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Chapter 13: The Nervous System How does the human body react to changes in its internal environment? How do the senses enable us to detect sensory information and perceive our environment? There are two main divisions of your nervous system: o o The central nervous system is used for what? What makes up the central nervous system? What is the peripheral nervous system? So what is the difference between the CNS and PNS? The PNS can be divided further into _________________________ and _______________________. Somatic nerves control the skeletal muscles, bones, and skin. The autonomic system can be divided into the _____________________________ and the _________________________________________. 2 There are two different types of cells found in the nervous system, these are ___________________ and ___________________. Glial cells are often called neuroglial cells, they are ______________________________________ cells. So what are they important for? Individual neurons are organized into tissues called nerves. Neurons are the functional units of the nervous system. All neurons contain what? What are neurons specialized to do? 3 Part Dendrite Function Cell Body Axon The axon carries the nerve impulse toward other neurons or to the ___________________________. Many axons are covered with a glistening white coat of fatty protein called the myelin sheath. If they have myelin, they are said to be ___________________________. What does the myelin sheath do? Schwann cells are a special type of glial cell that produces _____________________________________. 4 The areas between the sections of myelin sheath are known as the ____________________________________. Nerve impulses jump from one node to another, thereby speeding the movement of nerve impulses. Myelinated = _____________________. The speed of an impulse along the nerve fiber is also affected by the _____________________________________ of the axon. What is the relationship between the speed of the impulses and the axon diameter? Neurilemma is a delicate membrane that surrounds the axon of some nerve cells. What does neurilemma do? 5 Why is it that when you paper cut your finger, it starts to gain more feeling as time goes on? What is the difference between white and grey matter? Check your understanding: 1. Define homeostasis. 2. Explain why the nervous system is critical for maintaining homeostasis. 6 3.Create a table to identify the different systems in the nervous system and explain the structure and function of each. 4. Compare the basic function of neurons and glial cells. 5. Draw a neuron and label these parts: Dendrites, Schwann Cell, Myelin Sheath, Axon, Nodes of Ranvier, Terminal End Branches 7 Nerves are categorized into 3 groups: o o o Sensory neurons are also known as ______________________ neurons. What does a sensory neuron do? The cell bodies of sensory neurons are located in clusters called ______________________ that are located outside of the spinal cord. Interneurons link neurons to other neurons. They are only found in the ___________________ and __________________. What does an interneuron do? 8 Motor neurons are also known as ____________________________________. What does a motor neuron do? Structure Sensory Receptors Sensory Neurons Interneurons Motor Neurons 9 Funtion Effectors Label the following diagram using these terms: Sensory receptor, sensory neuron, interneurons, motor neurons, effector, CNS, PNS 10 Imagine you are driving late at night and a deer jumps out in front of your vehicle. Trace the pathway from sensory receptors to the effectors. 11 What types of cells have scientists been looking into to help rebuild damaged cells? Reflex Arc You should note that this is an ______________________________ movement but it is still part of the somatic NS. What is a reflex? Reflex arcs are known for being the simplest nerve pathway in our bodies. This means that it doesn’t involve coordination from the brain. 12 Check your understanding: 1. List the three types of neurons and identify their primary function. 2. Identify the basic neural pathway that is involved as you dodge a wayward tennis ball. Compare this pathway with a a withdrawal reflex. 3. Label the following diagram. 13 13.2: Electrochemical Impulses The action potential is the voltage difference across a nerve cell membrane when the nerve is excited. The resting potential is the voltage difference across a nerve cell membrane when it is not transmitting a nerve impulse. This is usually ___________________________. Like all cells, neurons have a huge supply of ___________________________________________________________ on both sides of the cell membrane. There is a higher the concentration of ___________________________________ ions inside the cell (+) and a higher concentration of _______________________ ions (+) outside of the cell. 14 Cell membranes are ___________________________________________. Ions pass through gated ion channels by the process of _____________________________________. There are many more K+ channels than Na+ in the membrane, so more K+ diffuses out of the cell than Na+ diffuses in. What is mainly responsible for creating the electrical potential? As K+ leaves the cell, it transfers the + charge outside of the cell in the _________________________________________________________. Large protein molecules that are ________________________ charged are present in the ___________________________________________. These large proteins are stuck inside the membrane and when K+ leaves this creates an overall charge of what? So how is this electrochemical gradient maintained? 15 When a neuron receives a stimulus, the cell membrane becomes more permeable to Na than to K. Na gates will open during an action potential and K gates will close. Why do the Na+ rush into the nerve cell? A rapid flow of Na+ causes a charge reversal or ________________________________________. Once the voltage inside of the nerve cell becomes (+), Na gates slam closed and the inflow of Na+ is halted. K gates are now open and K+ once again begins to diffuse out of the nerve cell. This restores the original polarity of the membrane and is called ___________________________________. K gates close relatively slowly and the outside of the cell becomes even more positively charged than the resting membrane as K ions continue to move out of the cell. This excessive diffusion is called __________________________________. 16 How is the original high Na+ on outside and the high K+ on the inside restored? 17 In order for a 2nd action potential to occur, the period of depolarization must be completed and the nerve must repolarize. This is called the ____________________________________________. Conduction of an action potential is not like conduction of charge along a wire conductor. The axon is actually a poor conductor of electrical charge. Many action potentials are generated one after another along the cell membrane, causing a __________________________________________________________. A good analogy of this would be what? A wave of depolarization is followed by a wave of what? Action potentials don’t decay in strength as they are conducted down the axon. Unidirectional Propagation: Moving the electrical impulse one direction. It spreads from the ________________________________ to the _________________________________. During repolarization, the Na+ gates are still closed so there is no possible depolarization. 18 What is saltatory conduction? What provides the ability for saltatory conduction? What type of neuron conducts faster? What is a threshold level? What happens if we increase the intensity of a stimuli above that critical threshold? What is an all-or-none response? 19 So how does your Nervous System detect various levels of stimuli? Check your understanding: 1. Summarize the events that occur as an impulse is transmitted along the length of the neuron using diagrams and/or a flow chart. 2. Why are action potentials only conducted in one direction? 20 3. Compare the structure and functions of myelinated neurons and unmyelinated neurons. 4. How does myelination of the axon speed up transmission of an action potential? How are organisms containing neurons without a myelin sheath cell’s structured to speed up transmission? 5. What is the all-or-none response? Explain a high pain tolerance, in terms of threshold levels. 21 The synapse is a small space between neurons or between neurons and effectors. This space contains small vesicles containing transmitter chemicals. Chemicals are released from end plates as nerve impulses move along the axon. Transmitter chemicals are released from presynaptic neuron and diffuse across the synapse. How does this work on the postsynaptic neuron? Acetylcholine can act as an excitatory transmitter chemical. It opens Na+ channels. This causes ________________________________________. How is acetylcholine stopped so that the postsynaptic neuron would not remain in constant depolarization? Acetylcholine can also act as an inhibitory transmitter. It opens more K gates so that the K+ on the inside of the neuron follow the concentration gradient and diffuse out of the neuron. 22 How does this work on the postsynaptic neuron? What are inhibitory transmitters? What is GABA used for? What is the principle of summation? What are the main purposes of serotonin? 23 What are the main purposes of dopamine? What do endorphins do? What is norepinephrine used for? When are endorphins released? How do opiates work? What is the problem with using opiates? 24 What are two examples of depressants and what do they do? Check your understanding: 1. What is the function of neurotransmitters in the nervous system? 2. Compare the excitatory and inhibitory effects of neurotransmitters on the postsynaptic membrane. 3. Compare and relate the function of acetylcholine and cholinesterase. 25 4. Cocaine affects a synapse by blocking the re-uptake of the neurotransmitters dopamine by the presynaptic neurons. Therefore, the levels of dopamine continue to build in the synapse causing certain affects on the body. o Explain how cocaine interferes with the neural transmission across the synapse. o Describe the role of dopamine in the brain. o Formulate a hypothesis about how cocaine could be addictive after only one use. 26 13.3: The Central Nervous System The CNS is made up of the __________________________________________________________. The brain is surrounded by 3 protective membranes known as the ____________________________. These three layers are : Where is cerebrospinal fluid found? What does the spinal cord do? Where is it located? What is the difference between the dorsal nerve tract and the ventral nerve tract? 27 There are three distinct regions of the brain: The forebrain is divided how? The midbrain is the smallest region of the brain and consists of mainly what? The hindbrain joins with the spinal cord. What is the cerebrum? What is the cerebral cortex? 28 What is the corpus callosum? Each hemisphere can be further subdivided into 4 lobes: 29 Using your textbook, create a table as to what each lobe of the brain is used for. There are three important parts of the forebrain: What does the thalamus do? What is the hypothalamus used for? 30 What are olfactory bulbs used for? What are the major regions of the hindbrain? What does the cerebellum control? What do the pons do? What is the function of the medulla oblongata? Check your understanding: 1. Identify the main structures of the CNS, and describe their general function. 31 2. Explain how the blood-barrier and the cerebrospinal fluid protect the brain and the spinal cord. 3. Identify the major structures in the hindbrain, midbrain, and forebrain, and the functions of these structures. 4. Identify the four lobes of the cerebrum, and describe the function of each. 5. Describe the primary areas of the brain that are responsible for fine motor control of the muscles, as well as the area that processes sensory information from the skin. 32 6. Compare different technologies used for studying the brain. 7. If the motor area of the right cerebral cortex was damaged in a car accident, which side of the body would be affected? Why? 8. Compare white and grey matter. Identify the location of each and describe its function. 9. Label the following diagram. 33 The peripheral nervous system is divided into 2 main systems: What does the sensory somatic do? What does the autonomic nervous system do? How is the autonomic nervous system divided? What is the sympathetic nervous system? What is the parasympathetic nervous system? 34 Copy table 1 on page 435 from your textbook. Check your understanding: 1. What generally triggers the sympathetic nervous system and what are the effects on the body? 2. What generally triggers the parasympathetic system, and what are the effects on the body? 35 36