse click)the sensory or afferent system, which transmits nerve impulses from the organs in the body to the central nervous system and the (mouse click) motor or efferent system. The motor system transmits nerve impulses from the central nervous system to peripheral organs, resulting in some effect or action. The motor system consists of the (mouse click) somatic and (mouse click) autonomic nervous systems. The somatic system controls voluntary muscles, such as those in the face and extremities. Involuntary muscles are controlled by the autonomic nervous system, which include the heart, smooth muscle, and glands. There are three components of the autonomic nervous system – (mouse click) the sympathetic, (mouse click) parasympathetic, and (mouse click) enteric systems. The sympathetic nervous system prepares the body for an emergency, while the parasympathetic nervous system’s goal is conserving and restoring energy. And finally, the enteric nervous system controls the gastrointestinal tract. But what is the building block common among these systems?
The basic functional unit of our nervous system is a neuron (or nerve cell). Neurons enable the parts of a human nervous system to communicate with each other at lightening speed. Neurons have specialized properties, such as irritability, capability to respondto a stimulus, conductivity, and ability to transport signals, or “messages.” They are the oldest and longest cells in our body.This image shows three neurons – two red and one yellow – sending messages to each other.
The second graphic is a simulation image that features a large cluster of galaxies (bright yellow) surrounded by thousands of stars, galaxies, and dark matter.Isn’t it remarkable how the very smallest network in life is so similar in appearanceto the largest?
Besides their ability to communicate with each other, what traits distinguish nerve cells from other cells in the body? Which of the following statements is true? (mouse click)Neurons have dendrites and axons to carry information back and forth. (mouse click)Neurons can communicate with other neurons.(mouse click)Neurons have specialized structures, like synapses and chemicals. (pause for answer. mouse click)In fact, all of these statements are true.
Here is the simplified classification of the three types of neurons: (mouse click)Sensory (afferent) neurons send information from sensory receptors (which are in the skin, eyes, nose, etc.) toward the central nervous system.Motor (efferent) neurons send information away from the CNS to muscles or glands.Interneurons are typically located within the CNS, and their primary responsibility is to send information back and forth between sensory and motor neurons.
So, how do neurons work? (pause ) Electrochemically! Chemicals in neurons cause an electrical signal and are “electrically charged” (remember the neurotransmitters). When you slide your feet across carpet and touch a metal doorknob, you get a SHOCK because you were “electrically charged.”When the chemicals in a neuron are “electrically charged,” they are called ions. (mouse click)The key ions are: Sodium (mouse click) Potassium (mouse click)Calcium (mouse click)Chloride (mouse click)These ions have two major characteristics in common (mouse click), #1 – they can be either negatively or positively charged and, #2 (mouse click)they can be either outside or inside a neuron’s membrane.
(The graph is an animated gif.)The charge of the ions determines the type of potential a neuron has. This graph shows the sequence: resting potential, action potential, and back to resting potential.The neuron is “resting” when it isn’t sending any signals, but that doesn’t mean it has a charge of zero. Because the inside of the cell is more negative than the outside during the resting potential, its resting potential charge is negative (-70mV, to be exact). When the neuron is at rest, there are more sodium ions outside and more potassium ions inside. The action potential happens when the ions exchange across the cell membrane, with the goal of sending a signal or message down the axon to other neurons, muscles,or glands.
Resting neurons are polarized;when a neuron is depolarized, an action potential occurs.Think back to ourcarpet example. We are polarized until we “charge” ourselves by sliding on the carpet. We then become depolarized, and as soon as we touch the doorknob, an electric shock occurs. In other words, with depolarization,the gate is open for transmission of electricity between the doorknob and us.(Source for screen shots: http://www.blackwellpublishing.com/matthews/channel.html, the 2nd animation cited on the next page)
Take a look at these animations to learn more about action potential.In the first, note that the axon becomes negatively charged outside with respect to the inside when the action potential passes along the axon. This animation represents the action potential actually traveling along the nerve.The second animation shows a myelin-covered axon. As the action potential travels along the axon, it passes quickly through the myelin and in essence “jumps” from unmyelinated section to unmyelinated section. This event speeds up the process of sending messages along the nerves. Note the difference in this animation and the first one, which is slower with no myelination.
(The graph is an animated gif.)Another important concept, conduction velocity, is the speed of a nerve impulse, or how long it takes a neuron to conduct an action potential. Conduction velocity is measured in meters per second.The wave on this graph represents the amount of time it takes for the nerve impulse to travel from the beginning to the end of the time line.
Is the speed of a nerve impulse (conduction velocity) always the same? (pause) Definitely not! (mouse click)Some factors that can affect conduction velocity are: (mouse click)Temperature (becausecold slows conduction velocity) (mouse click)Width of axon (the wider the axon, the faster the conduction velocity) (mouse click)Myelination (the more myelination, the faster the conduction velocity) (mouse click)Click the link to view an example of salutatory conductionhttp://www.brainviews.com/abFiles/AniSalt.htm(Image source for axon: http://faculty.stcc.edu/AandP/AP/AP1pages/nervssys/unit10/neurons.htmImage source for myelination: http://thebrain.mcgill.ca/flash/d/d_01/d_01_cl/d_01_cl_fon/d_01_cl_fon.html )
Throughout this course, we will explore the origin, classification, symptoms, and treatments of various diseases and disorders that we bothcommonly and rarely encounter. To fully appreciate these processes, we must not only understand the details of the body systems involved, but also (mouse click)the “big picture.” This image represents the “big picture” of our nervous system. We will call this graphic “Connecting to Our World, Inside and Out.”
Week 1 ppt and-lecture-transcript-with audio
The Nervous System <br />Development and Basics<br />
Nervous System<br />Enteric<br />Sensory (afferent) System – transmits impulses from organs to CNS<br />Sympathetic<br />Peripheral Nervous System<br />Central Nervous System<br />Somatic (controls voluntary muscles)<br />Autonomic (involuntary nervous system)<br />Parasympathetic<br />Motor (efferent) System – transmits impulses from CNS to peripheral organs to cause an affect or action<br />Human Nervous System Components<br />
Neurons vs. Other Cells<br />Neurons have dendrites and axons to carry information back and forth.<br />Neurons can communicate with other neurons.<br />Neurons have specialized structures, like synapses and chemicals.<br />
Neurons Work Electrochemically<br />Ions are the electrically charged chemicals in neurons. <br />The most common ions are:<br />Sodium<br />Potassium<br />Calcium<br />Chloride<br />Ions can be negatively (-) or positively (+) charged.<br />Ions can be outside or inside a neuron’s membrane.<br />
A Neuron’s Potential Depends on the Charge of the Ions<br />The charge of the ions determines the type of potential a neuron has. <br />This animated graph shows the sequence: resting potential, action potential, and back to resting potential.<br />
Polarized/Depolarized Neurons<br />Resting neurons are polarized. When they become depolarized, an action potential occurs.<br />Depolarization<br />Resting state<br />
Animations to Review<br />Propagation of the action potential<br />http://www.blackwellpublishing.com/matthews/actionp.html<br />Click the blue circles on the left to play.<br />Channel gating during an action potential<br />http://www.blackwellpublishing.com/matthews/channel.html<br />Click the “Begin Depolarization” gold circle to start.<br />
Conduction Velocity<br />Conduction velocity is the speed of a nerve impulse and is measured in meters per second (msec).<br /> <br />The wave on this animated graph represents the amount of time it takes for the nerve impulse to travel from the beginning to the end of the time line.<br />
Variations in Conduction Velocity<br />Factors that can affect conduction velocity:<br />Temperature<br />Myelination<br />Width of axon<br />lower the temperature, the slower the conduction velocity<br />wider the axon, thefaster the conduction velocity<br />moremyelination, the <br />faster the conduction velocity<br />Salutatory conduction example:http://www.brainviews.com/abFiles/AniSalt.htm<br />
The Big Picture<br />Sensory Neurons<br />Sensory Neurons<br />Motor Neurons<br />Motor Neurons<br />Internal Environment<br />External Environment<br />Central Nervous System<br />
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