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The Nervous System Anatomically, the nervous system can be divided into: 1. The central nervous system (CNS), which includes the brain and spinal cord 2. The peripheral nervous system (PNS), which includes cranial and spinal nerves that carry messages to and from parts of the body. Functionally, the nervous system can be divided into: 1. The somatic nervous system, which includes voluntary control of the skeletal muscles. 2. The autonomic nervous system (sometimes called visceral nervous system) which includes the involuntary control of smooth muscle, cardiac muscle, and glands. The autonomic nervous system (ANS) can be divided into: A. The sympathetic nervous system (stress, fight or flight) B. The parasympathetic nervous system (maintain homeostasis, rest, digest) Basic Anatomy of the Nervous System Neurons and Their Functions A neuron is: •A nerve cell •Carries nerve impulses between the CNS and the body tissues •Bundles of neurons in the PNS are called nerves •Bundles of neurons in the CNS are called tracts The neuron consists of: •Cell body •Dendrites •Axon •Myelin Sheath (Schwann Cells) •Nodes of Ranvier •Synapses The cell body of the neuron contains the nucleus and organelles. The axon and dendrites branch off of the cell body. illustration from wikipedia.com The function of the dendrites is to serve as receptors. They recieve stimuli from the body or from other neurons along a neural pathway. The axon is the neruon fiber that conducts nerve impulses away from the cell body. The nerve impulse may be delivered to another neuron, to a muscle, or to a gland. The axons are covered with myelin, which insulates the fiber and helps nerve impulses to travel down the length of the axon. Schwann cells wrap around the axon and produce layers of myelin. There are tiny gaps in between myelin sheaths. These gaps are called nodes. This creates a faster nerve impluse. The axon terminals, at the ends of the axon, send the nerve impulse from its neuron, to the dendrites of another neuron. Nerve impulses can also be sent to muscle cells or glands. This junction is called a synapse. How does a nerve impulse travel? The cell membrane of a resting neuron carries an electric charge. At rest, the inside of the membrane is negative and the outside is positive. This state is said to be polarized (ready for action!). A nerve impulse starts when a stimulus causes a reversal in the electrical charge (action potential), which travels down the membrane like an electric current. When the reversal of electric charges occurs, the membrane is depolarized. When the membrane returns back to its resting state, it is repolarized, and ready for stimulation again. What happens at a synapse? In the terminal branches at the end of a neuron, there are small vesicles (called butons) that contain chemicals. These chemicals are called neurotransmitters. When the nerve impulse reaches the butons, the neurotransmitter is released, and acts as a chemical signal, stimulating the next cell. The target cells, such as muscles or glands, that carry out responses from the neurotransmitters, are called effectors. •Open the "forms" tab. •On your paper, answer questions 1-10, answers only. This is individual work, not group work. •This is an assessment of your understanding of the material thus far. •I want to know what YOU understand, not what you can copy from your neighbor. •Please turn in your answers to the review questions when you finish. Bell Ringer: Use your computer and books to research and write about the following, in complete sentences. Write your name on your Bell Ringer and turn it in when you finish. What is Shingles? What virus causes shingles? What are the signs and symptoms of shingles? How can shingles be identified? Why is shingles considered a disorder of the nervous system? Moving right along..... The Spinal Cord and Spinal Nerves! The spinal cord sits protected inside the vertebrae, and stretches from the skull to the end of the sacrum. The brain and spinal cord are both protected by bones, and by three meninges (protective membrane layers) The outer layer is very tough, and is called the dura mater ("tough mother") The middle layer, the arachnoid mater, is avascular connective tissue. The innermost layer, the pia mater ("soft mother") is highly vascularized and very thin. The spinal nerves originate in the spinal cord, and each one innervates a different area of the body. Each area that is innervated by a spinal nerve is called a dermatome. The functions of the spinal cord: Carries information from the peripheral nervous system, up to the brain Carries information from the brain to the peripheral nervous system Plays a role in spinal reflexes and stretch reflexes, which do not require the brain to process sensory information, and create a quick response A diagram of a stretch reflex Sensory information enters the dorsal horn of the spinal cord, and travels upward to the brain in the ascending tracts. Motor impulses traveling down from the brain are carried in descending tracts, and exit through the ventral (anterior) horn of the spinal cord. Sensory neurons are referred to as "afferent" neurons, and enter the spinal cord at the dorsal horn. Motor neurons are referred to as "efferent" neurons, and enter the spinal cord at the ventral horn. Sensory = Afferent = Dorsal Root, Dorsal = Afferent. Ventral = Efferent. SAD DAVE The Autonomic Nervous System Remember the ANS is responsible for regulating glands, and controlling the function of smooth muscle (organs and blood vessels) and heart muscle. There are two functional divisions of the ANS: •The Parasympathetic Nervous System (PNS) •The Sympathetic Nervous System (SNS) The Sympathetic Nervous System Most organs are supplied by both sympathetic and parasympathetic nerve fibers. The SNS acts on organs to help us deal with a stressful situation (think of being chased by an animal). The SNS increases heartrate Increases blood pressure Dilates (opens up) blood vessels that supply skeletal muscles Dilates bronchial tubes to increase oxygen intake Stimulates the adrenal glands to produce hormones such as epinephrine Increases metabolism Dilates the pupil Fight or Flight! Because blood flow is increased to your skeletal muscles, there is less blood flow to other organs such as the stomach and intestines. What do you think happens to digestion during a sympathetic response? The Parasympathetic Nervous System The PNS works to reverse the stress response and maintain homeostasis in the body. Blood flow to the digestive organs is increased Digestive glands (pancreas, liver) are stimulated Heart rate and blood pressure decrease Bronchi of lungs constrict The PNS is responsible for our "rest and digest" actions. Recap Questions: 1. What division of the autonomic nervous system mediates the "fight or flight" response? 2. What division of the autonomic nervous system mediates the "rest and digest" response? 3. Describe the basic "spinal reflex." 4. Differentiate between "afferent" and "efferent" neurons. The Brain and Cranial Nerves The brain occupies the cranial cavity, and is coverd by the same meninges of the spinal cord (dura mater, arachnoid mater, and pia mater). The brain is surrounded by cerebrospinal fluid, which also circulates within the brain itself. • Meningitis is an inflammation of the meninges, usually caused by viruses, bacteria, or fungi. It is diagnosed by lumbar puncture and collection of cerebrospinal fluid. • Meningitis can be treated with antibiotics, but left untreated, can be deadly. • Vaccines can help prevent some cases of meningitis. The cerebrospinal fluid (CSF) provides a cushion to the brain and spinal cord, and carries nutrients and wastes. The CSF is produced in the four ventricles of the brain. Hydrocephalus is a condition that is caused when there is an obstruction to the flow of CSF. In the infant, hydrocephalus results in cranial enlargement. In the adult, the bones are fused and cranial enlargement cannot occur. What do you think happens when CSF builds up in the adult brain? Hydrocephalus can be treated by placing a shunt in the ventricle of the brain. The shunt drains excess CSF into either the peritoneal cavity (belly) or into the atrium of the heart. The body will absorb and eliminate the extra fluid if needed. The Structure of the Brain There are two cerebral hemispheres. Each cerebral hemisphere can be divided into four lobes: The frontal, parietal, temporal, and occiptal. • The frontal lobe is relatively large in humans. This lobe contains the motor area, and an area important for speech. • The parietal lobe contains the sensory area, and assists with estimation of sizes, shapes, and distances. • The temporal lobe contains the olfactory area and the autidorty area • The occipital visual area lobe contains the The corpus callosum is located between the hemispheres, and permits impulses to cross from the right side to the left side of the brain. The basal ganglia are masses of gray matter that help regulate body movement and facial expressions. The neurotransmitter dopamine is secreted in the basal ganglia. In the innermost part of the brain, near the corpus callosum and basal ganglia, the thalamus and hypothalamus are located. The thalamus functions to sort and route information to different parts of the cerebral cortex (like a post office of sorts). The hypothalamus maintains homeostasis by controlling body temperature, water balance, sleep, appetite, and some primal emotions. The limbic system is involved in emotional states and behavior. In the limbic system lies the amygdala, a mass of ganglia that control feelings of fear (sympathetic nervous system) The hippocampus is involved in learning, the formation of long term memory, and spatial navigation. The Cerebellum •The cerebellum aids in the coordination of voluntary muscles, •helps to maintain balance by processing messages from the inner ear, tendons and muscles, •And aids in maintaining muscle tone to ready the body for quick changes if necessary. The brain stem connects the brain with the spinal cord, and is a very primitive portion of our brain. The midbrain acts as a relay center for some eye and ear reflexes, and gives rise to cranial nerves III and IV. The pons lies just under the midbrain. The pons is an important connective link between the cerebellum and the rest of the nervous system. Some reflexes and involuntary actions (breathing) are controlled with help from the pons. The pons also gives rise to cranial nerves V, VI, VII, and VIII. The Medulla Oblongata The medulla oblongata is located between the pons and the spinal cord. The respiratory center in the medulla controls the muscles of respiration. The cardiac center helps regulate the rate and force of cardiac contractions. The vasomotor center regulates the contraction of smooth muscle in the blood vessel walls (thus controlling blood pressure). Cranial nerves IX, X, XI, and XII originate in the medulla. The Brain Made Simple Somethin' Wrong With His Medulla Oblongata No, Colonel Sanders, YOU'RE wrong! Mama Said the medulla oblongatta controls respirations, blood pressure, and cardiac contractility. Disorders of the Brain 1. Cerebrovascular Accident (abbreviated CVA) is also known as a stroke. 2. Cerebral hemorrhage, or bleeding within the brain, can be caused by a ruptured blood vessel (such as from an arteriovenous malformation, aneurysm, or an injury to the head) and can lead to brain damage or stroke in some cases. 3. Cerebral Palsy, as disorder caused by brain damage occuring during or before birth, and can lead to muscular disorders. 4. Epilepsy, an abnormality of the electrical activity of the brain, leads to seizures. 5. Tumors 6. Alzheimers disease, caused by degeneration of the cerebral cortex and hippocampus. 7. Parkinson's disease Answer the following review questions and turn them in... 1. What lobe of the brain is responsible for higher-order thinking, such as reasoning, planning, and personality? 2. What part of the brain helps us to form long term memories? 3. What is the structure that connects the right hemisphere to the left hemisphere? 4. What is the tough outer meninge of the brain called? 5. What brain disorder is characterized by difficulty controlling speech and movement due to a lack of the neurotransmitter dopamine? 6. What parts of the brain degenerate in someone with Alzheimer's? 7. What are the symptoms of Alzheimer's? 8. What part of the brain controlls respirations, the heart, and the dilation/constriction of blood vessels? 9. What is the function of the amygdala? 10. If the cerebellum is damaged, what symptoms might a person experience? 11. Research this: Has there ever been a person born without a cerebellum, and survive? Explain what you find in your research. 12. What part of the brain recieves visula stimuli and processes it? 13. In what lobe of the brain is the auditory processing area? 14. How many ventricles are in the brain? 15. What is the result of a buildup of cerebrospinal fluid in and around the brain?