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CHAPTER 13 THE NERVOUS SYSTEM Introduction: Christopher Reeve’s injury A. The Nervous System is the ultimate coordinator of homeostasis B. Two parts of the nervous system 1. central nervous system = brain and spinal cord (CNS) these two interpret sensory information and coordinate a response 2. peripheral nervous system (PNS) = nerves that carry messages coming in to and going away from the CNS These two systems work together and are connected Functions of the Nervous System 1. Receives sensory input (PNS) Sensory receptors all over the body pick up information about changes around and inside of us and send signals through nerves to the CNS 2. integration (CNS) The brain and spinal cord process information from the receptors and decide what to do 3. Generates motor output (PNS) Nerve messages from the CNS go to effectors (muscles and glands) Nervous Tissue 2 types of cells = neurons and neuroglia A. Neuron structure: A. three parts of a neuron are... 1. Dendrites- carry impulses to cell body 2. cell body – central part of cell 3. Axon – carries impulses away from the cell body Sensory Neuron Function Carries messages from receptors to the central nervous system (CNS) Incoming information Interneuron Function Found inside the brain and spinal cord Carry messages inside the CNS Integration: “thinking” and processing Motor Neuron Function Carries messages from CNS to muscles or glands (effectors) Outgoing instructions B. Myelin Sheath covers some axons in the PNS & CNS myelin is a lipid substance that insulates and protects neurons The myelin sheath is made by neuroglial cells myelin also helps with nerve regeneration the disease, multiple sclerosis (MS) develops when the myelin sheath becomes hardened and interferes with nerve conduction It is an autoimmune disease Leukodystrophy disorders are similar in that they are caused by destruction of the myelin sheath, but their cause is genetic C. The Nerve Impulse is an electrochemical signal passed along the neurons Electrical it involves + and – charges Chemical it involves elements like Na+ and Cl- Nerve Impulse Conduction 1. Resting Potential – the inside of the axon is neg. compared to outside sodium-potassium difference at rest “pump” maintains this A Neuron at Rest is Polarized!! 2. Action Potential – rapid change in polarity across the membrane when the impulse occurs. (all or none) * threshold = minimum stimulation needed to cause an impulse to start A Neuron Carrying a Message is Depolarized!! 3. Refractory Period – the membrane is restored to its resting potential Neuron cannot be stimulated during the refractor period During the Refractory Period the Membrane is Repolarized! Ch.12animations\nerveimpulseswf_lw22_-.swf D. Transmission Across a Synapse Neurons do not touch each other so messages have to be sent from one neuron to the next… synapse space between the axon of one neuron and the dendrites or cell body of another neuron (also between axons and muscle cells) neurotransmitter = chemical stored at the ends of axons that is responsible for transmission across a synapse (can stimulate or inhibit responses) http://www.youtube.com/watch?v=90cj4 NX87Yk Ch.12animations\chemical_syna pse-swf_ch.swf * at least 100 known * examples are acetylcholine (ACh) and norepinephrine (NE) * drugs that affect the nervous system can... (page 306) 1. promote action of neurotransmitters Xanax, valium, prozac for anxiety 2. decrease action of neurotransmitters Caffeine, antipsychotic drugs 3. mimic the action of a neurotransmitter Codeine, heroin, morphine for pain relief integration the sum of inhibitory and excitatory signals received by a neuron (threshold or not ??) Does the message get through or not?? The Central Nervous System (brain and spinal cord) A. Protectors of the CNS are... 1. skull and vertebrae 2. meninges 3. cerebrospinal fluid (CSF) Meningitis Any inflammation of the meninges Usually caused by bacteria or virus Swelling causes brain damage and death * hydrocephalus “water on the brain” Birth defect where brain swells due to a build up of fluid that isn’t circulating correctly Can cause permanent brain damage if not repaired Hydrocephalus CNS has gray matter and white matter... difference? Gray matter has no myelin sheath Used for processing information and memory White matter has a mylein sheath Used for sending messages B. Spinal Cord has… pairs of spinal nerves (PNS) which leave between vertebrae - because the white matter tracts cross as they enter the brain... The right side of the brain senses and controls the left side of the body and vice versa Functions of spinal cord 1. communication between brain and PNS 2. center for reflex arcs (internal and external) C. Brain Cerebrum – largest part of human brain - sensory input and motor output - learning, memory, language * divided into two sides or hemispheres * connected by corpus callosum * lobes are named the same as the skull Frontal, temporal, parietal, occipital Association areas are places where integration occurs Parkinson Disease due to lack of dopamine, a neurotransmitter cells making dopamine are being destroyed (autoimmune disease) Gradual loss of motor control Stem cell research may be the best hope for a cure 2. Diencephalon hypothalamus helps maintain homeostasis and controls the pituitary gland (links nervous and endocrine systems) Controls hunger, thirst, rage, sex drive, body temperature, etc. thalamus receives sensory information and sends it to the proper area of the cerebrum also helps integrate memory and emotions Gray matter pineal gland releases melatonin Melatonin helps regulate our sleep and wake cycles Puberty?? 3. Cerebellum maintains posture and balance - muscle coordination Cerebrum actually sends the signals that tell the muscles to contract “rote” muscle movements like tying shoes and typing are “programmed” here 4. Brain Stem midbrain acts as a relay station and reflex center - pons is the “bridge” between cerebellum and CNS and helps control breathing and reflex head movements medulla oblongata basic life support center Breathing, heart rate, etc. also reflexes like coughing, sneezing, etc. are triggered here reticular formation regulates alertness - Severe Coma can be caused by damage to this area - - Anesthetics often work here The Limbic System and Higher Mental Functions Limbic System blends primitive emotions with higher mental functions - a series of tracts that run through the cerebrum and diencephlalon Alzheimer’s disease Affects this part of the brain first, affecting short-term memory 1. Alzheimer Disease – gradual loss of reason due to plaques around axons and tangles around axons Cause unknown, diagnosis difficult Some new drugs are slowing the progression Memory is the ability to hold a thought or recall events 1. short-term memory 2. long-term memory is a mix of semantic (numbers, words, etc.) and episodic memories (persons, events, etc.) NEED BOTH 3. Skill memory helps us do automatic motor activities like...walking, playing an instrument, typing, driving, etc. Learning is retaining and using past memories !!! Language and Speech are combinations of recall, knowing what and how to say something and actually forming the words – all different parts of the brain. Left Brain verbal, logical, analytical, rational Right Brain nonverbal, visual-spatial, intuitive, creative The Peripheral Nervous System (PNS) A. Nerves are bundles of axons they can be sensory (incoming) or motor (outgoing) from the CNS or a mixture of these C. Cranial nerves (12 pair) are connected directly to the brain nervous system peripheral nervous system "nerves" central nervous sytem brain spinal cord somatic nervous system voluntary: skeltal muscles autonomic nervous system involuntary:cardiac, smooth and glands sympathetic emergency parasympatheti normal they send/receive messages to/from things like.... Seeing, hearing, tasting Muscles of the head and neck Sensations in the head and neck D. Spinal nerves (31 pair) are connected to the spinal cord they send/receive messages to/from things like... Sensations below the neck Motor activity below the neck E. Somatic System is the voluntary and muscle reflex part of the PNS it receives sensory information and takes messages to skeletal muscles Reflex Arc... Reflex = a rapid, involuntary response to a stimulus Reflex arc is the pathway that an impulse follows in a reflex from the receptor to the CNS and back out to the effector Locate the parts on the diagram on page 303 in the book A. sensory receptor B. sensory neuron C. interneuron D. motor neuron E. effector (muscle or gland) A stimulus is received by a sensory receptor Which initiates an impulse in the sensory neuron The impulse travels through the sensory neuron to the spinal cord and transmits it to the interneuron This neuron passes the impulse to the motor neuron Whose axons take the message to an effector which reacts to the stimulus. F. Autonomic System controls cardiac muscle, smooth muscle and glands system is divided into sympathetic and parasympathetic divisions Sympathetic “emergency response” system Speeds heart rate, sends more sugar and blood to muscles, slows digestion, dilates pupils, releases adrenaline, etc. When we are under STRESS, this system is too much in charge Parasympathetic “normal” system Increases digestive activity, slows heart and breathing, etc. - both function automatically - both have nerves in all internal organs both control reflexes involving homeostasis Comparison on page 305 Drug Abuse drugs can cause physical or psychological dependence and withdrawal Alcohol metabolized in the liver (damage from fat build up = cirrhosis) Brain and liver damage CNS depressant (decreases activity at synapses) Nicotine excess of neurotransmitter dopamine (mood) and mimics Ach CNS stimulant complications in pregnancy Caffeine CNS stimulant affecting many neurotransmitters Dopamine, seratonin, noradrenaline Increases brain metabolism but decreases blood flow to the brain?? Cocaine prevents uptake of dopamine so stimulation is constant body stops making its own neurotransmitters so the “crash” greater risk of stroke and heart attack Methamphetamine Keeps neurotransmitters in synapses so constant stimulation causes agitation, wakefulness and psychosis Tolerance increases with addiction Heroin opium derived as pain medication mimics the endorphins or “feel good” chemicals of brain body stops making its own so withdrawal is extreme Marijuana wide ranging neurological effects, some dependence Mimics a neurotransmitter Homeostasis A. the nervous and endocrine systems are most important in maintaining homeostasis