The Nervous System Anatomy & Physiology
The Basics • The nervous system is your body's decision and communication center. • The central nervous system (CNS) is made of the brain and the spinal cord • The peripheral nervous system (PNS) is made of nerves. • Together they control every part of your daily life, from breathing and blinking to helping you memorize facts for a test. Brain Power: 55 sec. http://www.articlesbase.com/videos/5min/114222865
Neurons • A neuron is a nerve cell that is the basic building block of the nervous system. • Neurons are specialized to transmit information throughout the body. • They are responsible for communicating information in both chemical and electrical forms. There are also several different types of neurons responsible for different tasks in the human body. 1. Sensory neurons (afferent) carry information from the sensory receptor cells throughout the body to the brain. 2. Motor neurons (efferent) transmit information from the brain to the muscles of the body. 3. Interneurons are responsible for communicating information between different neurons in the body. We’ll get back to these later…..
Do Now! • What are the two main parts of the nervous system? • What “organs” are these two parts made up of? • What is a neuron? • What are the 3 different kinds of nerves?
Use the definitions below to correctly label this neuron • axon - the long extension of a neuron that carries nerve impulses away from the body of the cell to other neurons. • axon terminals - the hair-like ends of the axon • cell body - the cell body of the neuron; it contains the nucleus (also called the soma) • dendrites - the branching structure of a neuron that receives messages (attached to the cell body) • myelin sheath - the fatty substance that surrounds and protects some nerve fibers node of Ranvier - one of the many gaps in the myelin sheath - this is where the action potential occurs during saltatory conduction along the axon • nucleus - the organelle in the cell body of the neuron that contains the genetic material of the cell • Schwann's cells - cells that produce myelin - they are located within the myelin sheath.
Neurons Neuron Parts:• Soma: body of the cell• Dendrites: receive messages• Axon: sends messages Anatomy of a nerve http://www.youtube.com/watch?v=XgIaAs_ONG4&feature=related A Neurons has three main parts. The cell body, or soma, is a neuron's main cellular space. The soma houses the nucleus, in which the neuron's main genetic information can be found. The axon sends messages to other neurons.The dendrites receive messages from other neurons.
Two parts of Nervous system & Neuron video clip • http://www.dnatube.com/video/2116/Anatomy-Nervous-System • http://www.youtube.com/watch?v=DF04XPBj5uc&NR=1
How messages are sent and received • 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 and potassium (both have 1 positive charge, +), calcium (has 2 positive charges, ++) and chloride (has a negative charge, -). There are also some negatively charged protein molecules. • 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. Watch Bill Nye’s Greatest Science Discoveries on Neutrotransmitters.
How messages are sent and received continued • Resting Membrane Potential : At rest, there is an excess of negative ions inside the neuron compared to the outside.
Membrane potential. . . Charge difference between the inside and outside of the membrane. The charge difference is due to the difference of concentrations of ions on either side of the cell membrane. Inside the membrane is negative and the outside is positive. This is due to the permeability of ions. There are more Na+ ions in the extracellular fluid and more K+ ions in the intracellular fluid. The membrane is more permeable to K+ which leaks out to the outside of the membrane giving it a positive charge. http://www.youtube.com/watch?v=iA-Gdkje6pg&feature=related
How messages are sent and received continued http://www.teachertube.com/viewVideo.php?video_id=153535 • Action Potential • When a point on the semi-permeable neural membrane is adequately stimulated by an incoming message, the membrane opens at that point, and positively charged ions flow in. • This process is repeated along the length of the membrane, creating the neural impulse that travels down the axon, causing the neuron to fire. • Electrical changes during the action potential.The incoming message must be above a certain threshold to cause a neuron to fire. After it fires, the neuron is returned to its resting state. This process happens very quickly, and within a few thousandths of a second the neuron is ready to fire again.
Action potential. . . A change in polarity across the membrane brought about by a stimulus. An action potential is also called a nerve impulse. In response to a stimulus the Na+ gates open. Na+ rushes into the cell. This causes the inside of the membrane to be positive and the outside to be negative. This reversal of charge is a depolarization. K+ gates open which allow K+ out of the cell: This causes a repolarization. This wave of depolarization followed by a wave of repolarization travels the length of a nerve axon and is called an action potential. It is also called a nerve impulse and it is how the nervous system communicates.
Refractory period. . . The period of rest before a neuron can be stimulated to fire off another action potential. The refractory period insures one way movement of action potentials along a nerve
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What causes this change in potential to occur? • The stimulus causes the sodium gates (channel) to open and, because there's more sodium on the outside than the inside of the membrane, sodium then diffuses rapidly into the nerve cell. All these positively-charged sodium ions rushing in causes the membrane potential to become positive (the inside of the membrane is now positive relative to the outside). The sodium channels open only briefly, then close again. • The potassium channels then open, and, because there is more potassium inside the membrane than outside, positively-charged potassium ions diffuse out. As these positive ions go out, the inside of the membrane once again becomes negative with respect to the outside.
A message passes from a sending neuron to a receiving neuron. The neurotransmitters leave the sending neuron and enter the space between the sending and receiving neurons. This space is called the synapse. The neurotransmitters then hook up to a receptor on the receiving neuron to deliver their message. • Once neurotransmitters have sent their message, they return and can be reabsorbed by the sending neuron in a process called reuptake. Reuptake allows the messengers to be reused. Two of these neurotransmitters are serotonin and norepinephrine. Low levels of serotonin and norepinephrine in the synapse are associated with depression and sadness. Some medications used to treat depression work by increasing the amount of certain neurotransmitters that are available to carry messages. • Each type of antidepressant works on brain chemistry a little differently. All antidepressant medications influence how certain neurotransmitters, especially serotonin and norepinephrine, work in the brain. • SSRIs and tricyclic antidepressants. Antidepressants, such as selective serotonin reuptake inhibitors, or SSRIs, and tricyclic antidepressants, work by slowing or blocking the sending neuron from taking back the released serotonin. In that way, more of this chemical is available in the synapse. The more of this neurotransmitter that is available, the more likely the message is received, and depression is reduced. To learn more about how these antidepressants work, see Tricyclic Antidepressants (TCAs) and Selective Serotonin Reuptake Inhibitors (SSRIs). • MAOIs. The antidepressants known as MAO inhibitors, or MAOIs, affect neurotransmitters differently. Monoamine oxidase (MAO) is a natural enzyme that breaks down neurotransmitters. The drug MAOI disrupts the action of the enzyme MAO. In that way, there is an increase in the amount of neurotransmitters in the synapse, making more messengers available to the receiving neuron, and thus reducing depression. To learn more about how these antidepressants work, see Monoamine Oxidase Inhibitors (MAOIs).
Nerve Function and Drug Action: http://www.utexas.edu/research/asrec/neuroncartoon.html
Neuron parts http://garyfisk.com/anim/neuronparts.swf Animated visual: http://www.classzone.com/cz/books/bio_07/get_chapter_group.htm?cin=9&rg=animated_biology&at=animated_biology&var=animated_biology
Myelin and Nodes of Ranvier • Axons are sheathed in a smooth fatty protein called myelin which insulates the axon, prevents the wrong ion channels from opening and considerably increases the speed that nerve impulses travel along the axon. • Without the myelin, the axons would have to be about one hundred times their volume to achieve the same speed of nerve transmissions. The myelin is wrapped around the axon in many thin layers. The myelin does not enclose the axon in one entire sheath, but has gaps at intervals called the nodes of Ranvier. • The precise function of these nodes is unknown but the nodes are major sites of sodium channels and may serve to prevent the decay of nerve impulses by effectively amplifying them. • They may also act to anchor the myelin sheath to the axon and to isolate each segment of myelin from its neighbors. • Work on rats with genetic deformities in their nodes of Ranvier has shown that these nodes are vital to efficient transmission of nerve impulses. How the myelin sheath works is discussed more fully in the section on myelin.
Quiz Time! Name the ….. 1. Part of the neuron that releases neurotransmitters into the synaptic cleft. 2. Fatty material that surrounds some axons. 3. Part that takes information away from the cell body.4. The gaps in the myelin sheath. 5. Part of neuron that contains the nucleus. 6. Part that takes information to the cell body.7. Organelle in neuron that contains genetic material. Answers are: 1.Axon terminal 4. Nodes of Ranvier7. Nucleus 2. Myelin5. Soma 3. Axon 6. Dendrites
The Central Nervous System Interesting Facts! • The central nervous system is divided into two parts: the brain and the spinal cord. • The average adult human brain weighs 1.3 to 1.4 kg (approximately 3 pounds). • The brain contains about 100 billion nerve cells (neurons) and trillons of "support cells" called gila. • The spinal cord is about 43 cm long in adult women and 45 cm long in adult men and weighs about 35-40 grams. • The vertebral column, the collection of bones (back bone) that houses the spinal cord, is about 70 cm long. Therefore, the spinal cord is much shorter than the vertebral column. young frankenstein part 1
The cerebrum -- which is just Latin for "brain" -- is the newest (evolutionarily) and largest part of the brain as a whole. It is here that things like perception, imagination, thought, judgment, and decision occur. • The surface of the cerebrum -- the cerebral cortex -- is composed of six thin layers of neurons (nerve cells) and is referred to as the grey matter. It sits on top of a large collection of white matter pathways. • The cortex is heavily convoluted with “ridges” called gyri and “valleys” called sulci. If you were to spread the cortex out, it would actually take up about 2 1/2 square feet (2500 sq cm). It includes about 10 billion neurons, with about 50 trillion synapses! • The cerebral cortex is divided into four sections, called "lobes": the frontal lobe, parietal lobe, occipital lobe, and temporal lobe.
Grey vs. White Matter • Grey matter – closely packed neuron cell bodies (making up the cerebral cortex) form the grey matter of the brain. The grey matter includes regions of the brain involved in muscle control, sensory perceptions, such as seeing and hearing, memory, emotions and speech. • White matter – neuronal tissue containing mainly long, myelinated axons, is known as white matter or the diencephalon. It makes up the cerebrum. • The nuclei of the white matter are involved in the relay of sensory information from the rest of the body to the cerebral cortex, as well as in the regulation of autonomic (unconscious) functions such as body temperature, heart rate and blood pressure. • Certain nuclei within the white matter are involved in the expression of emotions, the release of hormones from the pituitary gland, and in the regulation of food and water intake. These nuclei are generally considered part of the limbic system.
The Brain The cerebral cortex is comprised of the: frontal lobe, parietal lobe, occipital lobe, and temporal lobe.
What do each of these lobes do? • Frontal Lobe- associated with reasoning, planning, parts of speech, movement, emotions, and problem solving
Functions associated with the frontal lobes: • Conscious thought • Concentration • Perseverance • Judgment • Attention span • Impulse control - self monitoring and supervision • Problem solving • Organization • Critical thinking • Forward thinking • Ability to feel and express emotions • Empathy YouTube - NEURONS AND NEURO-TRANSMITTERS
What do each of these lobes do? • Frontal Lobe- associated with reasoning, planning, parts of speech, movement, emotions, and problem solving • Parietal Lobe- associated with movement, orientation, recognition, perception of stimuli
Parietal Lobe • The parietal lobes can be divided into two functional regions. • One involves sensation and perception and the other is concerned with integrating sensory input, primarily with the visual system.
What do each of these lobes do? • Frontal Lobe- associated with reasoning, planning, parts of speech, movement, emotions, and problem solving • Parietal Lobe- associated with movement, orientation, recognition, perception of stimuli • Occipital Lobe- associated with visual processing
Occipital lobes • The OC are the center of our visual perception system. They are not particularly vulnerable to injury because of their location at the back of the brain, although any significant trauma to the brain could produce subtle changes to our visual-perceptual system, such as visual field defects.
What do each of these lobes do? • Frontal Lobe- associated with reasoning, planning, parts of speech, movement, emotions, and problem solving • Parietal Lobe- associated with movement, orientation, recognition, perception of stimuli • Occipital Lobe- associated with visual processing • Temporal Lobe- associated with perception and recognition of auditory stimuli, memory, and speech
TEMPORAL LOBES: Located at sides of head above ears, the temporal lobes form the wings of the soul of our living caduceus. Functions: The dominant side is usually the left hand side and governs- Hearing ability Understanding and processing language Memory acquisition - particularly long term memory Some visual perceptions Categorization of objects. The no dominant side or right side governs- Recognition of facial expressions Decoding vocal intonation Rhythm Music Visual learning How your memory works?
A deep furrow divides the cerebrum into two halves, known as the left and right hemispheres. Sometimes the right hemisphere is associated with creativity and the left hemispheres is associated with logic abilities. • The corpus callosum is a bundle of axons which connects these two hemispheres. The right hemisphere controls the left side of the body, and the left hemisphere controls the right side.
Do Now! • What are the 4 parts of the cerebrum? • The convolutions of the cerebrum are comprised of ridges and valleys. What are the ridges called? The valleys? • What part of the brain is dedicated to visual perceptions? • What part of the brain isassociated with reasoning, planning, parts of speech, movement, emotions, and problem solving? 5. What part of the brain isassociated with movement, orientation, recognition, perception of stimuli? 6. What part of the brain is associated with perception and recognition of auditory stimuli, memory, and speech? 7. What is the deep furrow that divides the cerebrum into two halves known as?
The Cerebellum The cerebellum, or "little brain", is similar to the cerebrum in that it has two hemispheres and has a highly folded surface or cortex.
CEREBELLUM: Located at the base of the skull, and attached to the rear of the brain stem. Functions: Coordination of voluntary movement posture Balance and equilibrium Some memory for reflex motor acts.
Limbic System: • The limbic system, often referred to as the "emotional brain", is found buried within the cerebrum. Like the cerebellum, evolutionarily the structure is rather old. • This system contains the: • thalamus (almost all sensory information enters this structure where neurons send that information to the overlying cortex ), • hypothalamus (functions including homeostasis, emotion, thirst, hunger, circadian rhythms, and control of the autonomic nervous system. In addition, it controls the pituitary ) • amygdala (memory, emotion, and fear ), • hippocampus (important for learning and memory, for converting short term memory to more permanent memory, and for recalling spatial relationships in the world about us) Sense of smell
BRAIN STEM: Located deep in the brain, leads to spinal cord. Often referred to as The 'Reptilian' or 'Primitive' Brain. The majority of the cranial nerves exit from the brain stem at the pons. The midbrain is the smallest region of the brain that acts as a sort of relay station for auditory and visual information. The pons connects the medulla to the cerebellum and helps coordinate movement on each side of the body. The medulla is located directly above the spinal cord and controls many vital autonomic functions such as heart rate, breathing and blood pressure.